Cavalieri, John (2019) Absence of a corpus luteum and relatively lesser concentrations of progesterone during the period of pre-ovulatory follicle emergence results in lesser pregnancy rates in Bos indicus cattle. Animal Reproduction Science, 204. pp. 39-49.

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Abstract

Concentrations of progesterone before AI have had variable effects on fertility in both Bos indicus and Bos taurus cattle. The aim of this study was to determine if fertility and concentrations of progesterone after AI were affected in Bos indicus females when pre-ovulatory follicles develop in the absence or presence of a corpus luteum (CL). Between 6.5–7.5 days after a synchronised oestrus, all follicles ≥4mm in diameter were aspirated (Day 0) and cloprostenol was administered on Days 0 and 1 (LP4, n=36) or on Days 4 and 5 (HP4, n=40). Animals were inseminated on detection of oestrus until Day 9. Breeding continued using natural mating between Days 9 and 19, AI on detection of oestrus between Day 19 and 29 and natural mating between Days 29–90. Mean concentrations of progesterone were less on Days 2–4 in the LP4 compared to the HP4- treated animals but similar on Days 14 and 20. In the LP4- compared to the HP4-treated animals, the odds of being detected in oestrus and ovulating close to the first AI were similar, but odds of pregnancy to first AI (OR=0.19, 95% CI 0.07 – 0.52) and after 1, 4 and 13 weeks of breeding were less (P≤ 0.051). Absence of a CL and relatively lesser concentrations of progesterone during emergence of pre-ovulatory follicles resulted in lesser pregnancy rates to AI in Bos indicus cattle but did not affect concentrations of P4 after ovulation.

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