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

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