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Physiological mechanisms underpinning fertility differences in cows with divergent genetic merit.

R. C. Doyle




Physiological mechanisms underpinning fertility differences in cows with divergent genetic merit.
R. C. Doyle*1,2, C. Millar1, S. G. Moore1, S. A. Holden1, M. C. Lucy2, S. T. Butler1. 1Teagasc Fermoy, Cork, Ireland, 2University of Missouri Columbia, MO.

The objective was to examine the physiological differences between elite genetic merit Holstein Friesian (EL-HF), average genetic merit HF (NA-HF), Danish Jersey (DKJ) and New Zealand Jersey (NZJ) cows that may underpin differences in fertility. Vaginal discharge score (VDS) exams were carried out weekly on EL-HF (n = 72), NA-HF (n = 36), DKJ (n = 36) and NZJ (n = 36) until a sample with no purulent material was obtained (score = 0). Pre-ovulatory plasma estradiol (E2) and luteal phase plasma progesterone (P4) concentrations were determined in a subset of cows [EL-HF (n = 19); NA-HF (n = 11); DKJ (n = 10), and NZJ (n = 7)] managed under 3 feeding treatments (low grass allowance [LGA; n = 11); control (n = 21); high concentrate (HC; n = 17)] during a synchronized estrous cycle. Postpartum interval until VDS = 0 was recorded and analyzed using survival analysis. Plasma E2 and P4 concentrations were analyzed using a generalized linear mixed-model. An effect of genotype on days to VDS = 0 was observed (38.6, 38.5, 29.64 and 45.4 d for EL-HF, NA-HF, DKJ and NZJ, respectively; P < 0.0001). There was a shorter postpartum interval to a VDS = 0 with increasing parity number (44.0, 39.6 and 37.4 d for parity 1, 2 and 3+ respectively; P < 0.001), greater fertility index (40.4, 40.6 and 38.6 d for low, medium and high fertility index, respectively; P < 0.001) and reduced calving difficulty (39.2 vs. 43.7 d for normal vs. difficult calving; P < 0.001). Greater circulating concentrations of P4 were observed in EL-HF compared with NA-HF cows, and in DKJ compared with NZJ cows (genotype effect: P = 0.03). The LGA and control feeding treatment cows had greater plasma E2 (P = 0.03) and P4 (P = 0.03) concentrations than the HC treatment cows. Reproductive phenotypes including VDS and reproductive hormone concentrations were influenced by cow genetic merit, breed, parity, calving difficulty, and feeding regimen and environmental factors.

Keywords: progesterone, estradiol, vaginal discharge score.

Biography: I completed a Bachelors of Agricultural Science in University College Dublin in 2016 for which I received a first class honors degree. I am currently a PhD student with the University of Missouri and Teagasc splitting my time between both institutions trying to elucidate the physiological mechanisms that underpin the most important drivers of productivity; milk output and fertility. The PhD I will be carrying out aims to examine the effects of nutrition and genetics on fertility in dairy cows of high and average EBI. I have a background in sheep farming but have been lucky to work with some of the Ireland's top researchers and farmers in the dairy industry. I've always had a huge interest in Agricultural Industry and its importance for our economy. My aim is to further the knowledge on the factors contributing to reproductive performance and improve the productivity and efficiency of the Irish dairy industry.