Abstract
Data consisting of test performance records of 725 bulls was analysed to evaluate trends for growth and feed efficiency, and to determine environmental factors that influence growth of range performance tested bulls in the arid sweet bushveld of South Africa. Performance data were subjected to regression procedures to estimate parameters of the slope (β) and intercept (α) for average daily gain (ADG) and Kleiber ratio (KR). Mixed procedures were applied to test for sources of variation in ADG and KR. There was an increase of 3.481 g/day/year and 0.528 g/day/ year in ADG for Nguni and Bonsmara bulls, respectively. The ADG trends’ respective feed efficiency as reflected by KR was 0.093 and 0.059. Herd of origin and test-year were the sources of variation for ADG while the variation in KR was due to the herd of origin, test-year, start-age and start-weight. Results indicated a steady increase in ADG and KR for range performance tested bulls in the arid sweet bushveld.
Highlights
Given that natural grazing is the most important input resource at the disposal of range cattle farmers to convert low quality roughage into high quality protein, genetic improvement of cattle regarding growth and efficiency of production on natural grazing is crucial
In range growth tests, feed intake data is not recorded to enable for estimation of feed efficiency but Kleiber ratio which is a ratio of average daily gain (ADG) to metabolic weight (ME) is used as an alternative measure or indicator of feed efficiency [6]
ME is calculated as MWT0.73 [6]. [7] suggested that feed efficiency as measured in terms of Kleiber ratio (KR) is highly affected by the amount of grazing available
Summary
Given that natural grazing is the most important input resource at the disposal of range cattle farmers to convert low quality roughage into high quality protein, genetic improvement of cattle regarding growth and efficiency of production on natural grazing is crucial. Bull selection is the most rapid way to change the genetic composition of a herd of cattle [1]. While several traits are evaluated in a bull performance test, the most important is the bull’s ability to gain weight and the efficiency with which it gains. [5] indicates that, average daily gain (ADG) will be more appropriate than live weight when evaluating the growth potential of beef bulls. In general, is a measure of weight gained from feed consumed. In range growth tests, feed intake data is not recorded to enable for estimation of feed efficiency but Kleiber ratio which is a ratio of ADG to metabolic weight (ME) is used as an alternative measure or indicator of feed efficiency [6]. The KR in a range growth test is likely to be linked with the test-year effect
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