The effects of nitrogen and energy supplementation on the voluntary intake and digestion of heather by sheep

Abstract

SUMMARY: In three experiments the effects of amount and source of nitrogen and energy supplements, and their frequency of feeding, on the voluntary intake and digestion of winter-quality freeze-stored heather (digestibility of organic matter 45%, N content 1·3%) by Scottish Blackface castrated male sheep were examined. The continuous infusion of 0·5gN/day as urea or casein increased voluntary intake by 29% and digestibility of organic matter by 11 percentage units but higher amounts of N supplement gave no further responses. The continuous infusion of a supplement containing 100 g sucrose/day and 3 g N/day as urea gave similar responses in voluntary intake and digestibility of heather to those obtained when N alone was infused. A reduction in the frequency of feeding of the sucrose: urea supplement reduced the response in intake of digestible OM of heather but intakes of digestible OM were higher when an isocaloric supplement of starch: urea was given at the same frequencies (thrice and once daily). The results are discussed in relation to the use of ruminal NH³concentrations to assess the responses in voluntary intake to N supplementation and the balance required between the nitrogen and energy in the supplement. I t is concluded that the nitrogen and energy supplements could improve the nutrition of sheep grazing heather moorland in winter.