The effects of cosynch-56 protocol on pregnancy rates of cows and heifers presynchronized with a single dose of pgf(2 alpha)

Abstract

The objective of this study was to evaluate pregnancy rates to timed artificial insemination (TAI) following presynchronization with a single dose of PGF(2 alpha) ten days before CoSynch-56 protocol in Brown Swiss crossbred cows and heifers. Group I (GI) cows (n=89) and heifers (n=39) received PGF(2 alpha) ten days prior to Cosynch-56 protocol while Group II (GII) cows (n=82) and heifers (n=38) received CoSynch-56 protocol only. Pregnancy was evaluated using ultrasonography 30-35 days after TAI. Pregnancy rates did not differ significantly between GI and GII (34.4% and 28.3 %, respectively, P>0.05). However, pregnancy rates differed significantly (P<0.05) between cows and heifers in GII (34.1% and 15.7%, respectively). Furthermore, pregnancy rates of heifers in GI was significantly higher than that of heifer in GII (P<0.01, 41.0% and 15.7%, respectively). Notably, pregnancy was not achieved in GII heifers with plasma P4 values < 1ng/ml. In conclusion, presynchronization with PGF(2 alpha) before Cosynch-56 protocol did not enhance pregnancy rates in Brown Swiss cows but did in heifers. Also, high P4 levels may enhance overall pregnancy rates of cows and heifers subjected to the Cosynch-56 protocol.