. 2011. Modification of muscle inherent properties through age at slaughter, growth promotants and breed crosses. Can. J. Anim. Sci. 91: 635Á648. A 2 4 factorial experiment tested the interactions of slaughter age (12Á13 or 18Á20 mo), growth hormone use, b-adrenergic agonist (b-AA) use and breed cross [HerefordÁAberdeen Angus (HAA) or CharolaisÁRed Angus (CRA)] on the composition, fibre types, and connective tissue characteristics of m. semitendinosus (ST) and m. gluteus medius (GM) from 112 crossbred steers. Muscle weights increased with slaughter age, implantation and CRA genetics (PB0.05), but were not affected by ractopamine hydrochloride (RAC) (P 0.10). Animal age increased fast glycolytic (FG) and decreased fast oxidative glycolytic (FOG) fibre percentages by 7.2 and 6.6%, respectively, in the ST and increased slow oxidative (SO) and FOG fibre areas in both muscles (PB0.05). Cross-sectional areas of all fibre types were increased in the ST with implantation. In the GM, implantation increased SO (3.1%) and reduced FOG (3.2%) fibre percentages, while RAC reduced the SO (3.8%) and increased the FG (6.1%) fibre percentages (P B0.05). Only GM total collagen content increased with slaughter age (PB0.05), but collagen solubility decreased with slaughter age for both muscles (PB0.05). CRA genetics increased FG percentage in the GM of yearling-fed steers and increased moisture and protein and reduced fat contents of both muscles (PB0.05). In the muscles studied, IMP, slaughter age and animal genetics induced greater changes in muscle inherent properties than RAC.

Girard, I., Aalhus, J. L., Basarab, J. A., Larsen, I. L. and Bruce, H. L. 2012. Modification of beef quality through steer age at slaughter, breed cross and growth promotants. Can. J. Anim. Sci. 92: 175–188. A 23 factorial experiment tested the interactions of slaughter age (12–13 or 18–20 mo), growth implants use (Component E-S, TE-S), ractopamine hydrochloride (RAC) feed supplementation use and breed cross [Hereford–Aberdeen Angus (HAA) or Charolais–Red Angus (CRA)] on pH, temperature, objective colour measurements, relative myoglobin states, sarcomere lengths, shear force, and water losses of m. semitendinosus (ST) and m. gluteus medius (GM) from 112 crossbred steers. In the ST, age affected objective colour measurements by increasing chroma and decreasing lightness (L*) and hue angle (P<0.05). Metmyoglobin (MMB) content of the ST also increased with steer age (P<0.05). In the GM, yearling-fed steers had greater MMB content than calf-fed steers, while hue angle varied the opposite way (P<0.05). Other variations in meat colour and myoglobin contents were more complex in the GM than the ST as they involved three-way interactions between the different treatments. Shear force and purge loss of the ST increased with implantation (P<0.05) with no change in sarcomere length (P>0.05). Shear force standard deviation was similar for breed crosses when yearling-fed but greatest for CRA breed cross when calf-fed (P<0.05). In both muscles, purge loss was increased by RAC supplementation (P<0.05). RAC supplementation did not affect sarcomere length and shear force in both muscles (P>0.10). In the GM, shear force increased with age and with CRA genetics (P<0.05). Results indicated that producers seeking to reduce beef toughness should consider using British crossbreds, exclude the use of hormonal implants and slaughter process steers at 12 to13 mo of age.

