Applied Animal Nutrition-I

INTRODUCTION

• The influence of nutrition on reproduction begins early in the animal's life, as the plane of nutrition in young animals can affect the age at which they reach puberty.In mature animals, poor nutrition can reduce the production of ova and spermatozoa, so that the female either fails to conceive or produce fewer offspring than normal (i.e.litter size is reduced).
• The reproductive cycle may be considered to consist of three phases.

First phase

• The first phase, which is important to both the sexes, comprises the production of ova and spermatozoa.
• Nutrient requirements for these processes in mammals are small compared with the egg production in birds. foe eg; a boar, which produces a large ejaculate of 150 -250 ml, is estimated to require 0.4 MJ, ME per ejaculate, which is equivalent to less than 2 % of its maintenance requirement for metabolisable energy (23.8MJ/day).

Second phase

• The second phase of the cycle is pregnancy. Even in pregnancy, nutrient requirements for the growth of foetuses are in total, relatively small. for eg: a ewe producing twin lambs weighing a total of 7 kg at birth will deposit about 1.4 kg of protein in the foetuses and associated tissues (such as placenta),which over a gestation period of 147 days is less than 10 g/day. In contrast, a growing sheep gaining 300 g in liveweight per day would deposit in its tissues about 50 g of protein per day.
• However in assessing nutrient requirements for reproduction, several important features of reproductive processes must be borne in mind.The first of these is that reproduction is often not the sole productive process being carried out by the animal. In the case of cattle, for eg: young females may be expected to conceive at 15 -20 months of age, at about half of their mature body weight and will have to continue growing while producing a calf. After calving, the female will be expected to conceive again within 2 -3 months, at a time  when she is producing large quantities of milk.
• The second important feature of nutrient requirements for reproduction is that they vary considerably from one phase of the reproductive cycle to another. For example, the ewe conceiving twins will have very small protein requirements for foetal growth at the start of pregnancy, but by the last week of pregnancy she will be depositing as much as 30 g of protein per day in the foetuses.

Third phase

• Third phase is lactation
• In the female mammal, the quantities of nutrients required in excess of those needed for maintenance are small for the production of spermatozoa and ova, moderate for the  pregnancy and large for the lactation.
• Consequently, nutrient requirements fluctuate considerably during the reproductive cycle, especially when there is an interval between weaning and the next conception.
• Under natural conditions, such fluctuations in nutrient demand are partly matched with fluctuations in the food supply, but both in the wild and in intensive animal husbandry the mother often has to act as a buffer by depleting her body reserves in times of high demand and poor supply and restoring them when conditions are more favourable.