HAL Id: hal-00890018 https://hal.archives-ouvertes.fr/hal-00890018 Submitted on 1 Jan 2006 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Evaluation of the effects of synchronising the availability of N and energy on rumen function and production responses of dairy cows - a review Ana Rita Jordão Cabrita, Richard James Dewhurst, José Manuel Fernandes Abreu, António José Mira Fonseca To cite this version: Ana Rita Jordão Cabrita, Richard James Dewhurst, José Manuel Fernandes Abreu, António José Mira Fonseca. Evaluation of the effects of synchronising the availability of N and energy on rumen function and production responses of dairy cows - a review. Animal Research, EDP Sciences, 2006, 55 (1), pp.1-24. hal-00890018
Transcript
HAL Id: hal-00890018https://hal.archives-ouvertes.fr/hal-00890018
Submitted on 1 Jan 2006
HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, estdestinée au dépôt et à la diffusion de documentsscientifiques de niveau recherche, publiés ou non,émanant des établissements d’enseignement et derecherche français ou étrangers, des laboratoirespublics ou privés.
Evaluation of the effects of synchronising the availabilityof N and energy on rumen function and production
responses of dairy cows - a reviewAna Rita Jordão Cabrita, Richard James Dewhurst, José Manuel Fernandes
Abreu, António José Mira Fonseca
To cite this version:Ana Rita Jordão Cabrita, Richard James Dewhurst, José Manuel Fernandes Abreu, António JoséMira Fonseca. Evaluation of the effects of synchronising the availability of N and energy on rumenfunction and production responses of dairy cows - a review. Animal Research, EDP Sciences, 2006,55 (1), pp.1-24. �hal-00890018�
Evaluation of the effects of synchronising the availability of N and energy on rumen function and production responses of dairy cows – a review
Ana Rita Jordão CABRITAa,b*, Richard James DEWHURSTc**, José Manuel Fernandes ABREUa,b, António José Mira FONSECAa,d
a Centro de Estudos de Ciência Animal do Instituto de Ciências e Tecnologias Agrárias e Agro-Alimentares, Universidade do Porto, Campus Agrário de Vairão, Rua Padre Armando
Quintas, 4485-661 Vairão VC, Portugalb Faculdade de Ciências, Universidade do Porto, Campus Agrário de Vairão, Rua Padre Armando
Quintas, 4485-661 Vairão VC, Portugalc Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth,
Ceredigion SY23 3EB, UKd ICBAS, Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Campus Agrário
de Vairão, Rua Padre Armando Quintas, 4485-661 Vairão VC, Portugal
(Received 3 February 2004; accepted 2 August 2005)
Abstract – This paper reviews the effects of synchronising the availability of N and energy on rumenfunction and production responses of lactating dairy cows. The paper makes a key distinction betweenaltering the synchronicity of diets by changing dietary ingredients, or by altering the feeding fre-quency or the feeding patterns. Manipulating synchrony by changing dietary ingredients presentssome problems, since it is not possible to discount the possibility that apparent effects of synchronyare associated with the manipulation of the ingredients (level and type) themselves. These problemscan be overcome, at least partially, by altering the feeding patterns. This review shows that the evi-dence for the benefits of synchronising energy and N supply to the rumen is contradictory, both forefficient microbial protein synthesis and for maximising milk production responses.
dairy cow / energy / nitrogen / rumen / synchrony
Résumé – Effets de la synchronisation de la disponibilité en azote et en énergie sur la fonctionruminale et les performances de production des vaches laitières – revue. Cet article passe enrevue les effets d’une synchronisation entre les disponibilités en azote et en énergie sur la fonctionruminale et les performances de production des vaches laitières. Une distinction importante est faiteentre les effets d’une synchronisation obtenue en changeant les ingrédients de la ration, et celleobtenue en modifiant le schéma et la fréquence d’apport d’aliment. La première solution conduit àdes difficultés d’interprétation, car il devient impossible de distinguer les effets de la synchronisationde ceux dus à la nature et au niveau des ingrédients utilisés. La deuxième solution permet, au moins
* Corresponding author: [email protected]** Present address: Agriculture and Life Sciences Division, Lincoln University, Canterbury, New Zealand.
Article published by EDP Sciences and available at http://www.edpsciences.org/animres or http://dx.doi.org/10.1051/animres:2005045
partiellement, de pallier ce problème. L’analyse des données de la littérature est contradictoire et nepermet pas de conclure à l’avantage de synchroniser les disponibilités en azote et en énergie dans lerumen, que ce soit pour améliorer l’efficacité de la synthèse microbienne ou la maximisation desperformances de production des vaches laitières.
Maximising the utilisation of rumen degra-dable protein (RDP) and its conversion intomicrobial protein is a key objective of pro-tein feeding strategies. Although the impor-tance of balancing the supply of RDP to theavailability of fermentable energy on adaily basis is well recognised [14, 56], otherworkers have suggested that it may beimportant to optimise the diurnal patterns ofsupply of RDP and fermentable energy (the‘synchrony concept’) [42, 47].
The basic assertion of the synchronyconcept is that a lack of synchrony betweenthe diurnal patterns of supply of energy andN to the microbes reduces the efficiency ofmicrobial capture of N and results in aninefficient use of ATP for microbial growth[16]. The imbalance between N and energyavailability, in asynchronous diets, can pro-mote a considerable absorption of ammoniathrough the ruminal wall and the use ofamino acids (AA) as an energy source [67].Conversely, when the fermentation of thedietary carbohydrates reaches its peak, theN supply to the rumen microbes will bemarkedly deficient, leading to an uncou-pling of ATP production and microbial pro-tein synthesis, with fermentation occurringlargely without microbial growth [67].
Therefore, synchronising energy and Navailabilities in the rumen seems to have apotential to enhance the output of microbialprotein from the rumen and efficiency ofruminal fermentation, thereby improvingfeed utilization and animal performance. Itis possible to alter the synchronicity of diets,either by changing dietary ingredients, orby altering the feeding frequency or thefeeding patterns. The latter approach is anextremely useful one because it allows us to
alter synchrony without altering diet ingre-dients. The main nutritional and practicalconsequences of the kinetics of feed diges-tion on rumen metabolism and animalresponses were examined by Sauvant andVan Milgen [94]. Dijkstra et al. [32] high-lighted the fact that no current rumen mod-els attempt to describe the effects of synchronyon microbial protein supply.
