The metabolic profile test was designed as a diagnostic aid to show the presence or absence of ‘abnormal’ blood chemistry in dairy herds. The idea was not new. Blood chemistry had been used for many years to assess the metabolic status of individuals and groups of animals but a comparatively recent trend had been to link a number of these analyses together into a single package or multiphasic screening system. Parallel advances in this direction have been made in both human and veterinary fields and progress has been helped by the development of auto-analysers which can carry out several analyses simultaneously at relatively low cost.

Profiles of the blood concentration of the hormones of reproduction during the oestrous cycle and pregnancy have now been described in all farm animals. Advances in this field have been facilitated by the advent of highly sensitive radioimmunoassays of steroid and protein hormones in biological fluids (see Jaffe and Behrman, 1974). This paper summarizes the hormone changes that are normally associated with ovulation, the establishment and maintenance of gestation, and the onset of parturition. Emphasis will be given to progesterone and oestrogen in view of their important role in gestation and because we shall consider later the possible diagnostic or predictive value of their concentrations in the assessment of reproductive performance.

The need to assess the adequacy of nutrition arises frequently. It occurs in relation to individual animals and to groups of animals in both experimental situations and in commercial practice.

The measurement of food intake poses certain difficulties and involves a considerable amount of time and effort, particularly with grazing animals, but also with housed animals which are group–fed. Even where food intakes can be measured, the assessment of the adequacy of that nutrition necessitates a knowledge of the animal's requirements – and this too can present problems in some situations. Changes in live weight and in body condition are obvious and useful indices of the adequacy of nutrition, but in many cases the time taken for such changes to become manifest is too great. By the time an excessive rate of live–weight loss has been detected it may be either too late to effect a change in the level of feeding, or an unacceptable production penalty may have already been incurred.

The economic implications of sub-standard performance in animal production which result from the increased incidence of metabolic disorders such as bovine ketosis and ovine pregnancy toxaemia, and accompanying reduced reproductive performance, plus the detrimental effects of undernutrition, are well known. Together they pinpoint the desirability of being able to assess the adequacy of rations in supplying nutrients, particularly energy, to provide an appropriate diet. The assessment of nutritional status is becoming increasingly important as farmers attempt to maintain enterprise profitability by either reducing feed costs and maintaining production, or by maintaining feed costs and increasing overall production, or by a combination of these two procedures.

This paper will deal with the relevance of calcium, phosphorus and magnesium intakes to the variations which are seen in the plasma levels of these elements in dairy cows during lactation and the dry period.

Calcium

There is to my knowledge no report of any consistent effect of age, milk yield, season or level of calcium intake on the level of calcium in the blood of dairy cows. Changes do, however, take place in the blood level of calcium and it is the factors which influence the extent of such changes which I will discuss, particularly those relating to milk fever.

Many attempts have been made to implicate specific nutritional imbalances and deviations in blood indices with infertility in dairy cattle. Hignett (1959) proposed a relationship between dietary calcium, phosphorus and manganese intakes and found this to be related to fertility. McClure (1968) found that cows with a low plasma glucose concentration were much less likely to conceive than those with a normal level, although other work has not always substantiated this (Blowey, Wood and Davis, 1973). There have been instances where copper and iodine insufficiency have also been associated with infertility problems (Underwood, 1971).

The Compton Metabolic Profile Test was designed to monitor the health of dairy herds, but the possibility is now being investigated of using blood profiles as an aid in the identification of prediction of cows with superior production potential. The problem of determining whether blood profiles can be used in this way, however, is likely to be complex. Even if relationships can be found between individual blood profiles of cows and their current performance, it need not follow that such relationships could be predicted from samples collected earlier in life. Further, although it has been shown that cows maintain individual blood profiles over fairly long periods of time (Kitchenham and Rowlands, 1976) the important characteristic may not be the mean concentration of a blood constituent maintained by a cow, but the ability of a cow to maintain normal concentrations during periods of stress.

The relatively low economic return from enterprises involving suckler cows has required the provision of government subsidies and the exploitation of the physiological capability of beef cows to withstand periods of undernutrition when feed costs are high, and to replenish the loss of body tissues during the grazing season (Ball, Broadbent and Dodsworth, 197l). Progeny from young adult female cattle (heifers) in dairy herds provide a useful and readily available source of suckler cows such as the Hereford x Friesian which has the desirable beef characteristics and the capacity to produce milk during periods of underfeeding.

