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MacNeil, M. D. and Kemp, R. A. 2015. Genetic parameter estimation and evaluation of Duroc boars for feed efficiency and component traits. Can. J. Anim. Sci. 95: 155–159. The objective of this research was to produce a genetic evaluation for traits related to feed efficiency of Duroc boars. Meeting this objective required partitioning phenotypic (co)variance into additive genetic and environmental components for feed intake and traits indicative of growth and body composition. Boars (N=3291) were housed in group pens of 22 to 24 animals with two electronic feeders per pen and feed intake was recorded for 8 to 14 wk. Body weight was recorded for each boar at the start and end of test, at approximately 100 kg and at up to three times during the test. The pedigree used contained sire and dam of each boar with at least one recorded phenotype (N=4651) and their maternal and paternal grandsires. Variance components were estimated by restricted maximum likelihood for animal models in a series of uni-variate and bi-variate analyses. Two multiple trait genetic evaluations were conducted to predict estimated breeding value for feed intake using animal models. The first evaluation included feed intake (h2=0.33±0.05), age at 100 kg (h2=0.31±0.04), and subcutaneous fat depth (h2=0.47±0.05). The second genetic evaluation included feed intake, average daily gain (h2=0.27±0.04), mid-test weight (h2=0.33±0.05), and subcutaneous fat depth. Genetic correlations of feed intake with age at 100 kg and fat depth were –0.80±0.05 and 0.57±0.08, respectively. Estimated breeding values for measures of feed efficiency (residual feed intake and residual gain) were calculated from the results of the second analysis and the associated additive genetic (co)variance components.

Genetic parameters for three growth and five carcass traits were estimated for Charolais using a combination of carcass progeny test, purebred field performance and pedigree data. Heritabilities and genetic and residual correlations were derived from variance components for birth weight (BWT, n = 54 221), 205-d weaning weight (WT205, n = 31 384), postweaning gain (PWG, n = 19 403), hot carcass weight (HCW, n = 6958), average subcutaneous fat thickness (FAT, n = 6866), longissimus muscle area (REA, n = 6863), marbling score (MAR, n = 6903) and estimated carcass lean yield percentage (PLY, n = 6852) with an animal model (n = 78 728) and restricted maximum likelihood. Breed of dam and contemporary group appropriate to each trait were included as fixed effects in the model, whereas random effects included direct genetic for all traits, maternal genetic for BWT and WT205, and maternal permanent environmental for WT205. Carcass traits were adjusted to a constant harvest age of 425 d. Heritability estimates of 0.53, 0.22, and 0.21 were obtained for direct components of BWT, WT205, and PWG, respectively, and maternal heritabilities were 0.16 and 0.10 for BWT and WT205, respectively. Direct × maternal genetic correlations for BWT (-0.49) and WT205 (-0.35) were negative. Heritabilities for HCW, FAT, REA, MAR, and PLY were 0.33, 0.39, 0.43, 0.34, and 0.46, respectively. Genetic correlations among direct effects for growth traits were moderately positive and generally uncorrelated with maternal effects across traits. Lean and fat deposition in the carcass generally had negative, unfavorable genetic correlations, although improvement in lean yield and marbling score may not be strongly antagonistic. Genetic correlations of direct and maternal components of growth traits with carcass traits suggested that selection for increased growth rate would not be antagonistic to improvement in carcass yield or meat quality. Key words: Carcass, Charolais, correlation, genetic parameters, growth

The records of 282 young beef bulls from eight breeds tested from November 1981 to April 1987 at the Ellerslie Bull Test Station, Alberta, Canada, were used to study the variation in feed efficiency among young performance-tested bulls. Considerable variation existed among the animals in both residual metabolizable energy consumption and residual dry matter consumption. The heritability estimates for residual metabolizable energy consumption and residual dry matter consumption were 0.33 and 0.29, respectively. In addition, residual metabolizable energy consumption and residual dry matter consumption were moderately correlated (r = 0.43) with conventional feed-to-gain ratio, indicating that conventional feed-to-gain ratio only accounted for 18% of the variation in residual metabolizable energy consumption or residual dry matter consumption. It was, therefore, worthwhile to use residual metabolizable energy consumption or residual dry matter consumption as separate measures of feed efficiency. For rapid improvement in feed efficiency in beef cattle, selection pressure should be applied to both growth traits and residual energy consumption or residual dry matter consumption. Multi-trait optimum restricted selection indices and similar selection procedures may serve as useful means in balanced selection programs to improve the productivity of beef cattle. Key words: Feed efficiency, residual ME consumption, beef bulls

