CONTROL OF ESTRUS AND LITTER SIZE IN GILTS WITH AIMAX (ICI 33,828) AND PREGNANT MARE’S SERUM

A field trial was conducted to investigate effects of pregnant mare’s serum gonadotrophin (PMS) on estrus, farrowing rate and litter size in AIMAX-treated gilts. A total of 177 Yorkshire × Landrace gilts from 7 to 9 months of age and weighing 95 to 115 kg were group fed an average of 1.8 kg of a 14% sow ration containing 100 mg of AIMAX per female per day for 20 days. Twenty-four hours after the last feeding of AIMAX, 59 gilts were injected with 1000 I.U. PMS, 59 were injected with 1500 I.U. PMS and the remaining 59 served as noninjected controls. Gilts showing estrus were mated naturally or artificially inseminated with 100 ml of semen. None of the gilts showed estrus during AIMAX treatment. Injecting PMS increased (P < 0.05) the number of gilts bred between the 5th and 7th days after AIMAX withdrawal and reduced (P < 0.05) the interval between AIMAX withdrawal and breeding by 2.0 days. Injecting 1000 LU. PMS increased (P < 0.05) the total number of pigs born per litter by 2.0 pigs and increased (P < 0.05) the number of live pigs per litter 12 to 24 hours after farrowing by 1.5 pigs. In contrast, injecting 1500 I.U. PMS had no significant effect on litter size. These results demonstrate that 1000 I.U. PMS injected 24 hours after AIMAX withdrawal was effective in increasing the degree of synchronization and litter size of gilts under farm conditions.