This paper reviews the effects of syn-chronising the availability of N and energyby changing dietary ingredients, feedingpattern or feeding frequency on rumen func-tion and production response of lactatingdairy cows. The approach followed was todiscuss this subject mainly focusing onstudies with lactating dairy cows, includingthose that were not designed to evaluate theeffects of synchrony, but that can be inter-preted a posteriori as such, since the infor-mation obtained in production studies wasconsidered essential to draw general con-clusions for formulating diets as well as forfeeding management on commercial dairyfarms.
2. CHANGING DIET INGREDIENTS
Synchronising N and energy supply tothe rumen can be achieved either by alteringthe energy source, the N source or both.Altering the diet forage/concentrate ratiocan also be considered as a method of manip-ulating the synchronicity of diets. How-ever, factors like the level of forage intakeand its fermentation rate, composition ofconcentrate and its effect on the digestibil-ity of the forage, makes it difficult to dis-tinguish their effects from synchrony effectsper se [37, 62, 86, 101, 113]. The observedeffects may be more related to the amount
Synchronising the availability of N and energy 3
and fermentation rate of organic matter (OM)in the rumen than specifically to the forage/concentrate ratio [21]. Additionally, the fewstudies with dairy cows on the influence ofdiet forage/concentrate ratio on N supply tothe duodenum failed to establish the opti-mum ratio, suggesting that simply alteringthe ratio in the range required to maximisemilk production does not greatly affect AAsupply to the duodenum [53, 85, 86], prob-ably because both forage and concentratecomposition can contribute to optimisingrumen fermentation and the supply of nitrog-enous compounds to the duodenum [21].
2.1. Starch sources of different degradability
Few studies have simultaneously studiedeffects of changing dietary energy sourceson rumen function and productivity. Themajority has focused on the use of starchsources of different degradabilities. Themost recent work, mainly from Americanauthors, has evaluated the following: (1)different cereal species (particularly maizeand barley – which are common starchy feedswith very different degradation rates; [68]);and (2) effects of different grain processingmethods.
2.1.1. Effects on rumen function
Table I presents the dietary characterisa-tion of studies, with lactating dairy cows,that have evaluated the effects of changingstarch source and grain processing on rumenpH, volatile fatty acids (VFA) and ammoniaN concentrations, on sites of starch diges-tion and on N supply to the duodenum andon the efficiency of microbial protein syn-thesis. More degradable starch tends todecrease rumen pH, increase rumen VFAproduction and decrease rumen ammonia Nconcentration (Fig. 1).
The effects of rate and extent of starchdigestion in the rumen on microbial (or bac-terial) N supply to the duodenum and on theefficiency of microbial protein synthesis
are also presented in Figure 1. More degra-dable starch increased microbial N supplyin two studies [75, 112] and had no effectin five studies [5, 24, 54, 70, 72]. The effi-ciency of microbial protein synthesis wasonly increased in one study [75] with moredegradable starch. These generally smallresponses may be attributed to several fac-tors. More degradable starch sources may,on the one hand, increase starch fermentedin the rumen, but, on the other hand, lowerruminal fibre digestion for diets with moredegradable starch sources can negate thebeneficial effects of the higher ruminal starchdigestibility, resulting in a similar amountof OM fermented in the rumen [5]. Addi-tionally, differences among treatments withinand between studies may be related to dif-ferences in dietary sources of N and energy,the amount of feed intake, solid and liquidrumen outflow rates, asynchrony betweenN and energy availabilities in the rumen,uncoupling fermentation and other unknownfactors related to the diets [20, 69, 89].
Although the effects of starch sources onsynchronisation of energy and N are mainlydemonstrated by their differences in diges-tion rate in the rumen, the carbohydratesource per se can also have effects. That is,the effects of dietary rumen degradable car-bohydrates can reflect both its ‘pH effect’(determined by its rate of fermentation) and‘carbohydrate effect’ [64]. This latter effectis well demonstrated in studies where thedepression in fibre digestion is still observedeven when the addition of buffers has pre-vented the decrease in rumen pH [64, 109].The ‘carbohydrate effect’ of a given sourceis related with the microbial species that uti-lise it and with the interactions of thesemicrobes with cellulolytic bacteria [16].The information available about the ‘carbo-hydrate effect’ of different sources of rumenfermentable carbohydrates is scarce, but someevidence suggests that the effect of sugarsis greater than that of starch [98]. Therefore,more research is needed to fully understandthe effects of carbohydrate sources onmetabolism and animal performance and
4 A.R.J. Cabrita et al.
Table I. Diet descriptions for the studies used in the construction of Figures 1 and 2.
Ref. Base forage Starch source in the concentrate (%)
Ratio Forage/Concentrate
[70] Alfalfa hay Steam-rolled maize(66)
35/65 Dry-rolled sorghum(66)
Steam-flaked sorghum(66)
Dry-rolled sorghum(33) + steam-flaked sorghum(33)
[72] Alfalfa silage + maize silage Maize(72)
45/55 Maize(54) + steam-rolled barley(22)
Maize(36) + steam-rolled barley(45)
Maize(18) + steam-rolled barley(67)
Steam-rolled barley(89)
[75] Alfalfa hay Dry-rolled maize(0.52†)(70)
43/57 Steam-flaked maize(0.39†)(70)
Steam-flaked maize(0.32†)(70)
Steam-flaked maize(0.26†)(70)
[112] Barley silage + alfalfa hay Steam-rolled barley(84)
Figure 1. Effects of rumen starch degradability on rumen pH, volatile fatty acids and ammonia Nconcentrations, on rumen starch digestion, on microbial N supply to the duodenum and on theefficiency of microbial protein synthesis (EMPS; g microbial or bacterial N per kg rumendegradable organic matter). [70] ; [72] ; [75] ; [112] ; [24] ; [54] +; [5] *; [49] ; [31]
; [69] x.
6 A.R.J. Cabrita et al.
hence to make a better use of them in feed-ing the lactating dairy cow.
