Two trials were conducted to evaluate one trial, pregnancy first 21 d and total pregnancy in effects of Synovex C@ implants on replacement heifers, 63-d breeding season were decreased ( P = . 0 5 ) by given at two different ages. Crossbred heifer calves ( n implanting at 6 mo. At subsequent calving, an = 370) were allotted t o four treatments: 1) non-interaction existed between the effects of the implanted controls, 2) implanted at 2 mo, 3 ) im-2-and the 6-mo implant for calf birth weight and

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... anted at 6 mo, and 4) implanted at both 2 and 6 mo pelvic area:birth weight ratio. A single implant at of age. Heifers implanted at 2 mo gained 7 kg more ( P either 2 or 6 mo decreased ( P = . O l ) calving difficulty = .01) by 6 mo than those not implanted at 2 mo. No score; and implanting at both 2 and 6 mo showed the differences were found in 22-mo weights. All im-greatest reduction in calving difficulty. Implants had planted heifers had larger ( P = .01) yearling pelvic no significant long-term effects on reproduction or calf area than controls. All heifers implanted at 6 mo production of 2-yr-old cows. Results showed implantcontinued to have larger ( P = .01) pelvic area at 22 ing at 2 mo of age increased early weight gain and mo. All implanted heifers had higher ( P = ,051 decreased calving difficulty scores; implanting at 6 mo occurrence of non-ovulatory estrus. No differences increased precalving pelvic area and decreased calving were found among treatments in percentage of heifers difficulty scores; and implanting at both 2 and 6 mo puberal before breeding, in estrus first 21 d of increased early weight gain, decreased calving diffibreeding, or in first-service conception rate. In only culty scores, but tended to reduce early fertility.