Undernutrition in grazing sheep. I. Changes in the composition of the body, blood, and rumen contents

Abstract

Studies were made on three initially similar groups of adult Merino sheep at pasture; each group comprised eight animals of which four each had a rumen cannula. Group A was kept at about the initial mean liveweight of 35 kg; groups B and C were reduced in weight over 14 weeks by restriction of grazing and then held at about 26 and 23 kg respectively for 9 months. Measurements were made at intervals of 4-6 weeks of ruminal concentrations of volatile fatty acids (VFA) and ammonia, rumen volume and flow rate of digesta, tritiated water (TOH) space, and blood composition.

Haemoglobin concentrations and haematocrit values decreased in the undernourished sheep, but there were no marked changes in blood β-hydroxybutyrate, or lactate, or plasma urea nitrogen. Estimates of body composition from TOH space indicated that sheep in groups B and C lost 51 and 58 Mcal respectively during the first 14 weeks; estimated fat contents were thereafter about 9 and 7% of liveweight.

Metabolizable energy requirements for maintenance were calculated from estimated VFA production rates and changes in body energy content. During a 9 month period commencing shortly after shearing and extending into winter, requirements per unit liveweight were about 45% greater for the undernourished groups B and C than for group A.