Livestock ReproductiveTechnologies

on Commercial Farms

Breeding Cycles

Breeding cycles vary greatly from animal to animal.There are three main types• Monoestrus (mono = one) animals such as dogs and

cats where the female has one period of sexual activity per cycle. A bitch will come on heat once every six months

• Polyoestrus (poly = many) animals like rabbits and pigs which breed the whole year

• Seasonally polyoestrus animals like sheep, goats, horses and cattle where breeding is confined to one season of the year. But there are many periods of heat during this season.

This diagram shows a seasonal polyoestrus breeding animal. The peaks indicate ovulation.

Male Breeding Cycles

• Male breeding cycles are not so clearly defined as the female cycle, but three main types can be distinguished.

• Where there is a definite rutting season; as in deer, wild ox, and mountain breeds of sheep. Outside of this season they will not breed.

• Where the males are most efficient during the female’s season; as in sheep

• Where the males are equally efficient at any season; as in cats, dogs, pigs and cattle.

The Role of Hormones in Reproduction

• Hormones are chemical substances that stimulate the sex glands into activity causing the testes to make sperm and the ovaries to shed eggs.

The Female Hormones

• FSH (Follicle stimulating hormone) - Stimulates several follicles are to grow. Only one or two follicle reaches full maturity

• Luteotropic - Triggers one or two follicles to rupture releasing the ova into the fallopian tube to begin the journey to the Uterus. This is called ovulation.

• Oestrogen - Produced by the growing follicles. Triggers the animal to come into heat

• Progesterone - Produced by the corpus luteum. Triggers the animal to go out of heat

Stages of the oestrous cycle

• Mating animals at a time close to ovulation is essential so that sperm will still be alive when the eggs are shed. It is necessary to know the length of the cycle (ewe 16 days, cow 21 days) and also when ovulation occurs in relation to oestrus.

Animal Length of Cycle

When ovulation occurs

Mare 16 days 1 day before the end of heat

Cow 21 days 13 -15 hours after heat has ended

Ewe 16 – 17 days

Towards the end of heat

Sow 21 days 36 -48 hours after onset of heat

Synchronization of Oestrus

• occurs when females in a herd are given regular doses of progesterone which halts the oestrus cycle.

• When the farmers stops using the hormone, all the females will come into oestrus at one time. This is a common practice on dairy farms where the farmer is undertaking an artificial insemination (AI) programme.

• It means that he is able to inseminate all the cows at one time.

• It also means that calving can be condensed into a specific time frame.

Super ovulation

• Often used on New Zealand farms. For example when a dairy farmer is collecting eggs from high producing cows for transplanting into donor cows, or a sheep farmer wants to increase his lambing percentage by producing more twins or multiples

• Females are injected with FSH hormone which causes the ovaries to shed a greater number of eggs.

• See later notes on Embryo Transfer.

The Male Hormones

• FSH - Triggers the testis to produce sperm

• Testosterone - Responsible for the male characteristics

Sheep Reproduction

• With sheep there are several different factors that the farmer could be breeding for:

• Meat

• Fine wool

• Coarse (carpet) wool

• Dairy sheep (milk)

• Multipurpose breeds

• The choice the farmer makes when choosing the ram will depend on what is being bred for.

• The farmer will need to consider the different factors that are important to improve and select for these.

• When it comes to the reproductive tracts though, there is no difference between meat breeds, wool breeds and dairy breeds.

OVERVIEW OF THE EWE’SREPRODUCTIVE TRACT.

• Puberty is when a ewe first exhibits oestrus (heat).

• Puberty is influenced by age, breed, genetic selection, body size, nutrition, and season of birth.

• Most ewe lambs reach puberty between 5 and 12 months of age.

• Ewe lambs will tend to reach puberty their first autumn.

• Single lambs cycle at a younger age than twin and triplet-born ewe lambs, due to their size advantage.

• Lambs born early in the season reach puberty earlier than those born late in the season, due to their increased age and body weight.

• High levels of feed pre- and post weaning reduce the age at puberty.

• Ewe lambs from fine-wool, coarse wool, and late-maturing medium-wool breeds reach puberty later than many of the meat (Suffolk, Dorset, etc.) and hair sheep (Drysdale) breeds.

• Finnsheep and Romanov ewe lambs and their crosses reach puberty at an early age.

