Comparison of methods to quantify the number of bites in calves grazing winter oats with different sward heights

The requirement to measure the constituents of ingestive behaviour in grazing ruminants, such as the number and type of jaw movements, is essential for understanding the herbage intake process. In this experiment, three methods of recording grazing behaviour were compared: visual observation (VO; four trained observers), solid-state behaviour recorder (SSBR) and acoustic recorder (AR), in order to quantify the number of bites taken by Holstein–Friesian calves (138±11kg LW) grazing winter oat (Avena sativa) pastures with different sward surface heights (SSH): tall (T; 52.4±9.9cm), medium (M; 26.5±4.9cm) and short (S; 14.6±3.4cm). The number of bites was recorded on nine calves with VO, SSBR and AR during 5-min grazing sessions on each sward height. In addition, the total grazing jaw movements (GJM) and bites per GJM (PB) were calculated from the SSBR and the AR methods. The experiment was conducted on 3 days, and on each day three animals grazed on each of the three sward heights in a randomised sequence. Sound files from AR were analysed visually and aurally (Sound Forge 9.0) and recordings by SSBR were analysed using the dedicated software ‘Graze 8.0’. Data were analysed by three-way ANOVA. There were no statistical differences (P>0.05) in the number of bites counted by the observers. The number of bites did not differ significantly between AR and VO, but were lower for SSBR (P<0.001). Mean values of number of bites were: 191, 153 and 192 for VO, SSBR and AR, respectively. Comparison of recording analyses from AR and SSBR showed a small difference (<5%; P<0.05) in total GJM (388 and 407 for SSBR and AR, respectively) and a larger difference (19%; P<0.01) in PB (0.395 and 0.472 for SSBR and AR, respectively). The main problem appeared to be in the identification of bites using SSBR, which led to an underestimation of the number of bites and bites per GJM using that method under the present grazing conditions. The AR method proved to be accurate for identifying biting jaw movements.