Genetic studies of bloat susceptibility in cattle.
C.W. Morris, N.G. Cullen and H.G. Geertsema
AgResearch, Ruakura Agricultural Research Centre, Private Bag
3123, Hamilton.
Proceedings of the New Zealand Society of Animal Production. 1997,
57: 19-21
Bloat costs the dairy industry about $50 million per year and
one of the possible long-term solutions is to breed cattle with 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 2.75 genetic
standard deviations; (4) the recent response rate in the HS herd has
been approximately linear whilst the LS response has reached a plateau;
(5) 70% of the HS herd and 3% 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 and other definitions, a
mixed-inheritance segregation analysis was undertaken, which led to the
conclusion that a major gene for susceptibility is 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
removing all homozygous bloat-susceptible progeny from the population.
Keywords: NZSAPAB;
cattle; bloat; susceptibility; genetics; heritability.
Last Updated 12-09-1998
