A qualitative and quantitative evaluation of the seaweed diet of North Ronaldsay sheep

The rare breed of primitive sheep on North Ronaldsay, Orkney (Scotland) survives under extreme conditions on the beach shore of North Ronaldsay with seaweed as virtually their sole feed source. In this study, we evaluated the qualitative and quantitative seaweed diet of the sheep. The feral sheep were observed eating a broad variety of seaweed species but, due to apparent preference and availability, mainly brown kelps (Laminaria digitata and Laminaria hyperborea) were consumed during this summer study. A feeding study was completed with 12 North Ronaldsay sheep for 5 days. In order to reproduce natural conditions as close as possible each sheep was fed ad libitum with a L. digitata and Laminaria hyberborea mixture in a pen on the beach. To establish if the seaweed intake was dependent on an adapted micro-flora in the digestive system, six of the North Ronaldsay sheep were adapted to feeding on grass for 5 months before the start of the trial, and the remaining six sheep were kept on their normal seaweed diet. Seaweed intake between the two groups was not different (P = 0.66) and 1.4 +/- 0.2 kg (wet mass) was consumed daily. In view of the unusual diet and the potential for using seaweeds as feeds for ruminants elsewhere, dry matter degradation (DMD, 71.7%, at 48 h) and organic matter digestibility (OMD, 79.6%) were measured with L. digitata and Laminaria hyperborea in domestic sheep that had not eaten seaweed before. Measurements were carried out on a mixture of the two brown algae to reproduce the situation of the North Ronaldsay sheep. The high values of digestibility measured, and the fact that North Ronaldsay sheep apparently are able to meet their energy needs from their seaweed diet, suggests that the use of these seaweeds as an alternative feed source for ruminants may be possible under some circumstances. (C) 2003 Elsevier Science B.V. All rights reserved.