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The effect of dexamethasone on fibre production and body composition in Angora goats


P R King., P Griessel, P A Schlebusch and B R King

Grootfontein ADI, Middelburg Cape, 5900, South Africa



It is believed that the high fibre production rate of the Angora goat is responsible for the lack of hardiness in this breed. This is probably due to a decreased adrenal function. In sheep, crystalline water-insoluble dexamethasone (a synthetic glucocorticoid) administered sub-cutaneously at a dose rate of 7.7mg/kg0.75 resulted in a 80% decrease in wool growth 77 days after administration. The question arises whether dexamethasone will have a similar effect on mohair production and if so whether the nutrients normally used for mohair growth would be diverted to body reserves in treated animals. A pilot trial was therefore undertaken to establish the effect of these steroids on Angora goats. Six year old Angora wethers were given three dexamethasone injections at 21 day intervals, while six wethers served as a control group. Mohair growth on a tattooed patch, body mass and daily feed intake were determined for a two week period preceding treatment and five consecutive two week periods following treatment of each animal. Following the five two week periods the total nitrogen (N) retention of control and treated animals were determined in metabolic crates. Unfortunately only two treated animals adapted in the crates. Finally two treated and two control animals were slaughtered to determine the fat: protein ratio in the edible part of the carcass. The mean body mass of the treated animals decreased gradually and was 10.9% lower (P < 0.05) than that of the control animals at the end of the eight week experimental period. In the treated group the mean daily feed intake was 9.6% higher for the first four weeks (P > 0.05), approximately the same for the following two weeks and 23% lower than that of the control group for the last two weeks (P = 0.08). Mohair growth in the treated group declined linearly to 9.7% of that of the control group eight weeks following the commencement of treatment. Total N-intake (g/day) and total N excreted in the faeces (g/day) was similar for the two control and two treated animals. The average of 13.956 g N excreted per day in the urine of the treated group was considerably higher than the 9.083 g/day recorded for the control group. Accordingly, the total N-retention of the treated group (4.3104 g/day) was 56.2% lower than that of the control group (9.8325 g/day). The mean fat: protein ratio on a dry basis was 62.05% vs. 37.95% for the control group and 68.63% vs. 31.37% for the treated group. From this limited evidence it appears that dexamethasone influences carbohydrate metabolism, inhibits fibre growth and increases fat deposition.



Proceedings SASAS Congress 1994