Effect of a novel Ovsynch program using a second treatment of prostaglandin F2Α on fixed time artificial insemination results in pasture-based dairy herds
Document TypeMasters Research thesis
Access StatusOpen Access
© 2018 Johanna Marie Rheinberger
This thesis is largely based on a clinical trial that was conducted on dairy cows in Southwest Victoria, Australia. The objective of the clinical trial was to evaluate the effect of a second prostaglandin F2α injection, within the original Ovsynch program, on the conception rate of dairy cows in a fixed time artificial insemination program. The regression of the corpus luteum was also assessed and the results between the modified and original Ovsynch programs were compared. A randomized clinical trial was conducted, which involved 1703 dairy cows selected from five split calving, pasture-fed dairy herds in Southwest Victoria, Australia. These animals included both primiparous and multiparous animals. All of the lactating cows were divided into two groups at the start of the joining period in order that artificial insemination would coincide with mating start date. This is the day on which joining starts so that the calving period coincides with the greatest seasonal pasture growth. Group 1 (n = 851), the control group, received the original Ovsynch program: Gonadotropin-releasing hormone at day 0 in the morning, prostaglandin F2α at day 7 in the morning, Gonadotropin-releasing hormone at day 9 in the afternoon and fixed time artificial insemination on day 10 in the morning, approximately 12 to 16 hours after the second Gonadotropin-releasing hormone injection. Group 2 (n = 852), the treatment group, received a modified Ovsynch program: Gonadotropin-releasing hormone at day 0 in the morning, prostaglandin F2α at day 7 in the morning, prostaglandin F2α at day 8 in the morning, Gonadotropin-releasing hormone at day 9 in the afternoon and fixed time artificial insemination on day 10 in the morning, approximately 12 to 16 hours after the second gonadotropin-releasing hormone injection. All artificial insemination was performed by experienced technicians. A subset of animals from each group, in each herd (n=95 treatment cows and n = 99 control cows), had blood samples taken at the time of the first prostaglandin injection and at the time of artificial insemination. Serum progesterone concentrations were measured at the time of the first prostaglandin injection to assess the proportion of cows likely to be cycling in each of the groups and at the time of artificial insemination to assess the proportion of cows with complete luteal regression. After adjusting for the effect of herd, conception rates were 7.0% greater in cows in the treatment group compared with cows in the control group. The proportion of cows with plasma progesterone concentrations ≥1 ng/mL in the treatment group at the time of artificial insemination was 13.5% lower than that of cows in the control group at the time of artificial insemination. Compared with the original Ovsynch program, it was estimated that a total of 14 (95% CI 8 to 43) cows need to be treated using the modified Ovsynch program to return one additional pregnancy. In conclusion, the use of the modified Ovsynch protocol is likely to increase conception rates to timed artificial insemination programs in dairy cows in Southwest Victoria.
KeywordsOvsynch; double PG; second prostaglandin; dairy cows
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