Relationships between beef carcass shape and muscle to bone ratio.

Relationships between muscularity and muscle to bone ratio were investigated for beef carcasses of several breeds and crosses, and three genders using data from Bristol and Alberta. Side dissection data in terms of muscle, fat and bone weights were used to calculate muscle to bone ratios (MtoB) and muscularity indexes (MUSC) for the whole side or for the region around the femur bone. Highly significant breed and gender effects on MtoB and MUSC were shown for both the Bristol and the Alberta data sets, but the group differences for MtoB were not the same as those for MUSC despite the fact that these two characteristics were closely correlated. For both sets of data, for example, MUSC values at a common muscle plus bone weight were significantly higher for carcasses of bulls than heifers, but similarly adjusted MtoB values were generally higher for carcasses of heifers than bulls. Differences among breed groups were mainly in a similar direction for MUSC and MtoB, but the size of the differences varied widely. For example, relative to the Friesian, the Jersey breed had a significantly higher MtoB but a significantly lower MUSC, and carcasses of double-muscled bulls had a femur-region MtoB that was 19.2% greater than that of a group of Shorthorn-cross carcasses, but a MUSC that was only 1.7% higher. These findings show that because of the inconsistent relationships between muscularity and muscle to bone ratio among different classes of beef carcasses, lean meat yield cannot always be predicted without bias if measures of carcass shape are used as indicators of muscle to bone ratio.

Postnatal limb bone growth in relation to live weight in pigs from birth to 84 days of age.

Long limb bones were dissected from 30 Camborough x Canabrid pigs serially slaughtered at birth, 14, 28, 56, and 84 d of age to determine the growth patterns of long limb bones (humerus and radius for the forelimb and femur and tibia for the hindlimb) in relation to live weight from birth to 84 d of age, weighing up to approximately 31 kg. Relationships between individual long limb bone measurements (Y) and live weight or transformations of live weight (X) were evaluated using allometric analyses. Hindlimb bones tended to have higher growth coefficients than forelimb bones (P < .05), suggesting an anterior-posterior gradient of long limb bone growth. However, centripetal gradients of growth for long limb bones were not evidential (P > .05). Greater diameter growth compared with length growth of the long limb bones indicated that the differentiation in growth for diameter and length of the long limb bones was an effective response to the functional requirements of standing, walking, and running following birth.

Longevity and lifetime productivity of cows in a purebred Hereford and two multibreed synthetic groups under range conditions.

Records on 983 cows born during a period of 10 yr (1966 to 1975) were used to estimate longevity and lifetime productivity of cows raised under range conditions. The cows were from a purebred Hereford and two multibreed synthetic groups, one composed of beef breeds (Beef Synthetic #1) and the other composed of two-thirds dairy breeds and one-third beef breeds (Dairy Synthetic). The cows were raised under a stringent culling system in which all heifers were exposed to bulls as yearlings and were expected to wean a calf each year thereafter or they were culled. Cows were also culled for other reasons, such as severe calving problems, bad udders, and leg and feet problems. The mean longevity was 4.2 yr; cows from the synthetic breed groups produced longer (P < .01) than Hereford cows, due to a relatively faster rate of removal at all ages in the purebred Hereford group. The mean values per cow for lifetime productivity traits were 2.7 and 2.5 for number of calves born and weaned and 101.9 kg and 482.9 kg for weight of calf born and weaned, respectively. Male calves were not castrated, and weights of female calves were adjusted to a male basis. Over their lifetimes, Dairy Synthetic cows were more productive, in terms of number and weight of calves born and weaned, than Beef Synthetic #1 cows, which in turn were more productive than purebred Hereford cows (P < .01).

The effect of levels of concentrate in feedlot diets on the health status of beef calves.

