Evaluation of Variation Attributable to Lab and Technician for Measurements of Beef Carcass Traits Made Using Ultrasound

National cattle genetic evaluations assume technician and imaging lab do not contribute to phenotypic variation when measuring carcass traits by ultrasound. The objective of this study was to estimate variance components of ultrasound carcass measurements, specifically variance contributed by ultrasound technician and imaging laboratory. Accounting for technician and imaging lab variation may increase accuracy of genetic predictions for carcass traits. Ultrasound carcass predictions for ribeye area (REA), percent intramuscular fat (IMF), and backfat (BF) were provided by the American Angus Association (AAA; n=281,982 animals), American Hereford Association (AHA; n=49,602), and American Simmental Association (ASA; n=59,576) for a total of 391,160 animals. Data provided by each association included ultrasound carcass measurements, contemporary group, technician ID, imaging lab, and a three-generation pedigree for each animal with ultrasound measurements. Variance contributed by additive genetics, technician, and contemporary group on ultrasound carcass measurements were estimated for each breed separately. Because technician and lab were confounded, the contribution of lab to ultrasound carcass variation could not be separated from technician. Therefore, we assessed whether lab contributed to ultrasound carcass variation by estimating genetic correlations between laboratories for ribeye area, percent intramuscular fat, and backfat. This analysis separated carcass traits by laboratory and treated measurements interpreted by each lab as a separate trait. Technician explained 12-27%, 4-23%, and 4-27% of variance for IMF, BF, and REA respectively across all three breeds. On average, the variance contributed by technician was greater than the variance contributed by additive genetics but less than that explained by contemporary group. Genetic correlations between labs across breeds ranged from 0.79 to 0.95 for IMF, 0.64 to 0.94 for BF and 0.78 to 0.98 for REA. Technician contributed to variance in ultrasound measurements, but high genetic correlations between labs suggest lab plays a lesser role in contribution of variance to ultrasound measurements

Alternative approaches to evaluation of cow efficiency

The purpose of this study was to evaluate alternative expressions of genetic merit for cow efficiency. Weights of Pinzgauer cattle taken at birth, weaning, and maturity were extracted from the South African National Database. Average daily gain from birth to weaning (ADG) and cow weight (CWT) were analyzed with a multi-trait mixed model. The model included direct and maternal genetic effects, a permanent environmental effect attributable to dams on ADG, a direct genetic effect and a permanent environmental effect attributable to there being multiple observations from the same cow on CWT as random effects. Heritability estimates for direct and maternal additive effects on ADG were 0.27 ± 0.04 and 0.06 ± 0.02, respectively. The estimated heritability for CWT was 0.45 ± 0.06. Estimates of repeatability for ADG and CWT were 0.42 and 0.67, respectively. Estimated breeding values based on the preceding results and using the maternal genetic effect on ADG as a proxy for the direct genetic effect on milk production were combined in six indexes of cow efficiency. These indexes sought to increase output and decrease input simultaneously, to increase output holding input constantly, and to hold input constant while decreasing input. The diversity of emphasis applied across these indexes suggests the need for due diligence in developing breeding objectives for improvement of cow efficiency. Indexes that are consistent with the econometric definition of efficiency and seek to simultaneously increase output and reduce input are recommended.______________________________________________________________________________________Keywords: genetic parameters, multiple trait selection, Pinzgauer, selection inde

Genetic effects from an Afrikaner, Bonsmara, and Nguni three-breed diallel and top-crosses of Angus and Simmental sires

Individual and maternal breed additive effects and heterosis exist for most economically important traits in cattle. Crossbreeding may therefore be valuable for emerging and commercial beef farmers in improving the productivity of their herds. Calves were produced by mating Afrikaner, Bonsmara and Nguni cows to Afrikaner, Bonsmara, Nguni, Angus and Simmental bulls. The cows used were from Vaalharts Research Station or were purchased from other herds. Data were collected over three years. Individual and maternal additive effects and individual heterosis were estimated simultaneously as continuous linear variates. The estimated genetic effects were then used to predict production levels that may be achieved through implementation of top-cross, two-breed rotation, and terminal sire crossbreeding systems. The individual estimates of the genetic effects were relatively small and in most cases were not different from zero, with the exception of the maternal additive effects of Nguni on preweaning traits and their individual additive effect on cow weight, which were less than those of Bonsmara. However, the alternative crossbreeding systems differed across traits. The straight-bred breeding system was least efficient, followed by the crisscross system (+2%) and the terminal sire system that utilized Simmental (+4%), with the terminal sire system utilizing Angus being on average most efficient (+8%). The inter-generational genetic differences in cow weight that resulted from the use of different breeds of sire increased its standard deviation by 5 to 6% in rotational crossing. Despite the relatively small magnitude of the genetic effects, advantages of crossbreeding systems became evident.Keywords: breed additive, crossbreeding, heterosis, post-weaning, pre-weanin