Abstract
AbstractTwo hundred crossbred yearling heifers were used in a 3 x 2 factorial experiment to compare the effectiveness of two estrous synchronization programs (MGA-prostaglandin F2α and Syncro-mate-B) with a control group utilizing two types of breeding programs (Al or natural service). Heifers were stratified by estrous status (prepuberal or post-puberal) to one of six treatments. The MGA treatment group received MGA for 14 d followed by an injection of prostaglandin F2α (PGF2α), 16 d after the last day of MGA feeding. The Syncro-mate-B (SMB) group received the standard 9-d procedure. A third group served as the controls. One-half of the heifers in each of the three treatment groups were bred by Al and the other half by natural service. Yearling bulls were used in a ratio of 1 to 20 females and were rotated among treatment groups at 12-h intervals during the synchronization period. Estrous response rates did not differ (P>.05) between the MGA and SMB treatment groups for either the Al or natural service heifers. No differences (P>.05) were found in pregnancy rates during the first 6 d of breeding between MGA and SMB groups whether bred by Al (56 vs. 59%) or natural service (67 vs. 74%). First-service conception rates did not differ (P>.05) between treatments whether bred by Al or natural service. A higher percentage of the prepuberal heifers exhibited estrus following SMB treatment (100%) compared with controls (38%). Pregnancy rates in 6 and 30 d were slightly higher (P>.05) in heifers bred by natural service compared with Al. These data indicate both treatments were effective in inducing and synchronizing estrus, and natural service is a viable alternative to Al in synchronization programs.
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