Intake and excretion of nitrogen, potassium and phosporus by grazing steers

Abstract

SUMMARYIntake and faecal and urinary output of nitrogen, potassium and phosphorus by steers grazing high quality pasture at either of two intake levels were measured in three trials lasting 10–12 days. Intake was estimated from total faecal D.M. and in vitro D.M. digestibility of hand-plucked pasture. A known proportion of urine was sampled by a nonsurgical technique.Average urinary mineral output between trials ranged from 93 to 134 g N/day, or 40 to 51% of consumed N; 74 to 137 g K/day or 33 to 76 % of consumed K and no more than 1 g P/day, or 2 to 4% of consumed P. Faeces contained 36–62 g N/day, or 16–24% of consumed N; 12–46 g K/day, or 8–21% of consumed K and 10–23 g P/day, or 44–74% of consumed P. The volume of urine passed differed widely between days for individual steers and between steers within each trial. In trial 3, daily output ranged between 5–8 and 54.71 by different animals. For two steers over three 24 h periods, frequency of urination ranged between 13 and 73/24 h; urine volumes between 7.6 and 51.2 1/24 h; urinary excretion of N between 81 and 137 g/24 h and of K between 58 and 90g/24h.Urinary N and K concentrations were higher at night than during the day, ranging in trial 3 from 0.8 to 14.1 mg N/l, and 0.6 to 9.9 mg K/l. No clear diurnal patterns were found for P.