Effect of grazing method and herbage allowance on the grazing efficiency of milk production in organic farming

Abstract

In order to improve grazing management for organic farming systems two grazing experiments were conducted. In experiment 1, two rotational grazing methods (GMs), daily strip (S)-grazing or paddock (P)-grazing were evaluated. Herbage allowances (HAs) for S-grazing were 20.0 (1996) or 22.5 kg dry matter (DM) per day (1997). Cows were on an average allocated to paddocks for 6 days according to post-grazing sward height. S-grazing decreased ( P<0.001) pasture area requirement per cow by 26% and increased ( P<0.001 ) average milk yield per hectare by 36%. The duration of retarded growth was longer for P-grazing. In experiment 2, two levels of HA 18 and 24 kg DM per cow were compared in daily S-grazing of legume-rich swards. During the first grazing cycle the lower allowance was more effective ( P<0.001) in pasture utilisation than the higher allowance, due to a 18% decrease in grazing area requirement per cow. During three subsequent grazing cycles, HA had no significant effect ( P>0.05) on grazing area requirement per cow. The average grazing area requirement over the entire grazing season was decreased (8.8%) for the lower allowance ( P<0.01), but milk yield per hectare was similar between grazing strategies. High precipitation and tramping on silt soil protracted pasture re-growth, particularly at the lower HA. After the first grazing cycle pre-grazing herbage mass (HM) was lower for the lower allowance necessitating an expansion of grazing area. This clearly indicates the importance of grazing management to the success of organic farming systems, where pasture growth is not supported by soluble mineral fertilisers but relies on biological processes. In both experiments, nutritive value of herbage was relatively high (mean crude protein (CP) content 174 g kg −1 DM, neutral detergent fibre (NDF) content 498 g kg −1 DM, in vitro organic matter digestibility (OMD) 0.752), but the average pre-grazing HM was low (<2 t DM ha −1, above 3 cm).