Biostimulatory Effect of Bulls on Temporal Patterns of Leptin Concentrations and Resumption of Luteal Activity in Primiparous, Postpartum, Anestrous, Beef Cows.

Abstract

The biostimulatory effect of bulls to reduce the interval from calving to the resumption of luteal activity involves a change in the pulse frequency of LH. There is a possibility that pheromonal influence of the bull may alter metabolic hormones. Leptin, a metabolic hormone, is known to modulate activity of the hypothalamic-hypophyseal-ovarian axis, specifically to control secretion of LH in the bovine. The objective of this experiment was to determine if continuous bull exposure alters temporal patterns of leptin concentrations in primiparous, suckled cows. The null hypotheses were that concentration patterns of leptin do not differ among cows exposed to bulls (BE) or not exposed to bulls (NE); and, that there is no relationship between the resumption of luteal activity and leptin concentrations in BE or NE cows. Fifty-three Angus x Hereford cows were assigned randomly to be exposed (n=26) or not exposed (n=27) to bulls for 40 d. Progesterone patterns at 3-d intervals from d 0 to 40 were used to evaluate luteal activity. Proportions of BE and NE cows cycling on d 0 did not differ (P>0.10), but more (P<0.05) BE than NE cows resumed luteal activity by d 40. Temporal patterns of leptin concentrations did not differ between BE and NE cows. However, there was a treatment by day interaction (P < 0.05) for leptin concentrations in BE and NE cows that began to cycle after d 0. Leptin concentrations increased on d 15 and remained stable until d 21, then increased again by d 27. Whereas, concentrations of leptin in NE cows increased on d 18, decreased on d 21, then increased by d 27. There was a strong linear (P<0.05) relationship between leptin concentrations and days to the resumption of luteal activity within BE and NE cows. This indicated that as days until the resumption of luteal activity decrease, leptin concentrations increase. We conclude that bull exposure alters the temporal patterns of leptin concentrations as a result of accelerating the resumption of luteal activity. However, this effect is indirectly mediated through the physiological mechanism that stimulates the resumption of luteal activity in primiparous, postpartum, anestrous, beef cows. (poster)