Herbage intake, ingestive behaviour and diet selection, and effects of condensed tannins upon body and wool growth in lambs grazing Lolium perenne and Holcus lanatus swards in summer

Abstract

A comparative study was undertaken in New Zealand to investigate the effects of low concentrations of condensed tannins (CT) on diet selection, herbage intake, and performance in lambs grazing on four 0.2 ha paddocks each of perennial ryegrass (Lolium perenne) or Yorkshire fog (Holcus lanatus) with less than 10% white clover (Trifolium repens), continuously grazed at a constant height of approximately 6 cm from December 1992 to March 1993. The effects of CT on rumen metabolism and animal production were assessed by twice daily oral administration of polyethylene glycol (PEG; MW 4000) to half of the lambs on each sward. Bite weight was greater for Yorkshire fog swards than for ryegrass swards during January (111 vs 85 ± 5 mg OM/bite, P < 0.01), but not in December. In both December and January, grazing, ruminating, and idling times were similar between swards, while in January, the rate of biting in ryegrass swards was higher than in Yorkshire fog swards (64 vs 61 ± 1 bites/min, P < 0.05). The organic matter digestibility (OMD) of the herbage selected was higher in ryegrass swards in December (81 vs 78 ± 0.04 %, P < 0.01), but not in January (80 vs 79 ± 0.05 %). The herbage intake achieved by lambs grazing ryegrass swards was 23% higher than that achieved on Yorkshire fog swards in December (990 vs 800 ± 36 g OM/lamb/day, P < 0.05) whereas, in January, herbage intakes did not differ significantly. Lambs grazing on ryegrass swards had higher clean wool growth (1147 vs 1085 ± 15 ng/cm2 per day, P < 0.10) and carcass weight (17.5 vs 16.3 ± 0.22 kg, P < 0.05) than lambs grazing on Yorkshire fog swards. The stocking rate maintained on ryegrass plots was 25% greater than on Yorkshire fog plots. Low concentrations of CT were recorded in the diets of sheep on ryegrass and Yorkshire fog swards (< 0.2% on a DM basis). The low levels of CT had no significant effects on diet selection, herbage intake, grazing behaviour patterns, or lamb performance. However, the lambs grazing on Yorkshire fog swards showed small and non‐persistent responses to CT in terms of wool growth and liveweight gain. The results of this study indicate that: (i) under high fertility conditions and intensive management, perennial ryegrass/white clover swards appear to have higher feeding value than Yorkshire fog/white clover swards for lamb production and (ii) the low CT concentrations (< 0.2% in the DM) observed in both swards did not influence lamb performance significantly.