Soyhulls: the "almost perfect" feed
Soyhulls are the "almost perfect" feed. Depending upon price and availability, they can replace some (most or all) of the hay or grain in the diets of sheep, goats, and other livestock. Soyhulls are the ideal supplement for ruminants consuming low to moderate quality forages. Most producers are probably already feeding some soyhulls, as soyhulls are a common ingredient in commercial feeds.
Soybean hulls, or soyhulls as they are more commonly called, are the outer seed coat of the soybean (Glycine max). They make up approximately 8% of the bean [19]. Soyhulls are a by-product of soybean processing for meal and oil. They are removed during processing and either blended back with the meal to produce 44 percent soybean meal, or they are used as a feedstuff or ingredient in rations for livestock [19].
Soyhulls work best when they are pelleted or mixed with other feeds, as they are a bulky, dusty feed. Pelleted soyhulls have a higher bulk density and are easier to transport and store than unpelleted hulls. They are equal nutritionally [10]. Soyhulls can be stored for an extended period of time in an upright bin or open-fronted trench.
Soyhulls are palatable to different livestock. There is some risk of choking when animals eat too fast [13]. It is recommended that you not intervene if an animal is choking, as the animal will relieve the obstruction on it own [13]. The risk of choking can be minimized by mixing the hulls with other feeds or by top-dressing them with other feeds. Feeding soyhulls when the animals are "full" is another option.
Nutrient composition
The National Research Council (NRC) Nutrient Requirements of Small Ruminants gives the dry matter composition of soyhulls as 77 percent total digestible nutrients (TDN), 13 percent crude protein (CP), 0.55 percent calcium (Ca) and 0.17 percent phosphorus (P) [9]. Soyhulls have a similar nutrient composition as oats and ear corn, but with a more desirable ratio of calcium to phosphorus and more copper.
As with other by-product feeds, nutrient composition can vary considerably [10]. In fact, Kansas State University calls book values "almost meaningless" [10], as the nutrient composition of soyhulls differs according to source and diet composition. For this reason, it is recommended that each batch of soyhulls be analyzed to determine its specific nutrient composition.
Copper
According to various analyses, soyhulls contain about 17 parts per million (ppm) of copper [8]. This is more than most traditional feedstuffs, which usually contain 8 to 12 ppm of copper [8]. For sheep, the maximum tolerable level of copper is 15 ppm for diets containing “normal” levels of molybdenum and sulfur [8]. Soyhulls will likely raise the copper content of the ration by about 2 ppm (8]. On some farms, this could increase the risk of copper toxicity. However, sufficient molybdenum in the diet should prevent problems.
Energy feed
Soyhulls can be a decent source of protein, but are a poor source of rumen by-pass protein (3.5%) [9]. They are classified as an energy feed. However, in contrast with grains (the primary energy feeds), the energy in soyhulls comes from highly digestible fiber. Soyhulls are high in NDF (neutral detergent fiber) and low in starch. The bacteria that digest starchy feeds (e.g. corn and barley) are different from those that digest fibrous feeds. They are insensitive to acididy. Starchy feeds increase acidity in the rumen and can cause acidosis. Using soyhulls as an energy source reduces the risk of acidosis as compared to grain.
Effective fiber
On the other hand, soyhulls are not a good source of roughage or “effective fiber.” Diets deficient in effective fiber can have a detrimental effect on rumen health. The effectiveness of fiber in supporting rumen health is related to particle size. A high level of fiber in the diet does not guarantee that the diet is adequate in effective fiber. If the fiber is chopped or ground too short or fine, it may not be effective at promoting rumen health. This is the case with soyhulls. They are high in digestible fiber, but due to their small particle size, they are low in effective fiber. For this reason, it is usually recommended that adequate long-stemmed forage (fiber) be included in the diet.
Passage rate
Soyhulls have a high rate of passage through the digestive tract, decreasing the time for digestion. This usually results in an increased intake of dry matter, which may negatively affect digestibilty and feed efficiency. Limiting intake or adding a source of long fibrous hay may minimize the effect. Adding long fibrous hay contributes to the ruminal mat. The rumen mat acts as a filter and plays an important role in ruminant nutrition.
Research
Soyhulls have been successfully fed to many types and classes of livestock. Researchers have determined soyhulls to be equal to corn as an energy source when fed to beef cattle (cows and calves) grazing low to moderate quality forages [10,19]. When hay is expensive or in short supply, soyhulls can substitute for part of the hay or silage in a cow’s diet. However, as part of a high-concentrate diet, increasing levels of soyhulls have been associated with reduced performance in finishing cattle [10, 19].
Soyhulls can also replace corn as a creep feed source for calves [10]. If soyhulls are used as a creep feed, their intake should be limited to 1 percent of bodyweight, to force calves to eat more lower quality forage and slow the rate of passage and improve the utilization of the soyhullsl [19].
Soyhulls are utilized in diets for dairy cattle as partial replacements for forage and concentrate. As long as the effective fiber is high enough, soyhulls can serve as a source of energy in the diets of high-producing, early lactating dairy cows. Data from several studies has shown that soyhulls can comprise up to 20 to 25 percent of the diet of lactating cows [10, 19]. When diets contain less than 50 percent forage, soyhulls should not comprise more than 10 percent of the diet [10, 19]. In beef and dairy cattle studies, recommendations are to limit soyhulls to 40 percent of dry matter intake, to reduce the risk of bloat [10].
