Strategies to improve ovulation and embryo development in timed insemination programs using GnRH, LH and hCG in post partum Holstein cows.
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Fertility is a major problem in the dairy cow industry, the major cause of this problem is believed to be the rapid increase in milk yield of modern dairy cows. Due to poor fertility, calving intervals are prolonged, which resuls in economical losses due to reduced milk yield at the end of the lactation period and involuntary culling. As a result of these problems timed artificial insemination (TAI) procedures are being implemented on dairy farms. One of these procedures is ‘Ovsynch’ developed by Pursley et al in 1995. Ovsynch involves two injections of GnRH nine days apart and an injections with prostaglandin two days before the second GnRH injection. Artificial insemination follows one day after the second injection of GnRH. With this procedure pregnancy rates are around 40%. Conception rates are lower than when artificial insemination is based on observed oestrus and also early embryonic death is reported to be higher. In this study the GnRH injection is compared to LH and hCG injections. There were three treatment groups; treatment group 1 was given a normal Ovsynch protocol using GnRH, in treatment group 2 and 3 the GnRH injections replaced by respectively LH and hCG. The pregnancy rates of the treatment groups 1, 2 and 3 were 36%, 29% and 35% respectively, however no significant difference were found between the treatment groups.