Influence of iodine on nutritional, metabolic and immunological response of goats fed Leucaena leucocephala leaf meal diet

Abstract

SUMMARYFifteen indigenous nondescript kids (8·2 kg; 8 months initial age), randomly allotted into three equal groups, were used to study the effects of supplementation of extra iodine on their performance when fed a leucaena (Leucaena leucocephala) leaf meal containing diet. Group I (CON) was fed a control concentrate supplement consisting of a conventional protein source whereas the other two groups (LL and LLI) were fed a concentrate containing leucaena leaf meal so as to supply 0·5 of the net crude protein (CP) requirements. Additionally, animals in group LLI were given supplemental iodine (as potassium iodide solution) at 0·25 mg/head/day. Wheat straw was provided ad libitum as the sole source of roughage during the 120 days of the experimental period. A metabolism trial, conducted at the end of the feeding trial, revealed no variation in the dry matter intake (DMI) among the groups. A significant (P<0·01) decline was evident in digestibility of CP in both the leucaena-fed groups (0·463 and 0·482 versus 0·586) whilst that of the other organic components remained unaffected. Animals on the LL diet exhibited lower (P<0·01) nitrogen retention and average daily gain (ADG) in live weight (LW). Blood collected periodically was analysed for the thyroid hormones triiodothyronine (T3) and thyroxine (T4) as well as other biochemical parameters. At the end of the experimental feeding, the cell-mediated immune (CMI) response of the goats was assessed by intra-dermal inoculation of phytohaemagglutinin-P and measuring the change in skin thickness at various post-inoculation hours. The results revealed that the serum concentration of glucose was significantly (P<0·05) higher in the LLI group of animals fed leucaena with iodine. The concentration of cholesterol in serum of LL animals increased significantly (P<0·05) compared to the CON and LLI groups. No variation due to dietary interventions was evident in other indices of metabolic profile. While the concentration of circulating T3 remained unaffected due to dietary intervention, that of T4 reduced significantly (P<0·05) in the LL group. Moreover, the T4 concentration in the LLI group remained similar to that of control indicative of positive impact of iodine supplementation. The immune response revealed that the skin thickness of animals in the LL group was lower (P<0·05) as compared to the control, indicating a compromise of CMI response due to feeding of leucaena leaf meal. Supplementation of iodine appeared to be partially effective in potentiating the response. In conclusion, iodine supplementation could be adopted as a strategic management strategy to ameliorate the negative impacts of feeding leucaena leaf meal in growing kids.