Abstract

Grazing behaviour, diet selection, and herbage intake of ewes in mid- pregnancy were studied on perennial ryegrass/white clover and Holcus lanatus/white clover swards rotationally grazed at medium and high allowances (6% and 12% of liveweight as herbage dry matter respectively) during late autumn. Estimates of herbage mass and sward height before grazing were similar for the two pasture types. Animals on both pasture types concentrated grass rather than clover in the diet, and extrusa samples from both showed evidence of limited concentrations of condensed tannins. Herbage intake was 28% higher from ryegrass than from Yorkshire fog swards (1410 vs 1100 ± 29 g DM/day) and 19% greater at high allowance (1370 vs 1150 ± 50 g OM/day). Bite weight was 61% greater for Yorkshire fog than for ryegrass (139 vs 86 ± 7.0 g OM/bite) and 30% lower for medium allowance than for high allowance (90 vs 130 ± 7.0 mg OM/bite). Grazing time was higher on ryegrass swards and for medium allowance (610 vs 500 ± 34 mins and 620 vs 495 ± 27 mins) whereas differences in rate of biting were small. There was a small advantage in the organic matter digestibility of the herbage selected in favour of ryegrass swards (85.7 vs 82.2 ± 0.3%), while no differences were found between herbage allowances. It is concluded that herbage intake was influenced more by nutritional than by behavioural constraints, but that these effects need to be investigated in animals of higher production potential and nutrient demand.

FM, Montossi, Y Hu, J Hodgson, and ST Morris

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 71-74, 1994