Comparative studies of herbage intake and performance of lambs grazing Yorkshire fog (Holcus lanatus) and tall fescue (Festuca arundinacea) pastures under rotational management in summer

Abstract

Grazing experiments were conducted on Yorkshire fog (Holcus lanatus cv. Massey Basyri)/white clover (Trifolium repens cv. Grasslands Tahora) and tall fescue (Festuca arundinacea cv. Grasslands Roa)/white clover pastures in late spring‐summer (Nov‐Jan, Experiment 1) and summer‐early autumn (Jan‐Mar, Experiment 2) to assess behaviour and performance of lambs and to evaluate the effects of low concentrations of condensed tannins (CT) in the grasses on lamb performance. In each experiment, 48 lambs were allocated to three groups, balanced for previous grazing experience and sex, in sets of 16. One group was slaughtered at the start of the experiment to measure carcass weight; the other two groups of lambs rotationally grazed paddocks within each pasture. Half of the lambs within each pasture were drenched with 10 g polyethylene glycol (PEG; mol. weight 3350) twice daily at 0830 and 1630 hrs and the remaining lambs were drenched with water as a control. There were similar sward surface height, herbage mass, and bulk density on both swards. Yorkshire fog had a higher proportion of sown grass and lower proportions of other grasses and white clover than tall fescue. There was slightly higher total N (3.37 vs 3.30 ± 0.013%, P< 0.05) on tall fescue than on Yorkshire fog in summer, but no significant difference in organic matter digestibility (OMD) for the diets from the two pastures. The diet from Yorkshire fog had higher CT concentrations overall. Herbage organic matter (OM) intake was not significantly different between the two pastures overall, but was significantly reduced by PEG administration in Experiment 2 (P < 0.01 ). Previous grazing experience had no significant effects on lamb performance. Lambs had greater carcass weight (14.7 vs 13.9 ± 0.2 kg, P < 0.05) and faster carcass weight gain (32 vs 20 ± 3.1 g/day, P < 0.05) on Yorkshire fog than on tall fescue in Experiment 1, but not in Experiment 2, and faster rate of clean wool growth on Yorkshire fog than tall fescue in Experiment 2 (123 vs 112 ± 2.8 mg/ 100 cm2 per day, P < 0.05). It is concluded that Yorkshire fog cv. Massey Basyn offers potentially greater nutrient intake and weaned lamb performance than tall fescue cv. Grasslands Roa in summer pastures. The limited content of condensed tannins in the Yorkshire fog pasture had no measurable effects on lamb performance, and it is suggested that particularly low concentrations of CT measured in tall fescue may have been an artefact of the analytical process.