Factors affecting mature size and dry-season weight loss in Bos indicus cross cows in northern Queensland

Abstract

Mature size and dry season weight loss affect the feed requirements, mortality rate and fertility of cows in the dry tropics. The aim of the work reported here was to study the effects of genotype and selection for growth rate on these parameters. The data consisted of: growth rate to 18 months; weight, height and condition score of cows over 5 years old; the change in these parameters during the dry season; and the past fertility of these cows. The cows were + or + bred Brahman of Sahiwal crosses. The Brahman crosses had the same growth rate but a higher mature weight than the Sahiwal crosses. The +-breds lost less weight during the dry season than the +-breds, implying a lower maintenance requirement. Growth rate to 18 monthswas correlated with adult height (r = 0.54) and weight (r = 0.58-0.68). Growth rate was correlated with dry season weight loss (r = 0.36), but only because weight loss was correlated with weight at the start of the dry season. After correcting for this starting weight, growth rate was not correlated with weight loss, and in fact growth rate was positively correlated with condition score late in the dry season (r = 0.17). Adult height was weekly correlated with dry season weight loss (r = 0.13). Past fertility was correlated with current fertility and with ability to maintain condition during the dry season.