Mammary metabolism in the goat during normal or hormonally-induced lactation

Abstract

( 5 ) Station de Nutrition, I. N. R.A., 78350Jouy-en-Josas.Summary. Mammary metabolism was studied in 4 normal lactating goats (group N) and in 4 non-pregnant goats induced to lactate by hormonal treatment (group 1). Tissue was sampled by biopsy after 3, 9 and 18 weeks of lactation. Although milk potential was the same in both groups, group I produced 45 % less milk than group N.The RNA/DNA ratio, activities of lipoprotein lipase (LPL1, glucose-6-phosphate dehydrogenase and acetyl-CoA carboxylase, and the /3-casein % of in vitro protein synthesis were not significantly lower in the I than in the N goat mammary tissue. This suggests that differences in mammary cell hyperplasia during hormonal treatment, and not potential metabolic activities, partially accounted for the difference in milk yield levels.Milk composition was comparable in the two groups. However, milk fat in group N had a higher long-chain fatty acid content (stearic and oleic acids) during the first month of lactation due to the higher mobilization of body lipids in high-yielding animals. Another qualitative difference was the delayed increase in milk LPL secretion during the first 3 months of lactation in induced goats.Introduction.

Hormonal induced lactation in transgenic goats

“…This finding agrees with a number of other studies (Mellado, 1995;Chilliard, 1986;Narendran, 1974;Aldeen, 1980). However, the effect of the shortened lactation time in this study on the composition of milk can not be determined.…”

“…The ability to evaluate the metabolic activity of the gland during natural and hormonal induction of lactation has been reported (Chilliard, 1986). Milk compositions during natural and hormonally induced lactations have also been reported (Ryot, 1990).…”

Ruminant milk fat plasticity: nutritional control of saturated, polyunsaturated, trans and conjugated fatty acids

“…Furthermore, the proportion of C4:0, C6:0 and C8:0-FA was hardly changed by the addition of protected fat or by the duodenal infusion of fat (see also [41,55]). This is in agreement with the observation that body fat mobilisation increased C18:0 and C18:1 in milk fat at the expense of C10:0 to C16:0-FA without significantly decreasing the C4:0 to C8:0-FA [22,30,43,135]. These last mentioned FA are synthesised in part by non-malonyl CoA mechanisms, i.e.…”

“…Thus, when long-chain FA are available either from the diet, or from body fat mobilisation, there is a decrease in the percentage of medium-chain FA (C8:0 to C14:0 or C16:0) in milk fat (e.g. Chilliard et al [30,31]). This is due to both a higher secretion of long-chain FA from the blood (dilution effect), and a lower de novo synthesis of FA.…”

“…However, as in rodents, LPL activity is high in the lactating mammary gland of ruminants (e.g. Chilliard et al [30]). Consequently, the mammary gland uptake of triglycerides is generally well correlated to their plasma concentration [62], except in the higher range of concentrations (above ca.…”