In this two year study we investigated the effect that the level of concentrate in feedlot diet had on the occurrence of health problems in bull calves belonging to two multibreed groups.In each of the two years, the 168 day feedlot period was divided into two equal periods of 77 days with an intervening 14 day adjustment period. During the first period, the animals in half of the pens within each breed-group received a high concentrate (85% grain) diet (H) while the rest of the pens received a diet (L) of hay ad libitum and half as much concentrate as the bulls on high concentrate. The L diet contained an average of 48% grain. In the second period, diets of bulls in half of the pens within each breed-group were switched from L to H and vice versa. During the feedlot period, the incidence of sickness among bulls was recorded. Disease incidence was higher in the second year compared to the first. In the second year, 49 out of 56 (87.5%) calves on the high concentrate diet required treatment for respiratory infections compared to only four (7.14%) in bulls on the low concentrate diet. The results suggest that a high concentrate diet for animals in feedlots may be more stressful to calves coming directly to the feedlot following weaning compared to a low concentrate diet, thereby acting as an additional predisposing factor to respiratory infections.

The effect of breed-type and castration on bone growth and distribution in cattle.

Data from carcasses of 210 cattle (119 bulls and 91 steers) from 4 breed types, serially slaughtered from approximately 200-800 kg kg liveweight were used to test the hypothesis of similar gender dimorphism among breeds in relation to carcass bone growth and distribution. Relative to total bone weight, breed types tended to have similar growth rates for all bones other than the cervical vertebrae, ribs, tibia and fibula, and tarsus. Adjusted to the same total bone weight there were significant differences among breed types in bone weight distribution, but the differences were very small and probably of little economic importance. Castration stimulated growth of the lumbar vertebrae, hindlimb bones, patella and hindquarter bones but inhibited growth of the ribs, scapula, carpus, forelimb bone, and forequarter bone. At the same total bone weight, steers as compared to bulls showed a shift in bone weight distribution towards the hindquarter, pistol and long bones. There were small but significant breed x gender interactions in the distribution of some bones.

Genetic, phenotypic, and environmental parameter estimates of calving difficulty, weight, and measures of pelvic size in beef heifers.

The heritabilities for and the genetic, phenotypic, and environmental correlations among calving difficulty scores (CDS) and measures of size of the pelvic inlet were estimated using 547 records of 2-yr-old heifers from three synthetic breed groups. Calving difficulty score was treated first as a trait of the dam and then as a trait of the calf and was analyzed on three scales: raw scores from 0 to 3 (0 = normal birth, 3 = most difficult delivery requiring a hard pull, veterinary assistance, or surgical intervention), Snell-transformed scores, and a binary (0, 1) scale. Estimates of heritability for CDS as a trait of the dam were similar to those when it was considered a trait of the calf. Heritability estimates for CDS on the raw and transformed scales were similar and moderate in magnitude (.36 +/- .15 to .47 +/- .18) but were higher than most reported estimates. However, on the binary scale the estimates were lower (.26 +/- .17, .28 +/- .14). Estimates of heritability for the horizontal and vertical pelvic diameters and the pelvic area were high, implying that pelvic size in heifers might be readily modified by selection. The genetic and phenotypic correlations between CDS as a dam trait and pelvic dimensions were low, whereas the correlations between CDS and dam weight at calving were moderate. As a calf trait, CDS was highly correlated genetically with calf birth weight, but the phenotypic correlations were moderate.

Factors influencing calving difficulty in beef heifers.

Records of 547, 2-yr-old heifers of three breed groups were used to evaluate the relative influence of dam's body and pelvic measurements, calf birth weight, sire birth weight and some relative measures (ratios) of calf birth weight and dam weight at calving on calving difficulty. The data were analyzed by regression and least squares procedures. The full model explained 32.5% of the variation in calving difficulty score. The linear effect of calf birth weight was the most important variable, accounting for 17.8% reduction in the coefficient of determination, and together with dam weight at calving and the quadratic effect of calf birth weight it accounted for 92% for all the variation explained by the full model. Dam weight at calving was negatively related to calving difficulty. Breed, year and sex of calf did not influence calving difficulty score, except when the calf birth weight or dam weight or both were excluded from the model. When calf birth weight was expressed as a ratio of the dam's weight at calving, hip height and pelvic measurements, the total model explained 34.8% of the variation in calving difficulty score. The ratio of calf birth weight to dam weight was the most important variable (R2 = 26.8%). Ratios of calf to dam weight at calving and calf weight to the vertical pelvic diameter (R2 = 29.3%) were the only significant factors when the effects of calf birth weight and dam weight were removed from the model. Pelvic measurements, on their own, did not influence calving difficulty score in this study (P greater than .1), but small pelvic dimensions tended to be associated with higher calving difficulty scores.

