Metabolic fuels of the ruminant consist mainly of volatile fatty acidsproduced in the rumen by microbial digestion of dietary polysaccharides andamino acids derived from dietary protein. As almost no glucose is obtaineddirectly from its food, any specific requirements for this sugar are met bysynthesizing it from non-carbohydrate sources: principally propionate andthe glucogenic amino acids.

The two main types of kale grown in Britain, marrowstem and thousandhead,both belong to the species Brassica oleracea L. Marrowstemis a thick-stemmed plant, 1–1·5 m tall, whereas thousandhead has a higherratio of leaf to stem and is a shorter plant. Kale is sown in late springand normally harvested from October to February, thousandhead being the moreresistant to frost. The crop yields about 50 000 kg green matter per hectare(7000 kg dry matter) and is either consumed in situ or cutand carried to housed animals. Cattle are rarely fed on kale alone, butsheep may be; when kale is grazed its consumption is not closely controlled.Kale is grown widely in Britain and north Europe generally, and also in NewZealand.

Although the importance of calcium and magnesium homoeostasis has beenrecognized for many years the precise mechanisms by which this is achievedare still not clearly understood. Over recent years interest in bloodcalcium regulation has been stimulated by the discovery, isolation andsynthesis of calcitonin. Its significance in normal adults, however, remainsin some doubt (vide infra). In this paper is outlined ourpresent knowledge of the endocrine factors which help to regulate thecontrol of plasma calcium and magnesium concentration in ruminants throughthe operation of negative feedback mechanisms. Mention will also be made ofthose hormones which, although capable of altering the plasma concentrationsof either calcium or magnesium, are secreted independently of theseconcentrations. It will be seen that in many instances the chemicalsimilarity between calcium and magnesium is reflected in hormone effects orin hormone secretion rates. However, this is not always found to be so, e.g.the control of calcitonin secretion appears to be affected in differentdirections by plasma calcium and magnesium concentrations.

There has been an active interest in the toxicology of copper since themiddle of the 19th century and a review by Davenport (1953) covers the earlywork on the hazard to man and animals of both the acute and chronic forms.Review material specific to chronic copper poisoning in farm livestock hasalso been published by Broughton & Hardy (1934), Eden (1940), Todd(1962) and Bull (1964).

The first description of true chronic copper poisoning in farm animals wouldseem to be that of Mallory (1925) who produced the condition experimentallyin sheep. Beijers (1932) described similar symptoms in sheep grazingorchards which had been sprayed with a copper fungicide, and 2 years laterBroughton & Hardy (1934) published their detailed experimentalinvestigations showing the dangers of excessive copper intakes to sheep. Thesimilarity between the symptoms described in these reports and those of‘yellows’ or ‘toxaemic jaundice’ in Australia was recognized (Bull, 1964)and the experiments of Albiston, Bull, Dick & Keast (1940) confirmedthat this naturally-occurring condition was of similar origin. Theimportance of chronic copper poisoning as a nutritional hazard was,therefore, fully established.

Urolithiasis is not at present an important problem for the livestockindustry in the United Kingdom, but the probable introduction of moreintensive systems of management may change this position. The rapidfattening of male animals with high-energy diets predisposes to formation ofphosphatic calculi and obstructive urolithiasis in the feed lot system ofthe USA and it is a form of this type of management which is most likely tobe introduced to this country. For this reason, this review will be limitedto the problem of phosphatic calculus formation, although other calculi,especially siliceous forms cause economic loss in extensive areas of theworld.

Mycotoxins have for long been associated with disease and death in animals,but because of the great variety of fungi present in animal feedstuffs andthe detailed investigations needed to establish a causal relationshipbetween mycotoxin and a clinical disease, few disease syndromes have beenidentified.

In this paper, it is proposed to consider three confirmed clinical diseasescaused by mycotoxins, to review briefly their history and identification andto consider their biological effects in ruminants.

An international group (Advisory Committee on the Application of Science andTechnology to Development, 1968) has stated that ‘The protein gap in thenutrition of the population of our planet is becoming a most importantscientific, technological and health problem and a national andinternational policy issue. The Governments of developing countries shouldmake every effort feasible to supply their populations as quickly aspossible with sufficient high quality food and to develop and apply thenecessary supporting science and technology in the fields of nutrition, foodscience and technology’.

This paper was prepared at very short notice and no written version will bepublished.

The metabolism of the animal is equipped to adapt to changes in both theinternal and the external environment. Among internal factors are activityversus rest and sleep, and the menstrual cycle in the case of the female.Metabolism must also respond to variations in the external environment, suchas heat and cold, and notably the availability of food. Metabolic adaptationto nutrient supply is of two kinds. First, there are transient physiologicaladaptations to the intermittent intake of nutritionally adequate meals.These short-lived adaptations account for a large part of the diurnalvariations that have been observed in the protein metabolism of mammals(Wurtman, 1969). Secondly, long-term adaptive reactions occur when there isa decrease in availability of an essential nutrient in the diet. Under suchcircumstances, tissue constituents are lost to varying degrees fromdifferent parts of the body. It is proposed to discuss here mainlyshort-term physiological adaptations to variations in amino acid supply andtheir relevance to the needs of the body for dietary protein. Adaptivechanges resulting from long-term protein deficiency are considered in thepaper by Waterlow & Stephen (1969).

The earliest estimates of protein requirements, such as those of Smith(1863) and Pavy (1874) who recommended about 125 g per day for the averageworking man, were based on studies of the diets of individuals or of groupsof subjects who were considered to be healthy and leading normal activelives. Such estimates were simply a reflection of the dietary habits ofthose under study, but helped to establish minimum standards of feeding ininstitutions. About the turn of the century, similar recommendations rangingfrom 118 to 150 g were made by Voit (1881), Atwater (1895) and Rubner (1903)(Fig. 1), and these came to be vigorously defended as representing notmerely feeding standards but as irreducible minima below which a properstate of health and vigour could not be maintained.