Individual identification of beef cattle is not new to the Canadian beef industry, as traceback systems played a pivotal role in the eradication of bovine tuberculosis in the 1940s and 1950s and brucellosis in the 1970s and 1980s. Recent concerns over animal health (e.g., bovine spongiform encephaolopathy), export markets, product consistency, meat quality (e.g., tenderness, marbling) and safety (e.g., Escherichia. coli 0157:H7, Salmonella spp.) make reestablishment of a traceback system a logical approach to assuring consumer confidence in Canadian beef. Originally, simple Kurl-lockTM ear tags with a unique number were used to trace individuals back to their herd of origin. Although useful for addressing disease concerns, this system did not lend itself to compiling additional information (e.g., growth performance, animal health, breeding programs, carcass quality) for use in management or marketing decisions. More sophisticated electronic identification systems can readily interface with computers and make information management an even more pivotal component of beef production. Several electronic identification systems (e.g., bar codes, radio frequency identification, read–write systems) are being assessed for their effectiveness for identifying individual cattle under production conditions. In research applications, this technology has the potential for individual animals to become the experimental unit under group housing conditions. By combining electronic identification technology with devices that measure physiological (e.g., temperature, pH, body weight, feed intake) parameters, researchers will be able to collect data in natural production environments that were previously only obtainable under controlled experimental conditions with a limited number of animals. Key words: Electronic identification, beef, traceback, radio frequency identification

Genetic correlations of lifetime pregnancy rate with bull and heifer growth and reproductive traits in a beef composite population were estimated. Yearling scrotal circumference had an unfavorable genetic correlation (rg = −0.25) while yearling tonometer score was favorably related (rg = 0.22) to lifetime pregnancy rate. Heifer pregnancy rate, birth weight, weaning weight, yearling weight and age at puberty in heifers had significant genetic correlations (rg = 0.97, 0.58, 0.57, 0.33 and −0.21, respectively) with lifetime pregnancy rate. Lifetime pregnancy rate may be successfully predicted by easy-to-measure heifer growth traits. Using indices including scrotal and heifer growth traits, annual genetic change in lifetime pregnancy rate may be increased 3.1 times compared with direct selection. Key words: Scrotal circumference, tonometer, pregnancy, reproduction, puberty

Pre-slaughter ultrasound and carcass measurements of ribeye area (REA) and backfat (FAT) were recorded on composite beef bulls (n = 60), heifers (n = 60) and steers (n = 60). Breed composition of the composite was: 0.44 British (Hereford, Angus and Shorthorn) 0.25 Charolais, 0.25 Simmental and 0.06 Limousin. The Aloka SSD-1100 (AL) and the Tokyo Keiki CS 3000 (TK) ultrasound machines were compared by evaluating the difference between ultrasound and carcass measurements (bias), and the standard error of prediction (SEP). AL under-predicted REA in all three sexes while TK overpredicted heifers and steers and underpredicted bulls. Both machines were similar in accuracy among bulls for REA. For FAT AL underpredicted all three sexes while TK underpredicted heifers and had very small bias for bulls and steers. SEP for FAT were similar for both machines. Both machines underpredicted REA in larger muscled cattle and overpredicted in smaller-muscled cattle. Both machines also underpredicted FAT in fatter animals and overpredicted FAT in leaner animals. Machines were similar in accuracy among cattle with larger REA but differed significantly (P

Variance components were estimated for weight at birth, weaning, and 365 d of age, and yearling ultrasonic backfat thickness in a multibreed population of beef cattle. Data (n = 5880) were available on F1 animals and various crosses leading up to, and including, a composite breed (7/16 British, 1/4 Charolais, 1/4 Simmental, and 1/16 Limousin). Single- and two-trait analyses were conducted using an animal model and derivative-free REML procedures. Covariates representing fractional contributions of each of the four purebred groups and average heterotic effects, both direct and maternal, accounted for breed composition. Direct and maternal genetic, maternal permanent environmental, and residual effects were the random variables. Only minor differences existed between parameter estimates obtained from the various analyses. Mean direct heritabilities were 0.51, 0.33, 0.48, and 0.37 for weight at birth, weaning, and 365-d, and backfat, respectively, which, though well within the range of published estimates, seemed higher than average, indicating diversity in the founding purebreds. Mean maternal heritabilites were 0.09, 0.13, and 0.08 for the three consecutive weights. A likelihood ratio test showed maternal heritability and(or) the direct-maternal correlation was important (P

Preweaning and carcass trait records from crossbred steers (n = 1015) and heifers (n = 957) were used to estimate genetic parameters and to investigate the efficacy of maternal effects and preweaning growth information for improving estimation of EBV for carcass traits for crossbred beef cattle. Dams (n = 775) representing three F1 and twelve back-cross combinations involving the Charolais, Hereford, Angus, Simmental and Shorthorn breeds were mated over six years to Limousin bulls (n = 36) at two locations in western Canada. Four animal models, involving from zero to three maternal (co)variances were used to analyze four carcass traits. Rank and simple correlations indicated that maternal effects were relatively unimportant for estimation of direct carcass trait breeding values. Direct heritabilities were 0.28, 0.12 and 0.16 for birth weight, preweaning daily gain and weaning weight, and were 0.20, 0.35, 0.50 and 0.38 for hot carcass weight, fat thickness, ribeye area and percent lean yield, respectively. Maternal heritabilities were 0.21, 0.22 and 0.40 for birth weight, preweaning daily gain and weaning weight, respectively. Estimated genetic correlations between percent lean yield and hot carcass weight, fat thickness and ribeye area were –0.05, –0.85 and 0.39, respectively, and 0.30 between hot carcass weight and ribeye area. Direct genetic effects for birth weight had moderate (0.51 to 0.54) correlations with direct effects for carcass weight, ribeye area and percent lean yield. Direct genetic effects for fat thickness were negatively correlated with direct effects for birth weight (−0.44), preweaning daily gain (−0.15) and weaning weight (−0.25). Maternal genetic effects for preweaning traits had near-zero correlations with direct genetic effects for fat thickness and percent lean yield. Adding preweaning growth information to genetic evaluations for carcass traits slightly decreased prediction error variances for breeding values and would be recommended when information on carcass traits is limited. Key words: Genetic evaluation, carcass traits, beef cattle

