Research Stution, A,qriculture Cunudu, Lucombe, Alberta T)C 150. Contribution ntt.423, reteivetl I0 Apr. l9Bl, uctepred 23 Feb. 1982. O'Sur-r-rvnN, P. A., Kossrrz,V. C., Wtrss

Yield of commercially trimmed (CT), boned (B) and boned-defatted (BDF) pork in relation to weight and backfat thickness was evaluated from a sample of 3807 carcasses obtained from the kill lines of three commercial packing plants located in the provinces of Alberta, Ontario and Quebec. Sampling procedures at each plant were designed to provide carcasses from 10 males and 10 females in each cell of a grid defined by 10 weight classes (5-kg intervals ranging from 60 to 100 kg) and 13 fat classes (5-mm intervals ranging from 35 to 90 mm). Fat classes were determined on the basis of the sum of two measurements made at the points of minimum back and maximum loin. Fat class was the primary determinant of yield from the individual lean cuts (ham, loin, picnic and butt) with yield of CT, B and BDF product decreasing as fat class increased. Carcass weight had a negligible influence on yield after fat was considered and the effect associated with region and sex, while statistically significant, were also negligible. These results indicated that a single regression equation based on fat class would suffice for purposes of yield grading of Canadian hog carcasses. This equation identified a change in percentage yield of the combined lean cuts of 0.89% per fat class (5 mm of fat) with this relationship stable over the carcass weight range of 55–105 kg. Percentage yield of CT product from the total carcass (lean cuts plus belly) was less responsive to changes in total fat (0.50%) because belly yield, both untrimmed and trimmed, increased with increasing fatness.

Data were collected from nine farm fields over 2 yr to determine the relationship between percent yield loss of rapeseed and density of Canada thistle. Regression analyses of the data for percent yield loss of rapeseed and numbers of thistle shoots per square metre, using two representations of the data (untransformed and square root transformation), yielded the following equations:[Formula: see text]and[Formula: see text]where ŷ = estimated percent yield loss of rapeseed, x = the number of Canada thistle shoots per square metre, and 1.48 and 10.42 are the indices of competition for Eqs. 1 and 2, respectively. Equation 1 provides a more accurate estimate of percent yield loss at all levels of thistle infestation. Equation 2 provides acceptable estimates of yield loss at intermediate levels of infestation (5–40 shoots/m2) and is presented for comparitive purposes since the index of competition (10.42) is near the value proposed as a result of extrapolation from earlier studies (10.6) which utilized square root transformation of the data. The significance of this is discussed. The 95% confidence limits for Eq. 1 for the estimated percent rapeseed yield loss when four different samples sizes (n = 1, 5, 10 and 20) are used to estimate the number of thistle shoots per square metre are presented. An example of the utility of the linear equation is presented.Key words: Rapeseed, Canada thistle, crop loss, competition

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(-0,31). De mOme, la surface de la noix de c6te 6tait n6gativement corr6l6e avec l'indice de persill6 (-0,24

. Slaughter and carcass traits of cilves from first-cross and reciprocal back-cross beef cows. Can. J. Anim. Sci. 74: 621-632. Breed-of-dam and sex-of-calfeffects are reported based on observation of2007 heifer and steer carcasses' The carcasses were derived from Limousin-sired calves born to dams representing 15

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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