Effect of breed type, sex, method of rearing and winter nutrition on lifetime performance and carcass composition in a 20-month beef system: grazing performance

Abstract

In a lifetime study of spring born cattle managed in a 20-month beef system, four feeding treatments were imposed during the 5-month winter period and two grass heights (low 6 to 8 cm, high 8 to 10 cm) during the subsequent grazing period. Three slaughter weights were imposed over the grazing period, early, mid and late, at an average of 67,110 and 154 days post turn-out. A multi-factorial design was used with three animal factors — maturity (early maturing Hereford crosses v. late maturing Charolais crosses), sex (heifer v. steer) and method of rearing (suckled calves v. bucket-reared calves). There were significant differences in growth rate for both sex and maturity (P < 0·001) and a highly significant negative effect of winter food level on summer growth rate (P < 0·001), the growth rate of food treatment 4 being proportionately 0·61 of that treatment 1.Sward height significantly influenced summer growth rate (P < 0·001) but showed no interaction with winter food level in any of the three grazing periods. Growth rates increased over the summer but differences between winter food treatments decreased with daily gains for food treatment 4 being proportionately 0·44, 0·81 and 0·84 of food treatment 1 as the grazing season progressed.Eliminating winter feeding treatment as a factor and including condition score at turn-out as a co-variate improved the variation explained and reduced differences in growth rate for the main effects with only the main effect of grass height remaining significant. This suggests that the condition of animals at turn-out in conjunction with the subsequent grazing sward height provides a simple practical guide to subsequent animal performance.