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Blood samples, taken on 6 occasions during 1 year from 172 cows resident in a dairy herd, were analysed for packed cell volume, blood glucose, haemoglobin (Hb), serum albumin, urea N, total protein, Ca, inorganic phosphate, Mg, Na and K. The data were analysed statistically, firstly with respect to date of sampling, stage of pregnancy or lactation and the interaction between stage of pregnancy or lactation and date of sampling, and secondly with milk yield as an additional factor for the data for lactating cows.Concentrations of all constituents except inorganic phosphate and K varied significantly (P < 0-001) with stage of lactation and/or pregnancy. The most significant changes in concentrations were confined to the periods up to 3 months either side of calving. The greatest changes in concentration during these periods occurred for Mg which rose during late pregnancy and for albumin which fell at or near calving. Albumin, urea and glucose were all, on average, lowest in concentration during the first month of lactation; globulin concentrations showed the reverse trend. Haemoglobin concentrations decreased during late pregnancy and early lactation and were lowest in the period 30-120 d post partum. Calcium concentrations decreased during late pregnancy and rose during early lactation. Sodium concentrations rose during late pregnancy. Interactions between dates of sampling and stages of lactation or pregnancy were significant (P < 0-001) for all constituents, and most marked for glucose, urea, albumin, Hb, Ca and Na.Haemoglobin and K concentrations fell and Mg concentrations rose with increasing milk yield, but the proportions of the total variance accounted for by differences in milk yield were small in relation to those accounted for by stage of lactation. These findings are of significance in relation to the selection of animals for sampling in the Compton Metabolic Profile Test.

SUMMARYBlood samples were taken from groups of lactating and non-lactating cows on three occasions from each of 24 commercial dairy herds sampled eight herds at a time at 6-weekly intervals throughout 1972. The blood samples were analysed for packed cell volume, blood glucose and haemoglobin, and for the serum concentrations of albumin, total protein, urea nitrogen, Ca, inorganic phosphate, Mg, K, Na, Cu, and Fe.Clear seasonal patterns were evident for packed cell volume and the mean concentrations of urea nitrogen and haemoglobin each of which were highest during the summer months. The effect of season on the concentrations of the other constituents was smaller. Mean values of packed cell volume, haemoglobin and Fe were consistently higher in the non-lactating cows than in the lactating cows. Mean concentrations of Mg were lower in the blood of non-lactating cows throughout the year; Cu concentrations followed a similar trend in the autumn and winter.There was evidence of overall herd differences regardless of season, in particular for Cu, globulin, Fe and urea nitrogen concentrations.

Blood samples, taken from each of 231 calves on three occasions at 9,10 and 11 weeks of age, were analysed for packed cell volume, blood glucose and Hb; and serum albumin, urea nitrogen, total protein, Ca, inorganic phosphate, Mg, K, Na and Cu. Differences in the blood composition for individual calves were demonstrated for all blood constituents (P < 0-01) with variations among calves proportionally largest for albumin and smallest for sodium. Concentrations of glucose, Hb and K were inherited (heritability estimates > 0-4).There were significant correlations (P < 0-001) between the calves' growth rates from 1 to 12 weeks and the concentrations of each of the blood constituents, glucose Hb, K, Na, albumin and inorganic phosphate; in the cases of Na and albumin, comparison of the blood analysis at 9-11 weeks with body weights at 6 and 9 months showed that these correlations persisted, and that by 9 months differences in concentrations of Na and albumin among individuals were associated with an average difference of as much as 55 kg in body weight.The evidence that concentrations of certain blood constituents are both inherited and related to growth rate suggests that not only might calves be screened early in life for indications of rapid growth rate, but also that animals might be bred to have the blood characteristics indicative of this quality.