Milking frequency and nutritional level affect grazing behaviour of dairy cows: A case study

Abstract

The aim of this study was to evaluate the effect of milking frequency (MF) at two nutritional levels (NL) on grazing behaviour of dairy cows. Animals (n=48) were randomly assigned to one of four treatments from calving in a 2×2 factorial design for an entire lactation: once (OAD) or twice (TAD) a day milking at high (herbage allowance: 30.9kg dry matter/cow/day) or low (18.8kg DM/cow/day) NL. Grazing behaviour was recorded using IGER grazing behaviour recorders on three occasions at approximately 95, 157 and 208 days in milk. Data were analysed using the mixed procedure of SAS. OAD cows spent more time grazing than TAD cows (P<0.05), and had a higher number of grazing bouts (P<0.01). The initial grazing bout after morning milking was longer in TAD than OAD cows (P<0.001), and in low NL compared to high NL (P=0.01) cows. Twice daily milking disrupted grazing in the afternoon, indicated by shorter grazing bouts for these cows when initiated at 1300 (P<0.05) and 1400 (P<0.01). TAD cows initiated more grazing bouts at 1600 than OAD cows. Neither MF nor NL had an effect on time spent ruminating (P>0.05). As the grazing season progressed, cows increased the duration of the morning grazing bout, increased their bite rate, and decreased their mastication rate, probably as a result of decreasing grass quality. The additional time spent grazing after morning milking in the TAD and low NL cows likely reflects differences in hunger status between them and the OAD and high NL cows, respectively. The OAD cows had more time at pasture than the TAD cows and so were able to spend more time grazing than the TAD cows, and had less disturbance to their natural grazing pattern. This, combined with a lower milk production, could have resulted in them being less hungry. Although the behaviour of TAD cows was disturbed in the afternoon, cows were able to adapt to maintain daily grazing time budgets similar to OAD cows. This study provides valuable information about how dairy cows can adjust their grazing behaviour to cope with management strategies such as once a day milking.