Abstract

Bloat costs the dairy industry about $50 million per year and one of the possible long- term solutions is to breed cattle for reduced susceptibility. Studies on two herds established at Ruakura in 1972/73, and selected divergently for high susceptibility (HS) or low susceptibility (LS) to bloat, have shown that: (1) bloat score on any single day of serious challenge has a heritability of 0.19±0.04; (2) the within-animal repeatability of scores across days is 0.44±0.02; (3) divergence of bloat score between herds has now reached 2.4 genetic standard deviations; (4) the recent response rate in the HS herd has been approximately linear whilst the LS response has plateaued; (5) 75% of the HS herd and 2% of the LS herd are at risk of death from bloat if left untreated. Alternative definitions of the bloat syndrome have been investigated; one of these (maximal bloat score) has a heritability of 0.30±0.06. Using this definition, a mixed-inheritance segregation analysis was undertaken, which led us to the conclusion that a major gene for susceptibility was segregating as an autosomal recessive. The implication is that the use of non-carrier AI sires in industry could minimise the bloat problem in one generation, by avoiding production of all homozygous double-recessive progeny.

CW, Morris, and NG Cullen

Proceedings of the New Zealand Society of Animal Production, Volume 57, , 19-21, 1997