Nutrition plays a significant role in animal reproduction and there is always a positive correlation between the two. The influence of nutrition in animal reproduction begins early in the animal’s life as the influence of nutrition in young animals affect the age at which they reach puberty. In mature animals poor nutrition can reduce production of ova and spermatozoa, so that a female either fails to conceive or produce fewer offspring than normal. During pregnancy females have specific nutrient requirements for the maintenance and growth of fetus (es).The following features have to be borne in mind while assessing the nutrient requirements for reproduction.
- The reproductive process is not the sole productive process that is being carried out by the animal.
- The nutrient requirement varies widely from one phase of reproductive cycle to another.
- Reproduction is often ‘all or nothing’ phenomenon and consequence of failure can be severe for the farmer.
Nutrition and the initiation of reproductive ability:
The level of nutrition markedly influences puberty in livestock. The faster an animal grows the earlier it reaches sexual maturity .In cattle, puberty occur at a particular live weight or body size than at a fixed age.
Table: 1 Age and size at puberty of HF cattle reared on different planes of nutrition
- Plane of nutrition greatly influences the age at puberty.
- Liberal feeding of diets with high energy content induces puberty in cattle.
In sheep the attainment of puberty is complicated by their seasonal breeding pattern, spring born ewe lambs that are well nourished reach puberty in the same autumn of the same year (6 months of age) whereas poorly fed lambs come to puberty at 18 months of age.
In pigs high plane of nutrition do not advance puberty. The primary determinants in pig are age, (170-122 days) breed (cross bred reach puberty 20 days before purebreds) and the age at which gilts are mated with the boars.
In practice the factor that decides when an animal has to be first used for breeding will be body size. Although heifers of the large dairy breeds may be capable of conceiving at 7 months of age, they are not normally mated until 15 months of age. This is to ensure complete development of the females’ reproductive tract as well as the udder for nourishment of the newly born. Inadequate nutrition of the pregnant females retard fetal development and also milk production subsequently upon parturition.
Rapid growth and the earlier attainment of size appropriate to breed have the economic advantage of reducing the non-productive part of the animals’ life. In meat producing animals high plane of nutrition in the early life results in better body weight. One of the disadvantages of rapid growth in breeding animals is excessive fat deposition which interferes with breeding hence it is advantageous to keep them at a plane of nutrition which allows rapid growth but not excessive fat deposition.
Plane of nutrition, fertility and fecundity:
In female animals the primary determinants of fertility (whether or not the animals conceive) and fecundity (litter size) is the number of ova shed from the ovaries. In the cows the ovulation rate is normally one, in ewes it is normally one-three and in the sow it is 15-25.
It is well established that flushing of ewes i.e. providing them high plane of nutrition 3-4 weeks before mating results in improved conception and also chances of having twins and triplets. Flushing is not only advantageous for under nourished ewes but also for those on a higher plane of nutrition for high fertility and fecundity.
- Flushing improves the ovulation rate by increasing the release of gonadotropic hormones, FSH for increased ova production and LH for the maturation and release of oocytes.
- High plane of nutrition which leads to greater levels of glucose triggering increased production of insulin and steroid hormones by the ovary.
A high plane of nutrition in sheep at the time of ovulation can reduce the survival of oocytes and the embryos, after fertilization due to increased metabolism of progesterone, the hormone required for establishment and maintenance of pregnancy. After mating the plane of nutrition should be reduced to about maintenance levels from flushing levels.
In cattle a high plane of nutrition after mating and conception increases lactation, and progesterone supply will be augmented from fat reserves.
Plane of nutrition in males:
There is no reliable evidence that suggests correlation between male fertility and higher planes of nutrition, though it is recognized that underfeeding has deleterious effect on males. However males do have higher metabolic rates and therefore high energy requirements of maintenance than females and castrates.
Effect of specific nutrients on fertility:
Manynutrients and their deficiencies influence fertility in animals through their effects on general metabolism. Common nutrient deficiency that affects reproductive efficiency in livestock includes Energy, protein, vitamins and minerals.
Energy deficiency in young animals affects age at puberty, and sexual development due to reduced endocrinal activity. When mature animals are fed low energy diets for long libido and testosterone production are negatively affected.
Obesity or overfeeding reduces libido and sexual maturity in male animals.
Protein deficiency influences reproduction due to its impact on feed intake.
- Supplementation of dietary protein can increase the ovulation rate both in sheep and cattle.
- In pigs prolonged protein deficiency especially in young animal’s leads to reproductive failures.
