Effects of Being Dewormed with Oxfendazole and Implanted with Synovex-C® as Young Beef Calves On Subsequent Reproductive Performance of Heifers1

One hundred seventy-eight heifer calves at three locations were allotted randomly to four treatments in a 2 × 2 factorial design. To determine the effects of deworming and(or) implanting calves on subsequent reproductive performance, the treatments were: 1) control, not dewormed or implanted as calves;2) dewormed with oxfendazole (4.5 mg/kg BW) (Synanthic®3) at 2 to 3 mo of age and again at weaning; 3) implanted with Synovex-C®3 (two locations, n = 98) at 2 to 3 mo of age; and 4) dewormed and implanted. Dams of the dewormed heifers also were dewormed with oxfendazole when the calves were 2 to 3 mo of age and separated by treatment into different pastures. Fecal egg counts indicated that oxfendazole decreased eggs per gram (EPG) in treated calves compared to controls. Prior to breeding, cyclicity was determined by analyzing serum progesterone concentrations by radioimmunoassay from two blood samples taken at 10-d intervals. The heifers were considered puberal if at least one of the samples had concentrations in excess of 1 ng/mL. Prior to breeding, the heifers were weighed, body condition was scored (BCS), and pelvic area was measured. Estrus was synchronized in each group of heifers by an injection of prostaglandin F2α(PGF2α) with insemination 12 h after first observation of estrus. Those heifers not responding to the PGF2α were given a second injection 7 d after the first. Forty heifers from one location were evaluated for pelvic area prior to calving. Treatments had no effects on percentage cycling at start of the breeding season, percentage conceiving to artificial insemination, overall pregnancy rate, BCS, or weight. Pelvic area prebreeding did not differ by deworming treatment, but was larger in heifers implanted at 2 mo of age (P < .01). Precalving pelvic area also was larger for heifers treated with Synovex-C®(P < .05).