BACK TO QUEBEC CITY 2002 TITLES
Effect of high instantaneous
stocking rate on grazing behaviour of lactating dairy cows in Voisin’s
Rational Grazing
M.C.A.C da Silveira, L.C.
Pinheiro Machado Filho, G.R. Furlanetto and C.T. Berton
Lab. Etologia Aplicada,
Dep. de Zootecnia & Des. Rural, Universidade Federal de Santa Catarina,
Florianópolis, SC, Brasil
In Voisin’s Rational Grazing, high instantaneous stocking rate may increase feed competition, altering grazing behaviour and reducing pasture selectivity, although not affecting milk production. The objective of this experiment was to study the effect of two instantaneous stocking rates, Low (L) = 80 AU /ha and High (H) = 240 AU/ha on the grazing behaviour of dairy cows. Sixty lactating Holstein cows, from a commercial herd, were paired according to parity, stage of lactation and level of production and randomly assigned to the L or H group. Pasture availability was the same for both groups. The L group stayed three times longer in a three times larger paddock. For the grazing behaviour observations, the cows in each treatment were further divided in four groups, from each of which two cows were sampled. All groups were simultaneously observed for four hours following morning and evening milking, during two time periods (Nov 00 and Sept 01). To analyse the data, we divided each four hours in two periods of two. Data was analysed using Proc. GLM (ANOVA) in SAS. The treatments did not affect cow’s milk production (P>0.8). There was no treatment effect in the first two hours period. There were treatment x period interactions for the variables time spent grazing (P<0.007), ruminating (P<0.002) and standing (P<0.01). There was no treatment effect in the first two hours period. In the second two hours period cows from H, compared with those from L, grazed for longer (50.5 and 39.2 ± 2.9 min), but ruminated less (48.3 and 37.1 ± 2.1 min) and stood less (2.1 and 4.1 ± 0.7 min). Overall, cows grazed longer (P<0.001) and stood longer (P<0.002) during the morning than in the evening. By contrast, they ruminated longer (P<0.0004) and spent greater time lying down (P<0.01) during the evening grazing. Biting rate was higher during the evening (P<0.006) and in early Sept 01 (P<0.0001). The high instantaneous stocking rate increased the duration of grazing during the second 2-hour period, which may have increased ingestion and lead to the postponement of rumination.
AU = Animal Unit, equivalent to a 500 kg bovine