EFFECTS OF SWARD HEIGHT AND CONCENTRATE SUPPLEMENTATION ON THE INGESTIVE BEHAVIOR OF SPRING-CALVING DAIRY-COWS GRAZING GRASS CLOVER SWARDS

Forty-eight, lactating, spring-calving, multiparous, Holstein-Friesian cows, continuously stocked on mixed grass-clover swards, were blocked by calving date, parity and milk yields in week 2 of lactation and ra ndomly allocated to six treatments: 0 (U) or 4 (S) kg concentrate supp lementation at sward heights of 40, 60 or 80 mm as measured by a risin g plate meter. Jaw movements were recorded automatically for 24 h for a different cow on each treatment on each of 6 days during two periods (15-25 June (P1) and 25 July-6 August (P2)). Swards of 40 mm height w ere not used in P2. Total time grazing, ruminating or idling, and the number and duration of bouts of these activities, biting rate while gr azing and chewing rate, number of boluses and chews per bolus while ru minating were recorded. Data were smoothed to give a minimum bout dura tion of 5 min. Herbage intakes were estimated using n-alkanes. Grazing time was greater at 40 mm than at 60 or 80 mm when unsupplemented but less when supplemented. Proportionately 0.88 of grazing time and 0.67 of ruminating time by dairy cows occurred during daylight with a larg e evening meal particularly evident. On the 40 mm sward unsupplemented animals grazed for longer with a higher biting rate but lower bite ma ss and less mastication and rumination. When supplement was offered at the 40 mm sward height animals appeared to 'give up' harvesting the s ward more readily. Durations of ruminating and idling bouts were simil ar across all treatments with low variability.