During lactation, the cow partitions dietary energy between the production of milk and of body tissues. The balance between the two determines whether the cow is primarily a meat producer or a milk producer and the importance of this balance has been emphasized by Broster (1974). Differences between animals in partitioning ability are known to be inherited and are thought to be under endocrine control, but their effects on blood hormone and metabolite levels have not previously been studied. Knowledge and understanding of such differences may permit the early identification of the potentially high-yielding animal for selection purposes and may make possible the manipulation of energy partition towards a desired end.

I am not sure what the organisers had in mind when they selected the title for this talk. To me it suggests that two components may contribute to the concentration of a metabolite - one determined by the flow of nutrients, derived either exogenously or endogenously, while a second is derived from what I propose to call ‘transitory phenomena’, that is, produced from some fleeting or transitory response - stress, human/animal interaction or a response to feeding as distinct from food. Presumably it is the first component which we would hope to relate in some way to animal production, and I propose to begin by seeing to what extent we find a close relation between flow and concentration for several blood constituents. I have used the term ‘flux’ to encompass conveniently what has variously been called ‘entry rate’, ‘turnover rate’ and ‘irreversible’ loss. These terms are not synonymous, but for the present discussion the distinctions are not important.

The main objective when considering dietary energy levels in the dairy cow is to achieve optimum economical milk production, not necessarily energy balance, at all stages of lactation. Some cows may attain energy balance by reducing milk yield.

In the early part of lactation, while appetite is increasing, a negative energy balance is acceptable, particularly in the high-yielding cow, at the expense of body reserves. During this time and up to peak yield, maximum use must be made of the cow's feeding capacity in order to attain its full milking potential. This is important, since the peak yield considerably influences the rest of the lactation, as concluded by Broster (1972).

Failure to achieve a sufficient energy intake in early lactation may be reflected in excessive weight loss as well as in reduced milk production, whereas in the post-peak period, too rapid body-weight gain may be associated with over-generous feeding.

The protein requirements of farm animals cannot be considered in isolation from their energy requirements and studies on changes in blood composition due to changes in protein intake must be made with defined and preferably constant energy intake. Two experiments have been carried out in which groups of permanently housed cattle have been fed individually different levels of dietary protein while all were receiving the energy intakes recommended by the Agricultural Research Council (ARC, 1965).

In the first experiment the basic diet consisted of 6.8 kg hay and 1.8 kg concentrates of either 15.1 per cent digestible crude protein (DCP, high protein) or 6.8 per cent DCP (low protein), fed at 0.4 kg/kg milk produced. The peak milk yield was 13.5 kg/day and at peak yield, the daily metabolizable energy (ME) intake was 130 MJ in both groups. This experiment has been fully reported by Manston, Russel, Dew and Payne (1975).

There are two basic aspects of protein metabolism the measurement of which may assist in improving sheep management, first, the extent to which the daily requirement of the animal is met and secondly, the extent of depletion of body reserves. The need for the latter assessment arises because in some situations in which nutrient requirement and supply are not in phase it is often desirable for economic reasons to utilize the capacity of the animal to deplete and replete its body reserves.

Of the major nutrients, the prediction of energy metabolism from plasma parameters has received most attention. Thus the work of Annison (1960), Reid and Hinks (1962), West and Annison (1964) relating Free Fatty Acid (FFA) concentration to rate of fat mobilization allowed the prediction not only of energy balance but also rate of energy reserve mobilisation in controlled nutritional situations (Russel, Doney and Reid, 1967; Russel and Honey, 1969; Robinson, Fraser and Bennett, 1971).

The object of this paper is to discuss the practical application of blood profiles and the value of blood profiles as an advisory aid in the field. For this purpose, an attempt has been made to quantify the ‘success rate’ of blood profiles on a case study basis. It is hoped that the paper will serve to stimulate discussion by being as objective as possible. It is not presented as an original scientific paper and should not be interpreted as such.

The productivity of the dairy herd is primarily dependent on the metabolic and nutritional status of each dairy cow. All too frequently, there is a tendency for high output demands - milk and calves - to be associated with inadequate feed inputs, resulting in imbalances of body metabolites, which, if sustained, eventually become clinically apparent as ‘production diseases’ such as hypocalcaemia and hypomagnesaemia.

The holding of a symposium concerned with blood profiles was a success and this can be attributed to the degree of frankness with which people have disclosed their hitherto unpublished data and to the valuable discussion which ranged across species and disciplines. Occasionally people have tended to accept the validity of their own data and to question the validity of data from others which apparently leads to conflicting conclusions. In these circumstances it would have been more constructive to attempt to explain why research groups who were studying similar phenomena should obtain dissimilar results.