2.1.2. Effects on production response
Some of the dairy production studiesdescribed in Table I found a significantincrease in DM intake and milk productionwith an increase in starch fermentability [5,31, 75], others observed the opposite [72],while still others did not observe any effect[24, 54, 70, 112], (Fig. 2). Positive responsesin milk production were ascribed to higherDM intake [75], higher energy intake [5], anincrease in the digestibility of starch andneutral detergent fibre (NDF; [31, 75]), orhigher protein supply to the duodenum[75]. In the study of Khorasani et al. [49],only primiparous cows responded to thetreatment of substituting barley grain withmaize, with milk production varying qua-dratically with increasing barley.
Studies that measured the effects of chang-ing starch source on the production responseof lactating dairy cows (not included in Tab. I)also found markedly different effects of usingbarley in place of other sources of lowerrumen fermentable starch; some observed areduction in milk production and DM intakewith barley [6, 12, 14, 63], while in other
studies these parameters were similar oreven increased with barley inclusion [13,28, 35, 41, 85, 101]. The higher productiveresponses with barley may be attributed tothe more rapid fermentation of barley in therumen. Increasing starch digestion in therumen increases the proportion of propi-onic acid produced [18, 76], which mightresult in higher net energy absorption,higher glucose synthesis in the liver, lowerutilisation of amino acids [105], and henceenhanced animal performance. Addition-ally, rapid ruminal fermentation of barleycan increase microbial protein synthesis(Fig. 1). However, when excessive fermen-tation of starch to VFA in the rumen occurs,the buffering and absorptive capacity of thecow may be overwhelmed, leading to adecrease in rumen pH that may decreasemicrobial growth and DM intake. In thesesituations, the substitution of barley bymaize (less degradable starch source) canhave positive effects on productive responses.Maize can prevent the depression in rumenpH and increases DM intake, resulting in alarger quantity of energy, amino acids, andother nutrients being provided for the syn-thesis of milk and milk components. Theassociated increase in the rate of passagefrom the rumen enhances microbial growth
Figure 2. The effects of rumen starch degradability on dry matter intake (kg·day–1) and milkproduction (kg·day–1). [70] ; [72] ; [73] ; [112] ; [24] ; [54] +; [5] *; [49] ; [31] .
Synchronising the availability of N and energy 7
efficiency and amino acid supply to theduodenum. The variation between experi-ments in the effects of barley or maize onDM intake and milk production of cowswas also probably due to the dietary con-centrations of maize and barley, which havedistinct effects on rumen pH, to the higherstarch content of maize-based diets, whichincrease VFA production [14], and to thehigher fibre content of diets with barley [63].
Changing starch source affect the siteand the end products of digestion absorbedby the animal (Fig. 1). Ruminal digestion ofstarch is usually higher with diets based onhigher degradable starch sources (e.g., bar-ley), whilst post ruminal digestion is higherwhen less degradable starch sources (e.g.,maize) are used as an energy source [5, 72,75]. This along with the effects of starchsources of different degradabilities on rumenfunction, with the empirical and practicalrule that in diets for high producing dairycows (with high needs for glycogenic nutri-ents), based on maize silage, more rumendegradable starch sources can be used in theconcentrate feed. Conversely, in diets basedon grass silage, a greater contribution ofless degradable starch sources is advanta-geous, in particular for increased milk pro-tein content.
2.2. Protein nitrogen and non protein nitrogen
Changing dietary N source also representsa method of manipulating N and energyavailabilities in the rumen. In this sense,the replacement of true protein by non-protein N – often designed to reduce thecost of diets – can be considered a changein the synchronicity of diets. The studiesthat used this strategy have mainly focusedon evaluating the possible losses in produc-tion efficiency and not their effects on thesynchrony between N and energy availabil-ities in the rumen.
When interpreting the results of replac-ing true protein by non protein N we haveto consider both effects of AA supply on
microbial protein synthesis and of rate ofrelease of N. Several studies demonstratethat, although some rumen microorganismsare able to grow in the absence of true pro-tein, some microorganisms prefer preformedAA [8, 44, 46]. The presence of AA stimu-lates microbial growth [1, 58, 59], growthrate [108] and growth efficiency [1, 23, 60],as well as increasing the cell wall digestionand the production of VFA [36]. Addition-ally, there is some evidence [1, 60] that theeffects of AA supply on bacterial growthare superior with a mixture of AA than withspecific AA. However, the effects in vivohave been less consistent [2, 19], probablydue to differences in fermentation rates ofcarbohydrates.
To maximise the efficiency of microbialprotein synthesis with non-protein N, it isconsidered essential to guarantee a sourceof quickly fermentable energy in the dietthat allows the use, by rumen microbes, ofthe rapidly released ammonia (e.g., [45, 57,103]). Therefore, the energy source usedmust be taken into account when the effectsof changing N source are analysed. Indeed,carbohydrates differ greatly in terms ofpotential to promote the use of non-proteinN sources. Cellulose seems to be the leasteffective carbohydrate in promoting the useof ammonia released from urea and starchthe most effective, more so than sugars [38].The observation that cellulose does not pro-mote an effective use of urea N can beexplained by the low proportion of cellu-lose that is rapidly hydrolysed and becomesavailable when bacteria needs energy tocapture N [22, 78]. Sugars have been stud-ied more extensively in relation to their pos-itive effect on the intake of diets with ureathan in relation to their effects on urea N use[38]. However, this aspect was not sup-ported by Van Horn et al. [107] whoobserved that the intake of a concentratefeed with 1.9% of urea was not increased bythe addition of 4.7% of molasses. Sourcesof quickly fermentable starch decreaserumen pH, allowing the maintenance of agreater pool of ammonia for microbial pro-tein synthesis, since the rumen wall is more
8 A.R.J. Cabrita et al.
permeable to the free form (NH3), presentwith a higher rumen pH [91]. The effective-ness of starch can be increased by cooking,which making it more susceptible to micro-bial degradation, allows the supply ofenergy in a rate more closely related to thatof urea N released, theoretically enablingthe more efficient use of ammonia by rumenmicrobes, since it decreases the risk of tox-icity from urea [4].
2.3. Matching energy and N sources
Some authors have evaluated the effectsof changing N and energy sources in theconcentrate on rumen function and dairycow performance. These effects can be inter-preted retrospectively as effects of manip-ulating synchrony between N and energyavailabilities in the rumen (Tab. II).
