Over an 8-yr interval, (1975–1982) scrotal circumference (SC) was measured on 4557 1-yr-old beef bulls from 1796 sires and eight breeds. Measurements were taken upon completion of a 140-d growth performance test. During the period 1977–1983, SC was measured on 7835 2-yr-old beef bulls from 2570 sires and six breeds. Two-year-old bulls were measured during reproductive examinations at spring bull sales. All SC measurements were adjusted for fixed effects of location-year and age, and heritability estimates were calculated within-breed using a paternal half-sib analysis. Heritability estimates for the SC trait in Angus, Charolais, horned Hereford, polled Hereford, Shorthorn, Simmental, Limousin and Maine-Anjou breeds in 1-yr-old bulls were 0.22 ± 0.20, 0.46 ± 0.14, 0.89 ± 0.17, 0.83 ± 0.26, 1.01 ± 0.31, 0.63 ± 0.19, 0.94 ± 0.29 and 0.59 ± 0.22. Heritability estimates for SC in 2-yr-old bulls of the first six breeds were 0.00 ± 0.21, 0.60 ± 0.25, 0.57 ± 0.07, 0.65 ± 0.10, 0.69 ± 0.34 and 0.20 ± 0.24. Owing to the small number of sires or sons within sires for some breed-age groups and the exclusion of some sources of variation in the statistical model, the estimates of heritability may not be precise and should be used to indicate approximate levels of heritability for a particular breed. Key words: Heritability, testicular size, scrotal circumference, beef bulls

Feeding trials were conducted in two years to compare growth performance, carcass characteristics and quality of meat from beef cattle with 0, 50 or 75% Wagyu genetic influence. The cattle types used in the two years of the study were Continental crossbred steers (0% Wagyu), cattle with 50% Wagyu influence (Wagyu/Angus crossbreds) and 75% Wagyu influence (containing 25% from other European breeds). Cattle were housed in individual pens in the first year and in group pens in the second year. Cattle were fed a backgrounding diet containing 35% barley grain and 65% barley silage with protein, mineral and vitamin supplements until they weighed more than 380 kg, after which they were adapted to a finishing diet consisting of 80% barley and 20% barley silage with mineral and vitamin supplements. Cattle were weighed every 4 wk and at the end of the finishing period they were processed and carcass information was obtained. A three-rib section (10-12) was removed from 41 (year 1) and 44 (year 2) carcasses selected randomly from each group, and Warner-Bratzler shear force was determined. The year-by-cattle type interaction was significant for most parameters; thus all the data were also analysed by year using weight of cattle at initiation of the feeding trial as a covariate for the backgrounding and finishing phases of growth and using carcass weight and back fat depth as covariates for carcass and meat-quality parameters. Weight at the start of the trial influenced most growth parameters and age at slaughter. Continental crossbred steers had higher (P < 0.05) ADG than Wagyu crossbred cattle during the finishing phase (1.47 vs. 0.82 kg d(-1)) in year 1, but not in year 2. Carcass weights of 75% Wagyu crossbred cattle were lower (P < 0.05) than those of Continental crossbred steers in both years. Warner-Bratzler shear force values were less than 5.3 kg to shear cores of 19 mm diameter. However, 92% in year 1 and 71% in year 2 of the carcasses from Wagyu crossbred cattle graded Canada AAA, and contained more than a "small" amount of intramuscular fat. Thirty percent of the carcasses from Wagyu crossbred cattle in year 1 graded Canada Prime. Only 30% of Continental crossbred steers in year 1 and 10% in year 2 graded Canada AAA. Wagyu genetic influence enhanced marbling in beef cattle without loss in carcass size for the 50% Wagyu steers.

