Reproductive performance of dairy heifers after estrus synchronization andfixed-time artificial insemination

The reproductive performance of heifers after estrus synchronization and fi xed-time Al 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 PGF(2 alpha) an d were inseminated between 50 and 54 h after progesterone treatment. Return s to first service were resynchronized with progesterone treatment between 16 and 21 d after the fixed-time AI. The conception rate of synchronized he ifers to the fixed-time Al (53.2%) and to Al after resynchronization (53.1% ) was lower than that of control heifers (63.7%). However, pregnancy rate i n 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 heife rs (4.0%) failed to conceive. The interval from start of breeding to calvin g was earlier for synchronized (296.2 d) than for control (299.5 d) heifers . Jersey heifers had lower reproductive performance than did Friesian heife rs. 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.