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

Conformation scores can account for more than 20% of cattle price variation at Australian livestock sales. However, there are limited available references which define genetic factors relating objective live developmental traits to carcass composition. Weaning and post-weaning weight, height, length, girth, muscle (ratio of stifle to hip width) and fat depth of 1202 progeny from mature Hereford cows (637) mated to seven sire breeds (Jersey, Wagyu, Angus, Hereford, South Devon, Limousin and Belgian Blue) were examined for growth and development across ages. Crossbred Wagyu and Jersey were both lighter in weight and smaller in size (height, length and girth) than purebred Hereford and crossbred Angus, South Devon, Limousin and Belgian Blue. Within the five larger crossbreds, there were significant changes in relative weight from weaning to 600 days. Sire breeds differed in fat depth, with Angus being the fattest (9% on average fatter than Hereford and Wagyu), and Jersey 5% less fat than Hereford, followed by South Devon and Limousin (19% lower than Hereford) and Belgian Blue (39% lower than Hereford). Direct heritability ranged from 19 to 42% and was higher than the proportion of total phenotypic variance accounted for by maternal effects (which ranged from 0 to 17%) for most body measurement traits except for weight (38 v. 18%) and girth (36 v. 9%) traits at weaning, an indication of maternal effect on some body conformation traits at early ages. Muscularity (19 to 44%) and fat depth (26 to 43%) were moderately to highly heritable across ages. There were large differences for growth and the objective measures of body development between crossbreds with a degree of overlap among the progeny of the seven sire breeds. The variation between genetic (positive) and environmental (negative) correlations for dry versus wet season average daily gains in weight and fat, suggested the potential use of live-animal conformation traits for within breed selection of genetically superior animal in these traits across seasons.

An experiment examined delta9 desaturase activity and FA composition in subcutaneous adipose tissue in two differing breeds of cattle. Jersey-sired cattle had significantly higher rates of desaturase activity than Limousin-sired cattle (1.55 vs. 0.75 nmol/mg protein/min). This difference was also demonstrated by a lower concentration of individual (e.g., 18:0) and total saturated FA (38.3 vs. 45.1 wt%), and a higher concentration of individual (e.g., 16:1) and total monounsaturated FA (58.2 vs. 52.7 wt%) in the Jersey animals. Other indices of desaturation calculated from the FA composition showed this same difference. The slip point of adipose tissue of Jersey cattle (36.8 degrees C) was significantly lower than that of Limousin cattle (39.2 degrees C), but Jersey adipose tissue had a greater content of beta-carotene. The positive relationship between adipose tissue beta-carotene and desaturation opposes the negative relationship between dietary beta-carotene and desaturation determined elsewhere. These results, however, lead to the hypothesis that some cattle have a reduced capacity to metabolize beta-carotene to various forms of vitamin A, a compound that can reduce delta9 desaturase enzyme activity. In addition, the higher level of intramuscular fat in Jersey cattle (6.97 vs. 3.82%) is possibly related to a lack of inhibition of the adipocyte differentiation genes by vitamin A.

Fatty acid composition was measured in lipid extracted from adipose tissue and muscle collected at slaughter from 6 groups of crossbred cattle of about 2 years of age, grain-finished in a feedlot. The cattle ranged in biological type from late to early maturing. They were progeny of the following crosses: Charolais x (Simmental.Hereford), Simmental x (Simmental.Hereford), Charolais x (Jersey.Hereford), Hereford x Hereford, Hereford x (Jersey.Hereford), Jersey x Hereford. The fat content of muscle from the leanest late-maturing cross was 5.2% rising to 10.4% in the fattest early-maturing cross. There was no significant difference in the fatty acid composition of subcutaneous fat between the 6 crosses, but there was in the concentration of some of the fatty acids of intramuscular lipid. The latter was due on one hand to the increased deposition of neutral lipid in early-maturing animals and on the other to a higher proportion of polyunsaturated fatty acids in membrane phospholipid in late-maturing animals. The proportions of the monounsaturated fatty acids palmitoleic (C16:l) and oleic (C18:l) were higher in the early-maturing Jersey x Hereford crosses than in straight-bred Herefords or the other crosses, but only in the C16:l values was there a significant difference between breeds. There was also a significant difference between breeds in the sum of monounsaturates and the sum of polyunsaturates in intramuscular fat. The Jersey crosses had the highest level of monounsaturates and the lowest level of polyunsaturates. Intramuscular phospholipid was examined in the 2 breeds that were the most divergent in terms of intramuscular fat content, the Charolais x (Simmental.Hereford) and the Jersey x Hereford. The latter had significantly higher C16:l values and significantly lower C18:2 and polyunsaturate fatty acid values. The experiment demonstrated that breed differences occurred in fatty acid composition of muscle total lipid and phospholipid. The differences are of significance in human health and in identifying maturity breed-types of cattle.

As a component of the second term of the Cooperative Research Centre (CRC) for Cattle and Beef Quality, a project to further test and validate the effects of varying nutritional growth paths pre-finishing and slaughter on cattle of varying genetic potential for meat yield and eating quality was designed and implemented. This project, ‘Regional Combinations’, was a multi-site experiment, using Bos taurus cattle generated at 4 locations across southern Australia. The design of imposing different growth paths between weaning and finishing on cattle with specific genetic potential is common across sites. Treatment and interaction effects on beef production and meat quality were examined within and across sites. This paper describes the experimental designs, generation of experimental cattle at the various sites and the measurements, collection and storage of the data for multi-site analyses.