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Soybean Hulls in Pig Diets Reduce Cost but Hit Carcase Yield

09 May 2013

Finishing pigs fed soybean hulls will have reduced carcase yield and thus lower hot carcase weight, according to new research from Kansas State University.

Soybean hulls were used up to 15 per cent of the diet without affecting growth rate but feed conversion was poorer.

Grinding of the hulls impacted growth negatively in this trial.

The objectives of this research project at Kansas State University were to expand on current limited knowledge of feeding soybean hulls in diets for nursery and finishing pigs, according to J.M. DeRouchey. A series of four experiments were conducted in commercial and university facilities feeding increasing levels of soybean hulls in combination with distillers dried grains with solubles (DDGS) or in reduced particle size form on growth performance, caloric efficiency and carcase characteristics.

In both nursery and finishing diets under both commercial and university settings, feeding up to 15 per cent soybean hulls did not influence average daily gain or average daily feed intake. However, the data showed some inconsistency in results for feed:gain ratio between trials. Since the estimated dietary energy of soybean hull is lower than that of corn, feed efficiency would be expected to decline with increasing dietary levels. However, in the nursery, one study it was unchanged up to 10 per cent of the diet, in another it began to worsen at as little as three per cent, and in the third it was worse for 20 per cent than 10 per cent soybean hulls. In finishing, feed:gain ratio worsened as the level of soybean hulls increased in the diet, which was expected.

One consistent response in both nursery and finishing diets was for improved caloric efficiency on both a metabolisable energy (ME) and net energy (NE) basis as the level of soybean hulls increased in the diet. This means that the book energy values associated with soybean hulls is too low, thus an underestimation of the economic value in swine rations could occur.

In nursery diets when the highest levels of soybean hulls and DDGS are fed together (12 to 15 per cent soybean hulls with 30 per cent DDGS), average daily gain was reduced. While not fully understood, this could be due to lower diet bulk density, reduced diet energy and higher dietary fibre content leading to reduced nutrient digestibility or combinations of the above.

Reducing particle size of the soybean hulls negatively impacted growth performance in both nursery and finishing pigs, This was not anticipated but an important discovery. The data showed that nursery average daily gain and average daily feed intake and finishing feed:gain ratio was poorer when pigs were fed ground soybean hulls than unground. In finishing, this led to worse caloric efficiency, which indicated that the energy value of ground soybean hulls is lower than that of unground. These data suggest that soybean hulls do not respond similarly to cereal grains when fed at a reduced particle size in nursery and finishing pig diets.
Carcase yield was reduced as the level of soybean hulls increased in fishing diets. This data is similar to other research where increasing levels of dietary fibre leads to greater gut fill and an increase in digestive tract tissue weights, thus causing a reduction in carcase yield and hot carcase weight.

Bottom Line

Soybean hulls can be used up to 15 per cent of the diet without affecting average daily gain but feed:gain ratio will be poorer due to a lower diet energy concentration.

Data reveals that current book values of soybean hulls underestimate the actual energy concentration. Thus, more research to accurately determine the ME and NE of soybean hulls is needed to value them correctly in swine diets.

Soybean hulls should not be reground from the original particle size as growth performance was negatively impacted in both nursery and finishing pigs.

Finishing pigs fed soybean hulls will have reduced carcase yield and thus lower hot carcase weight. Therefore, removing or reducing the level prior to marketing should be practised, similar to feeding practices with other fibrous ingredients such as DDGS or wheat middlings.

March 2013

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