The activity of the triacylglycerol bioassembly enzyme, diacylglycerol acyltransferase (DGAT), was characterized in microsomal fractions prepared from bovine subcutaneous (SC) adipose, intramuscular (IM) adipose, and muscle (pars costalis diaphragmatis) tissue. The activity of DGAT was generally higher from SC adipose tissue than from IM adipose or muscle tissue. The characteristics of DGAT activity from the three bovine tissues resembled the activity characteristics observed in previous studies from various other organisms and tissues; the pH optimum was near neutrality, the activity was almost completely inhibited by pre-incubation with N-ethylmaleimide (NEM), and the enzyme accepted a broad range of acyl-CoAs and sn-1,2-diacylglycerols. In some aspects, the SC adipose tissue DGAT activity was different from the DGAT activity from the other two tissues. The SC adipose tissue DGAT activity was not as susceptible to inhibition by NEM as the enzymes from the two other tissue sources, and it exhibited increased specificity for substrates containing oleoyl moieties. The differences in DGAT properties between the three bovine tissues may account to some extent for the differences in the relative fatty acid composition and the positional distribution of fatty acids in triacylglycerol between bovine tissues. The observed differences in enzymatic properties also support recent biochemical and molecular genetic observations that imply the existence of multiple DGAT genes and/or isoforms.

Backfat depths, marbling scores, and concentrations of plasma insulin, cortisol, triiodothyronine (T3), and thyroxine (T4) were determined in 394 calves with and without Wagyu genetics. Hormone concentrations were determined three to five times for hormones between weaning and slaughter. Calves were weighed and backfat was ultrasonically determined at 28-d intervals, and assigned for slaughter when ultrasonic backfat depths approached 12 mm. Heifers weighed less (P < 0.001) and had more backfat (P < 0.05) and more marbling (P < 0.05) than steers at slaughter. Breed influenced slaughter weight (P < 0.001) and average backfat depth (P < 0. 001), with Wagyu/Angus and Wagyu/Hereford crosses and Angus purebreds generally having greater backfat depths and lower slaughter weights than other crosses and purebreds. Marbling scores were not affected by breed (P > 0.1), although Wagyu crosses had more marbling (P < 0.05) compared with purebreds when variability in marbling due to differences in backfat depth was removed. Plasma cortisol, T3 and T4 were affected by calf breed, although there were no clear patterns for groups of breeds or breed crosses. There was a slight trend (P < 0.2) towards higher insulin levels and lower cortisol, T3 and T4 levels in some groups of calves with more backfat. Higher mean levels (P < 0.05) of T3 and T4 were found in all but one group of animals with more marbling. Thus, thyroid hormones may have a role to play in enhancing marbling in cattle. Key words: Wagyu cattle, marbling, backfat, insulin, cortisol, thyroid hormones

The longissimus muscle area (LEA), width A and depth B, and backfat depth C were measured ultrasonically bi-weekly at the first lumbar vertebra in 74 Suffolk-cross ram and ewe lambs from weaning at a mean age of 65 days until the first lambs were slaughtered at 4.5 months of age. Lambs were born and raised as twins from mature ewes (age 2–5 years) and given free access to a 14.5% crude protein (CP) pelleted, barley-based lamb grower diet. Ewe lambs grew more slowly (P<0.01) than rams (297±4 and 339±5g per day for ewes and rams, respectively). Consequently, live weight of ewe lambs was less than that of the rams (P<0.05) after 90 days of age. However, LEA, A and B did not differ between ram and ewe lambs over the course of the study. As well, rates of longissimus muscle accretion as determined by ultrasound did not differ (P>0.05) between ram and ewe lambs. Ultrasound measurements of longissimus depth and area were the most repeatable (R=0.65 and 0.54, respectively), while measurement of longissimus width and back fat over the longissimus were less repeatable (R=0.24 and 0.28, respectively). In regressions by sex with age and weight in the model, age was the most significant predictor of LEA, A, B or C. The results of this study indicate that age is the most important factor affecting longissimus dimensions within a contemporary group.

The records of 282 young beef bulls from eight breeds tested from November 1981 to April 1987 at the Ellerslie Bull Test Station, Alberta, Canada, were used to study the variation in feed efficiency among young performance-tested bulls. Considerable variation existed among the animals in both residual metabolizable energy consumption and residual dry matter consumption. The heritability estimates for residual metabolizable energy consumption and residual dry matter consumption were 0.33 and 0.29, respectively. In addition, residual metabolizable energy consumption and residual dry matter consumption were moderately correlated (r = 0.43) with conventional feed-to-gain ratio, indicating that conventional feed-to-gain ratio only accounted for 18% of the variation in residual metabolizable energy consumption or residual dry matter consumption. It was, therefore, worthwhile to use residual metabolizable energy consumption or residual dry matter consumption as separate measures of feed efficiency. For rapid improvement in feed efficiency in beef cattle, selection pressure should be applied to both growth traits and residual energy consumption or residual dry matter consumption. Multi-trait optimum restricted selection indices and similar selection procedures may serve as useful means in balanced selection programs to improve the productivity of beef cattle. Key words: Feed efficiency, residual ME consumption, beef bulls

