An upper limit to the force animals exert to server a bite maybe important in maintaining grazing momentum. Structural strength of accessible pasture components would then determine bite dimensions and weight. Pure perennial ryegrass turfs (surface area 0.1m2 x 0.1m soil depth), were manipulated by clipping to produce 3 pasture heights (5, 10 and 15cm) x 3 sward structures (varying in leaf to pseudostem ratio and bulk density). Six sheep grazed 4 turfs fixed to a force plate of each height and bulk density. Mean peak bite force, bite weight, bite depth, bite area, bite volume and grazed stratum bulk density were calculated. Peak bite force increased with sward surface height but significantly so only between 10 and 15 cm. Sward structure had no effect except on the 5cm sward treatment with the highest grazed stratum bulk density. Bite depth and bite weight increased with pasture height and were not influenced by sward structure at a constant height. Bite area was similar at all sward heights, but decreased as grazed stratum bulk density increased. On short swards, proximity to the ground restricted bite depth and bite weight rather than peak bite force. Low bite weights per newton bite force may constrain bite depth and weight rather than absolute peak bite force.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 111-116, 1991
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