John A. Milne

The composition of the diet of red deer (Cervus elaphus) in a Mediterranean environment: a case of summer nutritional constraint?

Abstract The composition of the diet of red deer (Cervus elaphus) in a Mediterranean environment, in southern Portugal, was estimated during summer 1995–1997 using n-alkane analysis. Standing crop of herbage layer biomass was estimated between June and September 1995–1997 using the clipping quadrat method. There was a large variability between years in the availability of the herbage layer biomass. Biomass was three fold greater and availability of legumes higher in a wet than in a dry year. Live green material was available in the herbage layer in June, but not thereafter, even during a wet year. Red deer ingested a higher proportion of browse in summer during drier years (0.83–0.89) than during a wet year (0.47). In the drier years, the herbage layer was replaced in the diet by browse species that were uneaten in the wet year. Contrary to Atlantic environments, where red deer include a large proportion of browse in their diets during winter, summer is likely to be a season of nutritional constraint for red deer inhabiting Mediterranean environments.

Diet Selection by Grazing Animals

The subject of diet selection by grazing animals is a vast one. Whilst it is widely acceptcd that there may be a set of generalized principles underlying foraging behaviour and diet selection by grazing animals. the current philosophy is to develop appropriate models to describe the grazing behaviour for observed sets of specific food distributions and grazers rather than to attempt to seek a generalized foraging theory. The present paper follows this current philosophy in considering only large vertebrate grazing herbivores, and specifically ruminants, within the context of predominately temperate pastures. The domesticated ruminant animals which have been studied most frequently, i.e. cattle, sheep, deer and goats, have adopted slightly different foraging strategies along the continuum of grazers, mixed grazers/browsers and browsers with cattle considered as grazers and goats being the nearest species to a browser. There are a number of animal variables which influence these foraging strategies and they can be seen as adaptations to particular diets which have arisen over evolutionary time or as a result of selection imposed by man (Gordon & Iason, 1989). Possibly the most all-persuasive variable is the body size of the ruminant. Absolute feed requirements, the inability of fine-grained food selection and retention time in the gut all increase with bodyweight (Gordon & Illius, 1988; Illius & Gordon, 1987). Larger animals ingest food of potentially lower nutritive value (Hodgson, 1981). Rumen size relative to body size also differs between different species and this is in part responsible for changes in digestive capability for fibrous grasses and trees and shrubs (Demment & Van Soest, 1985). In gcneral terms, ruminants with a large body size will digest fibrous foods better because of relatively larger rumens and longer retention times, whilst small ruminants will digest fibrous feeds less well because of shorter retention times and rely o n foraging strategies which allow it to ingest a diet with a high cell content. Although the grazer-browser continuum and that of body size are correlated there are exceptions, but it should be clear that foraging strategy, diet selection and digestive ability are linked. An example of where the effect of retention time or rumen size on digestive capability does not hold is in the more efficient digestion of heather (Cafluna vulgaris) by deer than by sheep (Milne et al. 1978). These findings can be explained by the higher proline content of the saliva of deer than sheep, which …

Effects of oral administration of brassica secondary metabolites, allyl cyanide, allyl isothiocyanate and dimethyl disulphide, on the voluntary food intake and metabolism of sheep

Glucosinolates, such as sinigrin, and S-methyl cysteine sulphoxide (SMCO), which are found in forage brassica species have been implicated in the low intakes observed among lambs consuming such diets. To test both the individual and interactive effects of these compounds in sheep, all combinations of the sinigrin breakdown products, allyl cyanide (ACN) and allyl isothiocyanate (AITC; 10 mmol/d), and the SMCO metabolite dimethyl disulphide (DMDS; 25 mmol/d) were orally administered twice daily for 5 weeks to forty sheep offered dried grass pellets ad lib. As well as measuring voluntary food intake (VFI), a number of haematological and clinical function tests were conducted to assess the physiological effects of the compounds. VFI was significantly depressed by both ACN and AITC but not by DMDS. DMDS significantly ameliorated the effects of ACN on VFI (P < 0.001). Concentrations of reduced glutathione in the blood were depressed by ACN and AITC and elevated by DMDS but no significant interactions were evident. Elevated plasma gamma-glutamyl transpeptidase (EC 2.3.2.1) activity on ACN and AITC treatments indicated possible liver damage. DMDS elicited a rise in Heinz bodies to 11% by week 2 but this was not reflected in packed cell volume and blood haemoglobin levels which were unaffected by treatment. The increased Heinz body count caused by DMDS was not further influenced by ACN or AITC. In conclusion, the depressive effects of sinigrin breakdown products on VFI were not compounded by the additional presence of DMDS which, on the contrary, lessened the depression of VFI caused by ACN.

What Price Cheap Food

This paper is the report of a meetingthat gathered many of the UKs most senioranimal scientists with representatives of thefarming industry, consumer groups, animalwelfare groups, and environmentalists. Therewas strong consensus that the current economicstructure of agriculture cannot adequatelyaddress major issues of concern to society:farm incomes, food security and safety, theneeds of developing countries, animal welfare,and the environment. This economic structure isbased primarily on competition betweenproducers and between retailers, driving foodprices down, combined with externalization ofmany costs. These issues must be addressed by acombination of legislation, restructuring ofthe market, and use of public funds. Themeeting included workshops that made otherrecommendations for research and education. Themost urgent requirement is recognition thatchange is needed and development of a visionfor what that change must achieve.

Farmed Red Deer: An Example of Agricultural Diversification

In the present economic climate farmers have to diversify their current programmes for cattle, sheep, and cereal production. One form of diversification which is rapidly growing in popularity is to farm red deer. This article reviews the economic, health, and breeding problems involved, and concludes that the prospects for the future are good.