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Estrus synchronization protocols for planned breeding and GnRH-agonist after timed insemination for pregnancy rate enhancement in dairy cattle

University of British Columbia

The aim of was to develop management protocols to improve reproductive efficiency in dairy cattle. The objective of Experiment 1 was to compare two methods of estrus synchronization. Eighty-nine dairy animals (67 cows and 22 heifers) were randomly assigned to either the Ovsynch or the Prostaglandin F[sub 2α] (PGF[sub 2α]) treatment group. Animals in the Ovsynch group received gonadotropin-releasing hormone (GnRH) followed by PG[sub 2α] on day 7 and second GnRH on day 9. Animals in the PGF[sub 2α] group were given two injections of PGF[sub 2α] 14 days apart. Both synchronization methods were followed by timed artificial inseminations. Milk progesterone (P₄) concentrations during the cycle were used to asses corpus Luteum (CL) function. Pregnancy was diagnosed 35 days after insemination. Estrus synchrony, based on Kamar heat mount detector and milk P₄ concentrations < lng/ml on the day of breeding, was not significantly different between the two groups. Mean milk P₄ during the synchronized cycle was also not significantly different between the two groups. Pregnancy rates were higher (P<0.05) for cows in the Ovsynch group (57.5%) than those in the PGF[sub 2α] group (38.4%). No difference in pregnancy rate was observed in heifers. The objective of Experiment II was to determine the effect of treatment with GnRH at various times after breeding on the induction of accessory CL, P₄ concentrations and pregnancy rates. Each month, estrus was synchronized in 12 to 15 postpartum cows using the Ovsynch protocol followed by timed inseminations. Cows were then randomly assigned to receive GnRH on d7 (n=34), d14 (n=34), or d7 and 14 (n=35) after breeding or to serve as controls (n=33). During the first two months, six cows from each group underwent ultrasonographic examination of the ovaries on days, 7, 11, 14, 18, and 21 after insemination to observe the formation of any additional CL. Blood and milk samples were also taken at these times to determine P₄ concentrations. Pregnancy was diagnosed 35 days after insemination. Eighty-three percent of cows ovulated in response to GnRH on d7 as opposed to only 17 percent on d14. Mean milk P₄ concentrations in treated cows did not differ from control cows. Pregnancy rates did not differ between the groups. It is concluded from this study that a) pregnancy rates of dairy cows and heifers can be managed effectively without estrus detection by using the Ovsynch estrus synchronization protocol followed by timed artificial inseminations and b) treatment with GnRH following synchronized breeding does not increase pregnancy rates in postpartum dairy cows.

Thesis/Dissertation

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2009-07-13

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http://hdl.handle.net/2429/10717

Animal Science

University of British Columbia

UBCV

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