The straw bit is true, not sure about the chemicals but really you can call a lot of things 'chemicals' that are perfectly harmless really
There were a couple of posts on Saddle Up a while ago listing the ingredients:
40% straw fibre, 10-25% unmollassed beet, <10% oat fibre, expelled linseed, grass meal...expelled soya. Plus a few vitamins and minerals etc.
NUTRITIONAL ANALYSIS:
Oil 2.5 % Vitamin A 10,000 IU/kg
Protein 8.5% Vitamin D 1500 IU/kg
Fibre 27.0 % Vitamin E 100 IU/kg
Estimated DE 8.0 MJ/kg Calcium 1.1%
Starch 5.0 % VERY LOW Phosphorous 0.4%
Sugar 2.0 % LOW Copper 7 mg/kg
INGREDIENTS:
Cereal Straw - Fibre source provides Fibre for a healthy gut and to satisfy appetite without excess calories
Unmolassed Sugar Beet - highly digestible fibre, slow-release energy source.
Grass - protein & Fibre source.
Oat fibre - digestible Fibre source
Linseed - provides a concentrated source of calories, and omega –3 oils for a healthy skin, and a glossy coat
Limestone flour - calcium source.
Soya oil -provides a concentrated source of calories, and omega –6 oils for a healthy skin, and a glossy coat
Salt - provides essential electrolytes
Vitamins and Minerals - the vitamin & mineral supplement in these feeds provides Vitamin A, Vitamin D3, Vitamin E, Copper, Selenium, Vitamin K, Folic Acid, Nicotinic Acid, Pantothenic Acid, Vitamins B1, B2, B6, B12 , Biotin, Iodine, Cobalt, Iron, Manganese, Zinc, Calcium and Magnesium.
Mint - has a natural pre-biotic effect, creating the right environment for bacteria to grow
Yeast - supplies a natural bio-available source of vitamins
Fenugreek - very palatable and stimulates appetite
Garlic - rich in sulphur, aids digestion by supporting the development of
natural gut flora, whilst killing pathogens