Age Live Weight Research Articles

Potential of grazing management to improve beef cattle production and mitigate methane emissions in native grasslands of the Pampa biome.

We tested the hypothesis that improving sward structure through adjustments in forage allowance results in greater forage intake and live weight (LW) gains by beef cattle and lower CH4 emissions per unit LW gain and unit area in a native grassland ecosystem of the Pampa biome. The experiment was carried out during 2012 and 2013 in southern Brazil. The experimental design was a randomized complete block with two replicates. Treatments consisted of five contrasting forage allowances of a native grassland managed under continuous stocking: 4, 8, 8-12, 12, and 16kg of dry matter (DM) 100kg LW-1day-1 (or % LW). The 8-12% LW treatment had a variable forage allowance of 8% LW in spring and 12% LW in summer, autumn, and winter. Forage allowance was controlled by changes in stocking rate (kg LW ha-1). Average daily gain (kg LW day-1) was high for forage allowances of 12 and 16% LW but decreased at 8%, reaching the lowest value at 4% LW treatment (p<0.001). Live weight gain ha-1year-1 was the greatest at forage allowance of 8-12% LW (p<0.001). Forage DM intake peaked at a forage allowance of 12% LW (p=0.005). Individual CH4 emissions remained constant around 150gday-1 for the two highest forage allowances and decreased to 118 and 107gday-1 under forage allowances of 8 and 4% LW, respectively (p=0.002). Emissions per unit LW gain and unit area were driven by animal productivity changes and decreased with increasing forage allowance (p=0.001 and p=0.040, respectively). We propose that the combination of 8% LW forage allowance during spring and 12% LW during the rest of the year should be targeted to best balance animal production and environmental impact in the Pampa biome.

Thyroid activity in relation to growth rate and body composition in four breeds of sheep.

Four breeds of sheep, Hampshire, Southdown, Cheviot and Scottish Blackface, which differ in mature body size and body composition were intensively reared under an ad libitum or a restricted feeding regime. Thyroid activity was assessed at 13 weeks of age by the 131I uptake method. Slaughter at 24 weeks (ad lib) or 32 weeks (restricted) was followed by carcass dissection. The anticipated differences in body type represented by the 4 breeds was confirmed in terms of size and fatness. The Hampshires had the highest growth rate (liveweight for age) and the lowest thyroid uptake, and the breed differences in thyroid activity were shown to be independent of liveweight. Thyroid activity was positively related to growth rate in the Hampshires and negatively related to growth rate in the 3 other breeds. No association could be found however between the thyroid activity and the proportionate growth of body fat or lean. None of these conclusions were affected by a mild restriction in fed intake.

Selection of dairy cattle for growth rate and milk production

The genetic progress in live-weight-for-age (LFA), milk production, and in overall economic value expected as a result of performance and progeny testing of young bulls with respect to milk production and LFA was computed. It was shown that performance testing can contribute considerably to overall progress in economic value, while under certain circumstances progeny testing for LFA can also contribute to genetic progress in overall economic value, but to a lesser degree than performance testing. The relative economic value of LFA and milk production was derived and found to be relatively stable under differing economic conditions.

A note on heritability of live-weight-for-age in Israel-Friesian dairy bull calves and its genetic correlation with milk production

The design and evaluation of breeding programmes for live-weight-for-age (LFA) in dairy cattle requires estimates of the heritability and the additive genetic and residual components of variance for this trait, and also of its genetic correlation with milk production. A number of estimates of these parameters are available (summarised recently by Langelet, 1963; Mason, 1964; and Nichols and White, 1964). They are, however, generally based on rather limited data, on data from cows rather than bull-calves, or on data from dual purpose cattle. In this note estimates of the variance components and heritability for LFA in dairy cattle bull calves, and of the genetic correlation between bull calf LFA and milk production will be presented.