Cow Weight Change Research Articles

Economic values of net reproduction and weight-for-age for use in genetic calculations applied to Australian beef cattle herds

Economic values were estimated for net reproduction (N) and carcase weight production (P) in beef cattle herds. Weight selection referred to selecting for weight-for-age, not relative growth. Calculations were based on data that apply to the last seven years of Australian production. If considered only in terms of the change in total value of beef sold, a 5% increase in N or P gave an increase of about 4.1 %, according to the model. Improvements in biological efficiency, measured on a herd basis as total food energy input per unit weight of beef produced, were expected to be about - 2.5% per 5% dN/N, according to the model. Values for P were determined by the fundamental assumptions of the model, with literature review estimates having suggested no change in biological efficiency (as long as N remained constant). Small improvements in N resulted in a reduction in both food and non-food costs per unit of meat value sold. Economic efficiency (E) was defined as total costs per unit of meat value sold from breeding stock and growing-fattening stock, with reductions in E being favourable. In total, a 5% improvement in N yielded a change of about - 3% in E. The extent of change in E following selection for P (and for liveweight at the same time) depended on the assumptions applying, particularly with respect to food requirements and correlated cow weight changes. The most likely value was about - 2.5% dE/E for + 5% dP/P. Translated into a profit equation (H) on a dollar per cow-year basis, the most likely formula was H = 140n + 0.51 p, where n and p referred to small improvements in N and P per year, and N is a decimal fraction (not percentage), and P in kg.

FACTORS INFLUENCING WEANING WEIGHTS OF RANGE BEEF AND DAIRY-BEEF CALVES

June and September measurements of lactation were made using 206 (1976) and 242 (1977) cows ranging from 2 to 10 yr of age from the University of Alberta beef herd representing four beef and dairy-beef breeds and lines. Influences on calf weaning weight investigated were age and breed of dam, sex of calf, and the continuous variables of calf age, calf birth weight, cow winter weight loss, cow post-calving average daily gain, milk yields and constituent yields of butterfat, protein and lactose. Milk and constituent yields had similar relationships to calf weaning weight (r = approximately 0.6). Stepwise regressions involving age and breed of dam accounted for 48 and 45% of the variance in weaning weight. When age and breed of dam were ignored, milk or constituent yields accounted for approximately 40% of weaning weight variance. After removing main effects, milk variables explained from 6.2 to 10.4% of the total variance. A unit increase of 1 kg in average daily milk yield was associated with 7.7 kg increase in weaning weight. Birth weight of calf and cow weight change during lactation had minor effects on calf weaning weight. No significant source of variation in weaning weight was explained by cow winter weight loss. As a significant proportion of the variation in weaning weight is accounted for by milk and constituent yields, selection for increased lactation performance and the introduction of dairy breeds into the breeding program of a beef herd can effect meaningful increases in calf weaning weights.

INFLUENCE OF BODY WEIGHT AND CHANGES IN BODY WEIGHT OF THE COW ON PREWEANING TRAITS OF THE CALF

This study was designed to estimate and evaluate environmental factors affecting birth weight, weaning weight and preweaning average daily gain (ADG) of purebred Shorthorn calves from the control line of a selection experiment. Nine years of data consisted of 635 birth weight and 607 weaning weight records. Least squares analysis of variance revealed that sex of the calf was the most important source of variation: males averages 2.31 kg heavier at birth, were 14.3 kg heavier at weaning and gained 0.08 kg more per day from birth to weaning than females. Heavier cows in June, October, and December prior to parturition and at parturition produced heavier calves at birth. Heavier cows in October prior to parturition, at parturition, and in June or October following parturition produced calves which grew more rapidly from birth to weaning and were heavier at weaning. There was no apparent effect of cow weight changes before or after parturition on preweaning traits. Correlations of birth weight with weaning weight, preweaning ADG and cow weight at parturition were 0.56 ± 0.03, 0.43 ± 0.04 and 0.24 ± 0.04 respectively. Correlations of weaning weight and preweaning average daily gain with cow weights at parturition were 0.42 ± 0.04 and 0.40 ± 0.04. Correlations among cow weights in June, October, and December prior to parturition, at parturition, and in June and October following parturition were estimated.

Patterns of change in mature Angus cow weight and fatness during the year.

Postcalving cow weight and subcutaneous fatness change patterns were described for 80 mature spring-calving Angus cows. The cows grazed either high (regularly clipped fescue-legume) or low (fescue clipped once) quality pastures. Forage consumption was estimated continuously by an internal (acid detergent lignin)-external (Cr2O3) indicator technique. Milk production (calf-suckle technique) was estimated seven times during lactation. Wither height was measured during the fall after the period of intensive measurment. Angus cows grazing high quality pasture lost an average of 36 kg postcalving, whereas those grazing low quality pasture lost an average of 22 kilograms. Minimum weights were observed about April 1, prior to the season of large pasture quality differences in digestibility of consumed forage. Taller cows, when allowed increased nutrient density during midlactation (high versus low quality), responded by increasing (P < .05) fatness at a more rapid rate than less tall cows. For cows grazing high quality pasture, weight change was independent of level of milk production. Cows grazing low quality pasture and giving relatively large amounts of milk maintained less weight and fat during the middle and last part of lactation than did those giving smaller amounts of milk. Shapes of the curves depicting change in weight and fatness were closely related (P < .01) to digestible dry matter intake. Cows apparently consumed forage in such a manner that they became more alike in both weight and fatness as the grazing season progressed.

Analysis of some factors which affect the productivity of beef cows and of their calves in a marginal rainfall area of Rhodesia 3. Factors affecting calf birth weight, growth to 240 days and use of concentrates by cows and their calves

ABSTRACTThe birth weight and growth rate of sucking calves reared by three groups of cows grazing on veld and receiving different amounts of concentrates during winter and the first 8 weeks of lactation were studied over four successive calving seasons. Calves were weaned at either 150 or 240 days. The efficiency of use of concentrates for weaned calf production was calculated.Calves from cows given most concentrates were heavier (P&lt;0·01) than othei calves at birth, 150 days and 240 days. Milk consumption during the first 98 days of life accounted for most of the variation in pre-weaning growth. Time of weaning had little effect (P&lt;0·05) on birth weight of the next year's calf and although cows in the early- weaning groups produced calves which were the heaviest at 150 days (P&gt;0·05) these calves weighed less than other calves at 240 days (P&lt;0·001). Simple and multiple regression analyses were used to show that birth weight was affected significantly by cow-weight change during winter and these differences were in part independent of treatment and year. Calf birth weight increased as age of dam increased but this was due to increase in weight of cow with age. Within classes, calf birth weight had a significant and positive effect on weight gain after accounting for milk consumption and this was shown to be an effect of sex. Cows given concentrates produced more weight of 240-days-old weaned calf per year than those given none (P&lt;0·01), and late weaning led to the production of more weaned calf per annum than early weaning (P&lt; 0·001) even when allowance was made for differences in concentrate consumption.

Protein blocks for gestating beef cows wintered on bluestem pasture: soybean meal and starea compared

Pregnant Hereford and Angus cows wintered on native bluestem pasture were used to compare soybean-meal and Starea-containing blocks and protein supplements. Cow weight changes were similar with both supplements. Consumption of Starea supplement declined throughout the trial, while soybean meal block consumption remained constant.