Manipulating forage growth and grazing behavior: The essence of rational grazing

Dennis HancockExtension Forage Specialist

UGA – Dept. of Crop and Soil Sciences

2010 Georgia Grazing School

Forage Managed for Hay

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Rotational Grazing

Rational grazing: - André Voisin, Grass Productivity, 1959

• The rationing of pasture forage based on the needs of animal.

• Logical, thoughtful management of grazing based on measurements and observation.

Rational

“How does your forage grow?”

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“How does your forage grow?”

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The Paradox of Forage Quality and Quantity

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Digestibility

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Recreational Grazing(Selective)

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12000Growth CurveWhat happens when a mob stays in a

paddock too long?

What you don’t see….

Roots die back

Roots die back even more

Graze/CutRegrowth

Begins

Graze/CutAgainAdequate

Rest

“More than meets the eye…”

“How does your forage grow?”

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Root Carbohydrates - OptimizedRoot Carbohydrates - Cut Too Early

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Stubble Height

Rest Period or “Round” (d)

14 21 28in. -------------- (g TNC/m2) ------------

3 8.4 13.3 6.56 42.8 34.5 48.29 40.2 43.5 61.5

Management of residual stubble height and rest period (“length of round”) on carbohydrate storage in Tifton 85 stems/stolons.*

* Adapted from Liu et al., 2011. Crop Sci. TNC = Total non-structural carbohydrates.

Stubble Height

Rest Period or “Round” (d)

14 21 28in. -------------- (lbs/acre) ------------

3 8714 9844 118076 9160 8625 99939 11033 9100 8565

Management of residual stubble height and rest period (“length of round”) on effective Tifton 85 yields.*

* Adapted from Liu et al., 2011. Crop Sci. Yields are grazing season totals (3-yr avg.) and include only that forage above the managed residual stubble height. SH did not affect CP or IVOMD. Both CP and IVOMD dec. (L from 60.2% to 58.2%) as rest inc. from 14 to 28 d.

Animal productivity is primarily a function of feed intake.

Forage Intake

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mass Intake Forage

• Animal productivity (gains, milk, fiber, etc.) is primarily a function of feed intake.

• Forage Intake is a function of: Bite size Bite rate Grazing time

Forage Intake

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bitesx

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mass Intake Forage

What happens when:1. Pastures are very short2. Pastures are tall3. The animal’s mouth size is below

average4. Animal is ill or uncomfortable (heat

stress)5. Grazing time is restricted Extra Credit:a. Animal starts feeling fullb. Forage is very fibrousc. Intestinal passage rate is slow (fast)

Approximate Diet Selection of Grazing Animals when Given

Choice

Type of DietAnimal Species Grasses Legumes Browse

Cattle 65-75 20-30 5-10Horses 70-80 15-25 0-5Sheep 45-55 30-40 10-20Goats 20-30 10-30 30-50White-tailed deer 30-60 40-50 10-30

Source: Southern Forages, 4th edition.

Grazing Behavior: Cattle

Grazing Behavior: Cattle• Spend up to 8 hrs/day grazing

“Cows are union members. They refuse to graze more than 8 hours per day.” - Voisin

Longest bouts are at dawn, late afternoon, and at sunset.

• Grass length affects bite rate: 4-5 in. = swallowed right down 10-12 in. = it has to be masticated.

• Bite rate generally runs 30-90 bites/min.

Grazing Behavior: Cattle• Grazing time is genetically

influenced. Identical twins graze almost exactly the

same amount of time (+/- 2%), but differences between pairs of twins will differ (+/-40%).

Bite rate is relatively constant (48-54 bites/ min.), but some graze longer and sustain high rate longer.

Implication: Good grazers can be selected

• Grazing objectives: Exercise and activity Eat and retreat Meet nutritional needs Maintain relatively full gut

Grazing Behavior: Horses

• Spend 14.5 – 16.8 hrs/day grazing 60-70% of the day Mostly around dawn and before sunset

• Grazing time is altered by conditions. Time dec. with heat, insect, etc.

stressors. Low forage quality = inc. passage rate

& inc. forage intake

Grazing Behavior: Horses

• Tend to graze in 3 – 7 extended bouts/d

Bite rate ranges from 12-50 bites/min. Single grazing bouts of up to 180 min. Grazing bouts increase as group size

increases from 1 to 4 horses

• Grazing objectives: Meet nutritional needs Maintain relatively full gut Exercise and activity Social (implications for selectivity)

Recreational Grazing(Selective)

Grazing Habit

Goats prefer to graze above the shoulder.

Grazing close to the ground increases the opportunity for parasitic larva consumption.

Goat Grazing Preference TrialUK Robinson Station

2006

Goat Grazing Preference TrialUK Robinson Station

2006

(Most to least)

Sorghum SudanWhite clover

TurnipRed clover

ChicorySericea Lespedeza

Tall OatgrassAlfalfa

Warm Season Grasses(EGG, Switch, BB, Indian)

Reed CanarygrassOrchardgrass

Annual LespedezaNovel Endophyte TFEndophyte Free TF

Infected TFBluegrass

Bermudagrass

Resources

Grass Productivity – Andre’ Voisin, 1959.On Google Books or available for purchase

Horse Behavior – George Waring, 2003.On Google Books or available for purchase

Resources

Managing Grazing of Horses

Horse Feeding Behavior

Resources

I’ve run out of pasture.

Questions?