Soybean hulls have a high nutritive value for ruminants, and they are a highly digestible fibre source: supplementing diets with soybean hulls increases ruminal microflora flow and ruminal fibre digestion. However, soybean hulls do not provide as effective fibre (large particle size) as roughages, and this should be taken into account when replacing forages with soybean hulls (Boggs et al., 1997). Soybean hulls may be used as an energy source to supplement low to medium quality forage based diets, and they can also be used to replace part of the concentrate in the ration. In the USA, soybean hulls are often use to replace hay or maize, during winter in cattle diets (Boyles, 1999).
Lactating dairy cows
Soybean hulls are a highly digestible fibre source that is readily consumed by dairy cows. However, soybean hulls do not provide long fibre and are not a source of fibre as effective as roughages. Several experiments have attempted to define the optimal levels for soybean hulls in different diets (Blasi et al., 2000). Milk production of lactating dairy cows is very variable when soybean hulls are included in the diet (Bateman et al., 2000; Blasi et al., 2000). There are two ways to include soybean hulls in dairy cow diets. They can be used to replace part of the forage, or they can be used as an energy source and replace part of the concentrates.
When soybean hulls replaced a part of the roughage in dairy cow diets, they provided higher energy without causing acidosis that usually occurs with high energy feeds such as maize grain (Blasi et al., 2000). However, depending of the amount, type and physical form of the dietary forage it replaces, the influence of soybean hulls may be positive or negative.
Table 1. Effects of forage replacement by soybean hulls in dairy cow diets
From the results above, it could be concluded that in dairy cow diets containing more than 50% forage the inclusion of soybean hulls could range between 15 and 25% (dietary level, DM basis) and result in higher DM intake and yield higher fat-corrected milk (Blasi et al., 2000). It is generally advised to limit soybean hulls to 25% when it is replacing forages in a diet (Ipharraguerre et al., 2003). Cows in very early lactation (less than 30 days in milk) should probably not be fed soybean hulls since they are prone to displaced abomasum when effective fibre is low (Newkirk, 2010).
When soybean hulls were used to replace energy feed like maize grain, they were safely included in dairy cow diets at up to 40% dietary level without compromising milk yield, fat-corrected milk yield, milk protein or milk lactose. But as for the replacement of forages, caution should be exercised because the response to feeding soybean hulls is largely affected by the type of carbohydrates that is replaced by the hulls (Ipharraguerre et al., 2003). Milk fat increased linearly with increasing content in soybean hulls (Lima et al., 2009; Pedroso et al., 2007; Cunningham et al., 1993).
Table 2. Effects of concentrate replacement by soybean hulls in dairy cow diets:
Dry and gestating cows
Soybean hulls allowed cows to spend winter on stockpiled tall fescue without spending too much hay (281 kg hay were spared per cow) but also reduced weight losses in cows (Kerley et al., 1995). Gestating cows grazing on dormant native range could be fed on soybean hulls rather than on soybean meal. Cows on soybean hulls had higher weight gain than cows on soybean meal (Marston et al., 1992).
Soybean hulls enhance the performance of backgrounded calves placed on grass pastures or grass/clover hay (Boyles, 1999; Allison et al., 1993). Using soybean hulls as a supplement (instead of maize grain) to steers fed on tall fescue (Festuca arundinacea) (or any other low to moderate quality forage) gave similar positive results as maize supplement (about 1 kg daily weight gain) (Boyles, 1999). Many studies are consistent with this result (Galloway et al., 1993; Duff et al., 1993; Anderson et al., 1988; Highfill et al., 1987; Brown et al., 1981). It has been reported that feeding soybean hulls to steers grazing on tall fescue infested by Neotyphodium coenophialum could alleviate health problems due to toxic tall fescue, such as sleek hair coat (Carter et al., 2010). However, these results were not consistent with previous results obtained two years before (Aiken et al., 2008). Holstein steers fed on Bahia grass hay (Paspalum notatum) could be supplemented with soybean hulls (0.75% BW) or soybean hulls and molasses, or soybean hulls, molasses and urea. Cattle receiving soybean hulls had higher average daily gain but also higher urea nitrogen in plasma. The addition of molasses could reduce the urea nitrogen in plasma. Hay intake was not reduced by soybean hulls supplement (Kostenbauder et al., 2007). Fall-weaned steer calves grazing on higher quality forage such as wheat forage had similar performance with soybean hulls as with maize grain. The feed conversion ratio was improved, the stocking rate in pasture increased by 30%, and daily weight gains were 150 g higher (Cravey et al., 1993).
It was shown that supplementing cattle with only 1 kg soybean hulls had the same positive effect on hay intake as supplementing cattle with maize grain in spite of the difference between the two feeds for true digestible nutrients (91% in maize vs. 77% in soybean hulls). This could be attributed to the high digestibility of soybean hulls fibre (Blasi et al., 2000). It is important to notice that the high fermentescibility of soybean hulls may result in some ruminal distension if cattle consume high volumes of hulls (Blasi et al., 2000). When soybean hulls were used as the main ingredient of growing cattle diet, it has been shown that it could favourably compare wih traditional roughage-based diet: it resulted in lower feed intake, slightly lower daily gains and improved feed conversion ratio. When soybean hulls were compared to high-energy based diets fed under restriction (1.5% BW vs. 2.25%) they resulted in higher intake, higher weight gains and better feed conversion ratio (Blasi et al., 2000).
Soybean hulls could successfully replace maize grain in creep calves diets (Faulkner et al., 1994).
It was possible to use soybean hulls in high-concentrate diets for finishing cattle. Soybean hulls could replace 25% of grain sorghum without hindering daily gain or feed efficiency (Coffey et al., 1989). It was suggested that soybean hulls had 74% feeding value of maize grain when it was included at up to 60% (DM basis) in the diet (Ludden et al., 1995).
Lactating ewes fed on soybean hulls and distillers grains that completely replaced hay in the diet had a higher milk production than ewes fed a hay-based diet, but milk fat percentage was lower. Lamb performance was higher for the ewes that produced more milk (Zelinsky et al., 2014b). Soybean hulls were included in order to replace 33, 67, and 100% of the NDF of the hay in the diet of lactating ewes. Feed intake, milk production increased with soybean hulls inclusion (Araujo et al., 2008).
Soybean hulls were used as an energy and fibre source in lamb finishing diets. Lambs had a higher dry matter intake, but also reduced feed efficiency as compared to traditional corn-based diets (Zelinsky et al., 2014a).
In lactating goats, as in lactating cows, soybean hulls is an energy source and can replace maize grain. It could totally replace maize grain in maize silage-soybean based diets offered to lactating goats in early lactation (Zambom et al., 2012). Inclusion of soybean hulls had no negative effects on body weight, daily weight gain, and intake (kg/day) of dry matter, organic matter, crude protein or indigestible neutral detergent fiber. It increased NDF intake and digestibility coefficients and, while no changes were observed in milk yield, milk production efficiency and milk composition, the inclusion of soybean hulls increased the content of n-3 fatty acids in milk (Zambom et al., 2012).