• Crossbred ewe lambs cycle at a younger age than purebred ewe lambs.

The Oestrus Cycle

• Reproduction in non-human mammals is regulated by an oestrus cycle.

• In sheep, the length of the oestrus cycle ranges from 13 to 19 days and averages 17 days.

• The phases of the oestrus cycle are proestrus, oestrus, metaoestrus, and dioestrus.

• Oestrus is the period of time when the ewe is receptive to the ram and will stand for mating.

• It lasts approximately 24 to 36 hours. • Ovulation (release of eggs by the ovary)

occurs in mid to late-oestrus.

• Metaoestrus begins with the cessation of oestrus and lasts for about 3 days.

• Primarily it is the period of the formation of corpus luteum (CL).

• The corpus luteum produces progesterone and maintains pregnancy in the ewe.

• Dioestrus is the period of the oestrus cycle when the CL is fully functional.

• Proestrus begins with the regression of the CL and drop in progesterone and extends to the start of oestrus.

• Rapid follicular growth is occurring during this period.

• It usually extends from day 4 to day 13-15 of the cycle.

• Anoestrus refers to a state where the normal cycle stops.

Oestrous cycles and the seasons.

• The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones.

• Most sheep are seasonally polyestrus and short-day breeders. They will begin to exhibit oestrus when length of day begins decreasing.

• They will come into heat every 16 to 17 days until they are bred or return to anoestrus.

• Thus, the most natural time for sheep to breed in the NZ is autumn (approx May.).

• Some sheep breeds are less seasonal.

• They breed almost year-round or have an extended breeding season. The less seasonal breeds include Dorset, Rambouillet, Merino, Finnsheep, Romanov, and hair sheep.

• The most seasonal breeds are the British long wool and meat breeds.

• The closer the flock is located to the equator, the longer the breeding season and the less complete and shorter will be the seasonal anoestrus.

• The signs of oestrus in the ewe are much less pronounced than in the cow or doe and can usually not be detected unless a ram is present.

• When mature ewes are in heat, they will seek out the ram and stand still for him to mount them. Sometimes they wag their tails vigorously. They may nuzzle the ram around the belly or scrotum and even try to mount the ram.

• Young ewes rarely exhibit these behaviours.

• There is evidence to suggest that rams and ewes prefer to mate with their own breed, but when there is no alternative ewes will mate with almost any breed of ram.

OVERVIEW OF THE RAM’S REPRODUCTIVE TRACT:

• See sheet

Control Mechanisms

• Hormones are the main control mechanism in farm animals.

• Hormones are chemicals that are released into the blood stream to control body actions or processes.

• The main gland involved in controlling reproduction are the pituitary gland, the gonads (testes and ovaries) and in pregnant females the placenta.

Pituitary Gland:

• The pituitary secretes several hormones:1. Follicle stimulating hormone (FSH): this stimulate the

growth and development of follicles in the ovary and the production of sperm in the testis.

2. Luteinising hormone (LH): in females it acts upon the mature follicle causing it to rupture and to develop into a corpus luteum; in males it stimulates the production of testosterone in the testis.

3. Lactogenic hormone (prolactin): this is the hormone that helps maintain lactation in the females of some animals.

4. Oxytocin: this has 2 roles: stimulates the letdown of milk in the lactating animal and it stimulates muscular contraction of the uterus at mating and at birth to help expel the foetus.

The gonads:

• These produce the sex hormones.

• FEMALES: the ovaries produce 3 main hormones of reproduction:oestrogen, progesterone and relaxin.

• MALES: the testis produce one main hormone: testosterone.

TASK:

• read pg 128 of dynamic agriculture: make notes on the following:

• Oestrogen:

• Progesterone:

• Relaxin:

• Testosterone:

• Hormonal Aspects Definitions Activity sheet

• In some animals there are others mechanisms there to help prevent the animal becoming pregnant at the wrong time of the year.

• Particularly with seasonal breeding animals. They react to the changes in light (as mentioned earlier) and begin their mating cycle.

• This means they will be giving birth at a time when there is enough food to feed themselves so they can then produce milk.

TASK:

• Read pg 130, day length, dynamic agriculture

• Other control mechanisms include: TASK: make notes on each of the following from the dynamic agriculture

• Genetics, Nutrition, Climate, Disease and Management techniques