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 cow s were examined. Four groups of three cows were rotated around fasting treatments of 1, 3, 6 or 13 h following a balanced Latin-square desig n. Herbage intakes for each treatment group were assessed over a 1-h p eriod. As intended there were no significant differences in sward char acteristics between the experimental plots grazed by cows from differe nt treatment groups. However, total dry-matter (DM) intake, biting rat e and DM intake per bite, measured over the I-h grazing period, increa sed 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 beh aviour following fasting durations of 1 and 3, or 6 and 13 h. In a par allel study, undertaken to assess the influence of fasting duration on appetite independently of grazing, four groups of three cows were hou sed indoors and offered 30 kg of a high quality grass silage. Silage D ill intakes, measured over a 1-h period, increased significantly with extended fasting periods (P < 0.01), through silage DM intake was cons iderably lower than that of grazing cows for each fasting treatment. T hese results suggest that dairy cows grazing on good quality swards ma y be able to compensate for increased degree of hunger by increasing b oth biting rate and Dill intake per bite to increase DM intake rate. A lthough the DM intakes of silage and grazed grass followed similar pat terns of increasing intake with extended fasting duration, DM intake r ates were considerably higher in grazing cows for each fasting treatme nt.