A study of the herbage intake and efficiency of feed utilization of grazing cattle previously fed two winter planes of nutrition

Abstract

SUMMARYAn experiment was conducted using 36 Hereford × Shorthorn bullocks of about 350 kg initial live weight. Winter planes of nutrition 13 December to 23 March were ‘low’ (hay only) and ‘medium’ (hay plus 1·8 kg concentrate); the former group of 18 bullocks lost on average 21·5 kg while the latter gained 26·5 kg. Each group was then stocked at 2·5 (low), 4·3 (medium) and 6·2 (high) bullocks per hectare and rotationally grazed on 10 plots, 7 of which contained H.I.-white clover mixture and the remaining 3 contained permanent pasture. Pasture digestibility and intake were determined for 16 weekly periods between early April and the end of September. Organic matter digestibility (OMD) of grazed herbage was determined in vitro on samples obtained by means of two rumen-fistulated bullocks. One gelatin capsule containing about 10 g of chromic oxide was daily administered to each bullock to estimate organic matter output. Winter feeding planes had no significant effect on OMD, and increasing the stocking rate increased herbage OMD only during the final 6 weeks. Significantly more organic matter was ingested during the grazing season by animals which had previously been fed on a low plane of nutrition. Stocking rates also significantly affected OMI. Bullocks fed on a low plane during winter were slightly more efficient subsequently in converting herbage into live-weight gain but this was a reflection of their lower average body weight; when feed efficiency was expressed on the basis of metabolic size, bullocks fed on a medium plane were more efficient in converting feed to live-weight gain. It is concluded that the higher daily gains on pasture of bullocks previously fed on a low plane is largely the result of a significantly higher feed intake by these animals.