2.3.1. Effects on rumen function
Mean rumen pH was not, in general,affected (Fig. 3), though VFA concentra-tions increased with increasing fermentableenergy supply in two studies, and this wasreflected in a higher utilisation of degrada-ble N [61, 63]. It was expected that isoni-trogenous diets that were more synchronisedwould promote a lower rumen ammonia Nconcentration. However, the studies ana-lysed (Fig. 3) do not give a consistent trend,possibly due to differences in the level ofRDP supply (e.g., inclusion of urea in study[12]) or differences in the pattern of rumenfluid sampling. Furthermore, rumen ammo-nia concentrations are not necessarily relatedwith ammonia production, and could berelated for example with changes in ruminalvolumes [14] and absorption rates throughthe ruminal wall [12].
From the studies summarised in Table II,only five measured microbial N supply tothe duodenum and the efficiency of micro-bial protein synthesis (Fig. 3). The smallnumber of studies and the difficulty of dis-tinguishing the effects of protein and energysources do not allow us to reach a generalconclusion. Herrera-Saldana et al. [42]
showed that starch degradability affectedthe utilisation of nutrients in the rumenmore than protein degradability. They alsoshowed that diets synchronised for a fastrelease of N and energy, with barley andcottonseed meal, promoted a higher pro-duction and higher efficiency of microbialprotein synthesis than the diets synchro-nised for a slow release of N and energy,with milo and brewers dried grains, or asyn-chronous diets, with barley and brewersdried grain, or milo and cottonseed meal.
When the objective is to formulate syn-chronised diets by changing dietary ingre-dients, it seems that matching the availabilityof N and energy in the rumen is not suffi-cient. Care must also be taken about thenature of N and energy sources used andtheir effects on rumen environment andmicrobial growth efficiency. Indeed, pro-duction of microbial N in the rumen is oftenlimited by fermentable energy, but diet fer-mentability may also affect microbial effi-ciency by altering ruminal pH or rates ofpassage. For example, the rate of rumenstarch fermentation that allows the maxi-mal efficiency of starch use by ruminalmicrobes is affected by the ruminal envi-ronment and availability of N substratesrequired for microbial growth [49]. It iswell known that bacteria fermenting non-structural carbohydrates (NSC) may decreasemicrobial efficiency when peptides oramino acids are insufficient [90]. The nextsection discusses the extent to which posi-tive effects on rumen function achieved bysynchronised diets are reflected in produc-tion responses.
2.3.2. Effects on production response
The production response to synchrony ofN and energy supply to the rumen is not con-sistent (Fig. 4). Herrera-Saldana and Huber[41], using the same diets as in the previousstudy [42], showed that cows in early lac-tation, fed a synchronous diet for fast rumendegradation of energy and N, producedmore milk than those fed slowly fermenta-ble synchronised diets or asynchronous
Synchronising the availability of N and energy 9
Table II. Diet descriptions for the studies used in the construction of Figures 3 and 4.
Ref. Base forage Energy and N sources in concentrate Degree of synchrony considered†Ratio Forage/
†+ = more synchronised; – = less synchronised.AGH = alfalfa-grass haylage; AH = alfalfa hay; AHL = alfalfa haylage; B = barley; BDG = brewers driedgrains; BP = beet pulp; BR = barley rolled; CH = cottonseed hulls; CP = crude protein; CSM = cottonseedmeal; D = dextrose; DWW = dried whole whey; ESBM = extruded soybean meal; FM = fish meal; GH =grass hay; GM = ground maize; GS = grass silage; GSM = ground shelled maize; LSBM = lignosulfonate-treated soybean meal; M = milo; MDG = wet corn distillers grains; MR = maize rolled; MS = maizesilage; MZ = maize; O = oat; S = starch; SB = soybean meal; Sc = sucrose; SH = soybean hulls; SRB =steam rolled barley; U = urea; WC = whole cottonseeds.
10 A.R.J. Cabrita et al.
Figure 3. Effects of synchronising the availabil-ity of N and energy in the rumen of dairy cowsby changing the carbohydrate and N sources inthe concentrate on rumen pH, volatile fatty acidsand ammonia N concentrations, on microbial Nsupply to the duodenum and on efficiency ofmicrobial protein synthesis (EMPS; g microbialor bacterial N per kg rumen degradable organicmatter). [11] ; [12] ; [63] ; [13] ; [42]
; [10] ; [61] +; [73] x; [14] *; [95] ; [93] ♦.
Synchronising the availability of N and energy 11
diets, probably due to higher production ofmicrobial protein. By contrast, other authors[10, 13, 14, 61, 73, 95] found no effects ofsynchronising N and energy availabilitiesin the rumen on milk production.
The lack of production response to syn-chrony between N and energy availabilitiesin the rumen is not clearly explained by theeffects on rumen fermentation (Fig. 3).Casper and Schingoethe [12] and Casper etal. [13] state that the low milk productionof cows fed diets with barley and urea couldbe related to the fact that degradation ratesof barley and urea are incompatible, affect-ing DM intake. This opinion is, however,opposed to that of Blauwiekel and Kincaid[7] who found greater milk production fora diet high in soluble N (barley and urea)than for a diet also based on barley, but lowin soluble N. In response to these conflict-ing results, Casper et al. [13] suggested thatdifferences in NSC solubility, and not indegradability, can result in different animalresponses. Casper et al. [14] suggested thatthe minimal benefits of synchrony betweenNSC and RDP were due to the fact that thecows used were in the middle of lactation,with lower protein requirements.
From the foregoing discussion, it appearsthat the easiest practical strategy to matchenergy and N in the rumen is to select dietingredients based on rumen degradabilityestimates (NSC and structural carbohy-drates; protein and non protein N sources).Although this strategy could contribute toincreased microbial protein synthesis, it couldnot be the more efficient or low cost one.
