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Abstract
The results of 120 digestibility trials are reported, in whieh nonlaetating identieal twin eattle were fed fresh pasture herbage indoors for 6 months of the 1958–9 dairying season.
One member of eaeh twin set was fed to appetite, the other reeeiving approximately 60 per cent of this amount. Intake was measured in terms of dry matter, organic matter, energy, and emde protein. By increasing the amount of herbage available the proportion of fibre consumed was reduced. No such effect was obtained on either protein or energy.
Seasonal changes in the apparent digestibility of herbage were traced and the effect of these on voluntary intake was assessed. It was concluded that there was a useful relation between apparent digestibility and voluntary intake for herbages less than 70 per cent digestible. Above this level the assoeiation was poor. At high intakes mean herbage digestibilities were lower than where feeding was restricted. The extent of this difference changed markedly during the experiment and was signifieantly eorrelated both with between-group differenees in intake and with feeding level.
Changes in the emde protein eontent of the herbage eaten were measured and relations between the pereentage crude protein, crude protein digestibility, and the pereentage digestible emde protein were established. A signifieant seasonal trend oeeurred in the heat of combustion of unit digestible organie matter. Highest and lowest values were obtained in autumn and mid-summer, respectively.
These results have been diseussed with partieular referenee to their application in pasture-intake studies with free grazing animals.
