title: Reproductive performance of dairy heifers after estrus synchronization and fixed-time artificial insemination.
abstract: The reproductive performance of heifers after estrus synchronization and fixed-time AI was compared with nonsynchronized heifers in 25 spring-calving herds. Within herds, heifers were divided into a synchronized (n = 1123) or a control (n = 1125) group. Heifers in the synchronized group were treated with a combination of progesterone, estradiol benzoate, and PGF2 alpha and were inseminated between 50 and 54 h after progesterone treatment. Returns to first service were resynchronized with progesterone treatment between 16 and 21 d after the fixed-time AI. The conception rate of synchronized heifers to the fixed-time AI (53.2%) and to AI after resynchronization (53.1%) was lower than that of control heifers (63.7%). However, pregnancy rate in the first 24 d was higher for the synchronized group (72.4%) than for the control group (67.8%). More control heifers (5.7%) than synchronized heifers (4.0%) failed to conceive. The interval from start of breeding to calving was earlier for synchronized (296.2 d) than for control (299.5 d) heifers. Jersey heifers had lower reproductive performance than did Friesian heifers. Synchronized heifers gave birth to more female calves (53.8%) than did control heifers (45.7%). It is concluded that the above program can be used successfully to synchronize dairy heifers for fixed-time AI.
authors.affiliation: Livestock Improvement Corporation Ltd., Hamilton, New Zealand.
authors.forename: Z Z
authors.initials: ZZ
authors.lastname: Xu
authors.forename: L J
authors.initials: LJ
authors.lastname: Burton
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004973:Estrus Synchronization; D005260:Female; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*; D012744:Sex Ratio; D013997:Time Factors