Acute post-parturient haemoglobinuria in dairy cows and phosphorus status

During the conduct of an experiment designed to examine the nutritional management of dairy cows in late pregnancy, four cows out of 72 suffered from acute haemoglobinuria two to four weeks after calving. Thirty-six thin and 36 fat cows were individually fed one of three diets based on a total mixed ration with different energy or protein concentrations during the last 3 to 4 weeks before expected calving date. After calving, cows grazed pasture and were offered 6 kg dry matter of pelleted concentrates daily. The P concentrations of the feeds offered suggested that the cows' diets were marginally deficient in P relative to requirements. Plasma P concentrations were significantly (P < 0.05) lower in fat cows than in thin cows during the first 6 weeks of lactation (0.87 versus 1.12 mmol/L), but precalving diet had no effect (P > 0.05). Concentrations of plasma inorganic P of the four fat cows that developed acute haemoglobinuria were less than 0.3 mmol/L. However, plasma P concentrations in another 12 cows, none of which displayed overt symptoms, declined to similar levels. It appeared that inadequate dietary P may have predisposed cows to acute haemoglobinuria, but the precipitating cause was not readily obvious.