Significance of litter size, duration of dry period and stage of pregnacy on milk yield and composition in dairy animals

Abstract

The factors influencing the amount and composition of produced milk can be divided into two groups, namely internal and external factors. This is very important to remember when evaluating the milk quality and in the improvement of milk yield and composition in a dairy enterprise. Of the external factors it is possible to mention a few: litter size, duration of dry period and stage of pregnancy. The present discussion explores the significance of litter size, duration of dry period and pregnancy on milk yield and composition in dairy production. In goats and sheep dams bearing twins or triplets had higher milk yield than single bearing dams, and this significant increase in milk production in these dams that carried twins and triplets was followed by an increase in lactation length. Due to the amount of milk animal produce, the drying-off process is often more complicated for dairy animals (cattle, goats and some sheep). However, this period is essential to enables dams to regain the body condition needed to support the subsequent pregnancy and lactation. The majority of dairy animals dry off spontaneously because of the aforementioned natural decrease in daily milk production. The length of dry period influences milk production in the subsquent lactation, with shortening of the dry period showing a markedly negative effect on milk performance of dams. Lactating animals should have an opportunity to rest and regenerate mammary tissue between lactations. F or optimal dairy animal performance in the next lactation, lactating animals should have an opportunity to rest and regenerate mammary tissue between lactations. The amount of produced milk and its composition are influenced by the stage of pregnancy: in the first half of pregnancy it is not possible to observe any pronounced changes while in the second stage of pregnancy can observe a gradual decrease in milk production as well as an imcrease in levels of individual milk components. During pregnancy and the first few days postpartum, milk supply is hormonally driven – this is called the endocrine control system . This implies that in the course of lactation, changes in milk production are caused by changes in activities of the endocrine system that are caused by hormones sectreted by pitiutary gland (hypophysis cerebi) and placenta. During the latter part of pregnancy, the mammary gland is making colostrum, but high levels of progesterone inhibit milk secretion resulting reduced milk yield. Progesterone influences the growth in size of alveoli and lobes; high levels of progesterone inhibit lactation before birth. Progesterone levels drop after birth; this triggers the onset of copious milk production. Estrogen stimulates the milk duct system to grow and differentiate. Like progesterone, high levels of estrogen also inhibit lactation, while the hormone prolactin must be present for milk synthesis to occur.