March 5, 2013

Researchers from the University of Illinois, US, are exploring alternatives for pig diets, looking into the amino acid digestibility of rapeseeds, cottonseed meal and sunflower meal, in comparison to soy meal.

Digestibility of amino acids in rapeseed, cottonseed, and sunflower meal is lower than that of soy meal. The main reason for their reduced digestibility is that these products have higher fibre content than soy meal. With the exception of dehulled sunflower meal and soy meal, all of them include hulls.

Professor Hans Stein, the lead researcher, explained, "Soybeans do not contain as much oil as rapeseed and sunflower. When you take more oil out, the seed hull becomes a bigger proportion of what you have left over – and that's where you have all the fibre. So, sunflower is over 50% oil, and rapeseed is about 40% oil. Soybean is only 19% or 20% oil, so you concentrate the fibre more when you produce those meals."

Among the alternative meals, sunflower meal had the greatest values for digestibility of crude protein and the most amino acids. In cottonseed meal, values for most amino acids were the same as, or greater than, those in canola seeds or rapeseed meal.

Rapeseed meal and cottonseed meal contained the greatest concentrations of crude protein and indispensable amino acids after soy meal. Professor Stein said cottonseed is not used as much as it could be in pig production because it contains gossypol, an anti-nutritional factor that prevents pigs from utilising lysine.

"But low gossypol varieties are available now, and it's been shown that if you add enough iron to the diet, it can bind the gossypol, which will then not bind the lysine," he explained. "So you can use some cottonseed in the diets and they'll do fine. Cottonseed meal has a relatively good digestibility compared with canola and sunflower meal, so more of it could be used than is used today."

Stein added that sunflower meal and rapeseed meal need to be significantly less expensive than soy meal before they are an economical alternative as they have reduced amino acid digestibility and a lower concentration of amino acids and energy than soy meal.

The researchers have not determined inclusion rates for rapeseed, cottonseed, and sunflower products. Professor Stein said that this may be the subject of future research.