Delayed Post-ovulatory Progesterone Rise in Thai-Holstein Dairy Heifers: Association with Endocrine Events around Oestrus, Effects on Conception Rate and Possibility for Progesterone Supplement Post-insemination

Abstract

The current research aimed to further study the delayed post-ovulatory progesterone (P4) rise in Thai-Holstein dairy heifers in the points of an association with endocrine events around oestrus (experiment 1), effects on conception rate and possibility for P4 supplement post-insemination (experiment 2). In experiment 1, the P4 levels in the delayed P4 heifers reached 1 ng/ml later than in the normal ones (6.8±0.4 vs 3.3±1.5 days after oestrus, resp.) (p = 0.053). At ovulation the pre-ovulatory follicles of the delayed P4 were smaller than of the normal P4 heifers (11.8±0.5 vs 13.1±0.2 mm, resp.) (p = 0.013). The levels of LH at their surges in the delayed P4 were lower than in the normal P4 animals (1.1±0.1 vs 1.8±0.2 ng/l, resp.) (p = 0.044), while the OE2 levels on the day of oestrus were not different (30.5±1.5 vs 28.8±1.3 pmol/l, resp.) (p ≥ 0.05). In experiment 2, within the control group (no exogenous P4 supplement), the delayed P4 heifers yielded lower conception rate compared to the normal P4 ones (40% vs 68.75%, resp.) (p < 0.001). In the treatment group, at 8 hours following P4 supplement, the levels of P4 significantly increased from 0.73±0.92 to 2.57±0.73 ng/ml (p < 0.001) and at 48 hours after cessation of P4 supplement, the P4 levels declined from 3.01±0.79 to 2.56±1.39 ng/ml (p = 0.0996). The heifers in the treatment group had higher conception rate (62.85%) compared with the delayed P4 control heifers (40%, p < 0.001) and with the overall control ones (52.43%, p = 0.0416), but not different if compare to the normal P4 control heifers (68.5%, p ≥ 0.05). In conclusion, the delayed post-ovulatory P4 rise in Thai-Holstein dairy heifers showed a strong connection with the smaller pre-ovulatory follicle and the lower levels of LH at their surges. The negative effects of the delayed post-ovulatory P4 rise on pregnancy were clearly confirmed. Moreover, supplementation with P4 on day 3 to day 7 after oestrus enhanced conception rates.