Effect of winter nutritional levels on subsequent growth of beef heifers in the Highland Sourveld of Natal

Abstract

The effect of different levels of winter nutrition on the subsequent performance of Simmentaler weaner (seven-month-old) heifers on summer veld at different stocking rates was evaluated in the Highland Sourveld of Natal. The data from 300 heifers over a three-year period were analysed. During their second winter, the heifers were fed to achieve a target mating mass of 330 kg at 26 months of age. The feed cost to achieve a growth rate of 0,5 kg/ d during the first winter following weaning was 93% higher than the cost to achieve a growth rate of 0,25 kg/d. On summer veld, heifers run at a low stocking rate of 0,75 LSU /ha (for the grazing period) gained significantly (P < 0,01) more mass than heifers subjected to a high stocking rate of 1,25 LSU fha, irrespective of the previous winter nutritional level. Within each stocking rate, the heifers at a low winter nutritional level gained significantly (P < 0,01) more mass on veld than those on the high winter plane of nutrition. Significantly (P < 0,01) more compensatory growth occurred during the first half (94 days) of the grazing season. The data suggest that the ability of a beef heifer to achieve compensatory growth on summer sourveld in Natal should be exploited, but that the degree of compensatory growth might be significantly modified by stocking rate. The difference of R73 (at current money value) per head between the lowest and highest feed costs up to the mating stage underlines the importance of selecting the correct rearing strategy for heifers in the sourveld.

Die invloed van verskillende wintervoedingspeile op die prestasie van 300 Simmentalerspeenverse (sewe maande oud) op somerveld, is oor 'n periode van drie jaar ondersoek. Gedurende die tweede winter na speen (as 18-maande-oud diere) is die verse gevoer om 'n dekmassa van 330 kg (op 26 maande) te bereik. Die voerkoste om 'n daaglikse toename van 0,5 kg gedurende die eerste winter na speen te handhaaf, was 93% hoër vergeleke met koste vir 'n toename van 0,25 kg/ d. Teen 'n lae veebelading van 0,75 GVE/ha (vir die weiperiode) op somerveld, het verse betekenisvol (P < 0,01) meer in massa toegeneem vergeleke met 'n hoë veebelading (1,25 GVE/ha). Binne elk van die veebeladings het die verse op die lae voedingspeil gedurende die eerste winter betekenisvol (P < 0,01) meer in massa toegeneem op veld as verse wat teen 'n hoë voedingspeil oorwinter het. Betekenisvol (P < 0,01) meer kompensatoriese groei is gedurende die eerste helfte (94 dae) van die weiperiode behaal. Kompensatoriese groei op somerveld is 'n belangrike faktor, maar kan deur hoë veebeladings beperk word. Die verskil van R73 (teen huidige geldwaarde) per vers tussen die hoogste en laagste voerkoste tot en met dekking is 'n bewys van die belangrikheid om die regte grootmaakstrategie vir verse in die suurveld te kies.

Keywords: Compensatory growth, economics, heifers, winter nutrition.