K. 2015. Effect of post-weaning residual feed intake classification on grazed grass intake and performance in pregnant beef heifers. Can. J. Anim. Sci. 95: 369Á381. There is limited knowledge of how cattle tested for feed efficiency under drylot conditions perform when they graze on summer pasture. Residual feed intake adjusted for end of test backfat thickness (RFI fat ) was determined on 171 beef crossbred heifers under drylot conditions over 2 yr using an automated system. Upon completion of the test, the 10 lowest and 10 highest RFI fat ((0.5490.17 vs. 0.5890.15 kg DM d (1 ) heifers in 2012, and the 14 lowest and 14 highest RFI fat ( (0.4790.16 vs. 0.5390.19 kg DM d (1 ) heifers in 2013 were selected and placed on meadow bromegrass pasture to investigate the effect of RFI fat ranking on their grass intake and performance on the pasture. The pasture adaptation period (8 d in 2012 and 19 d in 2013) was followed by a pasture feed intake experiment during which heifers were dosed twice daily (0815 and 1415) with 500 g of C 32 -labeled feed pellet for 13 d (day 0 to 12) and fecal sampled twice daily (0815 and 1415) from day 8 to 12. Forage DM intake on pasture for each heifer was determined using the double alkane (C 31 /C 32 ) methodology. High and low RFI fat heifers were similar in body weight (BW), backfat and rump fat thickness, and average daily gain (ADG) during the grazing trial period, except backfat thickness at the end of test period. However, low RFI fat heifers consumed 5.3% less forage when expressed as kg DM d(1 (8.2090.08 vs. 8.6690.09, PB0.001) and 5.1% less when expressed as a percentage of body weight (1.8690.02 vs. 1.969 0.02% of BW, PB0.001) compared with high RFI fat heifers. RFI fat measured under drylot conditions in growing heifers was positively correlated to grazed RFI fat determined in pregnant heifers (r p 00.30, P 00.04). These results suggest that beef heifers classified as low RFI fat during the post-weaning drylot period had lower dry matter intake as heifers in their first pregnancy grazing tame pasture, with no negative impact on their body weight, back-fat thickness, and ADG compared with their high RFI fat herdmates.Key words: Beef heifer, residual feed intake, grazed forage intake, n-alkanes, productivity Manafiazar, G., Basarab, J. A., Baron, V. S., McKeown, L., Doce, R. R., Swift, M., Undi, M., Wittenberg, K. et Ominski, K. 2015. Les effets de la classification de la prise alimentaire re´siduelle apre`s le sevrage sur la consommation du foin brouteé t la performance chez les ge´nisses a`boeuf en gestation. Can. J. Anim. Sci. 95: 369Á381. Les connaissances sont limite´es sur la performance des vaches vis-a`-vis l'efficience alimentaire dans les parcs d'e´levage lorsqu'elles broutent en paˆturage d'e´te´. La prise alimentaire re´siduelle ajuste´e pour l'e´paisseur du gras dorsal a`la fin de l'e´tude (RFI fat ) a e´te´de´termine´e durant une pe´riode de deux ans sur 171 ge´nisses a`boeuf croise´es loge´es dans les parcs d'e´levage et nourries par syste`me automatise´. À ...

Mapiye, C., Dugan, M. E. R., Turner, T. D., Rolland, D. C., Basarab, J. A., Baron, V. S., McAllister, T. A., Block, H. C., Uttaro, B. and Aalhus, J. L. 2013. Short Communication: Erythrocytes assayed early ante mortem can predict adipose tissue and muscle trans-18:1 isomeric profiles of steers fed red clover silage supplemented with flaxseed. Can. J. Anim. Sci. 93: 149–153. Steers were fed a red clover silage-based diet with or without flaxseed to evaluate over time the effects of flaxseed supplementation on erythrocytes (ERC) trans(t)18:1 isomers composition and their relationships to adipose tissue and muscle t18:1 profiles at slaughter. Concentrations of most ERC t18:1 isomers in steers fed flaxseed increased (P<0.01) markedly in the first 2 mo and increased gradually thereafter. Strong (P<0.01) correlations of t9-, t10- and t11-18:1 isomers were observed from month 2 to 6 between ERC and beef tissues collected at slaughter from steers fed flaxseed. Findings suggest that ERC sampled as early as 2 mo into the feeding period can be indicative of variation in beef t18:1 isomeric profile at a later slaughter date when feeding red clover silage with flaxseed.