Weekly blood samples were collected from 42 Friesian cows between 5 weeks before and 10 weeks after calving, and analysed for serum cholesterol, albumin, total protein, glutamate-dehydrogenase, sorbitol-dehydrogenase and ornithine-carbamyl-transferase and blood glucose.Cholesterol concentrations increased 2^-fold during the first 8 weeks of lactation. There was also a transient decrease in glucose concentration at calving, but there was no relationship between conception rate and the concentrations of these two constituents.Albumin concentrations decreased at calving in some but not all cows and remained low for up to 2 weeks. Average concentrations of albumin determined by two analytical methods, a HABA dye-binding and a single radial diffusion assay method, were significantly lower (P < 0-05) between 0 and 2 weeks post-partum in eight cows which required four or more services than in 32 cows which conceived after fewer services. Similarly, the average decrease in concentration over calving was greater in those cows which conceived only after four or more services (P < 001).Globulin concentrations (total protein minus albumin) decreased during the 5 weeks before, and increased in the 3 weeks following calving. The net change over calving was significantly related to conception rate, and the albumin/globulin ratio was reduced (P < 0-001) in the eight cows requiring four or more services.Activities of all three enzymes doubled after calving, but there was no correlation between these increases and the decreases in albumin concentration, suggesting that, if liver insufficiency is a factor, it is probably due to malfunction rather than tissue damage. o r c l o s e t o calving, and have shown that concentrations may not return to pre-calving values until In a study of 351 dairy cows sampled between 2 or 3 months later. Little (1974) showed that the 40 and 100 days post-calving, Rowlands, Little & decrease does not occur in all cows, and concluded Kitchenham (1977) found a negative association that those affected synthesized less albumin. The between serum albumin concentration and both cows in which albumin concentrations decrease milk yield and the number of services required for least at calving, or recover most quickly, are likely conception.to be those with the highest concentrations in early Several authors (Hojovcova, 1966;Little, 1974; lactation. Manston et al. 1975;Rowlands et al. 1975; Szulc, The objectives of the study described Treacher et al. 1976) have noted decreases paper were to ascertain the degree to which indiin serum albumin concentration in dairy cows at vidual cows show such characteristic changes in • Present address: Nuffield Department of Clinical albumin concentration, to test the hypothesis Medicine, John Radcliffe Hospital, Oxford.(Rowlands, 1978) that cows which are better able

SummaryCows were fed either 75 or 100% of the recommended intake levels for protein and 100% of recommended energy levels (Agricultural Research Council, 1965) from 8 weeks pre-calving until 14 weeks post calving. From 14 weeks post calving and to the end of lactation all the cows received 100% of the recommended protein and energy intakes.The mean of the 305-d milk yields of the 2 groups was not significantly different and although cows on the lower protein intake produced less lactose during the first 14 weeks of lactation there was no significant difference in total lactose, fat, protein or total solids production between the groups. In both groups blood packed-cell volume, red cell count and haemoglobin decreased during the first 10 weeks of lactation and then began to increase in the high-protein group. The cows receiving the low-protein diet showed a similar increase only when they received the high-protein ration from 14 weeks post calving. The mean interval from calving to conception was 27·5 weeks in the high-protein group and 20 weeks in the low-protein group.It is concluded that feeding 75% of protein requirements to dairy cows during the first 14 weeks of lactation does not reduce milk yield or quality significantly and probably has no adverse effect on fertility.

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