Genetic divergence in residual feed intake affects growth, feed efficiency, carcass and meat quality characteristics of Angus steers in a large commercial feedlot

Growth, feed intake, feed efficiency, and carcass and meat quality characteristics of 136 Angus steers differing in genetic merit for post-weaning residual feed intake (RFIp) were measured over 251 days in a large commercial feedlot. The steers were evaluated in two groups, low (Low-RFI) and high (High-RFI) genetic RFIp, measured by estimated breeding values for RFIp (RFIp-EBV). The difference in RFIp-EBV between the Low- and High-RFI groups was 1.05 kg/day (–0.44 vs 0.61 kg/day; P < 0.05). The Low- and High-RFI steers were similar (P > 0.05) in age (445 vs 444 days) and weight (435 vs 429 kg) at induction, and at the end of the feeding period (705 vs 691 kg). Average daily gain (ADG) over 251 days had a small negative association with variation in RFIp-EBV (P < 0.05), reflecting a 3.6% greater ADG accompanying a difference of 1 kg/day in RFIp-EBV. Pen feed intake and feed conversion by the Low-RFI group were 10.4 kg/day and 9.3 kg/kg, and for the High-RFI group were 11.1 kg/day and 10.4 kg/kg, but without availability of individual animal feed-intake data it was not possible to test for significant differences. Carcass weight and dressing-percentage was similar for the Low- and High-RFI steers. High-RFI steers had a significantly (P < 0.05) greater depth of subcutaneous rib fat at induction and finished with 5 mm more (P < 0.05) fat at the 10/11th ribs on the carcass than the Low-RFI steers. Cross-sectional area of the eye-muscle and three measures of intramuscular or marbling fat did not differ (P > 0.05) between the Low- and High-RFI steers. Shear force was higher (P < 0.05) in meat samples aged for 1 day from the Low-RFI steers, but there was no difference (P > 0.05) from the High-RFI steers after 7 days of ageing. Compression values for meat samples aged for 1 day did not differ between the RFI groups but were higher in meat samples aged for 7 days from the Low-RFI steers. For these Angus steers, genetic superiority in RFI was associated phenotypically with superior weight gain, decreased rib fat depth, slightly less tender meat, and no compromise in marbling fat or other carcass and meat quality traits.

Carcass and meat properties of six genotypes of young bulls finished under feedlot tropical conditions of Mexico

The effect of six genotypes (Zebu = Z, European Brown Swiss = EBS, Holstein = H, Z × EBS, Zebu × American Brown Swiss = ABS, Z × ABS, Z × H) on carcass and meat characteristics of young bullocks finished under feedlot conditions was tested. The Z × ABS bullocks had the highest (P = 0.001) average daily gain. The highest (P = 0.017) final liveweight was observed with Z × ABS > EBS > H genotypes. The ribeye area was larger (P = 0.012) for EBS bullocks. Both H and EBS bullocks had lowest (P = 0.001) physiological maturity; although the H bullocks had higher (P = 0.006) pelvis and heart fat values. The best (P = 0.014) conformation was obtained with the Z × ABS and Z × EBS genotypes. The greatest amount of marbling (P = 0.001) was obtained with the H genotype. In general, the crossbred genotypes showed better feedlot performance and carcass characteristics, and it seems that Holstein breed could have a an advantage from the marbling score point of view.

Genetic effects on carcass quantity, quality, and palatability traits in straightbred and crossbred Romosinuano steers

