Calf removal improves conception rates to the Ovsynch and CO-Synch protocols

Beef cows (n = 473) from two locations were stratified by breed, postpartum interval, age, and AI sire and were randomly allotted to one of four treat ments for synchronization of ovulation. Ovulation synchronization protocols included the Ovsynch protocol with (n = 114) or without (n = 123) 48-h cal f removal from d 7 to 9 (d 0 = 1st GnRH injection) or the CO-Synch protocol with (n = 119) or without (n = 117) 48-h calf removal from d 7 to 9. The O vsynch protocol included administration of GnRH (100 mug; i.m.) on d O, PCF 2 alpha (25 mg; i.m.) on d 7, GnRH (100 mug; i.m.) on d 9, and timed insemi nation on d 10. The GO-Synch protocol included administration of GnRH (100 mug; i.m.) on d O, PGF(2 alpha) (25 mg; i.m.) on d 7, and GnRH (100 mug; i. m.) with timed insemination on d 9. Blood samples were collected from all c ows on d -10 and d O for analysis of serum progesterone. Cows with at least one serum progesterone concentration greater than 1 ng/mL were considered to be cyclic at the time of treatment. Conception rates of cows that receiv ed the GO-Synch + calf removal, Ovsynch + calf removal, GO-Synch, or Ovsync h protocol (63, 61, 54, and 52%, respectively) were not different (P = 0.50 ). Conception rates were not different (P = 0.80) among CO-Synch- and Ovsyn ch-treated cows; however, both estrual status and 48-h calf removal affecte d conception rates. Conception rates of cyclic cows (66%) were greater (P = 0.01) than those of anestrous cows (53%), regardless of which synchronizat ion protocol was used. When data were pooled across synchronization protoco l, conception rates of cows with 48-h calf removal (62%) were greater (P = 0.09) than conception rates of cows without calf removal (53%). The GO-Sync h + calf removal protocol induces a fertile ovulation in cyclic and anestro us cows, requires handling cattle just three times, results in high concept ion rates from timed insemination, and should be a useful program for synch ronization of ovulation in beef cows.