This experiment aimed at studying the behavioral strategies grazing dairy cows employ to satisfy their nutritional needs as the day progresses. For this purpose the day was divided into three main periods (6:00 to 12:00 h, 12:00 to 18:00 h and 18:00 to 24:00 h) where the three main grazing bouts (dawn, afternoon and dusk) of dairy cows usually occur. Four late lactating rumen-cannulated dairy cows were used in a repeated measures design, with the grazing bout as the within subjects factor. The cows had access to a 1-ha grass sward under a continuous stocking system, which assured ad libitum herbage allowance. To estimate dry matter intake (DMI), bite rate, bite mass (BM) and in- take rate at the three bouts, cows were rumen-evacuated at 6:00, 12:00, 18:00 and 24:00 h and jaw recorders were fitted to the cows between these time points. Time spent eating by dairy cows at the dusk grazing bout was much longer (P < 0.05) than that at the other two grazing bouts and made about 40 % of the daily total eating time. Total grazing jaw movements (TGJM) rate was constant during the day at around 75/min. Bite rate increased (P < 0.05) from 54 to 61/min, but chewing rate decreased (P < 0.05) from 20 to 16/min as the day progressed. BM (mg DM/bite) increased (P < 0.05) from 400 to 563 as the day progressed, but that was not due to increased bite dimensions, rather it was due to increased DM content of the grass at dusk time, which increased from 19 to 25%. Consequently, both intake rate and DMI increased (P < 0.05) from 22 to 34 (g DM/min) and from 3 to 7 (kg/bout) during the dawn and dusk grazing bouts, respectively. Therefore, it could be concluded that the main behavioral strategies dairy cows employ to satisfy their nutritional needs under continuous stocking include manipulating their eating time, biting rate and chewing rate, with little control over TGJM rate and BM.
|Journal||Journal of Dairy Science|
|Issue number||suppl 1|
|Publication status||Published - 2004|