Effect of duration of fasting period on short-term intake rates of lactating dairy cows

The effects of duration of fasting on the short-term feeding behaviour of 12 grazing and 12 silage-fed lactating Holstein-Friesian dairy cows were examined. Four groups of three cows were rotated around fasting treatments of 1, 3, 6 or 13 h following a balanced Latin-square design. Herbage intakes for each treatment group were assessed over a 1-h period. As intended there were no significant differences in sward characteristics between the experimental plots grazed by cows from different treatment groups. However, total dry-matter (DM) intake, biting rate and DM intake per bite, measured over the I-h grazing period, increased significantly when the duration of fasting was extended from 1 to 6 or 13 h (P < 0.05). There were only minor differences in grazing behaviour following fasting durations of 1 and 3, or 6 and 13 h. In a parallel study, undertaken to assess the influence of fasting duration on appetite independently of grazing, four groups of three cows were housed indoors and offered 30 kg of a high quality grass silage. Silage Dill intakes, measured over a 1-h period, increased significantly with extended fasting periods (P < 0.01), through silage DM intake was considerably lower than that of grazing cows for each fasting treatment. These results suggest that dairy cows grazing on good quality swards may be able to compensate for increased degree of hunger by increasing both biting rate and Dill intake per bite to increase DM intake rate. Although the DM intakes of silage and grazed grass followed similar patterns of increasing intake with extended fasting duration, DM intake rates were considerably higher in grazing cows for each fasting treatment.