Effect of iodine level in mustard (Brassica juncea) cake-based concentrate supplement on nutrient utilisation and serum thyroid hormones of goats.

To assess the influence of dietary iodine (I) supplementation on nutritional performance and serum thyroid hormones of goats, 12 adult Barbari goats (average weight 18.8kg) were assigned randomly to three dietary treatments. The goats were fed a mustard (Brassica juncea) cake containing concentrate supplement along with either 0mg (control, I(0)), 0.050mg (I(50)), or 0.075mg (I(75)) I per animal per day for 180 days. Oat hay was given ad libitum as basal roughage. There was no difference in intake and digestibility of various nutrients or N retention among the three groups in a metabolism trial after 90 days of experimental feeding. A second metabolism trial conducted at 165 days post-feeding revealed that daily intake of DM, DCP and ME were 39.9, 41.1 and 44.8g, 2.64, 3.01 and 2.97g, and 366, 414 and 415kJ per unit metabolic body size, respectively, for the I(0), I(50) and I(75) groups. Retention of N by goats was 1.75, 2.58 and 2.56g per day (P>0.05) for the three groups, but one of the control animal was in negative balance. Mean live weight of I(75) animals was higher (P<0.05) at the end of the experimental feeding period with net live weight gains of 2.6, 4.8 and 5.4kg for the three groups. Mean serum concentration of triiodothyronine was 1.20, 1.23 and 1.65ngml(-1), being significantly higher in I(75) group. Mean level of thyroxine was 18.3, 24.9 and 27.4ngml(-1), significantly (P<0.05) higher in both I-supplemented groups. It is concluded that supplementing I at the tested levels positively influenced the live weight gain of goats with no significant impact on the utilisation of nutrients. Serum thyroid hormones also increased in response to I supplementation.