The document discusses factors that affect fertility in livestock, including heredity/genetics, nutrition, age, climate, and disease. It provides examples of how each factor can influence fertility, such as genetic mutations causing infertility, poor nutrition reducing ovulation rates, climate affecting sperm production and mating behavior, and diseases stopping egg/sperm production or causing abortion. Proper management can help control these factors through strategies like vaccination, worm control, selective breeding, and meeting nutritional needs.
B.Sc. Agri II LPM U 2 Reproductive System In Livestock
1. Reproductive system in Livestock
Course : B.Sc. Agriculture
Sem II
Sub: Livestock production and Management
Unit 2
2. Measures and factors affecting fertility in livestock
The following factors may affect the fertility of farm
animals:
•Heredity/Genetics
•Nutrition
•Age
•Climate
•Disease
•Management
3. Heredity/Genetics
Genetics/heredity affects the fertility of farm animals in a variety of ways.
Some animals may be genetically infertile.
Genetic mutations can occur which can produce infertility. They can also
give rise to abnormal development in embryos so much so that the young
fail to develop properly and cause foetal death or atrophy. These are called
lethal factors. Poultry seem to be more affected with lethal factors than
other animals.
A peculiar form of sterility occurs in heifers born twin to a bull. In about
90% of such cases, the foetal circulations fuse. The male then remains
normal but the female becomes a freemartin. To some extent, the female
becomes masculinised by androgen produced by its twin.
4. Nutrition
Generally the heavier the animal the more fertile, but overfat animals
may have difficulty mating, conceiving, and birthing. Puberty is determined by
body weight not by age of the animal.
Poor nutrition may cause irregular cycles in females, reduced ovulation,
weak offspring, pregnancy toxaemia or reduced twinning.
In males poor nutrition may reduce sperm quantity and quality.
The amount of food given to ewes immediately before they are joined is
also of considerable importance. Experiments have shown that, if at that stage, a
ewe is given a generous plane of nutrition she is likely to shed more ova than
normal. This results in a higher lambing percentage by increasing the number of
twin births. This procedure is known as flushing. There is evidence to suggest
that the numbers of sperm produced by rams may be increased by feeding a high
energy and high protein diet for about six weeks before the mating season.
5. Age
The effect of age is closely linked with nutrition, as puberty is determined by
body weight not by the age of the animal. The physical size of animals may
affect their ability to mate, carry a foetus or give normal birth to offspring.
After puberty, fertility generally increases for some time then decreases when the
animal gets too old. In contrast, goats have a greater chance of twin kids as they
age.
The amount of food given to the pregnant mother also influences birth
weight of offspring and heavier offspring have a better chance of surviving.
Conversely, the undersized new born animal has less chance of surviving and
frequently dies in the first few days following birth. Such an animal is less able
to maintain its body temperature and may die quickly if born in cold weather.
If over-fed, the pregnant animal may suffer difficulties in birth which
could also lead to death of either the offspring or mother or both.
6. Climate
Daylength
Some species are polyoestrous (pigs and cattle), this means that they cycle
throughout the year. Other species are seasonally polyoestrous meaning that they
breed only during particular months of the year (horses, sheep, poultry and goats).
The decreasing daylight hours stimulate ewes and does to cycle while the
increasing daylight hours stimulate hens and mares to cycle.
The period of the year at which animals breed has evolved by natural
selection to ensure the young are born at a time giving them the best chance of
survivial. In sheep, the mechanism by which the breeding season is brought about
is triggered by hours of decreasing daylight. This stimulates the anterior pituitary
gland to produce FSH. Experiments have shown that, by the use of electric light,
sheep in the Northern Hemisphere can be made to breed at the same time of the
year as sheep in the Southern Hemisphere. When ewes are taken across the equator
from north to south, they change their breeding season to correspond with the hours
of daylight.
The daylength is also a factor with the production of sperm in the ram but
does not seem to be in other animals.
7. Temperature
High body temperatures produced in rams by high summer temperatures is a
cause of poor quality semen. This also affects semen formation in bulls.
High temperatures can also affect mating with reduced sexual activity.
Conception rate is also reduced. This affects the number of offspring born.
In males, the ability of the scrotum to reduce the temperature of the testes
sufficiently to produce sperm of sufficient number and viability is severely
restricted.
It is important, therefore, to have both climatically adapted animals and to
provide conditions conducive to proper spermatogenesis to ensure maximum
fertility.
8. Disease
Disease as a factor that can affect the fertility of farm animals can be
related to nutrition, climate, management and genetics. Disease may stop
sperm or egg production, may cause abortion, may reduce the health of the
foetus so reducing the chance of its survival.
Infective conditions include brucellosis, trichomoniasis,
leptospirosis and vibriosis. These diseases have dramatically reduced in
recent years due to diligent eradication campaigns.
Persistance of the corpus luteum, usually as a result of infection can
be a problem particularly in cows. This prevents the production of FSH and
consequently normally cycling does not occur.
9. Management
The farm manager has the ability to control or at least to maniupulate
the factors that have been discussed above. Examples of how farmers control or
manipulate these factors include:
•a suitable vaccination program
•strategic worm control program
•selection of both male and female animals on the basis of their ability to
produce offspring
•if using natural matings, ensuring the correct proportion of male animals to
female animals
•selecting animals suited to the environment
•providing correct nutrition for the stage of production of the animals
•selecting paddocks that minimise the detrimental effects of environmental
factors for newly born animals