COMPARISONS OF THE EFFECT OF GENOTYPE AND PROTECTED METHIONINE SUPPLEMENTATION ON GROWTH, DIGESTIVE CHARACTERISTICS AND FIBER YIELD IN CASHMERE-YIELDING AND ANGORA-GOATS

Ten Scottish male castrated cashmere-yielding (C) and 10 Angora (A) go ats with initial live weights of 38.2 (C) and 32.1 (A) kg respectively were used in a 112-day study in the time period August to December. T he goats were blocked within genotypes according to live weight and ra ndomly assigned to one of two treatments: either no supplementation (O ) or dietary supplementation (S) with 2.5 g/kg dry matter (DM) intake of rumen-protected intestinally available methionine (Smartamine(TM) M , Rhone Poulenc, Animal Nutrition, Antony 92164, France) in a 2 X 2 fa ctorial arrangement. The goats were offered a basal diet in the propor tion of 0.6, grass hay and 0.4 concentrate according to their live wei ght. Diet metabolizable energy (ME) and crude protein (CP) concentrati on per kg DM were estimated as 9.9 MJ (ME) and 107 g (CP) and DM intak e was restricted to 28 g/kg live weight daily. Apparent digestibility and nitrogen (N) balance studies were conducted from days 24 to 40 and 51 to 64. Measurements were made within three time periods of days 0 to 40, 41 to 75 and 76 to 112. Angora goats excreted less urinary N th an cashmere-yielding gents and had lower values for plasma urea and gl ucose and greater overall retention of N, associated with a two- to th ree-fold greater total fibre yield. Cashmere as a proportion of total fibre by weight, (guard hair plus cashmere) varied from 0.27 to 0.43. The main effects due to methionine supplementation were improvements i n live-weight gain and food conversion ratio. Reductions in urinary N excretion and increases in N retention were recorded, which were gener ally greater for Angora than for cashmere-yielding goats, and were aga in associated with the larger responses in fibre production. Clear evi dence was also obtained for methionine-induced increases in the weight of raw cashmere, although not guard hair tip to day 58. This response was obtained in the absence of significant effects on cashmere diamet er, although methionine supplementation consistently increased the ave rage diameter of mohair fibres.