The efficiency of energy utilization in growing cattle consuming fresh perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca)

摘要: 1. Twenty Friesian steers (225 kg live weight) were fed on mid- (M) (June-July) and late- (L) (August- September) season crops of either fresh perennial ryegrass (Loliumperenne cv. Melle) (G) or white clover (Trifolium repens Blanca) (C). Each the forage diets was offered at three restricted planes nutrition above main- tenance to compare effect species efficiency energy utilization. All harvested daily from swards regrowth intended equivalent digestibility.2. Faecal urine excretions measured for 7 5 d respectively, followed by two consecutive 24 h measurements methane, carbon dioxide oxygen exchange in open-circuit respiration chambers.3. The apparent digestibility (0.759) marginally higher (P 0.05)digestibilities. Metabolizable (ME):digestible (DE) diet G (0.837) significantly 0.05) between forages (G 62.8, C 63.4) seasons (M 63.2, L 63.1). Energy excretion cattle (77.5) compared with (60.5)(P (0.42) (0.46). Linear extrapolation values zero retention indicated that maintenance requirements ME (Em MJ/d) 23.3 28.8 C. extrapolated Emwhen expressed relation a fasting heat production (FHP) 22.8 (MJ/d) resulted derived utilization (km) 0.97 0.79 (C), suggesting an underestimate Em G.5. Asymptotic exponential curves (representing law ofdiminishing returns) fitted unscaled values, ME1 RE (MJ/d), intake. estimates FHP 18.0 22.0 (C) not different > observed value MJ/d. Using as additional data points, model accounted more variance < 0,001) linear regression method analysis. Exponential analysis 29.04 31.80 k, each calculated, assuming linearity response, 0.78 0.72 calculation fixed positions curve related (expressed multiples Em)indicated 1.65 Em, kt than 0.05). With increasing plane kf declined 0.53 0.29 0.55 0.36 over range during experiment.