SODIUM FERTILIZER APPLICATION TO PASTURE .2. EFFECTS ON DAIRY-COW PRODUCTION AND BEHAVIOR

Fifty-four lactating dairy cows were grazed for 24 weeks on pasture receiving 0 (Nil), 32 (Low) or 64 (High) kg Na ha-1 vr-1 and with (+) or without (-) 100 g NaHCO3 buffer included in a maize gluten concentrate supplement. Cattle grazed the Na-fertilized pasture to a tower height, particularly in the High treatment. Cows grazing pasture with Na fertilizer produced more milk, and milk fat concentration increased in direct proportion to amount of Na fertilizer applied and with NaHCO3. This increase was greatest in early season. Milk protein concentration was not affected by Na fertilizer application or NaHCO3 buffer addition. Milk lactose concentration was increased by Na fertilizer application but not by NaHCO3 supplementation. Cows in the Na-applied treatments gained more live weight but there was no effect of treatment on condition score change. Grazing time and drinking frequency increased linearly with increasing pasture Na. Ruminating time and biting rate were similar at the Low and High treatments and greater than the Nil treatment. NaHCO3 supplementation increased drinking frequency and decreased the rate of concentrate intake. Cow reproductive performance was not significantly affected by Na fertilizer application. During the residual period, cows that had previously grazed the Na-fertilized pasture had reduced milk fat and protein contents. It is suggested that changes in pasture growth and composition following Na fertilizer application increase cow production, liveweight gain, and grazing and ruminating times, but that changes in milk fat concentration are due specifically to increased Na intake by the cow.