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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.

ABSTRACT

Two or three foetal lambs regularly result in a varying degree of carbohydrate shortage in mother ewes in late pregnancy. We have investigated the correlation between plasma insulin, growth hormone and energy substrate concentrations in ewes 8 and 1 weeks before lambing.

Plasma growth hormone was fairly constant (2–3 ng/ml) throughout the 24-h cycle 8 weeks before parturition. Seven weeks later higher average levels and increased diurnal fluctuations were observed in 3 out of 4 multiparous ewes. The average post-absorptive insulin levels were reduced by 50 per cent during the same interval. Simultaneously decreased post-absorptive sugar and increased acetoacetate levels were observed. It is concluded that the hormonal adaptations to the increasing carbohydrate deficit in late pregnancy, especially among multiparous ewes, include:

a) reduced post-absorptive plasma insulin levels,

b) reduced insulin responses to feeding, and

c) increased levels of growth hormone in the plasma.

ABSTRACT

Marked diurnal variations were found in plasma growth hormone (GH), insulin, acetoacetate (AcAc) and sugar in two herds (U and A) of dairy cows kept at two different levels of feeding. Seven animals from each herd were tested. The main diurnal variations were related to food intake, a significant increase in plasma insulin, and a significant decrease in plasma sugar being found. The acetoacetate level rose significantly during feeding in herd U (moderately underfed), while no significant increase was found in herd A (adequately fed). Plasma growth hormone was found to decrease (P < 0.01) only during feeding in herd U, while no change in the GH level could be detected in herd A. The mean level of GH in herd U was found to be twice the value found in herd A. There were no significant differences between the herds in plasma insulin and sugar.

Significant differences in plasma levels of GH, insulin and sugar were found between animals when analysed within the herds. Variations in the levels of insulin and acetoacetate were very small during the night. This is contrary to GH, which shows the least variation during food intake. The correlation coefficient between the plasma components was low, although in many cases significant.

ABSTRACT

The pregnant ewe compensates the reduced carbohydrate availability in late pregnancy by increased fat combustion. The purpose of the present study was to examine the adaptation of plasma growth hormone (GH) and insulin levels to this change in energy substrate metabolism. Two groups of ewes were bled in the post-absorptive state at different stages of pregnancy. One group (7 animals) was fed adequately throughout pregnancy, while the other received a maintenance ration for non-pregnant sheep (28 animals).

Plasma GH increased from averages from 2–3 to 8–14 ng/ml during the last month before lambing. Shearing of the wool combined with a cold stress resulted in a clearly detectable peak in plasma GH in the underfed sheep. No significant difference in plasma GH attributable to differences in diet could be detected in late pregnancy.

Plasma insulin decreased steadily the last 5 weeks towards lambing, most in mothers with 3 lambs. Plasma free fatty acid levels (FFA) increased the last 2 months of pregnancy, most in the underfed sheep. GH and FFA were positively correlated (r = 0.50 and 0.30 in the two groups).

It is concluded that the adaptation of the maternal metabolism to reduced carbohydrate - and eventually energy-availability in late pregnancy included lowering of insulin and enhancement of plasma GH levels. These adaptations were detectable under the present conditions the last 5–6 weeks before term.