Forty-eight Hereford and 60 Simmental steers were used to evaluate breed differences as affected by dietary energy content on growth performance, carcass and chemical composition, and beef quality. Diets were based on corn silage, alfalfa haylage, whole corn, and SBM and were formulated to provide 2.52 to 2.81 Mcal kg−1 ME and 11.7 to 12.6% protein in the growing phase and 2.69 to 2.86 Mcal kg−1 ME and 9.7 to 10.4% protein in the finishing phase. Low- and high-ener-gy diets were formulated for each breed with the high-energy diet for Hereford serving as the low-energy diet for Simmental. Steers were slaughtered after attaining 8 to 10 mm backfat determined by ultrasound. Higher energy diets increased (P 0.10) between breeds. While shear force decreased (P = 0.043) feeding the low-energy diet to Simmental, other shear and palatability attributes were unaffected by dietary energy content or breed. Altering dietary energy content for Hereford and Simmental influenced growth performance without affecting carcass and chemical composition and beef quality. Key words: Hereford, Simmental, marbling, shear, palatability, growth performance, carcass

The effects of estrus suppression (none, oral melengestrol acetate (0.4 mg d−1) or ovariectomy via Willis spay technique) and an anabolic implant (none or Synovex Plus®) on growth performance and carcass characteristics were determined using 90 beef heifers of composite breeding in a 2 × 3 factorial experiment conducted in the last 50 d before slaughter. Spaying caused no morbidity or mortality and resulted in average daily gains (1.37 kg d−1) comparable to heifers fed melengestrol acetate (1.33 kg d−1). Implanting improved (P 0.05) carcass traits. Spaying and implanting represent an effective means of improving returns from heifers, even late in the finishing period. Key words: Ovariectomy, implants, beef heifers, carcass composition

A bioeconomic model is used to compare beef breeds and crosses for their economic performance in the feedlot. Breeding objectives for each breed and cross are also calculated. Comparisons are made on the basis of the expected purchase-price premium paid for a breed, cross or animal when slaughtered at its profit-maximizing end point. These comparisons are relevant to commercial beef producers who ultimately have to choose between genotypes. Purebred Charolais are expected to capture a premium over purebred Angus of approximately $71 and $45 animar−1 for steers and heifers, respectively. Simmental, Limousin and Hereford purebreds are intermediate, with differences between them relatively small in comparison with the expected effects of errors in model parameters. Crosses between exotic type (Charolais, Simmental and Limousin) and British type (Hereford and Angus) breeds have larger increases in purchase-price premiums over the mid-parent mean than crosses within the types. Averaged economic weights for 1% changes in the mean of +12 g d−1, −80 g d−1 and 0.6% in daily gain, daily feed intake and dressing percentage are $3.7 animal−1, $1.8 animal−1 and $8.4 animal−1, respectively. These are relatively consistent across breeds, crosses and sexes. In contrast, economic weights for fat depth at a constant weight are shown to be nonlinear and therefore are highly dependent on the breed, cross and sex and the slaughter end point at which they are calculated. At the economic optimum slaughter point in the base, exotic breeds and crosses between them tended to have negative economic weights for a reduction in fat depth, whereas British breeds were the opposite. Economic weights tend to be small and positive for a reduction in fat depth in crosses between the two breed types. Key words: Beef cattle, feedlot, end point, optimization, bioeconomic model

Published information on the relative performance of beef breed crosses was used to derive single estimates of purebred breed values for the predominant beef breeds in Canada. A range of commercial traits was considered. The breed cross estimates were taken from four large breed comparison trials from 1970 to 1983, each with representative samples of the breeds from the North American population. Variances of the breed cross estimates, derived allowing for the number of sires and progeny sampled, were used in a Weighted Least Squares analysis to obtain single purebred breed effects. Birth weight, and growth rate breed values were also expressed on a 1991 base by adjusting for the estimated breed genetic trends. Important genetic differences are shown to exist between the breeds for many of the traits. Breeds with larger mature size tended to be larger and leaner at a constant age and better for maternal calving ease and maternal calf survival. In contrast, smaller breeds were superior in their direct genetic contribution for calving ease and calf survival. Angus were more fertile and Simmental less fertile than the other breeds. Knowledge of these differences has a wide range of applications, including the provision of a biological basis for the economic comparison of breed crossing systems and for the definition of breed roles in beef production. Key words: Beef breeds, genetic differences, genotype-environment interaction