Estrus synchronization in Holstein cows using reduced doses of prostaglandin F 2α

Abstract

There is evidence that the dose of PGF 2α generally used to synchronize estrus (25 mg) is higher than required to induce luteolysis in cattle. To investigate this, 98 Holstein cows from three farms were assigned at random within farm to be treated with a single dose of 25 mg (n=33), 17.5 mg (n=33) or 10 mg (n=32) of PGF 2α on Day 10±0.5 (mean ± SEM) of the estrous cycle. Statistical analyses were conducted using analyses of variance and Chisquare test. Only 59.3% of the cows treated with 10 mg of PGF 2α were detected in estrus compared with 72.7 and 78.7% of the cows treated with 17.5 and 25.0 mg doses, respectively (P>0.05). There were no differences (P>0.05) in pregnancy rates at the first service (40.0, 66.6 and 50.0% for 25, 17.5 and 10 mg, respectively). Concentrations of progesterone in blood were different (P<0.05) for cows treated with 10 mg compared with those of cows treated with 17.5 or 25 mg of PGF 2α. The pattern of changes in progesterone concentrations between the last two groups was not different, and progesterone concentrations of less than 1 ng/ml of serum were observed within the first 36 h post PGF 2α administration. In cows treated with 10-mg dose of PGF 2α, concentrations of progesterone declined during the first 24 h, however, by the end of the experimental period, they were not different to pretreatment concentrations (treatment × time; P<0.05). It is suggested that reducing the dose of PGF 2α from 25 to 17.5 mg do not affect estrus response or pregnancy rate in Holstein cows.