Soybean hulls have a high nutritive value for ruminants, and they are a highly digestible fibre source: supplementing diets with soybean hulls increases rumen microflora flow and rumen 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 used to replace hay or maize in cattle diets during winter (Boyles, 1999).
Dairy cows
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 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 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 on 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
Control diet (% DM) |
Soybean hulls level (% DM) |
DM intake variation (kg/day) |
Fat-corrected milk variation (kg/day) |
FCM/DMI |
Reference |
43.2% forage (alfalfa hay + maize silage) |
4.6 |
0.4 |
-0.2 |
1.16 |
Sarwar et al., 1992 |
43.2% forage (alfalfa hay + maize silage) |
9.1 |
0 |
1 |
1.23 |
Sarwar et al., 1992 |
50% forage |
12.5 |
-0.6 |
-0.6 |
1.4 |
Cunningham et al., 1993 |
50% forage |
25 |
-1.8 |
-1.8 |
1.5 |
Cunningham et al., 1993 |
52.6% forage (alfalfa haylage + maize silage) |
14.1 |
|
4 |
|
Stone et al., 1993 cited by Blasi et al., 2000 |
50% forage (alfalfa haylage + maize silage) |
15 |
-0.66 |
-2 |
|
Weidner et al., 1994a |
50% forage (alfalfa haylage + maize silage) |
15 |
-0.84 |
-5.5 |
|
Weidner et al., 1994a |
50% forage (alfalfa haylage + maize silage) |
25 |
0.02 |
-2.4 |
|
Weidner et al., 1994a |
50% forage (alfalfa haylage + maize silage) |
25 |
2.65 |
1.6 |
|
Weidner et al., 1994a |
From the results above, it could be concluded that in diets for dairy cows containing more than 50% forage the inclusion of soybean hulls could range between 15 and 25% (of the diet DM) and result in higher DM intake and an increased yield of fat-corrected milk (Blasi et al., 2000). It is generally advised to limit soybean hulls to 25% when they are 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 amounts of soybean hulls in the diet (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 too much expenditure on hay (281 kg hay were spared per cow). Weight loss in cows was also reduced (Kerley et al., 1995). Gestating cows grazing on dormant native range were fed on soybean hulls rather than on soybean meal. The cows fed soybean hulls had higher weight gains than those fed soybean meal (Marston et al., 1992).
Beef cattle
Growing cattle
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 forage of low to moderate quality) gave similar positive results as a maize supplement (about 1 kg daily weight gain) (Boyles, 1999). Many studies confirm 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 can 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 earlier (Aiken et al., 2008). Holstein steers fed on Bahia grass hay (Paspalum notatum) were supplemented with soybean hulls (0.75% BW) or soybean hulls and molasses, or soybean hulls, molasses and urea. Cattle receiving soybean hulls had higher daily gains. They also had higher urea nitrogen in their blood plasma, which was reduced by the addition of molasses. Hay intake was not reduced by soybean hulls supplementation (Kostenbauder et al., 2007). Fall-weaned steer calves grazing on higher quality forage, such as wheat forage, gave similar responses with soybean hulls as with maize grain. The feed conversion ratio was improved, the stocking rate on 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 the fibre in soybean hulls (Blasi et al., 2000). It is important to notice that the high fermentability of soybean hulls may result in some rumen distension if cattle consume large quantities of the hulls (Blasi et al., 2000). When soybean hulls were used as the main ingredient in a diet for growing cattle, it compared favourably with a traditional roughage-based diet, resulting in lower feed intake, slightly lower daily gains and an improved feed conversion ratio. When soybean hulls were compared to high-energy based diets fed at a fixed rate (1.5% BW vs. 2.25%), they resulted in higher intake, higher weight gains and better feed conversion ratios (Blasi et al., 2000).
Soybean hulls successfully replaced maize grain in creep calf diets (Faulkner et al., 1994).
Finishing cattle
It was possible to use soybean hulls in high-concentrate diets for finishing cattle. Soybean hulls replaced 25% of grain sorghum without changes in daily gain or feed efficiency (Coffey et al., 1989). It was suggested that soybean hulls had 74% of the feeding value of maize grain when it was included at up to 60% (DM basis) in the diet (Ludden et al., 1995).
Sheep
Dairy ewes
Lactating ewes fed on soybean hulls and distillers grains, completely replacing 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). When soybean hulls were included in order to replace 33, 67, and 100% of the NDF of the hay in lactating ewe diets, feed intake and milk production increased (Araujo et al., 2008).
Growing lambs
Soybean hulls were used as an energy and fibre source in lamb finishing diets. Lambs had a higher dry matter intake, but also a reduced feed efficiency, compared to traditional corn-based diets (Zelinsky et al., 2014a).
Goats
In lactating goats, as in lactating cows, soybean hulls are an energy source that can replace maize grain. They totally replaced 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 NDF. They 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).