Applied Animal Behaviour Science 153 (2014) 1–9 Contents lists available at ScienceDirect Applied Animal Behaviour Science jou rn al hom epage : w ww.elsevier.com/locate/applanim Behavioural mechanisms of intake rate by heifers grazing swards of contrasting structures Jean Carlos Mezzalira a,∗ , Paulo César De Faccio Carvalho a , Lidiane Fonseca a , Carolina Bremm a , Carlos Cangiano b , Horacio Leandro Gonda c , Emilio Andrés Laca d a Grazing Ecology Research Group, Federal University of Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil b Instituto Nacional de Tecnología Agropecuaria, C.C. 276, 7620 Balcarce, Buenos Aires, Argentina c National University of Central State of Buenos Aires, Tandil, AR-B700, Argentina d Department of Plant and Environmental Sciences, University of California, Davis, CA 95616, USA a r t i c l e i n f o Article history: Accepted 24 December 2013 Available online 2 January 2014 Keywords: Cattle Grazing behaviour Grazing down Harvest and cropping time Intake mechanisms a b s t r a c t The relationship between herbage intake by herbivores and herbage available depends on the interaction between sward structure and animal behaviour. This relationship is a cru- cial component determining the stability, function and productivity of grazing systems. The present study aims at quantifying the mechanisms by which intake rate is determined in swards of contrasting structure and forage species, and it reveals the importance of animal choice in the interaction between animal and sward. We hypothesised that as sward height and herbage mass increased, bite mass and intake rate would increase. The relationship between 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 per unit dry mass of intake. In four different experiments, Cynodon sp. cv. Tifton 85 and Avena strigosa cv. Iapar 61 swards of different heights were obtained by various durations of short time high-intensity grazing or by different growth periods. Bite mass and intake rate were estimated by the double-weighing technique with correction for insensible losses. Num- ber and timing of jaw movements and bites were measured with behaviour recorders. Bite mass was the main variable determining intake rate. Contrary to expectations, bite mass first increased and then decreased with increasing sward height, a result that seems due to animal 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 per bite, had different time costs, and values were remarkably similar to previously published values. On average, each harvesting jaw movement took 1 s and a chewing jaw movement took 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 height and mass. © 2013 Elsevier B.V. All rights reserved. ∗ Corresponding author. Current address: Grazing Ecology Research Group, Faculdade de Agronomia, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸ alves, 7712 Porto Alegre, RS, Brazil. Tel.: +55 51 3308 7402. E-mail addresses: mezzalirajc@gmail.com (J.C. Mezzalira), paulocfc@ufrgs.br (P.C. De Faccio Carvalho). 0168-1591/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.applanim.2013.12.014