Onset of normal cycles in postpartum anovulatory dairy cattle treated with kisspeptin.

Abstract

The efficacy of a long-acting synthetic derivative of kisspeptin (Kp) to initiate normal oestrous cycles was tested in 24 mixed-aged, Holstein-Friesian cows that were 18-25 days postpartum on the day of treatment (D0). Groups of eight cows received saline (Sal) vehicle by intramuscular injection at 8:00 and 16:00 h (Sal-Sal), Kp at 8:00 h and vehicle at 16:00 h (Kp-Sal) or Kp on both occasions (Kp-Kp). The Kp dose was 15 nmol per 60 kg body weight. The ovaries of the cows were examined daily by ultrasonography between D4 and D14. Blood samples were collected from a tail vessel at 0, 2, 4, 8, 10 and 12 h relative to the time of the first injection for luteinizing hormone (LH) and follicle-stimulating hormone assay. Additional samples were collected daily from D4 until D14 and D19, 22, 26 and 29 for progesterone assay. LH surge-like responses were observed in cows treated with Kp at 8:00 h. Ovulation was consistently induced by Kp within 48 h when a dominant ovarian follicle of at least 10 mm in diameter was observed (8/14) but in no cases (6/14) during a new wave of ovarian follicular development comprising follicles <10 mm in diameter. The subsequent ovulatory cycle was of normal length in most cases as compared with short 8- to 12-day cycles observed in spontaneously ovulating cows. We conclude that Kp treatment can induce ovulation in postpartum dairy cows, with ensuing oestrous cycles of normal length, if administered when a mature dominant follicle is present in the ovaries.

Lay summary: Cow fertility is important for efficient, profitable dairy farming. Cows that take too long after calving to become fertile are problematic. We tested a synthetically made, long-acting hormone called kisspeptin (Kp) to advance the time that cows become fertile after calving. Twenty-four dairy cows that had been calved for 3-4 weeks were used. One group of eight cows received an injection of Kp at the morning milking, another eight cows received Kp at both the morning and afternoon milking, while the last group of eight cows served as untreated controls. Kp treatment caused a desirable hormone response from the cows' brain. Normal oestrous cycles resulted, but only when a mature follicle was present in the ovary. Further study is required to analyse whether the use of a long-acting Kp drug could be used as an effective treatment for stimulating dairy cows to become more fertile after calving.