Spectral Analysis of Dairy Cow Grazing Behaviour Patterns Relative to Sward Height

Abstract

Cattle and sheep graze 4 to 5 times in each 24h with the longest and most intense periods occurring in the early morning and between late afternoon and dusk. When the daytime temperature exceeds their thermal comfort zone, cows tend to increase their night grazing and graze less during the day. Interspersed between the periods of grazing are periods of idling/resting and ruminating. Understanding the factors that affect grazing behaviour and the subsequent behaviour patterns will help in the development of more efficient feed allocation systems and improve our understanding of how both behavioural and physiological processes control feeding (Fulkerson et al. 2005). Data on time spent grazing, ruminating and resting (min/h) were collected during an experiment designed to investigate the effects of sward height (SH, 10 v 13cm) and grazing duration (GD, 1, 2, 4, 8 and 15h) on grazing behaviour (Dobos et al. 2009). These were subjected to spectral analysis to determine if SH influenced grazing cyclicity. Spectral analysis enables the calculation of periodicities (cycles) within time series data and has been used successfully to determine differences in feeding behaviour due to selection for residual feed intake (Dobos and Herd 2008). Briefly, 6 dairy cows were randomly allocated to one of 2 SH x 5 GD treatments on kikuyu pastures over a 15h grazing period (1600h to 0700h) for 3 days (replicates). Cows were observed at 20-minute intervals for the first 2 hrs after entering their experimental paddocks at 1600h and thereafter at 30 minute intervals until 0700h the next day. Both SH treatment cows had similar patterns of grazing, that is two cycles of grazing 7.5h apart. The 10cm SH treatment cows had significantly (P<0.05) shorter periods of ruminating (5h) than the 13cm SH treatment cows. Both SH treatments exhibited similar idling/resting patterns, with a significant (P<0.05) cycle at 7.5h (Figure 1). ... The use of spectral analysis has revealed the behavioural cycles of dairy cows grazing kikuyu at different SH. This technique appears very robust for the analysis of this type of data.