Behavioural mechanisms of intake rate by heifers grazing swards of contrasting structures.

MEZZALIRA, J.C.; CARVALHO, P.C. DE F.; FONSECA, L.; BREMM, C.; CANGIANO, C.; GONDA, H.L.; LACA, E.A.

APPLIED ANIMAL BEHAVIOUR SCIENCE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 153 p. 1 - 9

0168-1591

The relationship between herbage intake by herbivores and herbage available depends onthe interaction between sward structure and animal behaviour. This relationship is a cru-cial component determining the stability, function and productivity of grazing systems. Thepresent study aims at quantifying the mechanisms by which intake rate is determined inswards of contrasting structure and forage species, and it reveals the importance of animalchoice in the interaction between animal and sward. We hypothesised that as sward heightand herbage mass increased, bite mass and intake rate would increase. The relationshipbetween intake rate and bite mass should exhibit a higher asymptote for the more succu-lent, less fibrous Avena than for Cynodon due to differences in chewing requirements perunit dry mass of intake. In four different experiments, Cynodon sp. cv. Tifton 85 and Avenastrigosa cv. Iapar 61 swards of different heights were obtained by various durations of shorttime high-intensity grazing or by different growth periods. Bite mass and intake rate wereestimated by the double-weighing technique with correction for insensible losses. Num-ber and timing of jaw movements and bites were measured with behaviour recorders. Bitemass was the main variable determining intake rate. Contrary to expectations, bite massfirst increased and then decreased with increasing sward height, a result that seems due toanimal choice and not from restrictions imposed by the swards. As expected, Cynodon sp.swards required more chewing per unit DM intake due to their higher DM content (39.5 vs.22.6, P < 0.0001) and higher fibre (67.8 vs. 51.3, P < 0.0001) content than A. strigosa. Harvest-ing and chewing jaw movements, the components of total jaw movements and time perbite, had different time costs, and values were remarkably similar to previously publishedvalues. On average, each harvesting jaw movement took 1 s and a chewing jaw movementtook 0.68 s. The reduction in bite mass with increasing sward height in tall swards is dis-cussed as a destabilising mechanism that generates spatial heterogeneity in sward heightand mass.