The aim of this study was to evaluate the effect of including concomitant body weight and(or) a random dam effect in genetic evaluation models on variance component estimates and standard error of prediction for scrotal circumference (SC) at 6, 8, 10, and 12 mo. Variance components and average standard errors of prediction were compared under models differing in either the number of related traits (M11 [SC], M12 [SC and BW]) or an uncorrelated random dam effect (M21 [SC], M22 [SC and BW]) using records on 1,547 bull calves. In a single-trait model (M11), estimates of direct heritabilities (h2a) for SC were .45, .49, .57, and .66 at 6, 8, 10, and 12 mo, respectively. In a two-trait model (M12), h2a were similar to those in M11 model. In M21, h2a for SC were .37, .42, .54, and .65, whereas the proportions of phenotypic variance due to dams (d2) were .12, .11, .04, and .02 at 6, 8, 10, and 12 mo, respectively. Similarly, in M22, h2a for SC were .36, .44, .56, and .65 and d2 were .13, .10, .02, and .02. Standard errors of prediction for SC EBV from M22 were reduced by 2.86, 1.21, 3.02, and 1.99% relative to M21 and by 6.45, 2.70, 2.72, and 1.21% relative to M11 at 6, 8, 10, and 12 mo, respectively. Standard errors of prediction for SC EBV from M12 were reduced by .06, .73, 1.56, and .87% relative to M11 at 6, 8, 10, and 12 mo, respectively. The importance of the dam effect decreased with age for both SC and BW. These results demonstrate that a two-trait (SC and BW) animal model would result in more accurate evaluations of yearling SC EBV in beef cattle than a single-trait model.

Genetic correlations of lifetime pregnancy rate with bull and heifer growth and reproductive traits in a beef composite population were estimated. Yearling scrotal circumference had an unfavorable genetic correlation (rg = −0.25) while yearling tonometer score was favorably related (rg = 0.22) to lifetime pregnancy rate. Heifer pregnancy rate, birth weight, weaning weight, yearling weight and age at puberty in heifers had significant genetic correlations (rg = 0.97, 0.58, 0.57, 0.33 and −0.21, respectively) with lifetime pregnancy rate. Lifetime pregnancy rate may be successfully predicted by easy-to-measure heifer growth traits. Using indices including scrotal and heifer growth traits, annual genetic change in lifetime pregnancy rate may be increased 3.1 times compared with direct selection. Key words: Scrotal circumference, tonometer, pregnancy, reproduction, puberty

The deposition of i.m. fat, or marbling, in cattle is recognized as a desirable carcass trait in North American beef grading schemes. In order to investigate the relationship between degree of marbling and fatty acid composition of whole bovine muscle, we extracted the total lipid from pars costalis diaphragmatis (PCD) (n = 23) and longissimus (n 36) muscles from Wagyu crossbred cattle that were assigned Canadian Grading Agency marbling scores ranging from 1 to 8 on an inverse 10-point scale (i.e., a score of 1 indicated "very abundant" marbling and a score of 10 would be assigned to a carcass "devoid" of marbling). Fatty acid methyl esters (FAME) of the total lipid and triacylglycerol fractions were resolved and quantified through GLC. Marbling scores were negatively associated with total lipid from both PCD (r = -.57, P < .01) and longissimus (r = -.80, P < .001). Differences between PCD and longissimus were found for almost all FAME studied from both lipid fractions, but no differences (P > .05) were seen when the monounsaturated:saturated fatty acid (MUFA/SFA) ratios were compared. Heifers had higher (P < .05) oleic acid content and lower (P < .05) palmi tic acid content in lipid extracted from both muscles, resulting in higher (P < .05) MUFA/SFA ratios than those for steers. The relative amount of myristic acid increased as the lipid content (total lipid and triacylglycerol) increased in either longissimus (r values from .48 to .55; n = 36; P < .01) or PCD muscles (r from .67 to .76; n = 23; P < .001). The relative amount of linoleic acid (cis-9, cis-12 isomer) from total lipid was negatively associated with all chemical measurements of lipid from the longissimus (r from -.52 to -.64; n = 36; P < .001) and PCD muscles (r from -.75 to -.85; n = 23; P < .001). This association was not significant (P > .1) for either muscle when linoleic acid from the triacylglycerol fraction was examined, suggesting the negative association between this fatty acid and lipid content was due to a dilution of membrane phospholipids with increasing triacylglycerol. Indices of fatty acid elongase activity, calculated from FAME data, implicated the balance between this enzyme activity and fatty acid synthase as a source of variation between animals displaying various degrees of marbling and worthy of further investigation to better understand the process of marbling fat deposition in beef cattle.

