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Growth patterns and calf performance of 2-yr-old F1 and reciprocal backcross females were compared in two contrasting environments, semi-intensive management (Brandon, Man.) and extensive range management (Manyberries, Alta.). At Brandon, 621 heifers of Hereford × Angus (HA), Simmental × Shorthorn (SN), Charolais × Shorthorn (CN) and reciprocal backcrosses from Charolais × Hereford (CH), Charolais × Angus (CA), Charolais × Shorthorn (CN), Simmental × Hereford (SH), Simmental × Angus (SA), and Simmental × Shorthorn (SN) were evaluated. At Manyberries, 271 heifers of HA, SN, CN and reciprocals of SH, SA and SN were evaluated. They were bred to Limousin bulls. The HA heifers were the lightest at 14, 18, 24, 26 and 30 mo of age at both locations. Location differences for dam crosses in common ranged from 5% at 14 mo to 19% for 30 mo weight (Brandon > Manyberries). At all ages, the 3/4 C 1/4 N and the 3/4 S 1/4 N dam crosses were the heaviest at Brandon and Manyberries, respectively. Differences in weights at all ages between the CN and their reciprocal backcrosses were not significant at Brandon. The SN dams exceeded their reciprocal backcrosses in weight at all ages at Brandon (P < 0.01) but none of the differences were significant at Manyberries. Very few of the differences recorded for gestation length and birth weight at either location were significant. Progeny from HA dams were the lightest at birth and when significant differences existed for gestation length the longest were associated with the 3/4 "exotics." At both locations, progeny from HA dams were lightest and the progeny from the 3/4 "exotics" the heaviest at weaning. Females at Manyberries produced calves that were 3.3% heavier at weaning than those at Brandon. The highest weaning weight ratios were recorded for the 3/4 S 1/4 A, 3/4 S 1/4 N and SN dam crosses at both locations and these dam crosses were intermediate in weight at 30 mo. Total overall conception for breed crosses common to both locations for breeding at 14 and 26 mo was 77.0% vs. 75.8% and 82.1% vs. 79.5% for Brandon and Manyberries, respectively. Few differences were observed between dam crosses for conception rate. At Brandon, CX females required significantly more services per conception at 14 mo of age than SX females which reflected itself in lower conception rates. Compared with the SX females, the CX females had 11.8% lower conception to 1st service and 4% lower total conception. Calves born at Manyberries experienced greater calving difficulty but this was not reflected in higher calf mortality rates. Key words: Beef cattle, growth, preweaning traits, crossbreeding

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were also reflected in the sex differences for age at slaughter (sexes equal at Brandon; heifers ) steers at Lacombe) and degree of finish (sexes equal in rib fat at Lacombe; steers > heifers at Brandon). Heifers at Brandon had a larger percentage of hide (P < 0.0001) and lower dressing percentage (p < 0.0001) than steers. Percentage of head, front feet and hind feet were also less for heifers than steers at this location. Rib eye was greater for steers but heifers had greater rib eye area per unit weight (P < 0.0001) and a higher percentage of kidney fat (p < 0.0001). The sex ranking for percentage chuck, shank and flank was steers > heifers (P < 0.0001) and the reverse for percentages of rib, long loin and the combined cuts of rib, round and long loin (P < 0.0001). For percentages of lean in the long loin, rib and chuck the ranking was sreers ) heifers (p < 0.0001) with heifers ) steers for percentage lean of round (P < 0.0001). Heifers relative to steers had significantly (P : 0.0001) lower percentages of bone in the round, rib and chuck and greater (P : 0.0001) lean to bone ratios for the combined trait of long loin and round. The sex differences observed at Lacombe for these traits were in good agreement with Brandon although sex by location interactron was not tested. Year differences were large but year-by-sex interactions were non-existent for virtually all carcass traits evaluated at both locations (P < 0.05). Sire-by-sex and dam-by-sex interactions were also absent.

. 1989. Rate and efficiency of gain in Hereford and Angus bulls from lines selected for rapid growth on high-energy and low-energy diets. Can. J. Anim. Hereford and Angus bull calves were obtained from lines selected for an average of 18 yr for rapid growth on a high-energy diet (concentrate) or a low-energy diet (forage). They were given a typical feedlot diet(70% concentrate and30% forage) in amounts about equal to 95% of the ad libitum intake and were slaughtered at a liveweight of 500 kg. Effects ofbreed, or ofthe selection diet given to the antecedents ofthe bulls, on rate and efficiency of gain of empty body, carcass, fat, protein, and energy were measured. Selection diet had no effect on rate or energetic efficiency of gain of the empty body or any of its constituents, nor on the distribution of the constituents of the gain between the carcass and the noncarcass portions of the empty body. This suggests that both selection diets exerted the same selection pressure for improved growth rate and feed efficiency when offspring resulting from selection were provided with a common high-energy diet and that either type of diet would, therefore, be appropriate for selecting animals for production systems that use high-energy diets. It was suggested that the main effect of selection was to increase the mature weight of the offspring. Comparing breeds, it was noted that Hereford bulls were heavier at birth, grew more slowly to weaning but more efficiently thereafter, and their carcasses were a smaller proportion of empty live weight than were those of Angus bulls. Animals were weighed every 2 wk, at 16 h after the previous feeding, and the allotment of feed was adjusted at that time. The animals were bedded on wood shavings and were allowed trace-mineralized salt and water free choice.Both concentrate and alfalfa cubes were sampled every day throughout the 4 yr of the experiment and the samples were pooled into one large batch that was used for a digestion trial at the end of the experiment. Composition and digestibility data are given in Table2. Procedures used for carrying out the digestibility trials were as described in an earlier report Maintenance energy requirements were estimated from a subsidiary experiment in which 24 bulls ranging from 280 to 520 kg liveweight were provided enough of the present feed, (70% concentrate, 3O% hay) to satisry their maintenance requirements according to data compiled by van Es (1978Es ( , 1980, and allowing their weights to reach equilibrium. This approach was based on the finding that body weights of cattle on fixed energy intakes eventually stabilized and remained fairly constant over long periods of time (Taylor et al. 1981