2.4. Synchronicity index
The studies analysed so far show that theeffects of the synchrony, achieved by chang-ing diet ingredients, between N and energyavailabilities in the rumen have differenteffects on microbial yield and efficiency.However, those studies could have useddiets which were synchronised on a widetemporal basis (e.g., day), but not synchro-nised over short periods (e.g., hour). Someauthors examined this point in sheep. Sinclairet al. [99, 100] used in situ feed degradationdata to try and to enhance the efficiency ofmicrobial protein synthesis, through themaintenance of appropriate amounts andrelations between hourly available carbo-hydrates and N supply. These authors
Figure 4. Effects of synchronising the availability of N and energy in the rumen of dairy cows bychanging the carbohydrate and N sources in the concentrate on dry matter intake (kg·day–1) andmilk production (kg·day–1). [11] ; [12] ; [63] ; [13] ; [10] ; [61] +; [73] x; [14] *; [95] ;[93] ♦.
12 A.R.J. Cabrita et al.
calculated a synchronicity index accordingto the following equation:
where 25 = 25 g N·kg–1 truly rumendigested OM, which is assumed to be theoptimum relation, and where an index of1 represents a perfect synchrony between Nand energy supply during the day, whilevalues less than 1 indicate progressivelyincreasing asynchrony.
Using this approach, Sinclair et al. [99]conducted a study with wether sheep, whichwas aimed at examining the effects ofhourly synchronisation of the supply ofenergy and N. The results suggest that thesynchronised diet never promotes a deficitin ammonia for microbial growth and pro-duces a more stable rumen microbial pop-ulation, resulting in less variation in molarproportions of VFA and a greater estimatedmicrobial protein synthesis. Conversely,the asynchronous diet resulted in a deficitin ammonia for microbial growth during20 hours per day and a greater estimated Nrecycling. The carbohydrate concentrationof rumen bacteria was measured to deter-mine if microbes store excess energy and,in this sense, to serve as a synchronicityindex. However, the amount of carbohy-drates stored was more affected by the formand rate of degradation of carbohydratesthan by the degree of synchronism betweenN and energy supply. Later, Sinclair et al.[100] conducted a study to examine theeffects of synchronising the hourly supplyof energy and N in diets with similar com-position in carbohydrates, but differing inrate of release of N. The efficiency ofmicrobial protein synthesis (g N·kg–1 trulyrumen degraded OM) was 11 to 20% higherin the animals fed with a synchronous dietthan with an asynchronous diet.
Witt et al. [110] also used in situ degrad-ability data to test the effect of hourly syn-chronisation on the productive response ofewes. They showed that the hourly synchro-
nisation of energy and N did not signifi-cantly affect milk production, milk fatproduction, milk protein percentage andDM intake, but decreased plasma urea con-centration during the day. They concludedthat the synchrony between N and energyavailabilities in the rumen does not have animportant effect on the milk production ofewes and suggested that the ruminantswhen fed with asynchronous diets, ad libi-tum, have the possibility to modify theirpattern of intake to achieve a more synchro-nised release rate of N and energy.
The previous discussion shows that manip-ulating synchrony by changing diet ingre-dients presents some problems, since it isnot possible to identify whether an increasein microbial protein synthesis through feed-ing of different ingredients, observed insome studies, is an effect of synchrony or afactor associated with the manipulation ofthe ingredients (level and type) themselves,since clear effects that can be attributed tosynchrony can be specific effects, for exam-ple of individual nutrients, particularly pro-tein and energy [30].
3. CHANGING FEEDING PATTERN
The problems related to the study of syn-chronisation between N and energy availa-bilities in the rumen achieved by changingdiet ingredients, can be overcome, at leastpartially, through the utilisation of in vitromediums, that allows the control of theamount and supply rate of nutrients [65], orthe infusion of nutrients directly in therumen or the supply of the same ingredientsto the animals according to different pat-terns of feeding [30].
3.1. Studies in vitro
Few studies have evaluated, in vitro, theeffects of synchronisation between N andenergy availabilities on microbial proteinsynthesis and on the efficiency of microbialprotein synthesis (Tab. III). Henning et al.
25/)24/)/25(25241
2
⎟⎟⎠
⎞⎜⎜⎝
⎛−− ∑ hourlyOMN
Synchronising the availability of N and energy 13
[39] concluded that, for acceptable levels ofN supply, synchronisation between availa-bilities of N and energy in the rumen is lessimportant than the pattern of energy supply.Newbold and Rust [65] demonstrated thatthe asynchrony between N and energyavailabilities in the rumen has only short-term effects on bacterial growth. However,the authors emphasise that these observa-tions do not allow the conclusion that theasynchrony is unimportant in vivo. This isbecause of the following: (1) alterations in
N degradation rate due to changing Nsource can be accompanied by changingAA supply; (2) if N and energy supply ratesare not synchronised, any change in rumenpassage rate will decrease the efficiency ofrumen utilisation of N and carbohydrates,depending on which nutrient is in excess (infact, in this study there was no difference inthe number of microorganisms betweentreatments, for a simulated rumen retentiontime of 12 hours, but if this time was short-ened, N supply in relation to the energy
Table III. Effect of synchronisation between N and energy availabilities in in vitro studies onmicrobial protein synthesis and on the efficiency of microbial protein synthesis.
Ref. Nutrients added in vitro Observations
[39] Glucose (25 g) as pulse dose at time 0 + N in excess Synchrony decreased concentration and fluctuation of rumen ammonia, but did not affect microbial growth and efficiency of microbial protein synthesis. A single pulse dose of glucose improved the efficiency of microbial growth, being less important for acceptable levels of N supply, synchronisation between availabilities of N and energy in the rumen than the pattern of energy supply.
Glucose (25 g) as an intermediate pattern of gradually increasing, followed by gradually decreasing
increments + N in excess
Glucose (25 g) as 24 even increments at 0.5 h intervals + N in excess
Glucose (12.5 g) as pulse dose at time 0 + N in excess
Glucose (12.5 g) as an intermediate pattern of gradually increasing, followed by gradually decreasing
increments + N in excess
Glucose (12.5 g) as 24 even increments at 0.5 hintervals + N in excess
Glucose as a pulse dose at time 0 and N in 24 even increments at 0.5 h intervals
Glucose in 24 even increments at 0.5 h intervals and N as a pulse dose at time 0
Glucose and N in 24 even increments at 0.5 h intervals
[65] 26 mg urea-N·g–1 glucose Bacterial population size was higher in synchrony conditions between 5 to 8 hours of incubation, but at 12 hours of incubation there were no differences. Asynchronous supply of N and energy yielding substrates only had short-term effects on bacterial growth.
