Low phosphorus intakes by beef suckler cows in late pregnancy and early lactation

Two groups each of 10 suckler cows were given a basal diet of oat straw and pressed unmolassed sugar beet pulp for the last 19 weeks of pregnancy and the first 6 weeks of lactation. One group received 0.88 kg extracted soya bean meal (SBM) in pregnancy and 1.03 kg in lactation. The other was given 0.27 kg of a liquid supplement (LS) (containing inter alia urea and phosphoric acid) in pregnancy increasing to 0.33 kg in lactation. Both diets provided about the same amounts of digestible crude protein and about 10 g phosphorus (P) per day in pregnancy and 12 g P per day in lactation. Cows given SBM consumed marginally more straw but there were no differences in total diet digestibility. Cows given LS lost significantly more liveweight but their calves grew equally well. There were indications that cows given LS had slightly higher mean blood inorganic P and lower mean blood calcium (Ca) concentrations. Mean blood inorganic P concentrations were not below 1.4 mmol/l in pregnancy or 1.2 in lactation. There were no signs of reduction in voluntary straw intake or depraved appetite. When transferred to grass with a bull at the end of the experiment all cows were served within 24 days. It is concluded that these amounts of dietary P were adequate over the 25 weeks.