Amino Acid requirements for Mohair fibre growth
By Dr Mackie Hobson BSc(Agric),BVSc

1. Nutrition

Angora goats are the most efficient animals in producing fibre. The genotype determines the fibre producing capacity by the number density of the hair follicles.

Fibre production will compete with other tissue for nutrients and fibre growth will change as the nutrient supply changes.

The major limitations for fibre growth are

(1) The amount of amino acid (aa) available and

(2) the composition of the aa

A 40kg Angora goat will produce 79g of ruminal bacteria a day when Sulphur and Phosphorous do not limit bacterial growth. This amount of bacteria will meet all the aa requirements except those aa containing sulphur.

Amino acid imbalance and effect on fibre growth

An  aa imbalance can be created by the addition of aa.

When excess aa is catabolised then all aa metabolism is increased and results in decreased feed intake and resulting decreased growth. Aa imbalance arises by adding 1 or 2 non limiting aa to a low protein diet.

Supplementation with the growth limiting aa enhances appetite.

The initial metabolic response to an aa imbalance is increased protein synthesis by the liver. This decreases the size of the pool of the limiting aa.

Increased aa is not stored but leads to an increased rate of aa metabolism. This results in the accentuation of the limiting aa.

Aa imbalance are thought to decrease keratin production

The effect of methionine on fibre growth

Keratin is rich in Cysteine and a little Methionine. 75% of methionine is converted to cysteine. Studies in demonstrated that supplementation with methionine stimulated mohair growth.

D-methionine can be converted to L-methionine so both promote fibre growth. Effect of methionine on fibre growth is dose related. However excess methionine may depress keratin supplementation due to increased aa metabolism.

Effect of Lysine on fibre growth

Lysine forms component of inner root sheath. Mohair diameter and clean yield was increased with methionine infusions but decreased by Lysine.Mohair length was however increased by the Lysine

An ideal ratio between methionine and lysine is required for optimal fibre growth

Reference/Extracts:

A review of Amino acid requirements for fibre growth of Sheep and angora goats

Qi, Lupton and Owens

Sheep and Goat research Journal 1994