Exponential increase of 0.013 mg N·g–1 glucose from 00:00 h to 48.9 g N·g–1 glucose at 11:00 h
[65] Large corn particles + soybean meal
Large corn particles + papaic digest soybean meal
Small corn particles + soybean meal
Small corn particles + papaic digest soybean meal
14 A.R.J. Cabrita et al.
would be reduced and bacterial growthwould be limited); and (3) the short-termeffects of excess N cannot be adequatelystudied in simple culture mediums that donot simulate the losses of excess N throughabsorption by the rumen wall. Furthermore,in vitro studies also suffer from problemsassociated with the accumulation of the endproducts of fermentation that could affectbacterial growth [74].
3.2. Infusion of nutrients in the rumen
The results of the effects of synchroni-sation of N and energy availabilities in therumen, achieved by nutrient infusion, onthe synthesis and on the efficiency of micro-bial protein synthesis are summarised inTable IV. Due to the reduced number ofstudies with lactating dairy cows, studieswith steers and wethers were, also included.
From the experimental evidence pre-sented in Table IV, there were only twostudies that showed positive effects of syn-chrony per se on microbial growth and effi-ciency of microbial protein synthesis [51,88]. Although a number of earlier studieswith grass silage, which is considered to bevery asynchronous, have shown positiveeffects on microbial growth [27, 87, 88],these studies did not test the synchronyeffect as the principal objective. Other fac-tors could have an important function andhad masked the effect of synchrony per se.The results obtained by Kim et al. [50, 51](Tab. IV) are difficult to explain. Indeed,the asynchrony associated with grass silagesis related to the low availability of quicklyfermentable energy when the availability ofpeptides, AA and ammonia is high. How-ever, Kim et al. [50] observed that in situa-tions of asynchrony, the infusion of sucrosedid not result in an improvement in micro-bial N supply and Kim et al. [51] found that,when they offered grass silage alone, sugarinfusion had no effect on microbial proteinsynthesis, but when they offered grass silageand concentrates, the infusion increasedmicrobial protein synthesis. The authorssuggested that synchrony will only affect
microbial protein synthesis with diets alreadycontaining high levels of readily fermenta-ble carbohydrates, although this is onlylikely if the capacity of the microbes to storestarch is exceeded.
Although synchrony affected the varia-bility of rumen ammonia N concentration inthe study by Henning et al. [40] (Tab. IV),microbial N supply and efficiency of micro-bial protein synthesis were not affected.This observation can be explained by thefact that, although the pattern of variation ofammonia N concentration differed betweentreatments, the actual concentration, in rela-tion to microbial growth resulting from thevarious patterns of energy supply, was neverlimiting. Additionally, N recycled to therumen can partially explain the lack ofresponse to synchronising N and energyavailabilities. However, although in thisstudy, N recycling could explain the absenceof response to greater synchrony, this can-not hold true in situations of high supply ofenergy and N, because, in this case, excessN can be absorbed and excreted in urine andthe later recycling of N to the rumen maybe insufficient to match the high availabil-ity of energy [43].
In the second experiment reported byHenning et al. [40], increased synchronyresulting from a higher feed intake level didnot improve the microbial protein supply,nor the efficiency of microbial synthesis.These results are in agreement with thoseobtained by Salter et al. [92] who did notobserve a positive response to synchronywhen they added tapioca and glucose (as anenergy source) to the rumen of steers fedstraw, provoking different levels of syn-chrony. It should be noted, however, thatthe results of Salter et al. [92] could beexplained by the fact that the treatmentsalso differed in the amounts of N and car-bohydrates added to the rumen.
However, the fact that in the in vivostudy of Henning et al. [40] the energy sup-plied gradually to the rumen resulted in ahigh and more efficient microbial proteinsynthesis than the same amount of energy
Synchronising the availability of N and energy 15
Table IV. Effect of synchronization between N and energy availabilities in the rumen manipulatedby nutrient infusion in the rumen on microbial protein synthesis and on the efficiency of microbialprotein synthesis.
Ref. Exp. Unity Base dietDistribution
Infusions Observations
[92] Steers Straw (60) +Concentrate (40)
Starch and urea as a single dose (09 h)
Synchrony and pattern of energy supply without effect on efficiency of microbial protein synthesis.
Straw 1× d–1 Starch as a single dose (09 h) and urea in 3 doses (09, 11 and 13 h)
Concentrate 2× d–1 Glucose as a single dose (09 h) and urea in 3 doses (09, 11 and 13 h)Glucose and urea in 3 doses (09,
11 and 13 h)
[88]† Cows Grass silage Casein (21 g N·d–1 + 0.17 kg OM·d–1) Infusions of glucose increased microbial growth. The efficiency of microbial protein synthesis increased, only, by the infusion of casein and glucose syrup.
2× d–1 Urea (28 g N·d–1)Glucose syrup (0.87 kg OM·d–1)
Casein + Glucose syrup(17 g N·d–1 + 0.93 kg OM·d–1)
[87] Cows Grass silage Sucrose† (170 g·kg–1 DM of silage) Infusion of casein increased microbial growth (P < 0.05) and efficiency of microbial protein synthesis (non significant effect).
Synchrony at maintenance level (Exp. 1) or higher (Exp. 2) decreased concentration and fluctuation of ruminal ammonia, but did not affect microbial growth and efficiency of microbial protein synthesis. Continuous infusion of sugar increased efficiency of microbial growth.
6× d–1 Energy and N as 12-hourly pulse-doses (08/20 h)
Energy as 12-hourly pulse-doses (08/20 h) and N as a continuous
infusionEnergy as a continuous infusion and N as 12-hourly pulse-doses (08/20 h)
6× d–1 One-half of energy plus all of the N as two equal pulse-doses (08/20 h), and the remaining half of the energy
as a continuous infusion
16 A.R.J. Cabrita et al.
supplied rapidly, is on the contrary to thatobserved in vitro by Henning et al. [39] forsimilar treatments. These conflicting resultscan be explained by the fact that in the invitro study, pH was maintained above 6 andthe values of microbial protein synthesis wereonly calculated until the point of depletionof energy substrates, while in the in vivostudy there were periods of low pH andreduced levels of readily fermentable sub-strates. The results of this in vivo study alsoconflict with those observed by Salter et al.[92] with no significant differences in theefficiency of microbial protein synthesis, inspite of the low rumen pH (<5.5) with pulsedose supply.
