Economics of weight gain
Previous research at Teagasc Grange on the optimum weanling winter growth rate for steers and heifers destined to return to pasture for a second grazing season suggested an optimum winter daily weight gain in the region of 0.4-0.7kg liveweight/head/day.
These studies showed that over the course of the subsequent grazing season, animals that had the higher winter weight gains had proportionately lower daily weight gains at pasture, and animals that grew at lower gains for the winter had best gains at pasture.
Thus the latter animals showed an ability to compensate such that the weight differences at the end of the winter, due to higher levels of supplementation, were reduced, and by the end of their second grazing season, approximately two-thirds of the winter weight differences had disappeared.
If liveweight differences that arise due to differential winter feeding are greatly reduced by the end of the subsequent grazing season, then the economics of additional concentrate
feeding to boost winter growth rates to a level above some optimum rate of gain is questioned.
One recent study at Grange was undertaken where spring-born sucker bulls had their grass silage diet supplemented with concentrates aimed to achieve winter liveweight gains ranging
from 0.6-1.2kg/head/day. At the end of the winter, the animals supplemented with 4 or 6kg concentrates/head/day were 30 and 68kg liveweight heavier, respectively, than bulls supplemented with 2kg/head/day. However, after ~100 days at pasture, the weight difference between the 2 and 4kg concentrate winter supplemented groups had disappeared
and the weight difference between the 2 and 6kg supplemented groups had diminished to 25kg liveweight.
A second study, again using spring-born suckler bulls, offered concentrate supplementation to achieve an end of winter liveweight difference of ~50kg, and observed that after ~100 days at pasture, the end of winter animal weight difference had disappeared. These two studies, using spring-born weanling bulls, suggest that where bulls are destined to return to pasture for a second spring, there is questionable economic value in feeding weanling bulls to grow faster than 0.6- 0.7kg liveweight/head/day.
Optimum winter growth rates for weanling suckler bulls when returning to pasture in spring have been studied by EG O’Riordan, D Marren, K McMenamin, M McGee, AP Moloney, Teagasc, Grange, Dunsany, Co Meath