The optimum duration of test for measurement of growth rate, feed intake, feed conversion, and residual feed intake was examined using postweaning feed intake and weight data from 760 Angus, Hereford, Polled Hereford, and Shorthorn heifer and Angus bull progeny from 78 sires. Variance components, heritability, phenotypic and genetic correlations, and the efficiency of selection using shortened tests compared with a 119-d test were used as criteria to assess the optimum test length. The results indicated that a 35-d test was sufficient for measurement of feed intake, whereas a 70-d test was required to measure growth rate, feed conversion, and residual feed intake without compromising the accuracy of measurement. When a 70-d test is used to measure growth rate, feed conversion, and residual feed intake there is minimal loss in accuracy when weights are collected every 2 wk instead of weekly, but a further increase in the interval between weights to 5 wk caused a decline in the accuracy of the test. Therefore a 70-d test with cattle weighed every 2 wk seems to be optimal for measuring these traits in British breed cattle.

The fatty acid composition of the triacylglycerol fraction of shoulder fat from Limousin and Jersey yearling heifers, yearling steers, and non-lactating cows was investigated. Significant breed differences in the degree of fatty acid saturation were apparent between Jersey and Limousin cows, but were not observed in the yearlings. Jersey cows had less saturated fatty acids than the Limousin. Jersey cows showed an increased percentage of monounsaturated fatty acids compared with the Jersey yearlings. In contrast, the level of monounsaturated fatty acids in the Limousin cows was the same as in the Limousin yearlings. The calculated indices of enzyme activities also differed between the breeds. Jersey cows had higher indices of ?9-desaturase and elongase activities than Limousin. This was also reflected by differences in the ratios of total unsaturated and polyunsaturated to saturated fatty acids. Breed differences were also observed in the triacylglycerol fatty acid chain length. In this case, however, yearlings showed significant breed differences that were not detected in the cows. Limousin yearlings had more long chain fatty acids (C16 and C18) than the Jersey yearlings. Limousin yearlings also had a higher elongase activity index than their Jersey counterparts. Thus, breed and age affect the fatty acid composition in these cattle.

Mature Hereford cows (766) were mated to 97 sires from seven breeds (Jersey, Wagyu, Angus, Hereford, South Devon, Limousin, and Belgian Blue), resulting in 1,215 calves born over 4 yr (1994 to 1997). These cattle comprised Australia’s “Southern Crossbreeding Project.” Heifers were slaughtered at an average of 16 mo with hot standard carcass weight of 219 kg and 9 mm fat over the rump. Steers were slaughtered at an average of 23 mo with carcass weight of 319 kg and 13 mm fat over the rump. Meat and fat samples were taken from the carcass on the day after slaughter for subsequent laboratory analysis of i.m. fat content and fatty acid composition. Data were analyzed using uni- and bivariate animal models containing fixed effects of cohort, management group, birth month, and sire breed. March-born calves had fat with a 0.5°C lower melting point, 0.6% higher total monounsaturated fatty acids, and 0.7% higher fatty acid desaturation index than calves born in April. Steers born in 1997 were the only cohort finished on pasture, and they had much more yellow fat than the other cohorts. Four heavy breed crosses (Angus, South Devon, Limousin, and Belgian Blue) averaged 284 kg carcass weight, followed by purebred Hereford (268 kg), Wagyu (244 kg) and Jersey (236 kg). Angus had the greatest fat depth (14.3 mm), ahead of Hereford and Wagyu (11.9 mm), Jersey (10.7 mm), South Devon and Limousin (9.9 mm) and Belgian Blue (8.0 mm). Jersey, Wagyu, and Angus had the most i.m. fat (4.6%), followed by Hereford and South Devon (3.8%), and Limousin and Belgian Blue (3.1%). The highly marbled Jersey and Wagyu had softer fat (6% lower fat melting point) than the other breeds. Angus were more highly marbled, similar to Jersey and Wagyu, but had harder fat similar to the leaner breeds. Heritabilities for all traits were low to moderate (16 to 36%). Genetic correlations between fatty acid composition and carcass traits were not significant, indicating little evidence of antagonisms between traits that would prevent genetic progress in both production and quality. Copyright © 2002. . Copyright 2002 Journal of Animal Science

We investigated the fatty acid composition of the phospholipid fraction of the shoulder muscle (triceps brachii) from Jersey and Limousin yearling steers, yearling heifers, and nonlactating cows. The aim was to study breed, sex, and age differences. Significant breed differences in some individual fatty acids were apparent between Jersey and Limousin cows. Limousin cows had more palmitate, vaccenate, arachidonate, and less gammalinolenate and eicosapentanoate than Jersey cows. Age differences were significant: proportions of palmitate, stearate, and oleate decreased and linoleate, arachidonate, and total polyunsaturates increased with age. Most of the breed × age interactions were not significant. Also, phospholipids of Jersey and Limousin cows did not differ in total saturated, monounsaturated, and polyunsaturated fatty acids. Yearling data revealed significant sex differences in most of the fatty acids, including total monounsaturates and polyunsaturates. Yearling steers had more myristate, palmitoleate, stearate, and total monounsaturates and less linoleate, arachidonate, eicosapentanoate, and total polyunsaturates than heifers. Breed differences were also significant: Limousin yearlings had more dihomogamma-linolenate and erucate and less eicosapentanoate and nervonate than their Jersey counterparts. The sex × breed interaction was not significant for most of the fatty acids. These results imply that breed, age, and sex are important factors that influence the fatty acid composition of muscle phospholipids in cattle.