Improving dairy cattle reproduction through development of synchronization of ovulation protocols and economic decision support systems

A series of experiments were conducted to develop resynchronization of ovulation protocols to improve the fertility of timed artificial insemination services, assess the effect of circulating progesterone concentrations on LH secretion from the pituitary gland after GnRH treatment (Section I), and to evaluate the association between timing of embryonic demise and hormonal dynamics after induced pregnancy loss in lactating dairy cows (Section II). In addition, decision support systems to make economic based decisions at the time of selecting reproductive management programs for dairy herds were created based on simulation models (Section III). Results from three experiments in Section I showed that the use of presynchronization of the estrous cycle before the initiation of Resynch improved the fertility of resynchronized services in lactating dairy cows. Presynchronization was effective to improve fertility by increasing the percentage of cows with a functional corpus luteum at the initiation of Resynch and the percentage of cows responding to the protocol injections. Also, increased progesterone concentrations similar to those observed in cows with a functional corpus luteum at the time of GnRH treatment suppresses release of LH from the pituitary gland. This suppressive effect of progesterone on GnRH-induced LH release can be partially overcome by increasing the dose of GnRH. The experiment presented in Section II showed that cows induced to lose their pregnancy by progesterone depletion or embryonic demise at 39 d of gestation had a steady decrease in Pregnancy Associated Glycoproteins (PAG) after treatment when compared to cows maintaining their pregnancy. In Section III, two decision support systems created based on Markov-chain simulation models were described. These models are capable of simulating the dynamics of a dairy herd based on input reproductive, productive, and economic parameters. The resulting reproductive performance determines the economic value of the different reproductive management programs under consideration. Results from case studies performed using these decision support systems demonstrated that the economic value of a reproductive program is influenced by many factors. Among the most critical are the percentage of cows inseminated after a detected estrus versus timed artificial insemination and the outcome of these artificial insemination services.