Consumo e ambiente ruminal de vacas Holandês-Zebu em lactação sob pastejo de Brachiaria spp suplementadas com diferentes quantidades de concentrado

Abstract

The objective of the experiments were to evaluate the effect of the amount of concentrate fed on drymatter intake (DMI), neutral detergent fiber intake (NDFi) and into ruminal fluid pH, ammonium nitrogenand volatile fatty acid (VFA) concentrations of lactating dairy cows grazing Brachiaria grass. Cows (n =48) were assigned to either groups (G). G-I cows (n = 24; weighing 513 Kg with 155 days in milk andproducing 16,3 Kg of milk) were divided in three treatments to receive 4, 6 or 8 Kg of concentrate daily,as fed, divided equally to the am and pm milking time. G-II cows (n = 24; weighing 523 Kg with 311days in milk and producing 8,4 Kg of milk) were divided in others three treatments to receive 1, 2 or 4 Kgof concentrate daily, as fed, divided equally to am and pm milking time. Cows from G-I were always thefirst to graze followed by G-II cows. These two experiments were assigned to be a random block design.Three rumen canulated milking cows were managed as the G-I cows (G-III). Ruminal fluid was removedfrom canulated cows before the first meal at milking time (time zero) and at 1, 3, 5, 7, 9, 12, 14, 17, 24hours. The experiment was a latin square design (3x3) at a split splot scheme. The DMI as % of liveweigth were 1,81, 1,79 and 2,03 for cows that receive 4, 6 or 8 Kg (G-I) and 1,97, 1,92 and 2,46 for cowsthat receive 1, 2 or 4 Kg (G-II) of concentrate daily. Cows that receive more concentrate in both G hadgreat total DMI than the others cows (P<0,05). The NDFi, as % of live body weigth, was greater by G-Icows fed 8 Kg of concentrate than G-I cows fed 4 or 6 Kg (1,17 vs 1,03 and 1,17%, p<0,05) and G-IIcows fed 4 Kg of concentrate intake more NDF than the ones fed 1 or 2 Kg of concentrate (1,49 vs 1,19and 1,16%, P<0,05), respectively. As the time of increasing the amount of concentrate fed the pHdecreased (6,67, 6,59 and 6,43, p<0,05) and the ammonium nitrogen increased (11,09, 12,27 and 15,04mg/dl, p<0,05) for 4, 6 or 8 Kg of concentrate/cow/day, respectively. No difference (p>0,05) wasobserved on VFA concentrations and on acetate:propionate ratio. It was concluded that rumenenvironment allowed an increased intake of DM and NDF in relation to live body weight in boths groups