S. Lemosquet et al., EFFECTS OF A DUODENAL GLUCOSE-INFUSION ON THE RELATIONSHIP BETWEEN PLASMA-CONCENTRATIONS OF GLUCOSE AND INSULIN IN DAIRY-COWS, Journal of dairy science, 80(11), 1997, pp. 2854-2865
The effects of duodenal infusion of glucose on the relationship betwee
n plasma concentrations of glucose and insulin and on milk composition
were investigated in a crossover design. Eight dairy cows were contin
ually infused with water (control) or glucose (1.5 kg/d). Cows receive
d diets consisting of dehydrated whole-plant maize in restricted amoun
ts to equalize the energy supply between treatments. Basal (before mea
l) plasma concentrations of glucose and insulin were increased, but co
ncentrations nonesterified fatty acids (NEFA) were decreased, by gluco
se treatment. During the first 2 h after feed distribution, plasma ins
ulin increased, and plasma glucose and NEFA decreased, in both control
and treated cows. Afterward, plasma glucose increased in treated cows
but further decreased in control cows. The difference reached 8 mg/10
0 ml without any change in plasma insulin. During the meal, concentrat
ions of growth hormones in plasma were inhibited to a similar extent i
n both groups. In response to intravenous glucose or insulin challenge
s, changes in plasma glucose, NEFA, and insulin stimulated by glucose
were also very similar in both groups. In conclusion, duodenal infusio
n of glucose increased basal plasma concentrations of glucose and insu
lin, increased postprandial plasma glucose, and decreased NEFA without
inducing insulin resistance. Glucose treatment did not change milk yi
eld but decreased milk fat yield, mainly through a decrease in the yie
ld of C-18 fatty acids that were derived from circulating fatty acids.
In the absence of insulin resistance, the decrease in the yield of C-
18 fatty acids might be attributed to an inhibition of adipose lipolys
is or an increase in adipose lipogenesis.