Relationship between reproductive efficiency and vitamins has been long recognized. In general all the vitamins are essential for reproduction due to their specific roles in cellular metabolism maintenance and growth
Vitamin A and E are of great importance because of their role in maintaining cellular integrity and antioxidant property respectively. They also help in maintenance of immune status of animals which in turn directly impacts upon the health of the animal.
Vitamin D can be synthesized by skin in the presence of sunlight, and vitamin K by the microbes in the ruminants. Hence from practical point of view only vitamin A and E need to be supplemented.
Vitamin A is necessary for normal epithelial development in all species. Failure of epithelial development negatively impacts reproductive function in all species.
Clinical manifestation of infertility related to vitamin A deficiency includes
- Delayed onset of puberty in males and females.
- Abortions and birth of weak, blind or deformed calves.
- Increased incidence of retained placenta with kerartinization
- Suppressed libido in males
Nutritionists recommend supplementing all diets with vitamin A as an inexpensive insurance against deficiency. But excess supplementation should be avoided. Nitrates and aflatoxin destroy vitamin A stored in liver, under such situation large doses of injectable vitamin A are recommended.
Vitamin E promotes immune function of animals due to antioxidant property, protecting cells and tissues in the body from oxidative damage due to action from free radicals. In subclinical mastitis supplementation of vitamin E @740 IU/cow/day during dry period led to 37% reduction in the incidence of clinical symptoms. Supplementation of vitamin E and Se reduces incidence of retention of placenta and improved reproductive performance.
In non ruminants deficiencies of B complex vitamins such as riboflavin and folic acid have been shown to reduce the survival of embryos.
Phosphorus ‘P’ deficiency in grazing ruminants is associated with poor fertility, probably by affecting the general metabolic processes, feed intake and the general plane of nutrition .However there is evidence that ‘P’ deficiency has a direct effect on reproduction through suppressing estrus cycle.
Selenium (Se), copper (Cu), Molybdenum (Mo), Iodine (I), Manganese (Mn) and zinc (Zn) are the other trace minerals that affect fertility.
Selenium deficiency is associated with deficiency of Vitamin E. It reduces fertility by affecting fertilization and viability of spermatozoa. In selenium deficit areas supplementation of selenium in the diets of ewes increases the lambing percentage. Se supplementation along with Vitamin E in dairy cows reduces the incidence of retention of placenta.
Herbage copper levels of less than 3mg/kg DM delay the return of estrus and lengthen the calving interval in cattle. Copper deficiency can be induced by excessive molybdenum in the diet resulting in depressing the estrus, because it reduces the secretion of LH. Deficiencies of Cu and Iodine reduce egg production in poultry.
Delayed ovulation and poor conception rates have been associated with Mn deficiency in cow’s goats and ewes. Manganese deficient ewes and cows may require more services per conception and respond to Mn supplementation.
Zinc deficiency affects the reproductive performance of males by preventing spermatogenesis. Zinc is a component of enzyme thymidinekinase, which is required for spermatogenesis. In the female Zn deficiency may passively increase embryo mortality and reduced hatchability in poultry.
Nutrition and growth of fetus:
Total requirements of nutrients for growth of the fetus increases exponentially during gestation and are quantitatively significant in the last trimester of the pregnancy. Nutrients are also required for the growth of the fetal membranes, uterus, mammary glands and the body reserves of the mother. The placenta has a key role in ensuring that the fetus receives optimal supplies of all nutrients required but overfeeding during mid pregnancy restricts the size of placenta and hence reduces birth weight. Underfeeding in late pregnancy also reduces birth weight. Nutrient deficiencies in pregnancy may affect either the mother or the fetus or even both. Many vitamin and mineral deficiencies are first manifested in the fetus. Pregnancy toxemia is a condition in ewes caused by deficiency of glucose due to reduction in feed intake during gestation. This condition can be prevented by ensuring adequate feed supply in late pregnancy by using foods that supply glucose or its precursors rather than acetate, i.e. concentrates rather than roughages.
Consequences of impaired or deficient nutrients to livestock can be severe to the farmer. In dairy industry animals are kept solely to produce milk and rear calves. If cow fails to conceive, her output will be zero and the farmer suffers financial loss. Small litters in sheep and pigs can be the critical factor between profit and loss. Hence great care must be given to nutrition in farm animals to ensure optimal reproduction and profitability in livestock.
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- McDonald P Edwards RA, Greenhalgh JFD and Morgan CA 2002, Animal Nutrition, Sixth edition, Pearson education, Delhi.
- Sorenson.AM et al 1959, Bulletin of the cornel university Agricultural experimental station No.936.
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- Underwood EJ and Suttle NF 1999 The Mineral Nutrition of Livestock, 3rd edition, Wallingford, CABI Publishing.