Measurement of feed intake of grazing sheep: I. Rate of passage of inert reference materials through the ruminant digestive tract

Abstract

Experiments are described which give some basic information on the rate and pattern of marker excretion by sheep on pastures ranging in digestibility from 70 to 80% and on hay of barely 50% digestibility.The faeces output of individual sheep varied from 100 g. to more than 400 g. daily, and the estimated feed intake from below 400 to over 1,900 g. daily.Despite these wide ranges a typical pattern for the passage of single doses of markers was quite consistently repeated in the trials on pastures:1. Markers first appeared in the faeces 5–8 hr. after dosing.2. Concentrations rose rapidly to peak values about 10–18 hr. after dosing.3. Concentrations fell thereafter by about 50% each 6–10 hr. until 60–70 hr. after dosing when marker content could no longer reliably be determined by the methods used.Factors affecting the basic pattern1. The overall quality of the feed was of prime importance, in that peak concentrations occurred progressively later on poorer pastures and on hay.2. For any given feed a high level of (estimated) feed intake was often associated with earlier appearance of marker in the faeces, an earlier peak of concentration, and slightly faster fall in marker concentration.3. There was evidence that the time of administration might slightly affect rate of passage, presumably through its relation to grazing periods, for doses given at or near times of greatest feed intake were passed rather more rapidly.4. It did not appear that there was any considerable retention of either marker within the tract beyond 72–96 hr. after dosing.