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The influence of growth related hormones on mohair production

P R King. and P A Schlebusch

Grootfontein ADI, Middelburg Cape, 5900, South Africa


Angora kids are renowned for their poor growth rate, especially from weaning up to 18 months of age. These kids, however, produce considerably more fibre per metabolic mass during this period when compared to other fibre producing species. If mohair production could be decreased during this period, it may be expected that the available nutrients would be utilised for body growth instead. Accordingly an investigation was undertaken to determine whether hormones which influence body growth, also affect mohair growth. Groups of weaned Angora kids were given one of the following treatments: zeranol implants (Ralgro, 12 mg) administered at two-monthly intervals, bovine somatotropin (BST) injections (125 mg) fortnightly, testosterone propionate implants (24 mg) at two-monthly intervals and a group was thyroidectomized. A control group was run with each treatment. Experimental animals received a ration consisting of milled lucerne hay only. Mohair growth, body mass and horn growth of each experimental animal were recorded at regular intervals while the mean daily feed intake per animal was determined on a group basis. Mean mohair growth, average daily gain (ADG), daily feed intake and mean horn growth of the BST and zeranol treated groups did not differ from that of their respective control groups. Over a six-month experimental period the testosterone propionate treated group had a 39.3% higher ADG (P < 0.01), 11.9% higher feed intake and produced 19.8% (P < 0.05) less mohair per metabolic mass than the control group. Mean horn diameter at the base was 15.8% thicker (P < 0.05) and mean horn length 22.8% longer (P < 0.05) than that of the control group. Mean daily feed intake, ADG and mohair production of the thyroidectomized group were 38%, 41.9% (P > 0.05) and 34.3% (P < 0.01) respectively lower than that recorded for the control group. The removal of the thyroid gland did not influence horn growth significantly (P > 0.05). It therefore appears that hormones having a substantial effect on protein metabolism in general influence mohair and body growth similarly. Testosterone, however, which has a anabolic effect on specific tissues most probably influences mohair and body growth differently.



Proceedings 33rd SASAS congress