Heterosis, maternal and direct effects in double-muscled and normal cattle: I. Reproduction and growth traits.

Data from a two-breed group diallel experiment involving double-muscled (DM) and normal (N) cattle were analyzed to evaluate the importance of heterosis, maternal and direct effects for reproduction and growth traits. The DM cattle were from a composite of primarily Angus, Charolais, Galloway and Hereford breeds, and N cattle were crossbred cattle with at least 50% Hereford breeding. The data comprised a total of 491 matings and 389 calvings in four breeding seasons. Records on calving performance, calving date, calf crop born and weaned, sex ratio of progeny and weight of calves were analyzed using least squares procedures. Significant heterosis of 5 to 12% was observed for all the calf crop and growth traits, except for birth weight. Heterosis resulted in 24% reduction in the incidence of dystocia and perinatal calf mortality (P less than .05). The significant heterosis was due mainly to poor production in DM X DM crosses. The DM cows were superior (P less than .05) to N cows in reciprocal crossing (maternal effect) for all the calf crop traits, but had higher incidence of calving difficulty and a higher proportion of male progeny. Significant direct effect was observed for all the traits except calving date and sex ratio among progeny. The N sires were superior for all the calf crop traits and caused less incidence of dystocia and perinatal mortality compared with the DM sires. Significant differences were obtained between the straightbreds for all the traits except calving date. The N straightbreds were superior to the DM straightbreds for all the significant traits.

Heterosis, maternal and direct effects in double-muscled and normal cattle: II. Carcass traits of young bulls.

Data on 135 young bulls from a two-breed group diallel experiment involving double-muscled (DM) and normal (N) cattle were analyzed to obtain estimates of heterosis, maternal and direct effects for carcass traits. When carcass traits were adjusted to a constant age at slaughter (398.5 d), significant positive heterosis was observed for slaughter and carcass weights, carcass length and s.c. fat thickness. Maternal effect was relatively unimportant for the traits studied. The progeny of N sires and DM straightbreds were heavier at slaughter and had higher carcass weight, s.c. fat thickness and carcass length (P less than .01), whereas DM-sired progeny and DM straightbreds had higher dressing percentage (P less than .05) and cutability (P less than .01). Heterosis was significant for all the 10-11-12th rib joint dissection traits except for percentage of muscle. Although there was negative heterosis for percentage of bone, there was positive heterosis for rib joint weight, fat weight and percentage, muscle weight and muscle:fat and muscle:bone ratios. For direct effect and straightbred differences, N-sired progeny and N straightbreds, respectively, had significantly larger values for rib joint weight, fat weight and percentage and bone weight. The DM-sired progeny and DM straightbreds had larger values for percentage of muscle, muscle:fat and muscle:bone ratios. When the carcass and dissection traits were adjusted to a constant carcass (303.7 kg) and rib joint (4,812 g) weight, respectively, the results were similar to those observed on age constant basis except for rib eye area, for which DM-sired progeny and DM straightbreds had larger values.

Growth and body composition of mice selected for high body weight.

To elucidate the influence of high body weight selection on body compositional relationships, the accumulation of lipid, protein, and ash was investigated in two lines of mice selected for high 42-day body weight (H lines) and an unselected foundation population (FP). The two H lines differed in population size and were designated as the high-large (HL) and high-small (HS) lines. Logistic body growth curves revealed that HL mice exhibited an accelerated growth rate and reached a higher mature body weight than FP or HS mice. Over the range of body weights examined, HL mice had more lipid, less protein, and less ash than FP or HS mice of the same sex and body weight. However, HL lipid accumulation (relative to body weight increase) was not accelerated in comparison to that of FP mice. This study suggests that the existing model of selection-mediated compositional changes requires expansion to account for the ability of high-growth selection to direct an acceleration of body growth without a correlated enhancement of the relative rate of fat accumulation.