Effect of Dose of GnRH Used in the Ovsynch System on AI Pregnancy Rates in Beef Cows

Abstract

Estrous synchronization advances have the potential to dramatically increase the utilization of artificial insemination (AI) in beef cattle operations. Ultimately, the level of usefulness of these programs and AI in general will be the cost effectiveness of programs which are developed. Programs involving the use of GnRH and prostaglandins have been reported that allow for acceptable pregnancy rates using timed insemination and thus dramatically reducing handling, a significant deterrent to AI in beef cattle. One such scheme, Ovsynch, has utilized 100mg of GnRH for each of two injections in the scheme. Research conducted with dairy cattle has suggested that 50 mg GnRH provides similar pregnancy rate outcomes. Beef cow reproduction is significantly different than dairy reproduction due to different body composition, lactational demands and typical nutritional provision. If a lower dose of GnRH produces similar pregnancy outcomes, a significant economic advantage to the program would result. This trial was designed to compare the outcome of the four different combinations of 50 mg and 100 mg of GnRH in Ovsynch protocols.