NOCTURNAL PLASMA INSULIN LEVELS IN COWS WITH VARYING LEVELS OF PLASMA KETONE BODIES; RELATIONS TO PLASMA SUGAR AND ACETOACETATE

Abstract

ABSTRACT The interrelations of plasma values of insulin, sugar and acetoacetate (AcAc) have been investigated on nocturnal blood samples from 544 dairy cows at different stages of lactation. A wide range of plasma levels was observed (plasma sugar 42–106 mg/100 ml, insulin 0.3–2.2 ng/ml, AcAc 0.05–27 mg/100 ml). Nocturnal samples were taken to exclude as much as possible variations in plasma components induced by feeding. The following correlations were found: sugar/insulin r = 0.45, P < 0.001; insulin/AcAc r=–0.23 (P <0.001); sugar/AcAc r=–0.61 (P <0.001). The partial correlation between insulin and AcAc was not significant (r = 0.07) when glucose was eliminated. A simultaneous decrease in plasma insulin and sugar was found, hypoglycaemic cows having the lowest insulin levels. It is concluded that this decreased insulin level is probably of importance in facilitating lipolysis during hypoglycaemia, thus being a prerequisite for the development of ketosis. Ten cows were sampled twice, one sample being taken before partus and the other during the 45 first days of lactation. After the onset of lactation indications of a more diabetic metabolism was found. The mean plasma insulin level was reduced from 1.3 to 0.6 ng/ml; a significant fall in plasma sugar and a rise in AcAc was also observed. Nine samples from cows developing ketosis and 23 with elevated AcAc levels, but without clinical symptoms, were compared to 26 samples of cows with low AcAc levels from the same herds and in the same stage of lactation. The mean insulin levels were 0.42, 0.52 and 0.71 ng/ml, and sugar 50.5, 59.5 and 73.6 mg/100 ml, respectively. It is concluded that the low insulin values found in the samples from the ketotic cows were due to reduced glucose stimulation of the pancreatic β-cells.