Forage intake and grazing times of yearling beef steers grazing nitrogen-fertilized Russian wildrye (Psathyrostachys junceus)

Abstract

Forage dry matter intake of yearling steers from nitrogen- (N) fertilized Russian wildrye (Psathyrostachys junceus) pastures was determined by an external indicator technique on five occasions during the summers of 1986 and 1987 at Swift Current, Saskatachewan. The N fertility levels were: 55 kg ha−1 N and 110 kg ha−1 N (the sum of available N and annually applied N fertilizer) and an unfertilized control (15 kg ha−1 available nitrate-N). Forage dry matter intake by steers (290 kg at turn out in May) was 1.5% of steer body weight (BW) when forage dry matter digestibility (DMD) was 48% and averaged 2.3% of steer BW when DMD was 54–62%. Forage dry matter intake was indirectly related to the N fertility level of the pasture by the positive effect of N fertilizer level on forage DMD. Fecal output, as determined by chromic oxide dilution, varied from 0.86% of BW in August 1986 to 1.12% of BW in July 1987. There was no relationship of fecal output to the N fertility of the grazed pasture. Time spent grazing during a 1-d period was determined in each of June, July and August of 1986 and 1987. Grazing time averaged 8.0 h d−1 and was not affected by season or fertility treatment. Forage and fecal contents of acid detergent lignin, ash and N were significantly correlated with the N fertility level of the pasture from which they came. It was concluded that forage intake of animals grazing N-fertilized pastures may be affected indirectly by the effect of soil N fertility on DMD. Key words: Psathyrostachys juncea, fecal output, feces composition, forage digestibility