A selection experiment which has resulted in dairy cows of extremes susceptibility to bloat is reviewed. The low susceptibility cows had a higher liquid milk production and a lower milkfat percentage than the high susceptible ones. They showed little or no bloat on highly potent pastures. Comparison of the herds was directed towards physiological differences and relationships which could explain the origin of low susceptibility and lead to phenotypic definition useful for selection. Some differences were found in proportions of salivary proteins and progress has been made in their separation, definition and measurement. In vitro experiments have not indicated sufficient differences in gas or foam production per litre of rumen fluid to explain bloat grade variation but observation followed by direct experiment has shown that a greater volume of rumen fluid is associate4d with a high susceptibility to bloat. This could form a basis for commercial selection if appropriate measurement methods can be devised.
Proceedings of the New Zealand Society of Animal Production, Volume 43, , 93-96, 1983
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