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Moore, Ainsley

University of British Columbia

Concentrations of progesterone (P4) in the estrous cycle preceding AI is positively associated with estrous expression and fertility. Recent research has also shown associations between the estrus to ovulation interval and estrous expression. The aim of this study was to evaluate the associations between P4 concentrations during diestrus with intensity of estrous expression and time from estrus to ovulation in nulliparous Holstein cows. In a randomized cross-over design experiment, post-pubertal heifers (n=31) were pre-synchronized and fitted with a leg-mounted automated activity monitor (AAM). On d-17 relative to estrus, the animals received GnRH, P4 implant for 7 d and GnRH again on d-8. From d-7 to -1, heifers in the high P4 group (HP4) received a new CIDR while the heifers in the low P4 group (LP4) received a second use CIDR. Additionally, heifers in LP4 received multiple PGF2α injection during the diestrus. Heifers in both treatment groups received PGF2α on d-1, and estradiol cypionate on d0. Upon estrus activity alert, and every 4 h after, until ovulation, the ovaries of the heifers were scanned by ultrasonography for the occurrence of ovulation. Blood samples were taken at estrus and 7 d later for P4 analysis. The HP4 treatment had significantly lower P4 concentrations on d0 than the LP4 treatment (P=0.001) and a tendency for higher P4 on d7 after the HP4 treatment (P=0.07). There was no effect of treatment on ovulation timing (hazard of ovulating=1.17 when in the LP4 treatment, 95% CI=0.69–1.98, P=0.56). Estrous expression was not affected by treatment when measured by duration (HP4: 17.7±0.8 h vs LP4: 17.4±0.8 h; P=0.72) or relative increase of activity (HP4: 364.4±24.6 index value vs LP4: 344.6±24.6 index value; P=0.55).

Text

2024-04-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87859

Applied Animal Biology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/