The development of a biochemical or molecular marker for predicting the propensity for cattle to deposit intramuscular (i.m.) fat would reduce the time required to improve for this trait. In the current study, diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) activity was investigated as a potential biochemical marker for predicting the deposition of i.m. fat. The activities of DGAT were determined in microsomal fractions of subcutaneous (s.c.) adipose tissue, i.m. adipose tissue and muscle tissue sampled from Wagyu crossbred cattle at slaughter weight. The i.m. adipose and muscle tissues were dissected from the pars costalis diaphragmatis (p.c.d.) muscle. The lipid content (LC) of the p.c.d. muscle correlated with the LC of the longissimus muscle (r = 0.51; P < 0.05). There was an inverse correlation between p.c.d. i.m. adipose tissue DGAT specific activity and LC of the p.c.d. (r = −0.50; P < 0.05) suggesting that DGAT activity was down-regulated as i.m. adipose tissue became filled. There was a strong correlation (r = 0.74; P < 0.001) between DGAT total activity in i.m. adipose tissue and muscle DGAT total activity, suggesting DGAT activity is coordinately regulated in these two tissues. Key words: Bovine, intramuscular fat, diacylglycerol acyltransferase, Bos taurus

Growth performance, carcass characteristics and meat quality of European and British crossbred (EBC; no Wagyu genetics; 28 heifers and 30 steers) cattle were compared with crossbred cattle with 75% Wagyu genetics (WC; seven heifers and 14 steers) to determine the influence of Wagyu genetics on marbling grade of beef cattle fed barley-based diets in a factorial design experiment. Weaned calves (250 d average age) were fed, one of two diets (diet 1, 35% barley grain; diet 2, 40% hay cubes on DM basis, with barley silage, protein and vitamin/mineral premix) for 84 d and then fed diet 1 until they weighed 394 to 432 kg. All cattle were finished on an 80% (DM basis) rolled barley diet and slaughtered. Carcasses were graded and samples procured for meat quality and Warner–Bratzler shear force determination. Number of days on backgrounding diets to arrive at target weight (380 kg) was greater (P < 0.05) for the WC cattle, owing to relatively lower ADG, but days on the finishing diet were fewer for these cattle, compared with EBC cattle. Warm carcass yield (dressing percent) was greater (P < 0.05), but backfat depth was lower (P < 0.05) for WC cattle relative to that of EBC cattle, yet proportion of lean meat yield was similar. Eighty three percent of WC cattle carcasses had Canada AAA (small or more) marbling grade compared with 13% for EBC cattle carcasses. Mean shear force of meat samples from EBC and WC cattle was 4.2 and 3.8 kg, respectively. Results indicated that the extent of carcass marbling can be increased by incorporating Wagyu genetics but age at slaughter of WC cattle was 19 d greater than that of EBC cattle and carcass size was reduced. Key words: Average daily gain, carcass characteristics, European and British crossbred, feed to gain ratio, meat quality, Wagyu crossbred cattle

