Selection In Beef Cattle Research Articles

SERUM GROWTH HORMONE CONCENTRATION IN HEREFORD AND ANGUS CALVES: EFFECTS OF BREED, SIRE, SEX, AGE, AGE OF DAM, AND DIET

Serum growth hormone (GH) concentrations were determined in 172 Hereford and 172 Angus bull and heifer calves before weaning and while restricted to the feedlot for 5.5 mo and fed either an 80% concentrate plus 20% roughage or roughage only diet. Blood samples were taken 1 mo before weaning (27 Sept.; T1), 2 mo into the feedlot period (5 Jan.; T2), and 5 mo into the feedlot period (5 Apr.; T3). GH concentrations and ratios of GH to body weight were greater in Angus than in Hereford at all sampling times. GH levels were higher in bulls than heifers 1 mo before weaning and at 5 mo into the feedlot period. However, the ratio of GH to body weight was higher in bulls than heifers only at 1 mo before weaning. The heritability estimates (h2) for GH and GH/100 kg body weight were generally low. The h2 of GH concentration 1 mo before weaning was 0.16 ± 0.13. Calves at 5 mo of age (T1) tended to have higher serum GH concentrations than at 8 (T2) or 11 (T3) mo of age. Age of dam and plane of nutrition had little effect on GH concentrations or its ratio with body weight in the calves, but had various degrees of influence on the performance traits. Correlations among GH and GH/100 kg body weight estimates with performance traits were also generally low. GH levels at the three sampling times that corresponded to 5, 8, and 11 mo of age in young beef bulls and heifers in this study will, apparently, not be a reliable indicator or predictor of the performance of a particular animal in a beef cattle selection program.

Selection in Beef Cattle III. Correlated Response of Carcass Traits to Selection for Weaning Weight, Yearling Weight and Muscling Score in Cattle

Selection in Beef Cattle III. Correlated Response of Carcass Traits to Selection for Weaning Weight, Yearling Weight and Muscling Score in Cattle

CATTLE DIETS AND DISTRIBUTION ON SPRING–FALL AND SUMMER RANGES NEAR KAMLOOPS, BRITISH COLUMBIA

A 2-yr investigation of the herd distribution and diet selection of beef cattle on range was conducted near Kamloops, British Columbia. Two ranges were studied: one grazed in spring and fall, and the other in summer. Diet selection was determined by grazing two rumen-fistulated beef cattle, by clipping plots before and after grazing on the spring–fall range, and by conducting browse surveys on the summer range. Cattle distribution was determined on the spring–fall range. During the 2 yr, the diet composition averaged 93% grass, 2% forbs, 2% shrubs, and 3% trees. Grass was consumed more in the spring (95%) than in either summer or fall (93 and 92%, respectively). Interseasonal change in the consumption of the four plant types (grass, forbs, shrubs, trees) was greatest in the summer and fall. In the summer, consumption of forbs and trees increased, while consumption of grasses remained constant and consumption of shrubs decreased. In the fall, grass and shrub consumption increased, while forb and tree consumption decreased. Three open range habitats (south slope, knoll, flat field) and one treed habitat were defined for distribution studies. The south slope and flat field were utilized for feeding, while the knoll and treed habitats were used for both resting and feeding. The treed habitat was most important in providing shelter from adverse weather. Grazing intensity was generally less on the treed habitat than on the others.

Selection in Beef Cattle. I. Selection Applied and Generation Interval2

Selection applied and generation interval were studied in three 150-cow-6-sire lines selected for (1) weaning weight (WWL), (2) yearling weight (YWL), or (3) an index of yearling weight and muscling score (IXL). Data were birth weights, weaning weights, yearling weights and muscle scores of 2,956 calves raised at the Fort Robinson Beef Cattle Research Station, Crawford, Nebraska during the years 1960 to 1970. Formulas were presented for calculating average cumulative selection differentials and generation coefficients in populations with overlapping generations. Generation interval based on actual age of parents for the 2,956 calves weaned was 4.6 years. Sire age was 4.1 years and dam age was 5.1 years. By 1970 an average of 2.0, 1.8 and 1.9 generations of selection had been practiced in the weaning weight, yearling weight and index lines, respectively. Average sire selection differentials, per generation, in WWL, YWL and IXL were, respectively: weaning weight 1.51, 1.18, 0.86; yearling weight 1.42,1.79, 1.22; muscling score 0.51, 1.11, 2.13 standard deviations.

Selection in Beef Cattle II. Selection Response2

Selection in Beef Cattle II. Selection Response2

Selection of beef cattle for single traits.

Selection of beef cattle for single traits.

Beef Cattle Selection Indexes Involving Conformation and Weight

Beef Cattle Selection Indexes Involving Conformation and Weight

Birth Weight as a Criterion of Selection in Beef Cattle

Birth weights of calves in the beef Shorthorn herd at Beltsville, Maryland tended to increase at the rate of 0.2 pound per month of increase in the age of the dam until the dams were six years old, after which there was no effect of age of dam. When birth weights were adjusted to the basis of six-year old dams, male calves averaged 4.2 pounds heavier than females. Weight of dam was found to be related to birth weight of calf to about the same extent as was the age of the dam. The multiple correlation between both age and weight of dam and birth weight was 0.56, or very little higher than the simple correlations. A significant but relatively low positive correlation was found between the length of the gestation period and birth weight. With the use of half-sib correlations, heritability of the original birth weight was 29 percent, while for birth weights corrected for age of cow, sex, and dam's index (average birth weight of all calves from a given dam) the heritability was 11 percent. Of the calves which were fed out as steers, the largest ones at birth and those with the highest prenatal growth rates tended to reach 500 pounds (weaning weight) and 900 pounds (slaughter weight) the soonest. There was little relationship between birth weight or prenatal growth rate and the length of the feeding period from weaning to slaughter. Correlations between birth weight or prenatal growth rate and economy of gain during the feeding period showed there was practically no association. The results of this study indicate that birth weight should be given some consideration in selection, in view of the fact that it had an influence on the time required for the animals to attain a slaughter weight of 900 pounds. The results also indicate that since the dam had a considerable maternal influence on birth weight as well as on the subsequent development of the calf, greater care should be taken in the selection of the dams and in the evaluation of their influence in progeny tests of sires.