SEX-RATIO VARIATION BETWEEN EJACULATES WITHIN SIRE EVALUATED BY POLYMERASE-CHAIN-REACTION, CALVING, AND FARROWING RECORDS

Ejaculates from sires were examined by polymerase chain reaction to de termine percentage of sperm bearing the Y chromosome. Results were ver ified by examining the percentage of male calves per ejaculate used in artificial insemination (AI) and the percentage of male piglets per l itter from a controlled mating program. Spermatozoal DNA was amplified by polymerase chain reaction with specific primers for the Y chromoso me. Image analysis measured the fluorescent intensity of the 194-bp ba nd. Ejaculates were compared with a pooled standard of spermatozoal DN A equated to a 50% Y-bearing sperm ejaculate. Calving data were obtain ed from information collected for the National Association of Animal B reeders for dystocia evaluation of cows bred to AI bulls. Breeding dat a were obtained from Al technician receipts. Calving and breeding data were merged on cow, sire, calving date, and breeding date. The percen tage of males was calculated per sire, ejaculate, and herd combination . Farrowing data were evaluated for the percentage of male piglets per litter. Ejaculates within bulls contributed to variation (24 +/- 9.8% to 84 +/- 9.8%) in the percentage of sperm bearing the Y chromosome. Ejaculates from the same brill contributed to variation in, the percen tage of male calves (16.1 to 72.3%). Ejaculates from the same boar con tributed to variation in the percentage of male piglets that ranged fr om 7.8 to 94.7%. These percentages and the results obtained by polymer ase chain reaction analysis of ejaculates suggested that spermatozoa b earing X and Y chromosomes were unequally represented in ejaculates. T he use of ejaculates screened by polymerase chain reaction could enhan ce production of the desired sex of calf.