A study was conducted to determine differences in length of intestinal villi and crypts and activity of mucosal carbohydrases of several breeds of beef cattle. Tissue samples, from three locations in the small intestine, were obtained from heifers and steers of Wagyu (W) × Angus (W × A), W × Hereford (W × H) and W × Holstein (W × O) crossbred cattle and from Holstein, Parthenais and Piedmontese steers at slaughter. In W × A cattle villi were shorter and crypts were longer (P < 0.05) than in cattle of other breeds. Mucosal protein concentration was highest (P < 0.05) in the mid- and distal intestinal regions in the W × A cattle. Maltase activity was highest (P < 0.05) for W × H heifers and least (P < 0.05) for W × A heifers in the proximal intestinal region. Holstein and Piedmontese steers had the highest ADG, and Holstein steers had the highest lactase activity in the mid-intestinal region. Lactase activity in the mid-intestinal region appeared to be weakly associated with ADG of cattle (r = 0.454, P = 0.015, n = 28). These data suggest that differences due to breed of cattle exist in villus and crypt lengths and mucosal carbohydrase activity; however, the influence of these intestinal parameters on cattle performance may be relatively small. Key words: Intestinal villi, crypt, cellobioase, maltase, lactase, beef cattle

Average backfat thickness measurements (liveweight of 92.5 kg) were made on 276 pigs using the Krautkramer USK7 ultrasonic machine. Immediately preceding and 1 h after slaughter real-time ultrasonic images were made between the 3rd and 4th last ribs with the Tokyo Keiki LS-1000 (n = 149) and/or CS-3000 (n = 240) machines. Image analysis software was used to measure fat thickness (FT), muscle depth (MD) and area (MA) as well as scoring the number of objects, object area and percentage object area of the loin to be used for predicting meat quality. Carcasses were also graded by the Hennessy Grading Probe (HGP). Prediction equations for lean in the primal cuts based on USK7 and LS-1000 animal fat measurements had R2-values (residual standard deviations, RSD) of 0.62 (27.0) and 0.66 (25.7). Adding MD or MA to LS-1000 FT measurements increased the R2-values to 0.68 and 0.66. Prediction equations using animal fat measurements made by the USK7 and CS-3000 had R2-values (RSD) of 0.66 (26.5) and 0.76 (22.4). Adding MD or MA to CS-3000 FT measurements made no further improvement in the R2-values. Estimation of commercial lean yield from carcass FT and MD measurements made by the HGP and LS-1000 had R2-values (RSD) of 0.58 (1.72) and 0.65 (1.56). Adding MA to LS-1000 measurements made no further improvement in the R2-values. Prediction equations based on carcass FT and MD measurements made by the HGPandCS-3000 had R2-values (RSD) of 0.68 (1.65) and 0.72 (1.54). Adding MA to CS-3000 measurements made no further improvement in the prediction equation. It was concluded that RTU has most value for predicting carcass lean content and further improvements in precision will come from more accurate FT measurements from RTU images made by image analysis software. Correlation of the number of objects, object area and of percent object area of image from RTU images with intramuscular fat or marbling score made on the live pig or carcass were low, and presently do not appear suitable for predicting intramuscular fat. Key words: Carcass composition, meat quality, marbling, intramuscular fat, sex, pigs

Records of young AN and young HE bulls were analyzed to evaluate the influences of dietary energy planes on growth and heritability estimates of growth traits during 168-d postweaning test. Estimates of h2a for end of test weight (WT168), average daily gain on test (ADG 0–168) and relative growth rate on test (RGR 0–168) were much higher in the MED line than in the HED line. Between lines, maternal heritability estimates (h2m) for WT0 and ADG 0–168 were similar. Estimates of h2m for WT168 was much higher in the HED line than in the MED line. All direct-maternal genetic correlations (ram) were negative. These results may indicate that the antagonism between direct and maternal genetic effects for postweaning growth traits in the MED line was much less than that in the HED line. Key words: Beef cattle, energy plane, growth, heritability