As the results obtained by Henning et al.[40] suggest that the simple improvement
of synchrony of N and energy supply to therumen do not increase microbial yield, theseauthors suggest that the objective, whenformulating diets, should be, first, to obtainan even supply of energy and then to ensurethe supply of an appropriate amount ofrumen available N in relation to the amountof fermentable energy. Only then, wouldthere be any advantage in avoiding a veryquick release of N in the rumen.
3.3. Feeding frequency of total diet
Studies of feeding frequency have focusedon possible effects on microbial efficiencymediated by changing metabolite patternsin the rumen, and effects on voluntary intake,resulting from changes in the degradation
Table IV. Continued.
Ref. Exp. Unity Base dietDistribution
Infusions Observations
One-half of the energy as two equal pulse-doses (08/20 h), and the remaining half of the energy
plus the N as a continuous infusion Energy as a continuous infusion and N as two equal pulse-doses
(08/20 h)Energy and N as a continuous
infusion
[50] Cows Grass silage Without infusion Synchronous conditions where infused sucrose did not improve micro-bial protein synthesis.
7.9 kg DM·d–1 Sucrose (1 kg·d–1) as continuous infusion
2× d–1 (10/22 h) Sucrose (1 kg·d–1) as two 6-h infu-sions starting at 10:00 and 22:00 hSucrose (1 kg·d–1) as two 6-h infu-sions starting at 16:00 and 04:00 h
[51] Cows Grass silage + barley + peanuts meal
Without infusions Maltodextrin infused synchronously increased microbial protein synthesis.
8 kg DM·d–1 + 4.2 kg DM·d–1 + 1.8 kg DM·d–1
2 kg maltodextrin as continuous infusion
2× d–1 (10/22 h) 2 kg maltodextrin as two 6-h infu-sions starting at 10:00 and 22:00 h2 kg maltodextrin as two 6-h infu-sions starting at 16:00 and 04:00 h
† Infused intraruminally at a constant rate; ‡ Fed in two equal portions.
Synchronising the availability of N and energy 17
rates of feeds. However, the increase infeeding frequency is, in fact, a method thatallows us to overcome almost all problemsof asynchrony between nutrient availabilityin the rumen.
Feeding frequency effects are clearlymore important with housed animals, whenthe amount of ingested feed and feeding fre-quency are mainly regulated by the farmer.This is because in the wild state, ruminantscan ingest feed during the day, from sunriseuntil sunset, or even during the night. Theamount ingested and the frequency of mealsare basically dependent on the desire of theanimal and the availability of feed.
Offering the diet once daily can promotesubstantial diurnal fluctuations in rumenconcentrations of ammonia [15, 96, 97],VFA [48, 81] and lactic acid [81]. Theseextreme conditions of metabolites can inhibitmicrobial growth and activity and, conse-quently, microbial degradation of feed [79].Therefore, an increased frequency of feed-ing and decreasing metabolite fluctuations[15, 55, 71, 97, 104], can, theoretically,increase the efficiency of utilisation ofnutrients in the rumen [3, 47]. However, ahigh frequency of feeding can decreasedaily fluctuation of rumen pH [15, 71, 97,104], but the average pH can also decrease[29, 97, 104]. Note that if the frequency offeeding results in a rumen pH variationbetween 5.7 and 5.9, the effect on fibre fer-mentation can be more negative than a lowfrequency of feeding that promotes a pat-tern of variation that decrease pH to valuesof 5.3, but, also, reach values of 6.7 in dif-ferent parts of the day [9, 79].
The effects of frequency of feeding ondigestibilities of DM, OM, CP, starch andNDF are inconsistent. In several studies,total diet digestibility [31, 77, 96] and feedintake [31, 52, 66, 96, 102] were not affectedby distributing the total diet more than onceper day. However, Shabi et al. [97] showedincreases in post-ruminal digestibility ofOM, CP and NSC with increasing feedingfrequency, but did not observe effects on
synthesis and efficiency of synthesis ofmicrobial protein.
The reduced fluctuation of rumen ammo-nia N concentration with a high feeding fre-quency is probably related to increasedammonia utilisation and a decrease in theamount of ammonia that is absorbedthrough the ruminal wall, which is reflectedin a low N excretion in the urine [25]. Thelow frequency of feeding decreased the meanconcentration of ammonia N [96, 111] anddecreased microbial CP supply to the duo-denum [15, 17, 96]. The increased ammoniautilisation can result from the increase infermentable OM content, the more stablepH and the natural rumen buffering, whichprevents the decrease in the number of pro-teolytic bacteria [79], increasing proteoly-sis and decreasing the amount of dietaryprotein that escapes fermentation [17]. Inthese situations, the number of protozoa tendsto increase [96]. There appears to be aninteraction between the energy level andfrequency of feeding in relation to the appar-ent and true efficiency of bacterial N synthe-sis, suggesting that the efficiency of bacterialN synthesis can be improved when dietswith moderate or high levels of concentratefeeds are offered more frequently [15].
On the basis of effects on rumen func-tion, it is expected that the effects of fre-quency of feeding on rumen fermentationwould be reflected in positive productiveresponses. However, in the 35 studies pub-lished between 1949 and 1983, reviewed byGibson [33], and in later studies [31, 52, 66,96], the response to the high frequency offeeding, in terms of milk production, wasnot always positive. Nonetheless, many pro-ducers report beneficial effects [79] and thelack of responses may reflect the greaterdegree of control over feeding in an exper-imental situation. Commercial cows areoften group-fed in free stalls, with intensecompetition for feed space and a tendencyfor meals to be concentrated in the first sixhours after feeding.
