Improving pregnancy rates in problem breeder cattle by administration of 15 mg of progesterone on days 3–5 post-mating

Abstract

Days 3–5 post-ovulation is when the embryo is entering the uterus, undergoing genomic activation and progesterone (P4) increases; therefore, this may be a physiologically important time in the cow. The objective of these experiments was to determine the effect on pregnancy rates through the administration of a low dose of P4 or altrenogest (ALT; Regumate) on days 3, 4 and 5 of the estrous cycle among repeat breeder (RB) cattle. In Trial 1, RB cows (n=14), that failed to conceive to 3 breedings with a fertile bull, and fertile control cows (n=14) that were an average of 120 days post-partum were used. In Trial 2, RB cows (n=6), RB heifers (n=4) (identified as in Exp 1) and fertile control cows (n=8) that were an average of 135 days post-partum were used. In Exp 1 and 2, all cattle were exposed to a fertile bull for one estrus and the onset of estrus was considered day 0. The respective treatments and blood sample collections were on days 3–5. In Trial 1, RB cows were administered 15 mg of P4 in 3 ml of ethanol sc and in Trial 2 they were administered 15 mg of ALT (orally) on days 3, 4 and 5. Controls in Trial 1 and 2 were only restrained for blood sample collection to determine plasma P4 levels using radioimmunoassay (RIA). For both trials, pregnancy rates were empirically lower and similar (P>0.05) between treatments vs. controls. Pregnancy rates for Trial 1 controls were 72% (10/14) and 43% (6/14) for Treatment and for Trial 2 controls were 50% (4/8) and 50% (3/6) for Treatment cows. The mean±SE plasma P4 levels were higher (P < 0.05) in pregnant controls (1.87±0.2 ng/ml) compared with nonpregnant controls (0.89±0.2 ng/ml) on day 5. In addition, the mean±SE increase in plasma P4 from day 3–4 was higher (P < 0.05) in pregnant controls (0.42±0.06 ng/ml) compared with nonpregnant controls (0.18±0.11 ng/ml). These resulting pregnancy rates support the hypothesis that P4 supplementation during this time improve pregnancy rate in RB cattle.