Heifers were given either one or two Ralgro implants or one DES implants during the suckling period with no obvious effect on later reproductive performance when the heifers were bred as yearlings. However, conception rates in control heifers were low in two trials, so more studies are needed for conclusive results.
Forty-seven of 50 heifers were in estrus 1 to 5 days after an injection of prostaglandin given when an ear implant of Synchro-mate B was removed. The implant had been in place one week. Thirty of the 47 (63.8%) heifers with synchronized estrus conceived on first artificial insemination. Twenty untreated heifers were in estrus in 27 days; 13 (65%) conceived on first artificial insemination.
Two years of research with nine herds indicated one of two yearling bulls with a herd usually will sire most of the calves. In six of the nine cases, the bull we pre-evaluated as most sexually active was the sire of the most of the calves. So a brief pre-breeding libido evaluation may help estimate breeding potential. In data from one herd the bull dominant as a yearling continued to be dominant as a two-year-old. Our data also indicated active breeding yearling bulls easily breed more than 20 to 25 cows during their first breeding season.
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