Selection In Beef Cattle Research Articles

Beef cattle selection and evolution

There is an area of cow-calf production that is very important to the economic health of this industry, and also difficult to measure and document. The area I am referring to is the phenotypic expression of characteristics that affect production efficiency, the evolutionary forces that act on these phenotypes, and the significance of selection of genetic material.
 We have many people in cow-calf production today who are advocating the selection of a few characteristics which they feel are highly heritable. They believe that to select for many things at once will slow down the improvement of the characteristics desired, as well as being of no real enonomic benefit. (1) The most economically important characteristic in a beef cow is her ability to breed and wean a relatively large amount of pounds consistently and with low imputs of energy from the herdsman. This is a problem of the animal’s fitness to its environment in all areas that affect its productive level and cost of production. The evolutionary process that has been going on for hundreds of thousands of years is now being affected and directed by herdsmen’s ideas of their ideal.

The effect of correction factors on response to selection in beef cattle

ABSTRACTProgeny of younger dams grow more slowly than those of older dams. When the environmental effects of dam age are not allowed for in selection for growth rate, selection differentials and genetic responses to selection are reduced.In a model herd, with cows aged 2 to 8 years, it was found that neglecting the dam age effects reduced genetic gains by about 15% when selection is for weaning weight, and by 11 to 7 % when selection is at an age of 12 to 20 months. Much of the reduction occurs because of the selection of higher proportions from genetically inferior groups.If genetic differences among dam age groups are small the reduction is only 7% at weaning and less at older ages. The effect of ignoring calf age was also estimated. It was found that if calves born within a period of 33 days were compared and calf age was neglected, the response to selection for weaning weight would be reduced by about 6%.

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.