Association of deficiency of uridine monophosphate synthase with production and reproduction.

Interaction between genotype at locus for uridine monophosphate synthase and parity was reexamined for 305-d mature equivalent milk and fat production and calving interval. Three lactations for cows of known genotype defined two data files corresponding to different sampling procedures. The first data file selected by herd contained records on 23 cows that were deficient in activity of uridine monophosphate synthase and on 1081 cows with normal activity; the second data file contained records on 19 cows with deficient activity and on 17 cows with normal activity, all daughters of bulls known to be heterozygous at the locus for uridine monophosphate synthase. Results from the mutually exclusive data files were determined independently and then pooled. Genotype and parity interaction, tested against mean square error, was not supported for any of the three traits. Mean differences of the two genotypes, averaged across data files, were, for first, second, and third parities, respectively, 360, 568, and 299 kg for milk; 6, 9, and 8 kg for fat; and 22, 9, and 12 d for calving interval. Main effect of genotype indicated a 417-kg advantage for heterozygotes but 17-d longer calving interval. The main effect of genotype on milk production adjusted for calving interval was 343 kg but was nonsignificant.