Variability in Forage Intakes by Sheep

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Abstract
Standard deviations (SD) and coefficients of variation (CV) were calculated from 441 determinations of ad libitum forage intake involving 2,427 individual animal/period measurements expressed as gm./W0.75 daily. The data include various species of grasses, legumes, grass-legume mixtures and straw; various physical forms: frozen, artificially dried, field cured, ensiled and pelleted; several environments: metabolism stalls, individual pens and group housed but tie-stall fed. Animal variability was high with an average SD of 9.7 and an average CV of 16.4%. Forage Species. No marked between species variation occurred. SD ranged from 6.7 to 13.9 and CV from 14.9 to 19.1%. Physical Form. SD were similar (7.1–9.7) for all forage types except pelleted (17.6). CV ranged from 10.5–16.4% except for silage (21.0%) and straw (23.8%). Environment. SD for metabolism stalls (8.21) and slatted-floor individual pens (7.4) were lower than for bedded individual pens (11.1) and group housed but tie-stall fed (10.8). CV for metabolism stalls (11.5%) were lowest, individual bedded (16.2%) and slatted-floor (19.4%) pens intermediate and group housed but tie-stall fed (25.9%) highest. Repeated assays on the same forage by the same animals did not reduce animal variability. The SD and CV were not consistent from period to period but appeared to fluctuate at random. Estimates of the number of sheep required to give an 80% chance to detect intake differences at P=.O5 show that 10 to 15 sheep are required per forage to detect real differences of approximately 10 intake units.

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