Milk-fed calves: 2. The effect of length of milk feeding period and milk intake upon herbage intake and performance of grazing calves

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Abstract
SUMMARY: Forty-eight Hereford × Friesian steer calves purchased at 7–10 days of age were reared on reconstituted milk substitute and groups of 12 were weaned at 86, 128, 170 or 212 days. Six calves at each weaning age were fed high (H) and low (L) quantities of milk normally associated with 240-day lactation yields of 2000 or 1000 kg. Calves were housed until day 63 of the experiment and then strip-grazed on swards of Loliun perenne with a daily allocation of herbage dry matter equivalent to 60 g/kg LW.Herbage intake per unit live weight prior to weaning was consistently greater for the calves receiving low quantities of milk. Following weaning there was a rapid rise in herbage intake towards a maximum of 30 g OM/kg LW when sward conditions were non-limiting. The amount of milk fed prior to weaning affected herbage intake after weaning, and H groups did not achieve similar intakes to their L contemporaries until some weeks after weaning. The H groups grew faster from birth to weaning than the L groups but they experienced a more severe check in live-weight gain after weaning which nullified the advantage of better weight gains between the start of the grazing period and weaning. In consequence, there was no significant effect of the quantity of milk consumed prior to weaning upon live-weight gain during the grazing season. The results indicate a marked benefit from distributing a given quantity of milk over a longer feeding period as similar growth rates occurred for the H86 v. L128, H128 v. L170 and H170 v. L212 groups. Calves receiving milk consumed less herbage and spent a smaller proportion of the day grazing than weaned contemporaries, which suggests that metabolic rather than physical or behavioural factors are likely to limit their intake.