The use of a novel approach to determine the influence of sward characteristics on the discriminatory grazing behaviour of dairy cows

W.M. Griffiths, J. Hodgson, C.W. Holmes and G.C. Arnold

Department of Plant Science, Massey University, Palmerston North, New Zealand.

Proceedings of the New Zealand Society of Animal Production, 1996, 56: 122-124

Dairy cows were offered choices of patches of vegetation (0.8m2) on a perennial ryegrass (Lolium perenne L.) sward providing combinations of five levels of sward height (8.9 - 19.6 cm) and three levels of herbage bulk density (1.3 - 1.6 mg DM/cm3) in linear sequence. Four cows were used, each of which grazed two out of a balanced set of eight sequences, each sequence being replicated three times in a set of 27 patches in linear sequence. Animal responses were monitored in terms of grazing time and number of bites per patch.

Bite number per patch increased from zero to 54 (SEM ± 1.63) across the range of grazing heights (P<0.001) with evidence of an asymptotic relationship on the taller patches. Likewise, grazing time per patch increased with sward height, ranging from zero to 55 seconds (SEM ± 1.56, P< 0.001). Effects of variation in bulk density at equivalent height were not significant. However, measurement of trade-offs in grazing choice between variations in sward height and bulk density requires greater control of herbage mass and bulk density than was achieved in this study.

Keywords: NZSAPAB; discriminatory behaviour; grazing preference; sward height; bulk density; herbage mass; grazing bites; grazing time; dairy cows.

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Last Updated 18-03-1997