Tactical versus continuous stocking in perennial ryegrass-subterranean clover pastures grazed by sheep in south-western Victoria - 3. Herbage nutritive characteristics and animal production

A 4-year grazing experiment was carried out in south-western Victoria to co mpare the effect of tactical stocking with continuous stocking on the persi stence of perennial ryegrass (Lolium perenne L.) and the productivity of sh eep used for prime lamb production. Tactical stocking consisted of variable length summer, autumn and winter rotations and continuous stocking in spri ng. The 2 grazing strategies were compared on 2 contrasting pastures: an up graded pasture, sown with newer cultivars of perennial ryegrass and subterr anean clover (Trifolium subterraneum L.) with 26 kg phosphorus/ha. year, an d a naturalised perennial ryegrass pasture receiving 6 kg phosphorus/ha. ye ar. Paddocks were grazed by Border Leicester x Merino ewes, which were mate d to a terminal sire to lamb in September. In this final paper of the serie s, the effects of the grazing systems and pasture treatments on animal prod uction and herbage quality are presented. The liveweights of the ewes were similar across all treatments during autum n and winter, but the tactically stocked ewes were 3-6 kg lighter than cont inuously stocked ewes during spring and summer. The lower liveweight was at tributed to the lower (P< 0.001) herbage quality on the tactically stocked pastures in spring (P< 0.001). Both digestibility and crude protein concent ration were about 4 percentage units lower with tactical stocking in spring . This lower quality was associated with the higher herbage mass (by 500-90 0 kg dry matter/ha) on the tactically stocked pastures, which presumably ha d a higher stem: leaf ratio and showed reproductive growth earlier than the continuously stocked pastures. Although there were differences in ewe live weight, this did not affect individual lamb weaning weight or ewe fleece we ight. There were significant increases in production per hectare from tacti cally stocked or upgraded pasture treatments due to the higher stocking rat es that could be carried, 9 and 51%, respectively. In 1998, 544 kilograms o f lamb per hectare was weaned from continuously stocked paddocks and 607 kg /ha from tactically stocked paddocks (P< 0.05), and 449 and 702 kg/ha from the typical and upgraded pastures, respectively. This study reinforces the view that soil fertility and pasture improvement have a much greater impact on animal productivity than changes to grazing m ethod with little effect on per head productivity. The negative impact of r otational stocking on herbage quality reinforces the need to use these syst ems strategically when benefits from increased herbage mass are expected to increase animal production or overcome sustainability or pasture persisten ce problems.