An inherited condition has been discovered in dairy cattle wherein identified animals have half the normal activity of uridine monophosphate (UMP) synthase and are heterozygotes for a trait expected to be lethal in the homozygous state. UMP synthase is an enzyme that converts orotic acid to the pyrimidine UMP, which is needed for the formation of nucleic acids. Daughters of heterozygous bulls had 330 kg more 305d, 2x, mature equivalent milk production than daughters of normal bulls that were siblings of the heterozygous bulls. Heterozygous females in second or later parities had the most 305d, 2x, mature equivalent milk production and longest calving intervals while heterozygous females in their first parity had the least milk production and shortest calving intervals. Normal females in both parity groups were intermediate for both milk production and calving interval.

R. D Shanks, J. L Robinson, M. H Healey

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 78–83, 1986
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