A comparative study of herbage intake, ingestive behaviour and diet selection, and effects of condensed tannins upon body and wool growth in lambs grazing Yorkshire fog (Holcus lanatus) and annual ryegrass (Lolium multiflorum) dominant swards

An experiment was carried out from August to early November 1994 to examine differences in diet selection, herbage intake, grazing behaviour and anima l performance between weaned lambs rotationally grazing swards of annual ry egrass (Lolium multiflorum)/white clover (Trifolium repens) and Yorkshire f og (Holcus lanatus)/T. repens with or without Lotus corniculatus. There wer e four replicate groups of six lambs per treatment. The effects of condense d tannins (CT) on lamb production were assessed by twice-daily oral adminis tration of 10g polyethylene glycol (PEG; molecular weight 4000) to half the lambs on each sward. The Lotus content of all swards was very low, and res ults are presented here for main sward comparisons meaned over lotus treatm ents. Overall mean estimates of pre-grazing herbage mass and sward surface height for the annual ryegrass and Yorkshire fog swards respectively, were 5820 v. 4360 +/- 190 kg DM/ha (P < 0.001) and 29 v. 21 +/- 0.6 cm (P < 0.00 1). The coefficient of organic matter digestibility (OMD) of the diet selec ted and herbage intake were higher on Yorkshire fog than on annual ryegrass (0.78 v. 0.74 +/- 0.080 g/kg; P < 0 05, and 1070 v. 860 +/- 57 g OM per la mb per day, P < 0 05 respectively), reflecting the higher content in the di et of grass green leaf (980 v. 930 g/kg +/- 14 g/kg, Pt 0 05) and the lower content of dead material (80 v. 110 +/- 15 g/kg, P < 0.08). Lambs grazing on Yorkshire fog swards had higher clean wool growth rate (1470 v. 1280 +/- 30 mg/cm per day, P < 0.01) and greater fibre diameter (31 v. 29 +/- 0.2 m u, P < 0.001), greater liveweight gain (152 v. 108 +/- 5.5 g/day, P < 0.001 ), final weight (42 v. 38 +/- 0.5 kg, P < 0.001), carcass weight gain (89 v . 69 +/- 2.5 g/day, P < 0.001), carcass weight (19 v. 17 +/- 0.3 kg, P < 0. 001) and soft tissue thickness (GR value 11 v. 8 +/- 0.5 mm, P < 0.01), and lower faecal egg counts (FEC; square root transferred values 9.2 v. 11.0 /- 0.4 eggs/g fresh faeces, P < 0.01) than lambs grazing annual ryegrass sw ards. Similar dietary concentrations of condensed tannins (CT) between York shire fog and annual ryegrass swards (4.2 v. 3.7 DM +/- 0.2 g/kg, P < 0.08) increased clean wool growth (1440 v. 1310 +/- 32 mg/cm(2) per day, P < 0 0 5), fibre diameter (30.7 v. 29.5 +/- 0.21 <mu>, P < 0.01) and liveweight ga in (141 v. 120 +/- 4.3 g per lamb per day, P < 0.01), although differences in carcass weight (17.9 v. 18.2 +/- 0.3 kg) and FEC transformed values (9.6 v. 11.0 +/- 06 eggs/g fresh faeces) were not significant. The effects of C T on animal performance were greater in Yorkshire fog swards. CT had no sig nificant effects on diet selection, herbage intake and grazing behaviour pa tterns.