%0 Journal Article
%T Pregnancy success of lactating Holstein cows after a single administration of a sustained-release formulation of recombinant bovine somatotropin
%A A Bell
%A OA Rodr¨ªguez
%A LA de Castro e Paula
%A MB Padua
%A J Hern¨¢ndez-Cer¨®n
%A CG Guti¨¦rrez
%A A De Vries
%A PJ Hansen
%J BMC Veterinary Research
%D 2008
%I BioMed Central
%R 10.1186/1746-6148-4-22
%X The first experiment was conducted in a temperate region of Mexico. Cows inseminated following natural estrus or timed artificial insemination were given a single injection of bST or a placebo injection at insemination (n = 100 cows per group). There was no significant difference between bST and control groups in the proportion of inseminated cows diagnosed pregnant (29 vs 31% pregnant). The second experiment was performed during heat stress in Florida. Cows were subjected to an ovulation synchronization regimen for first insemination. Cows treated with bST received a single injection at 3 days before insemination. Controls received no additional treatment. As expected, bST did not increase vaginal temperature. Treatment with bST did not significantly increase the proportion of inseminated cows diagnosed pregnant although it was numerically greater for the bST group (24.2% vs 17.8%, 124¨C132 cows per group). There was a tendency (p = 0.10) for a smaller percent of control cows to have high plasma progesterone concentrations (¡İ 1 ng/ml) at Day 7 after insemination than for bST-treated cows (72.6 vs 81.1%). When only cows that were successfully synchronized were considered, the magnitude of the absolute difference in the percentage of inseminated cows that were diagnosed pregnant between bST and control cows was reduced (24.8 vs 22.4% pregnant for bST and control).Results failed to indicate a beneficial effect of bST treatment on fertility of lactating dairy cows.Treatment of lactating cows with recombinant bovine somatotropin (bST) can increase milk yield in thermoneutral and heat-stress environments [1-6]. The consequences of bST treatment for fertility are not clear. In early studies, cows treated with bST had an increased calving to conception interval that was attributed, at least in part, to increased anestrus [7,8]. In contrast, bST either increased [9,10] or had no effect [6,11,12] on pregnancy rate per insemination when cows were inseminated using a timed arti
%U http://www.biomedcentral.com/1746-6148/4/22