Two groups of nine British Friesian cows were fed from about 32 weeks before calving to achieve condition scores at calving of 2-5 (thin) and 4 (fat). For 10 weeks after calving all cows were offered 7 kg hay daily in four feeds, with concentrates given five times daily according to appetite.During early lactation, the group of fat cows had lower dry-matter intakes and daily milk yields and yielded less milk protein and lactose than the group of thin cows. The mean yield of milk over the whole lactation was 500 kg less in the fat cows but the difference was not significant. The fat cows lost 48 kg body weight and 1-20 units condition score during early lactation compared with 27 kg body weight and 0-52 units condition score in the thin cows. No difference in reproductive performance was found between the two groups but significantly more cases of disease occurred in the fat cows than in the thin cows.It is concluded that cows that are fat at calving eat less than thin cows, give the same or less milk than thin cows, mobolize more body tissue and lose more weight after calving than thin cows and suffer more disease.

A survey of the incidence and severity of post-parturient fatty liver in high yielding dairy cows was carried out on 151 cows and 46 heifers from four Friesian herds and one Guernsey herd. In Friesian and Guernsey cows from the second lactation onwards fat occupied a significant proportion (15 to 32 per cent) of the hepatic parenchyma at one week after calving but decreased to low values at eight weeks after calving. Fatty liver was insignificant in heifers of either breed. When the fatty liver was classified according to the amount of fat at one week after calving, 66 per cent of Friesian cows and 33 per cent of Guernsey cows had a moderate or severe fatty liver. The severity of the fatty liver was related to the loss of condition score after calving but not the condition score at calving.

An experiment was performed with two groups of nine British Friesian cows to compare the effect of calving in fat or thin condition on (1) the mobilization and functional activity of subcutaneous adipose tissue, (2) the mobilization of skeletal muscle, (3) the development and resolution of fatty infiltration of the liver and (4) the chemistry and haematology of blood. Sampling was performed at various times during the dry period and subsequent lactation. There were no differences between groups in the amount of adipose tissue mobilized between 4 weeks before and 26 weeks after calving. The lipogenic and lipolytic capacities of isolated adipocytes were also not different between groups at any time although major changes occurred in both over the calving period and during early lactation. Acetate oxidation to carbon dioxide was higher in adipocytes isolated from thin cows particularly after calving. More muscle fibre area was lost in the fat cows compared with the thin cows between 4 weeks before and 4 weeks after calving and the fat cows had greater infiltration of fat in the liver at 1 and 4 weeks after calving than the thin cows. The mean white-cell count was lower and the packed-cell volume was higher in the fat cows than in the thin cows at 1 week after calving. The major differences between groups in blood composition were increased concentrations of copper, non-esterified fatty acids, bilirubin and enzymes such as ornithine carbamyl transferase in the fat cows after calving. These results suggest that fat and thin cows respond differently to the metabolic demands of early lactation and that some of these differences render fat cows more susceptible to disease.

High yielding dairy cows undergo a period of energy deficit in early lactation and mobilise body reserves for milk production. In this period a high proportion of cows develop moderate or severe fatty liver. Fat is deposited in other tissues at the same time, particularly skeletal muscle. The relationship between measurements of fat mobilisation and fat deposition in liver and muscle has been investigated in a group of 19 cows in the post calving period. Cows with higher levels of indices of mobilisation, namely plasma free fatty acid and D(--) -3- hydroxybutyrate concentration and subcutaneous adipose tissue loss, had higher indices of fat deposition in liver and skeletal muscle. Statistical analysis of the data indicated that fatty liver was part of a more general fat mobilisation syndrome which was not specific to any one organ or tissue.

No abstract