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OVULATION, FERTILITY AND PRENATAL MORTALITY IN HEIFERS TREATED WITH PMSG OR PORCINE FSH

Summary.: Ovulation rate, fertilization rate and prenatal mortality were studied in yearling beef heifers treated with PMSG or FSH and in non-treated controls. Oestrus was synchronized in 50% of the animals in each treatment with an oral progestagen. The gonadotrophin injections were given during the normal oestrous cycle or during the progestagen-administration period. All heifers were inseminated 6 to 10 hr after observation of standing oestrus. Ovulation rate and percentage fertility were determined in approximately a third of the animals in each treatment group. The reproductive tracts of the remaining animals were examined 81 to 104 days after insemination for number and condition of fetuses, number of corpora lutea and condition of the uteri.

Ovulation and fertilization rates were 1·0±0·4 and 100% for the controls, 1·6±1·0 and 87·5% for the PMSG treatment and 4·4±4·9 and 56·5% for the FSH treatment. Treatment with a gonadotrophin during progestagen administration resulted in higher ovulation rates than gonadotrophin treatment during the normal oestrous cycle, 36% higher in heifers given PMSG and 47% higher in those given FSH.

There was a negative relationship between ovulation and fertilization rates; therefore, the average number of fertilized ova/heifer increased as ovulation rate increased, but at a slower rate. Percentage fertility was not affected by the progestagen in the control and PMSG groups, but it was lower when FSH was given during progestagen treatment than when it was given during the normal oestrous cycle.

At 81 to 104 days after insemination, abortions had occurred in 20% of the animals treated with PMSG or FSH. There were no apparent differences in prenatal mortality between the PMSG- and FSH-treated animals.