Possible causes of differences in glucose metabolism between Angora goats of two different phenotypes

Abstract

AbstractPrevious results have shown that certain phenotypes of Angora goat differ in respect of glucose metabolism and it has been proposed that this is linked to the high incidence of abortions in this breed. The aim of this experiment was to investigate adrenal function, food digestion and nutrient partitioning as possible causes of differences in glucose metabolism between a phenotype which produces a relatively large amount of mohair of a large fibre diameter (high producers) and a phenotype which produces less mohair of a smaller fibre diameter (low producers). Two groups consisting of 15 3-year-old Angora bucks each and representing two different phenotypes were given a maintenance diet for the duration of the trial. Plasma glucose concentrations during a 4-day fast were lower (P < 0·01) in high producers than in low producers and plasma glucose concentrations following insulin injection also fell to a greater extent in high producers than in low producers (P < 0·05), indicating that high producers were less able to mantain plasma glucose concentrations during periods of increased demand than low producers. The decrease in glucose concentration following insulin injection was accompanied by a rise in plasma cortisol concentrations until 60 min after the insulin injection but there were no differences between phenotypes (P > 0·05). Similarly, cortisol concentrations rose to a peak 60 min after ACTH injection and there were no differences between phenotypes (P > 0·05). In both instances, the pattern of cortisol concentrations was consistent with normal adrenal function and there were no indications of adrenal insufficiency. Although differences in digestion were observed between phenotypes (P < 0·01), these were small. There were no differences in nitrogen (N) intake or retention (P > 0·05). High producers deposited substantially more (proportionately 0·56) N as fleece than low producers (P < 0·01), and partitioned a greater proportion of N intake to fleece production (P < 0·01). It was concluded that adrenal insufficiency was not implicated in the observed differences in glucose metabolism between phenotypes but differences in digestibility and nutrient partitioning may play a role.