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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.
2011 Project Description
The primary output from this research is a better understanding of how new technologies can be used to improve detection of estrus in dairy cows. This continues to be a major problem in the field. The knowledge gained from this research is disseminated to other scientists and industry professionals through presentations at national and international meetings. The results have also been presented to farmers and other dairy farm workers so that they are better informed about available technologies, their application and limitations.
An experiment was conducted to evaluate the utility of reticular and vaginal temperature measurements in predicting the time of ovulation in lactating dairy cows.
Lactating Holstein (n=26) and crossbred (n=4) cows were used in the study. The study was conducted in six replicates with 4-6 cows per replicate. Cows within replicate were synchronized using an OVSYNCH protocol preceded by G6G. The first injection of prostaglandin F2a (PGF) was administered 40-90 days postpartum. The OVSYNCH protocol was modified by omitting the last injection of GnRH, allowing for the synchronized expression of estrus. Reticular and vaginal temperature were monitored using SmartBoluses (TenXsys Inc., Eagle, ID) inserted approximately 5 days prior to anticipated estrus. Boluses were placed in the reticulum as described by the manufacturer. Boluses were attached to CIDR devices (Pfizer Animal Health, NY) using rubber bands and inserted into the vagina using the CIDR speculum. Beginning at 48 after the PGF injection of OVSYNCH, jugular venous blood samples were collected at 2-h intervals to measure luteinizing hormone (LH). Rectal temperatures were taken using a standard thermometer at the same time.
Immediately after sampling, cows were observed for estrus behavior for 30 min. Beginning 72 h after PGF, the ovaries were scanned ultrasonographically every 4 h to monitor follicle growth and determine time of ovulation. Intensive sampling was maintained for approximately 60 h or until ovulation was confirmed. Jugular venous blood samples were collected daily throughout the experimental period and for an additional 7 days to measure progesterone as an indicator of luteal regression and subsequent ovulation. The time intervals from injection of the OVSYNCH PGF, onset of estrus, LH surge, peak rectal temperature, first detected increase in reticular and vaginal temperatures to ovulation were determined for each cow. The mean and standard deviation for each time interval was calculated.
Of the 30 cows that started on the experiment, only 18 ovulated with the intensive sampling period. Of these 14 displayed estrous behavior during the observation period. The average intervals in hours (X +/- SD) from injection of the OVSYNCH PGF, onset of estrus, LH surge, peak rectal temperature, first detected increase in reticular and vaginal temperatures to ovulation were 93+/-11, 31+/-8, 24+/-6, 46+/-11, 47+/-31, 45+/-27, respectively.
The most precise (least variation) predictor of interval to ovulation was the LH surge. While the average interval between increases in reticular and vaginal temperature to ovulation were similar to the interval determined using rectal temperature, the variation was much greater indicating that the precision of the interval estimate based on the bolus technologies was much less.
Reames, P.S., T.B. Hatler, S.H. Hayes, D.L. Ray and W.J. Silvia. 2011. Differential regulation of estrous behavior and luteinizing hormone secretion by estradiol-17b in ovariectomized dairy cows. Theriogenology 75:233-240