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’.

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.

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.

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.

Before considering the various possible protein sources, we must make somesort of estimate of the possible protein need by—say—the end of the century.That estimate controls the amount of effort we should put into work onprotein supplies and the degree of novelty that we should envisage. Theestimate depends on the number of people to be fed and the amount of proteinthat each needs. Both quantities are uncertain: the first because it must beguessed, the second because it is hotly disputed.

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.

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).