Effect of the addition of oil-based injectable progesterone to an estrus synchronization protocol in early weaned beef cows

Abstract

In order to compare the effect of the addition of oil-based injectable progesterone (P4) (MAD-4) to a Select Synch (SS) protocol + eCG, 120 grazing beef cows (22 primiparous and 98 multiparous) with body condition score of 3.4 ± 0.03, 64 - 79 days postpartum and weaned ten days earlier, were used. The treatments were: Group SS + eCG (n=59; 11 primiparous and 48 multiparous): Day 0: GnRH and Day 7: Prostaglandin (PG) plus 400 IU equine chorionic gonadotropin (eCG); group SS + eCG + P4 (n=61; 11 primiparous and 50 multiparous): similar treatment except that on Day 0 together with GnRH cows received 200 mg of MAD-4 subcutaneously. Estrus was detected from Day 4 to 13 and cows in heat were inseminated 12 hours later. Pregnancy was diagnosed on Day 43. On Days -10, 0, and 7 blood samples were collected from all the cows to determine P4 concentrations. Weaning induced cyclicity in 91% of the cows. The addition of MAD-4 did not prevent the occurrence of premature heats (SS + eCG: 15%, SS + eCG + P4: 10%, P = 0.42), did not increase the percentage of cows detected in heat (SS + eCG: 60% vs. SS + eCG + P4: 65.5%, P = 0.40), or the conception rate (SS + eCG: 70% vs. SS + eCG + P4: 80.6%, P = 0.48), nor the pregnancy rate (SS + eCG: 46% vs. SS + eCG + P4: 54%, P = 0.36). In the conditions of the present study, addition of MAD-4 to the SS + eCG Protocol, did not improve the percentage of heats or pregnancy.