Performing Department
Dairy Science
Non Technical Summary
Although Wisconsin continues to lead the U.S. in total number of dairy farms, Wisconsin ranked 24th among all U.S. states in the amount of milk produced per cow, a measure of production efficiency. Total milk production is determined by the proportion of cows producing milk at any given time and the level of milk production of the individual cows within the herd, both of which are directly affected by reproductive efficiency. Experiments in this proposal will generate new knowledge aimed at improving dairy farm competitiveness and profitability by increasing reproductive efficiency through development and refinement of strategies for managing reproduction. The purpose of this project is to develop practical reproductive management strategies to improve reproductive efficiency in lactating dairy cows, thereby improving profitability and competitiveness of dairy farms in Wisconsin.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The first objective is to develop breeding protocols to maximize fertility in lactating cattle with special emphasis on anovulatory or anestrous cattle. The second objective is to determine the efficacy of using the CIDR to enhance pregnancy rates at a synchronized breeding in cattle and to resynchronize the first eligible estrus in non-pregnant cows after a previous insemination.
Project Methods
Objective 1, Experiment 1. Lactating Holstein cows will be submitted for first postpartum (pp) timed artificial insemination (TAI) using Ovsynch. Cows will be randomly assigned to each of two treatments (n=500 cows/treatment) for presynchronization before initiating Ovsynch. Cows in the first group will receive a Presynch protocol (control, PP) using two injections of PGF2alpha; (34 and 48 d pp) administered 14 d apart with the second PGF2alpha; injection administered 14 d before the first GnRH injection (62 d pp) of Ovsynch. Cows in the second group (GP) will receive an injection of GnRH (44 d pp) followed 7 d later by an injection of PGF2alpha; (51 d pp) administered 11 d before the first GnRH injection (62 d pp) of Ovsynch. Objective 1, Experiment 2. At calving, cows will be blocked by parity and randomly assigned to either a 60 or an 88 d voluntary waiting period (VWP) for TAI after Presynch/Ovsynch. Pregnancy status will be evaluated using transrectal
ultrasonography 32 and 60 d after TAI to determine treatment effects on conception rate and pregnancy loss. The proportion of anovular cows at the first GnRH injection of Presynch/Ovsynch will be assessed. The effect of treatment parity, and the two-way interaction on conception rate using a backward selection procedure with treatment retained as a fixed factor in each of the models. Objective 2, Experiment 3. Lactating Holstein cows (n=80) will be allocated weekly to breeding groups, each of which will include cows scheduled for Presynch/Ovsynch and TAI. After TAI, cows will be randomly assigned to each of two treatments (n=40 cows/treatment) to receive either 100 micrograms GnRH or vehicle (control) 19 d after TAI. To evaluate follicular and luteal dynamics before and after treatment, cows will undergo daily transrectal ultrasonography for 7 d before treatment to 7 d after treatment. To evaluate P4 and estradiol 17-beta; concentrations, blood samples will be collected daily after
each ultrasound examination. Blood samples will be collected every 2 h for 12 h after the GnRH injection to encompass the expected time of the LH surge. Transrectal ultrasonography will be conducted every 2 h until ovulation beginning 12 h after GnRH administration to encompass the expected time of ovulation. Serum samples will be assayed for progesterone by RIA. Objective 2, Experiment 4. Lactating Holstein cows (n=800) will receive Presynch/Ovsynch for first TAI and will be randomly assigned to either Resynch or Presynch/Resynch, and cows will remain in each Resynch treatment until diagnosed pregnant or culled from the herd. Estrous behavior will be detected using an on-farm computerized pedometry system currently in place on the farm. Any cow identified in estrus after first TAI will receive AI, whereas cows not detected in estrus will be submitted for TAI based on the Resynch treatment they are assigned to. Pregnancy status will be evaluated for all cows 31 d after TAI using
transrectal ultrasonography, and cows diagnosed pregnant will be rechecked using ultrasound 61 d after TAI to assess pregnancy loss, whereas nonpregnant cows will be resynchronized for subsequent TAI service.