The Effects of Ewe Diet on Progesterone Concentration and Colostrum Production

Abstract

In well fed ewes with one or two lambs, large volumes of colostrum accumulate in the mammary glands during the last few days of pregnancy and copious milk secretion begins soon after birth. In underfed ewes, prenatal colostrum accumulation is reduced markedly, lactogenesis is delayed. (Mellor and Murray, 1985). Robinson (1985) has shown that there is a sharp increase in the ewe's net protein requirements for udder growth and colostrum production in the last two weeks pre-partum. McPherson, Robinson and Fraser (1981) found that the detrimental effects of a maternal energy deficit on the ewes colostrum supply at parturition can be ameliorated by increasing her supply of amino acids through the provision of a dietary supplement of rumen UDP. The peri-parturient transitions from udder growth to colostrum accumulation and then milk secretion depend largely on withdrawal of progesterone and surges in prolactin, Cortisol and oestrogen, with the progesterone inhibiting and Cortisol potentiating the lactogenic actions of prolactin (Delouis, 1978). The slower progesterone withdrawal in the underfed ewes was associated with a delay in lactogenesis. Thus the objective of this experiment was to study the effects of feeding different diets on ewe colostrum production and quality, and on progesterone concentration pre and post lambing.