A study was conducted to determine the effects of lignosulfonate and heat treatment of canola meal on protein degradability, and to evaluate whether feeding treated canola meal to nursing beef calves enhances preweaning growth. Four supplements were formulated to contain 31% crude protein (CP) using either: (1) untreated canola meal (UTC), (2) heat-treated canola meal (HTC; 100 °C for 1 h), (3) lignosulfonate-treated canola meal (LTC; 5% calcium lignosulfonate and 100 °C for 1 h), or (4) corn distillers' dried grains (DDG). Degradability of canola meal CP was reduced significantly from 55.1% (measured in sacco) to 43.2% by heat, and to 26.7% by lignosulfonate treatment. One hundred and three nursing crossbred calves were given access to either no supplement (control) or one of the four supplements. Weight gain (kg d−1) increased (P < 0.05) from 0.90 for the control to 1.05 for calves fed DDG, and further increased (P < 0.05) to 1.16, 1.16 and 1.18 for calves fed UTC, HTC, and LTC, respectively. Consequently, calves fed canola meal gained 30.8 kg more (P < 0.05) than those fed control, and 12.8 kg more (P < 0.05) than those fed DDG. The performance of suckling calves during the grazing season and body condition of their dams were enhanced by offering canola-based creep feeds. Although degradability of canola meal CP was substantially lowered by lignosulfonate treatment, calf performance was not further enhanced by feeding treated canola meal. Key words: Beef cattle, creep feeding, canola meal, lignosulfonate, heat-treatment, distillers' dried grains, protein degradability

Area and maximum depth of the longissimus muscle were measured using real-time ultrasound on 25 male Alpine goat kids. To our knowledge, this is the first report of use of real-time ultrasound to estimate carcass quality in goats. Ultrasonic measurements were taken: (A) between the 12th and 13th ribs and (B) at the first lumbar vertebra. Live weight, condition score, circumference of the widest part of the hind leg, length of the hind leg from the hip, heart girth, body length from shoulder to tail and length of the hind leg from hip to hock were also recorded. Kids were slaughtered 5 d after ultrasound measurements were taken. From carcass measurements, area of the longissimus muscle at both sites A and B averaged 5.6 cm(2), and ranged from 4 to 8 cm(2) at site A and from 3.6 to 7.6 cm at site B. At site A, the 12th and 13th ribs were very close together and it was difficult to obtain a distortion-free ultrasound image. Ultrasonograms at site B were free from rib-caused distortion, but this site was more difficult to locate repeatably. Despite these complications, the accuracy of measurement of longissimus area did not differ (P>0.05) between the two sites. Maximum longissimus depth was more accurately measured at site A than at site B (P<0.05). Regression equations and residual standard deviation (RSD) values indicated that longissimus area at site A was the indicator of carcass muscling most accurately predicted by ultrasound and body dimension measurements (R(2)=0.81, RSD=3.6). Longissimus area could not be predicted from body dimensions without ultrasound data at site B, while for site A, length of the hind leg (P<0.05) was the only predictor (R(2)=0.22, RSD=7.2). Therefore, the use of real-time ultrasound would improve the selection of meat goats for improved muscling.

Sixteen Hereford bulls (16 mo of age, 462 kg average body weight) were used in each of 2 yr to evaluate the effects of hypovitaminosis A on seminal quality and sperm production. Bulls were fed a high-concentrate diet with (+VIT) or without (-VIT) supplemental Vitamin A until the apparent onset of hypovitaminosis A (28 and 32 wk in Year 1 and 2, respectively). Half of the bulls on each treatment were then slaughtered and those remaining were re-alimented with Vitamin A. Plasma retinol concentration in -VIT bulls reached a nadir at approximately 25 wk. In Year 1, the proportion of progressively motile spermatozoa was lower in -VIT bulls after 17 wk but returned to that of the +VIT group after re-alimentation. The proportion of spermatozoa with primary morphological defects appeared to be greater in -VIT bulls compared to +VIT bulls by 26 and 24 wk in Year 1 and 2, respectively. The incidence of these defects declined in -VIT bulls upon re-alimentation, and approached the incidence observed in +VIT bulls by 8 to 12 wk of re-alimentation. Hypovitaminosis A decreased paired testes weight, daily sperm production, and epididymal sperm reserves but did not affect daily gain. Prolonged dietary Vitamin A deficiency impaired semen quality and sperm production in the absence of other clinical symptoms. However, under practical feeding conditions, diets that result in long-term, marginal Vitamin A deficiency or a relatively short-term absence of Vitamin A intake probably would have minimal effects on spermatogenesis.