The interpretation of results of studies inwhich the feeding pattern is changed is not
18 A.R.J. Cabrita et al.
always clear. This is particularly true whenthe diet is rich in quickly fermentable car-bohydrates [16]. This is because if the fre-quency of feeding of a whole diet or of thecompound rich in quickly fermentable car-bohydrates is changed, there are generallypronounced effects on rumen pH, molarproportions of VFA, or other rumen factorsthat can influence microbial growth. Thus,the experimental design that offers the clear-est interpretation of synchrony effect is onein which the pattern of feeding the proteincomponent of the diet is changed, while allthe others are maintained constant [16].
3.4. Changing the frequency and pattern of feeding protein supplements
The effect of changing the feeding fre-quency (two or five times per day) of theprotein supplement (soybean meal or bloodmeal + maize gluten) on rumen functionand on the productivity of dairy cows fed abasal diet comprising 47% alfalfa silageand timothy and 53% concentrate feed, con-taining barley and maize was evaluated byRobinson and McQueen [80]. Although theresults do not support the benefits of a syn-chronised release of N and energy in therumen on productive response, they suggestthat soluble protein or peptides or both canact as a pool to supply N for microbialgrowth at specific times when ammonia Nconcentrations are too low.
The available information about rumenfermentation and passage kinetics of parti-cles in the rumen suggests that there is atime period after feeding when the condi-tions of fermentation favour the passage ofparticles recently ingested with character-istics of an appropriate density [79]. Incows fed twice per day, rumination activityis the highest during the night [106] andrumen contents are maximal at midnightand minimal at about 7 a.m. [82]. Theperiod between midnight and the morningfeed may be the period of the day with themost rapid passage from the rumen – rep-resenting an opportunity for increased pas-
sage of undegraded dietary protein from therumen. This passage can benefit the readilyfermentable protein and starch sources thatcould negatively affect rumen fermentationand that are more efficiently digested in theintestine.
However, Gill and Robinson [34] andRobinson et al. [83] observed increasedundegradable protein supply when the pro-tein supplement was added in the day thanwhen it was added in the night, suggestingthat the manipulation of feeding strategiescan change the synchrony of nutrient absorp-tion. Robinson et al. [83] also observed thatgiving the protein supplement at night didnot affect pH and rumen ammonia N con-centration, but increased rumen apparentdigestion of OM and CP and rumen VFAconcentrations and decreased non ammoniaand non bacterial N supply. Robinson et al.[84] varied the time of feeding protein sup-plements within the day and suggest thatthere is considerable diurnal variation in thepatterns of bacterial protein and dietary pro-tein that escape degradation. Although it is,generally, assumed that the feeds ingestedby the dairy cow with a particle size smallenough to leave the rumen will have a shortrumen retention time, this study [84] showedthat there was a delay (6 to 7 hours) betweenthe ingestion of the protein supplement andchanges in the AA profile in duodenaldigesta. The long retention times for feedswith small particle size suggest that theamount of dietary protein that escapesrumen fermentation cannot be rigorouslypredicted through first-order models andthat the evaluations of CP fraction, and, per-haps, of other fractions of feeds made onthis basis can have little value, unless lagtimes of passage and digestion are includedin the evaluation model.
4. CONCLUSION
Although benefits are expected whendairy cows are fed diets that provide a syn-chronised nutrient supply for the rumenmicrobes, the analysed literature shows con-tradictory evidence of synchronising energy
Synchronising the availability of N and energy 19
and N supply to the rumen achieved bychanging dietary ingredients, the feedingfrequency or the feeding patterns, on rumenfermentation, microbial protein synthesisand on productive responses of dairy cows.
Synchronising N and energy supply tothe rumen by changing dietary ingredientscan be achieved either by altering theenergy source, the N source or both. Studiesthat measured the effects of changing starchsource on rumen fermentation show thatmore degradable starch tends to decreaserumen pH, increase rumen VFA production,decrease rumen ammonia N concentrationand alter the site and the end products of fer-mentation. The effects of more degradablestarch on microbial N supply and microbialefficiency of microbial protein synthesis aregenerally small and production responses arenot consistent. Replacing true protein withnon-protein N can be considered a changein the synchronicity of diets. However,when interpreting the effects we have toconsider not only the effects of rate ofrelease of N, but also the effects of N sub-strates supplied – peptides, AA or ammonia– on microbial protein synthesis. The effectsof changing N and energy sources on rumenfermentation are not consistent and thesmall number of studies that have measuredmicrobial N supply and the efficiency ofmicrobial protein synthesis along with theconjugated effects of protein and energysources do not allow us to draw general con-clusions. The lack of production response,using this strategy, is not clearly explainedby the effects on rumen fermentation, sug-gesting the influence of other factors.
The above strategy for altering synchronypresents some problems, since it is not pos-sible to identify whether the responsesobserved in some studies are an effect ofsynchrony or a factor associated with themanipulation of the ingredients (level andtype) themselves. These problems could beovercome, at least partially, by supplyingthe same ingredients according to differentpatterns of feeding.
Although some in vitro and rumen infu-sion studies have observed beneficial effectsof synchrony on microbial growth and effi-ciency of microbial protein synthesis, oth-ers suggest that asynchrony between N andenergy availabilities in the rumen have onlyshort-term effects on bacterial growth. There-fore, the objective when formulating diets,should be first, to obtain an even supply ofenergy, and second, to ensure the supply ofan appropriate amount of available N and onlythen would there be any advantage in assur-ing a synchrony supply of energy and N.
The interpretation of the results fromproduction studies in which the feeding pat-tern of a whole diet is changed is not alwaysclear, in particular, when the diet is rich inquickly fermentable carbohydrates. This isbecause there are generally pronouncedeffects on rumen fermentation that can influ-ence microbial growth. Thus, the experi-mental design most suitable for studyingsynchrony effects seems to be the one inwhich only the pattern of feeding the pro-tein supplement is changed. Altering thetime of day in which the protein supplementis supplied seems to alter microbial proteinsupply to the duodenum and the passage ofdietary protein that escapes degradation.The studies analysed suggest that the amountof dietary protein that escapes rumen fer-mentation cannot be rigorously predictedthrough first-order models and that lagtimes of passage and digestion should beincluded in the models.
The results found in this review suggestthat synchrony effects are less importantin vivo than was theoretically expected,agreeing with the opinions of Sauvant andVan Milgen [94] and Dawson [26] thatruminants have developed some mecha-nisms to overcome or minimise the effectsof asynchrony.
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