The objectives of this work were to estimate heterosis and breed genetic effects for carcass quantity, quality, and palatability traits of steers (Bos spp.) produced from matings of Romosinuano, Brahman, and Angus cattle. Steers (n = 464) were weaned at 7 mo of age and transported to the Southern Great Plains where they grazed winter wheat for 6 mo and were then fed a finishing diet until serial slaughter after different days on feed (average 130 d). Carcass quality and quantity traits were measured; steaks (aged 7 d) were obtained for palatability evaluation. Heterosis was detected for BW, HCW, dressing percentage, LM area, and yield grade for all pairs of breeds. Generally, Romosinuano-Angus heterosis estimates were smallest, Romosinuano-Brahman estimates were intermediate, and Brahman-Angus heterosis estimates were largest. The direct Romosinuano effect was to decrease (P < 0.05) BW (-67 ± 16 kg), HCW (-48 ± 10 kg), dressing percentage (-1.4 ± 0.5 units), 12th rib fat thickness (-5.2 ± 0.8 mm), and yield grade (-0.9 ± 0.1), and to increase LM area per 100 kg HCW (3.6 ± 0.3 cm(2)/100 kg). Significant Brahman direct effects were detected for BW (34 ± 17 kg), HCW (29 ± 10 kg), dressing percentage (1.6 ± 0.6 %), LM area per 100 kg HCW (-3.3 ± 0.4 cm(2)/100 kg), and yield grade (0.6 ± 0.1). Significant Angus direct effects were to increase 12th rib fat thickness (3.8 ± 1 mm). Among sire breed means, Romosinuano had reduced (P = 0.002) marbling score (393 ± 9) than Angus, but greater mean sensory tenderness scores (5.8 ± 0.1), and reduced percentage Standard carcasses (10 ± 2%) than Brahman (P < 0.002). Angus sire breed means for marbling score (475 ± 10), overall tenderness (5.8 ± 0.1), and percentage Choice carcasses (75 ± 5%) were greater (P < 0.05) than Brahman sire breed means (360 ± 11, 5.4 ± 0.1, 31 ± 5%). From consideration only of characteristics of the end product of beef production, Romosinuano did not provide a clearly superior alternative to Brahman for U.S. producers, as they had some quality and palatability advantages relative to Brahman, but at lighter HCW.

Nutritional research to meet future challenges

Nutrition is a mature science with well established principles for energy, protein and mineral metabolism based on known metabolic pathways. The quantitative requirements are summarised within various international feeding standards and models. However, when these are applied to specific circumstances, especially in northern Australia, the response of the animal to nutrient supply does not always agree with that predicted from the feeding standards or the error of prediction is not sufficiently accurate for practical use. There is a need for the continual testing of these relationships within production systems. Molecular methods have the potential to discover new metabolic relationships within tissues and characterise the microbial ecology and its relationship to rumen function. Suitable problem models based on growth, meat quality, reproduction, milk and fibre production, and environmental consequences need to be identified. We suggest that production systems designed to meet market weight for age specifications, growth paths and compensatory growth, skeletal growth, parasites, fatty acid isomers, adaptation to low crude protein diets, rumen microbial ecology, epigenetics, remote data acquisition and animal management, greenhouse gas emission, and C balance of various production systems are important problem models, the research of which will benefit the future of the livestock industries in Australia.

Brahman and Brahman crossbred cattle grown on pasture and in feedlots in subtropical and temperate Australia. 1. Carcass quality

