Effect of growth hormone and IGF-I on fiber growth in Angora goats

R. Puchala, S. G. Pierzynowski, T. Wuliji, A. L. Goetsch, I. Prieto, T. Sahlu, and M. Lachica

E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK

The effect of bST and IGF-I on mohair growth in Angora goats was investigated. In experiment 1, sixteen Angora goats (5 mo old; 16 ± 0.5 kg initial BW) were used to evaluate two levels of recombinant bST (0 and 100 g/d). The bST was a slow release zinc-based suspension designed to sustain delivery of bST over a 14-d period. The experiment consisted of a 2-wk pre-treatment period and 8-wk of bST treatment. Goats were given ad libitum access to a mixed diet (15.0% CP; 2.34 Mcal/kg ME; DM basis) and were individually housed in raised, indoor stalls under ambient lighting. Increased plasma IGF-I (P <0.01) was observed in the bST-treated group (1,080 ng/ml compared with the control group (78 ng/ml). Average daily gain increased (P < 0.05) in bST-treated animals (80.9 vs. 63.3 g/d in control group). Mohair production was similar in both groups (0.10 g/100 cm²/d). In experiment 2, six Angora wethers (22 ± 2 kg initial BW) were implanted bilaterally with silicon catheters into the superficial branches of the deep circumflex iliac artery and vein. The area that was supplied by arterial catheter was approximately 300 cm². For 14 d animals were infused into deep circumflex iliac arteries with either IGF-I (1.7 g/h in 2.4 ml of saline; experimental side) or saline (control side). IGF-I infusion increased the concentration of several essential amino acids in the venous blood of the perfused site, suggesting decreased uptake. The lack of effect of bST on mohair growth is probably due to a lack of anabolic effect on skin tissue of bST/IGF-I with increased nutrient availability to muscle and decreased availability to skin.