Efecto del nivel de suplementación con concentrado sobre el consumo voluntario y comportamiento ingestivo en vacas lecheras a pastoreo primaveral

Abstract

The purpose of this study was to evaluate the effect of different levels of concentrate supplementation on grazing behaviour of dairy cows fed spring pasture. The study was conducted at "Vista Alegre" Experimental Farm, from September to November 2005. Twenty eight spring calving Friesian cows were assigned to four experimental treatments: SP, grazing alone; PSC3, pasture plus 3 kg/d of concentrate; PSC6, pasture plus 6 kg/d and PSC9, pasture plus 9 kg/d of concentrate. Dry matter intake was estimated using chromic oxide capsules of automatic liberation as an indigestible marker. Individual measurement of feeding behaviour was carried out in two opportunities, recording the grazing, ruminating, laying, standing, walking and milking activities every ten minutes during 24 hours. The cows were supplemented twice a day and were managed under a strip grazing system on pasture consisting mainly of perennial ryegrass. The pasture intake decreased (P < 0.001) in all treatments with concentrate supplementation (17.6; 15.2; 11.4 and 7.7 kg dry matter/day, for PS, PSC3, PSC6 and PSC9, respectively); meanwhile total dry matter intake was decreased by supplementation only in treatment PSC9 (P < 0,05). The substitution rate was 0.92; 1.17 and 1.25 kg dry matter of pasture/kg dry matter of concentrate for PSC3, PSC6 and PSC9 treatments, respectively. Total grazing time decreased (447, 414, 413 and 381 min/day, for PS, PSC3, PSC6, and PSC9, respectively) and total ruminating time increased (463, 473, 495 and 501 min/day, for PS, PSC3, PSC6, and PSC9, respectively), as a result of supplementation, but it was significant only between PS and PSC9. Unsupplemented cows and cows receiving 3 kg/day had a higher bite rate (P < 0.001) than supplemented cows receiving 6 and 9 kg/day. The results suggest that high levels of supplementation (9 kg/day) decrease pasture dry matter intake and grazing time, while increasing ruminating time, but have no effect on total dry matter intake.