Genetics and handling around slaughter contribute to meat quality, and nutrition does as well to a lesser extent. Great nutrition will not be able to overcome poor genetics or handling, and nutritional research on meat quality is variable likely due to the other two factors. Meat quality is subjective can be assessed by various measures, but carcass characteristics are typically used. Leanness and fat characteristics, such as firmness, type and colour, are often used to evaluate carcass characteristics. Feed withdrawal up to 24 hours before slaughter can reduce risk of meat contamination during processing, and improve meat colour and pH. Adding vitamin E to diets can result in darker, more stable colour and reduce drip loss and fat oxidation, but requires high concentrations to do so. Vitamin D does not affect tenderness or subjective colour. Vitamin C may be able to improve meat colour and drip loss, but increases fat oxidation. Magnesium, iron, and manganese supplementation have all shown variable results. Niacin studies are limited, but it may be able to improve colour, pH, and drip loss. Creatine also has shown variable results. Ractopamine increases carcass leanness, and carnitine could enhance protein deposition and increase meat quality when used along with ractopamine.