Performance testing of future A.I. bulls for growth rate, feed efficiency and muscularity. Genetic parameters, adjustment for systematic environmental factors, selection indices

Abstract

Based on data from 2217 bulls distributed among 296 sires and four breeds from the Danish performance testing system, genetic parameters have been estimated for growth rate, feed efficiency and muscularity. Muscularity was measured on the live animal with ultrasonic equipment. The heritability of daily gain and muscle area was estimated at 0.53 and 0.71 respectively. The estimate of the genetic correlation between daily gain and muscle area was negative (−0.30). This is probably caused by the large gene import from North America giving higher daily gain and lower muscle area. When correcting for systematic environmental factors it was necessary to use linear models, instead of the often used rolling average for each trait and test station, to avoid bias from single heavily used bull sires. Selection on a multiple trait index for daily gain and muscle area simultaneously resulted in a 1.6–2.7 times higher total expected economic progress, compared to selection on daily gain or muscle area alone. The multiple trait index did not change birth weight. The total economic response was insensitive to changes in the economic weights, while the correlated responses in daily gain and muscle area were very sensitive. Hence if the economic weights chosen do not deviate too much from the true weights, biological considerations (which type of animal is desired from a biological point of view) rather than economical considerations determine which economic weight should be used in the index.