Endocrine profiles and follicular development in early-weaned postpartum beef cows

Abstract

This study investigated whether treatment with progestagen, which improves fertility after early weaning in postpartum cows, altered concentrations of gonadotrophins or development and function of follicles. Patterns of luteinizing hormone (LH), oestradiol and follicle-stimulating hormone (FSH) and of follicular growth before first postpartum ovulation were compared in two experiments. At 17 to 25 days post partum, suckled anoestrous beef cows received an ear-implant containing 6 mg progestagen (norgestomet) for 9 days or served as untreated controls. Calves were weaned from all cows 7 days after initiation of treatment. Cows were observed for oestrous behaviour twice a day until 10 days after weaning. As expected, the proportion of anoestrous cows that formed a corpus luteum with a normal lifespan was greater (P < 0.01) in cows treated with norgestomet (Expt 1, 17 of 24; Expt 2, 18 of 22) than in control cows (Expt 1, 2 of 16; Expt 2, 3 of 18). In general, patterns of secretion of LH and oestradiol and of final growth of the preovulatory follicle did not differ between control and norgestomet-treated cows. However, there was a transient rise in FSH in association with weaning in control cows that did not occur in norgestomet-treated cows. In addition, mean LH increased more rapidly and mean oestradiol was higher during the 3 days immediately before the preovulatory surge of LH in the norgestomet-treated cows (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnancy Rates for Embryos Transferred from Early Postpartum Beef Cows into Recipients with Normal Estrous Cycles1

“…Estrus was predicted to occur at an average interval of 4-5 days after weaning [15,17,18]. Cows were observed for estrous behavior twice daily throughout the experiment.…”

Postpartum Ovarian Resumption in Native Dairy Cows in Upper Egypt and their Relation to Oxidant Antioxidant Status

“…However, pregnancy is not maintained, apparently because the corpus luteum is regressing before the ovary receives the uterine signal that a pregnancy exists [30,31]. Short cycles are also common after induced ovulation in the postpartum period by weaning, weaning plus GnRH injection, a single injection of GnRH, intermittent injection of GnRH and continuous infusion of GnRH as well as after the first ovulation at puberty [32][33][34][35][36][37]. Premature release of prostaglandin F2α (PGF2α) from the uterus on day 5 of a short estrous cycle is probably the mechanism involved in subnormal luteal function in sheep and cattle [38].…”

Delayed Resumption of Cyclicity in Postpartum Dairy and Beef Cows

“…Finally, management and hormonal programmes have been combined in beef cows to enhance the acute stimulatory effects of calf and progestagen treatment removal on LH pulse frequency, DF final differentiation and ovulation. Progestagen was administered for 7-9 days before calf removal, and led to onset of oestrus within 5 days after weaning (Breuel et al 1993) and normal luteal phases subsequently (Ramirez-Godinez et al 1981, Rivera et al 1998). It appears, however, that the advantages of calf removal in addition to a hormonal treatment regime have not been conclusively shown.…”