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Methods to Increase Reproductive Efficiency in Cattle
Department of Animal and Food Sciences
Need: Reproductive efficiency continues to be a major problem in lactating dairy cows. Improved procedures for estrous synchronization in heifers and lactating dairy cows will increase farm income by increasing milk production, through reduced days open and genetic improvement (widespread use of artificial insemination). The increase in milk production is conservatively valued at $100/cow.
Accomplishments/Outputs: The effect of reproductive status on the metabolic clearance of progesterone was clearly demonstrated in our preliminary research. This needs to be verified. Using CIDRs to deliver the progesterone allowed us to show that the concentration of progesterone maintained in lactating dairy cows is remarkably low and approaches the threshold required for effectiveness as an estrous synchronization tool. Our results suggest that estrous synchronization protocols utilizing these devices in lactating dairy cows may require the use of multiple CIDRs or a reformulation of the device by the manufacturer to increase the rate of progesterone release. Future work will be conducted to determine concentrations of progesterone maintained by multiple CIDRs in lactating dairy cows.
2009 Project Description
Reproductive physiological and endocrine parameters during the first periestrual period postpartum were compared in lactating dairy cows that conceived versus those that did not. Holstein (n=48) and Holstein X Jersey crossbred (n=7) cows were used in the experiment. A modified Ovsynch protocol was initiated 52 to 94 days postpartum (100 ug GnRH, i.m., Factrel, Fort Dodge Animal Health). Seven days later (day 0), two injections of prostaglandin (PG) F2a (25 mg, i.m., Lutalyse, Pfizer Animal Health) were administered, 12 h apart, to induce luteolysis. The ovaries were examined ultrasonographically 2x daily beginning on day 0. Blood samples were collected at 6-h intervals for quantification of estradiol-17b. On day 2, the frequency of sample collection was increased to every 2 h for quantification of LH. Beginning on day 2, cows were observed for estrus behavior at 4-h intervals. For each cow, 27 variables were calculated from the data collected. These included the timing and magnitude of estradiol-17b and LH secretion, time of onset, intensity and duration of estrus, maximum follicle diameter, time of ovulation and intervals from onset of estrus to peak of LH and ovulation. Preovulatory surges of LH and ovulation were observed in 31 cows. Differences between cows that conceived (n=13) and those that did not (n=18) for each variable were examined by t-test. Estrus began at 74.4 h after PGF2a and lasted for 12.6 h. Peak LH occurred at 77.3 h. Ovulation occurred at 104.1 h, 25.7 h after peak LH. Peak concentration of estradiol-17b occurred at 75.8 h and averaged 2.6 pg/ml. The diameter of the preovulatory follicle was 15.4 mm. None of these variables were different between cows that conceived and those that did not (p > 0.2). The interval from onset of estrus to peak LH tended to be different between groups (p = 0.08) (4.7 h in cows that conceived, 1.6 h in cows that did not). The impact of this asynchrony in time of estrus relative to peak LH on fertility remains to be determined.
We failed to detect any dramatic difference in endocrine or other physiological parameters between lactating dairy cows that conceived and those that did not. This included differences in follicle size at ovulation, duration of estrus, the maximum concentration of estradiol or LH achieved during the periestrual period. There was a tendency for the onset of estrus to occur late relative to the time of the LH surge in cows that failed to conceive. This would lead to a delay insemination relative to the time of ovulation; however, this effect was relatively modest and seems unlikely to be an adequate explanation for the failure to conceive.
Understanding the basis for poor fertility in heifers and lactating dairy cows will increase farm income by increasing milk production, through reduced days open and genetic improvement (widespread use of artificial insemination). The increase in milk production is conservatively valued at $100/cow.