MATERNAL AND CONCEPTUS FACTORS AFFECTING HISTOTROPHIC NUTRITION AND SURVIVAL OF EMBRYOS

It is well established that embryo survival in sheep is influenced by a range of factors including maternal nutrition, maternal age, stage of the breeding season, number of oocytes shed at the time of mating and maternal endocrinology. However, the impact of these factors on the finely balanced relationship between the embryo and the uterus is less well understood. Ovine and caprine conceptuses secrete a range of proteins during the second and third weeks after mating, which are believed to be involved in overcoming luteolytic mechanisms, and in stimulating biochemical changes in the endometrium to facilitate the maintenance of pregnancy. Furthermore, endometrial secretory products are involved in the nutrition and growth of the developing conceptus. Endometrial secretory activity is modulated by changes in levels of ovarian steroids, which in turn are affected by extrinsic factors including maternal feed intake and the stage of the breeding season, and by intrinsic factors such as ovulation rate.