Summary The aim of this study was to develop a multiple trait genetic evaluation and selection tool for maternal productivity in beef cattle, particularly in the Hereford breed. Component traits of the maternal productivity index (MPI) were chosen on the basis of their potential to contribute to consistently weaning heavy calves over a sustained herd life, while controlling cow maintenance costs. (Co)variance components were estimated with a multiple trait model including direct and maternal birth weight, direct and maternal weaning weight, weight of the cow at the time her calf is weaned and survival, defined as the ability of a female to produce at least three calves given she became a dam. Although direct and maternal birth weight were included in the (co)variance parameters model, these traits were not included in the index. Estimates of heritability were 0.19, 0.18, 0.50 and 0.07 for direct and maternal weaning weight, cow weight, and survival, respectively. The correlation between direct and maternal components of weaning weight was −0.42. The genetic correlation estimated between direct weaning weight and cow weight was 0.85, while a low genetic correlation of −0.17 was estimated between maternal weaning weight and cow weight. Survival had a near zero (−0.01) genetic correlation with maternal weaning weight, but negative genetic correlations with direct weaning weight (−0.52) and cow weight (−0.48). The MPI was constructed as a linear function of derived economic weights multiplied by estimated breeding values for the four component traits from the model. Estimated economic values were $3.00, $2.70, $−0.49 and $2.39 for direct and maternal weaning weight, cow weight, and survival (expressed as a percentage), respectively. Relative economic weights were 0.30, 0.26, 0.17 and 0.27 for direct and maternal weaning weight, cow weight, and survival, respectively. A simulation study indicated that positive genetic trend would be expected in all component traits although increases in cow weight would be moderate.

. 2000. Selection for cow lifetime pregnancy rate using bull and heifer growth and reproductive traits in composite cattle. Can. J. Anim. Sci. 80: 507-510. 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 (r g = -0.25) while yearling tonometer score was favorably related (r g = 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 (r g = 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. Ce paramètre peut donc se prédire à partir des caractères de croissance faciles à mesurer de la génisse. En utilisant des indices réunissant les mensurations scrotales et les caractères de croissance de la génisse, on pourrait améliorer l'évolution génétique annuelle du taux de gravidité par un facteur de 3,1, par rapport à la sélection directe.

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The aim of this study was to evaluate the effect of including concomitant body weight and(or) a random dam effect in genetic evaluation models on variance component estimates and standard error of prediction for scrotal circumference (SC) at 6, 8, 10, and 12 mo. Variance components and average standard errors of prediction were compared under models differing in either the number of related traits (M11 [SC], M12 [SC and BW]) or an uncorrelated random dam effect (M21 [SC], M22 [SC and BW]) using records on 1,547 bull calves. In a single-trait model (M11), estimates of direct heritabilities (h2a) for SC were .45, .49, .57, and .66 at 6, 8, 10, and 12 mo, respectively. In a two-trait model (M12), h2a were similar to those in M11 model. In M21, h2a for SC were .37, .42, .54, and .65, whereas the proportions of phenotypic variance due to dams (d2) were .12, .11, .04, and .02 at 6, 8, 10, and 12 mo, respectively. Similarly, in M22, h2a for SC were .36, .44, .56, and .65 and d2 were .13, .10, .02, and .02. Standard errors of prediction for SC EBV from M22 were reduced by 2.86, 1.21, 3.02, and 1.99% relative to M21 and by 6.45, 2.70, 2.72, and 1.21% relative to M11 at 6, 8, 10, and 12 mo, respectively. Standard errors of prediction for SC EBV from M12 were reduced by .06, .73, 1.56, and .87% relative to M11 at 6, 8, 10, and 12 mo, respectively. The importance of the dam effect decreased with age for both SC and BW. These results demonstrate that a two-trait (SC and BW) animal model would result in more accurate evaluations of yearling SC EBV in beef cattle than a single-trait model.

2000. Machine effects on accuracy of ultrasonic prediction of backfat and ribeye area in beef bulls, steers and heifers. Can. J. Anim. Sci. 80: 19-24. 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 < 0.05) among smaller-muscled cattle. Machines were comparable in accuracy among animals of all FAT sizes. This study demonstrates that there is an important relationship between machine and the size and depth of muscle and backfat, respectively, and consequently between machine and sex, in accuracy of ultrasound prediction.. et Mwansa, P. B. 2000. Effets dus à l'appareil sur l'exactitude des prédictions par ultrasons de l'épaisseur du gras dorsal et de la surface de la noix de côte chez des taurillons, des bouvillons et des génisses à viande. Can. J. Anim. Sci. 80: 19-24. Des évaluations par ultrasons des animaux sur pied et des mesures sur carcasse de la surface de la noix de côte (NSC) et de l'épaisseur du gras dorsal (EGD) ont été prises sur des taurillons, des génisses (tau-res) et des bouvillons à viande de race composite. La composition génétique de la race était 44 % races britanniques : Hereford, Angus et Shorthorn, 25 % Charolais, 25 % Simmental et 6 % Limousin. Nous comparions les appareils à ultrasons Aloka SSD-1100 (AL) et Tokyo Keiki CS 3000 (TK) d'après l'écart entre les valeurs ultrasoniques et les valeurs mesurées sur carcasse et d'après l'erreur type de prédiction (ETP). L'appareil AL produisait une sous-prédiction de la NSC pour les trois types sexuels, tan-dis que TK la surprédisait pour les génisses et les bouvillons et la sous-prédisait dans le cas des taurillon, les deux appareils démon-trant chez ces derniers une exactitude comparable. L'épaisseur du gras de couverture était sous-prédite sur les trois types sexuels par AL et sur les génisses par TK lequel, pour les taurillons et les bouvillons, fournissait des prédictions très proches des valeurs mesurées. L'ETP pour EGD était de même amplitude avec les deux a...