Postweaning gain performance and individual feed intake on 271 Hereford and 263 Angus bulls were recorded during three 168-d test periods from 1984 to 1986. Each breed was composed of two lines and within each breed bulls were fed either a high-energy (HD) or a medium-energy (MD) diet. Energy intake was partitioned into energy for maintenance and growth based on predicted individual animal requirements. Estimates of heritability were obtained using Restricted Maximum Likelihood with an individual animal model including fixed effects of year, diet, and covariates of initial weight and backfat change by breed and with line effects for overall data. Bulls fed the HD grew faster and had higher metabolizable energy intake per day (MEI), residual feed consumption (RFC), and gross and net feed efficiency (FE and NFE) (P < .001) than those fed the MD. Estimates of heritability for Hereford and Angus bulls, respectively, were .46 and .16 for 200-d weaning weight (WWT), .16 and .43 for average daily gain (ADG), .19 and .31 for intake per day (MEI), .43 and .45 for yearling weight (YWT), .07 and .23 for RFC, .08 and .35 for FE, and .14 and .28 for NFE. Genetic and phenotypic correlations between MEI and ADG, MEI and YWT, ADG and YWT, ADG and FE, YWT and FE, and FE and NFE were moderately to highly positive for both breeds. Negative genetic and phenotypic correlations between NFE and ADG show partial correlations of FE with ADG after accounting for energy requirement for maintenance. Residual feed consumption was negatively associated with YWT, FE, and NFE, indicating a possible genetic improvement.

Milk yield and composition from three distinct milkings (spring, August, and fall) were evaluated on first-cross and backcross cows maintained under two contrasting environments. The dam crosses at Brandon (semi-intensive cultivated pasture management) were HA, SN, CN, ACA, CCA, ASA, SSA, HCH, CCH, HSH, SSH, NCN, CCN, NSN, and SSN with H = Hereford, A = Angus, N = Shorthorn, C = Charolais, S = Simmental and a SSA cross was 3/4 Simmental-1/4 Angus. At Manyberries (semi-arid and short grass rangeland) the dam crosses were HA, SN, ASA, SSA, HSH SSH, NSN, and SSN. All cows were bred to Limousin bulls and milkings took place from 1981 to 1985, inclusive. Definitive differences among the backcrosses and between the backcrosses and the F1 crosses were not present. Possible genotupe × environment interactins were observed for milk yield and composition. Milk yield and composition were affected by age of cow and influenced cow and calf weight changes. Key words: Beef cattle, crossbreeding, backcrosses, milk yield, milk composition

Breed-of-dam and sex-of-calf effects are reported based on observation of 2007 heifer and steer carcasses. The carcasses were derived from Limousin-sired calves born to dams representing 15 F1 and backcross genotypes reared at two locations over a period of 5 yr. The calves represented Hereford × Angus, Charolais × Shorthorn, Simmental × Shorthorn and all backcross combinations involving Charolais or Simmental with Hereford, Angus or Shorthorn. Carcass traits were analyzed on an unadjusted, a constant hot-carcass weight, and a constant rib-fat depth basis. The slaughter criteria dictated that steers were heavier at slaughter than heifers. They also exhibited higher dressing yield, greater longissimus thoracis area, and lower fat depth. Charolais and Simmental breeding was associated with less rib fat depth, greater longissimus thoracis area, a higher proportion of preferred cuts, less dissectible fat, more bone and more lean in the preferred cuts than British beef breeding. Within the European (Charolais and Simmental) and British beef (Hereford, Angus and Shorthorn) breed groups, breed effects were smaller, but for carcass composition traits they were frequently significant. When compared with Simmental, Charolais breeding tended to be associated with less marbling, less rib fat depth, less dissectible fat and more lean in the preferred cuts. Among the British beef breeds, Hereford was associated with the highest proportion of preferred cuts, Shorthorn with the lowest rib fat depth — but the highest dissectible fat — and Angus with the most marbling, the greatest longissimus thoracis area and the lowest bone content. This research has demonstrated that breed effects for carcass composition traits tend to be additive and that a significant effect may be associated with substitution of as little as one-eighth of the breed composition. Key words: Beef cattle, slaughter traits, carcass traits, breed type, crossbred dam, backcross dam