Brahmans are known to have poorer carcass quality relative to Bos taurus breeds and crossbreds under temperate environments; however, little is known of their performance in subtropical environments. The Cooperative Research Centre for Cattle and Beef Industry (Meat Quality) initiated a crossbred progeny test experiment to compare straightbred Brahmans with Brahman crossbreds finished on pasture and grain, in subtropical and temperate environments, to carcass quality specifications of Australian domestic and export markets. Brahman, Belmont Red, Santa Gertrudis, Angus, Hereford, Shorthorn, Charolais and Limousin sires were mated to Brahman females in subtropical Queensland over 3 years to produce 1750 progeny. At a common age at slaughter, Charolais crossbreds had the highest hot carcass weight (CWT) but were not significantly heavier than Limousin or British crossbred progeny. At common carcass weights, breeds within breed type (British, Continental, tropically adapted) performed similarly. British and Santa Gertrudis crossbreds had the fattest carcasses and lowest yields. British and Belmont Red crossbreds had the highest intramuscular fat percentage (IMF). Continental crossbreds had the highest retail beef yield (RBY), kilograms of retail primals (RTPM) and percent retail primals (pcRTPM) and leanest carcasses. Brahmans had the lowest CWT, intermediate subcutaneous fat cover, high yields and low IMF. Animals finished in the subtropics on pasture were significantly older, leaner and had higher RBY, RTPM and pcRTPM than subtropical feedlot-finished contemporaries. Temperate feedlot animals had significantly more IMF, less subcutaneous fat at the P8 site and slightly lower yields than subtropical feedlot contemporaries, indicating possible effects of postweaning growth path on fat distribution. Belmont Red crossbreds demonstrated the advantages of adaptation with the highest IMF in both subtropical finishing regimes, while Angus progeny had the highest IMF in the temperate feedlot environment and highest IMF overall when analysed across finishing regimes. Significant interactions were mainly the result of scale effects rather than breed re-ranking for carcass traits across markets and finishing regimes. Therefore, breeds that performed well for certain carcass traits in subtropical environments performed consistently for those traits in temperate environments relative to other sire breeds, regardless of market endpoint or finishing nutrition.

Brahman and Brahman crossbred cattle grown on pasture and in feedlots in subtropical and temperate Australia. 3. Feed efficiency and feeding behaviour of feedlot-finished animals

The objective of this experiment was to quantify differences in feed efficiency and feeding behaviour of 470 heifers and steers by Brahman, Belmont Red, Santa Gertrudis, Angus, Hereford, Shorthorn, Charolais and Limousin sires mated to Brahman dams. Animals were bred in subtropical Queensland and finished in a temperate New South Wales feedlot. Animals averaged 598 days of age and 425.8 kg at the start of the feed intake test period. Sire breeds did not differ for eating rate, feed conversion ratio or relative growth rate. Generally, higher daily feed intakes (DFI) corresponded with higher average daily gains (ADG). Straightbred Brahmans fed the most frequently (16.6 ± 0.8 sessions/day; P < 0.05) but spent the least time eating of all breeds (67.4 ± 2.7 min/day; P < 0.001). Least squares means for Brahman, Belmont Red, Santa Gertrudis, Angus, Hereford, Shorthorn, Charolais and Limousin sired progeny, respectively, for residual feed intake (RFI; P < 0.05) were 0.02 ± 0.16, 0.14 ± 0.13, –0.10 ± 0.23, 0.54 ± 0.17, –0.27 ± 0.18, 0.29 ± 0.18, –0.46 ± 0.16 and –0.21 ± 0.13 kg/day, and for ADG (P < 0.001) were 1.06 ± 0.05, 1.17 ± 0.04, 1.52 ± 0.08, 1.47 ± 0.06, 1.46 ± 0.06, 1.46 ± 0.06, 1.35 ± 0.06 and 1.38 ± 0.05 kg/day. While straightbred Brahmans did not differ from all other sire breeds for RFI, their lower appetite relative to crossbred contemporaries resulted in the lowest DFI (P < 0.001) and lowest ADG (P < 0.001) overall. Angus sired crosses were the least efficient feeders and spent the most time eating, consumed the most feed and had the highest RFI, but were not significantly different to Santa Gertrudis and Shorthorn crosses for these traits. Angus sired crosses spent 24.1 and 15.4 min/day more time eating (P < 0.001) than straightbred Brahmans and Charolais crosses, and consumed 35 and 13% more feed (P < 0.001) respectively. Charolais sired crosses were the most feed efficient with the lowest RFI and intermediate DFI, and did not differ significantly from the highest ranking sire breeds for ADG or Kleiber ratio. While Belmont Red crosses did not differ from all breeds for RFI, they had significantly lower DFI than British and Santa Gertrudis crosses resulting in lower ADG (P < 0.001) relative to these sire breeds. Therefore, selection of Charolais, Hereford, Limousin and Santa Gertrudis sire breeds would result in the most feed efficient (low RFI) crosses with Brahman without any sacrifice in ADG.