Effects of sodium fertilizer application to pasture, or its direct supplementation, on dairy cow production and grazing behaviour

The sodium (Na) requirement of dairy cows is dependent on the level of production and the physiological state of the animal (ARC, 1980). In a previous paper (Chiy and Phillips, 1991), it was shown that changes in pasture growth rate and composition following sodium (Na) fertilizer application in mid-season to a dairy cow perennial ryegrass pasture leads to increased grazing and ruminating times, milk yield and milk fat concentration. Adding Na to concentrate also increased ruminating time and milk fat concentration. The effects of different levels of Na fertilizer have not been reported. The aim of the present experiment was to compare the effects of 0 (Nil), 32 (Low) and 64 (High) Kg Na /ha/year appied as fertilizer, with ( + ) or without (-) a sodium bicarbonate (NaHC03) buffer added to a concentrate supplement on cow production and ingestive behaviour during the grazing season. Fifty four cows in their second or later lactation, and with a mean calving date of 4 February 1990, were allocated to sextets. Within sextets, cows were allocated to one of six treatments in a split-split-plot design arranged in a 24 X 3 X 2 factorial: weeks 1 to 24 of experiment; 0 (Nil), 32 (Low) or 64 (High) Kg Na ha/year and with (+) or without (-) 100 g NaHC03included in 2 Kg maize gluten supplement/ cow/day.