Choice of grazed herbage or maize silage by lactating dairy cows: influence of sward height and concentrate level

Abstract

The preference of lactating dairy cows for grazed herbage or maize silage (MS), simultaneously offered ad libitum in the field, was examined at two sward heights (SH 4-6 and 8-10cm) and two concentrate levels (CL 0 and 6kg day -1 ) in a 2x2 factorial arrangement within a completely randomised experimental design. The experiment lasted 35 days and was carried out in spring using 24 multiparous Holstein Friesian cows. On average, the cows proportionately spent more time grazing than eating MS (0.85:0.15) and even though the higher rate of intake (RI) of dry matter (DM) of MS compared with grazed herbage (76 versus 26g DM min -1 ), the proportion of total DM intake as herbage was higher compared to that of MS (0.56:0.44). The higher crude protein and low fibre content of grazed herbage appeared to have a higher priority of choice than RI, as the cows chose to graze for longer (grazing time 385 min, MS feeding time 67min) despite the lower RI of herbage. The low proportion MS intake indicated that RI was a secondary factor of choice. Concentrate supplementation had a greater depressing effect on herbage intake than on MS intake. These results suggest that the animals reduce the intake of feed with lower RI when the labor associated to eat is decreased. The factors influencing the choice for herbage over maize silage remain unclear.Keywords: milking cow, diet selection, concentrate, sward height (0,85:0,15) SM (0,56:0,44 RESUMO A preferência de vacas leiteiras em lactação por pasto ou silagem de milho (SM) oferecidas ad libitum simultaneamente no pasto foi avaliada quanto a duas alturas de pastagem (4-6 e 8-10cm) e dois níveis de concentrado (0 e 6kg dia -1 ), em um arranjo fatorial 2x2 dentro de um delineamento inteiramente ao acaso. O experimento, com duração de 35 dias, foi executado na primavera utilizando 24 vacas multíparas da raça Holandesa. As vacas passaram, em média, proporcionalmente mais tempo pastando do que comendo SM e, mesmo considerando a maior taxa de consumo (TC) de matéria seca (MS) de SM comparada com a da pastagem (76 versus 26g MS min -1 ), a proporção do total do consumo de MS como pastagem foi mais alta comparada com aquela da

Dry matter intake and milk production of grazing dairy cows supplemented with corn silage or a total mixed ration offered ad libitum in a subtropical area

“…Few other interesting studies investigated the feeding choice between grazed herbage and the forage‐based supplement, by offering ad libitum access to the forage‐based supplement, generally at night. In these studies, the forage based‐supplement was grass silage (Roberts & Leaver, 1986; Sairanen et al., 2006), TMR (Hernandez‐Mendo & Leaver, 2004, 2006), or corn silage (Hernandez‐Mendo & Leaver, 2010; Morrison & Patterson, 2007). In the four above‐cited studies investigating ad libitum corn silage or TMR supplementation of grazing dairy cows, herbage intake was measured only in the study of Morrison and Patterson (2007), in which access to the supplement was only 2 hr daily.…”

“…Few other interesting studies investigated the feeding choice between grazed herbage and the forage-based supplement, by offering ad libitum access to the forage-based supplement, generally at night. In these studies, the forage based-supplement was grass silage (Roberts & Leaver, 1986;Sairanen et al, 2006), TMR (Hernandez-Mendo & Leaver, 2004, or corn silage (Hernandez-Mendo & Leaver, 2010;Morrison & Patterson, 2007).…”