Non-ruminants
Ruminants aren’t the only livestock that can be fed soyhulls. Soyhulls can replace up to 75 percent of the forage in the diets of horses [11]. Lesser amounts of soyhulls can be fed to rabbits (another hindgut fermenter), as they are less efficient at utilizing the fiber in soyhulls. Researchers were able to replace up to 27 percent of the alfalfa hay in the diet of fattening rabbits [14]. Lactating does tolerated up to 32.5% of soyhulls in the diet, when it was fed in combination with grape seed meal [14].
Soyhulls are not typically fed to swine, since pigs are a monogastric and not able to efficiently utilize fiber. However, including soyhulls in the diet of pregnant sows increases the bulk density of the ration, allowing the sow to eat more, without increasing her intake of energy [18]. The increased gut fill satiates the sow’s appetite and makes her calmer [18]. The inclusion of 10 percent soyhulls with supplemental fat in the diets of growing/finishing pigs may offer environmental advantages (manure composition and air quality), without compromising the performance or carcass traits of pigs [6].
Sheep
Much of the research evaluating soyhulls as a feedstuff for sheep has been done at South Dakota State University, where soyhulls have been successfully fed to both ewes and lambs, often in combination with DDGS (dried distiller's grains with solubles). In one study, non-pregnant ewes were fed 4 lbs. of soyhulls and 1 lb. of long-stemmed alfalfa hay, with no ill effects [19]. In another study, researchers were able replace all of the hay in the diet of lactating ewes with soyhulls and DDGS. Milk production was higher in the ewes fed soyhulls and DDGS, as compared to the ewes fed a more traditional hay-based diet; however milk fat percentage was lower [1]. Lamb performance was higher in the ewes that produced more milk [1].
Soyhulls have also been use as an energy and fiber source in lambing finishing diets. In most studies in which lambs have been fed soyhull-based diets, there has been a higher dry matter intake and reduced feed efficiency as compared to traditional corn-based diets. The increased dry matter intake is due to the high passage rate of soyhulls through the rumen. The lower feed efficiency means that soyhulls have to be lower in cost than corn (or barley) to justify their use in lamb finishing diets.
As compared to diets in which hay was the fiber source, soyhull-based diets may result in a lower rumen pH. A rumen pH below 5.5 is considered to be the treshhold for risk of acidosis [1]. In the absence of clinical acidosis, a lower rumen pH may reduce feed intake and efficiency.. As for copper, lambs fed soyhull-based diets have been shown to have higher concentrations of copper in their livers, but levels have been below the levels considered to be toxic, and no copper toxicity has been observed in research lambs [1].
Researchers at Virginia State University are currently evaluating soyhulls as a supplemental feed source for hair sheep lambs consuming forage-based diets. In two pen-feeding trials in which orchardgrass served as the forage source, intake and growth rate of hair sheep lambs increased linearly as supplemental feeding of soyhulls increased from 0 to 3 percent of body weight [17]. Grazing lambs supplemented with soyhulls grew faster than those supplemented with cracked corn at 2% of bodyweight [17]. Soyhull supplementation improved growth rates of lambs by 80 percent as compared to those grazing pasture only [17]. In another study with hair and hair x wool lambs, soyhull supplementation improved the color and texture of the meat [3]
Dairy females
In Israel, dairy ewes fed pellets containing soyhulls (as a starch replacer), had a higher DM and NDF intake than the controls [15]. They had a significantly higher milk yield and milk fat content than ewes fed the more traditional diet [15]. Similar results were obtained in a small study with dairy goats [15]. In Brazil, researchers concluded that soyhulls can replace ground corn in diets for Saanen does in early lactation, because soyhulls improve digestablity of the diet and do not change productive performance or milk quality [12]. The soyhull diets also increased the content of n-3 fatty acids in the milk [12].
Meat goats
Researchers at North Carolina State University found soyhulls and other fibrous feeds to be suitable feed ingredients for meat goats, when fed at 1 percent of body weight, along with orchardgrass hay [2]. In Kentucky, meat goats produced more economical gains when fed rations containing by-product feeds, including soyhulls [7]. Researchers at Kansas State University also determined soyhulls to be a viable alternative feed source for meat goat kids, when protein requirements were met and hay was offered ad libitum [4]. In a study comparing corn and soyhull-based pelleted diets, no differences were observed in average daily again and blood serum mineral composition; however (similar to lamb studies), dry matter intake was higher for the goats consuming the soyhull diet [4].
In the 2015, Western Maryland Pasture-Based Meat Goat Performance Test, supplementation with soyhulls (1 lb. per head per day) seemed to improve resilience to internal parasites, as evidenced by high fecal egg counts, but lack of clinical parasitism. Soyhulls may be less beneficial as a supplement when forage quality is high.
Feeding soyhulls
In a feeding program for small ruminants, there are two primary uses of soyhulls: 1) as an energy supplement for animals consuming low to moderate quality forage; and 2) as a replacement for some (most or all) of the hay or grain in the diet of ewes, does, lambs, and/or kids.
As a supplement
The most natural use of soyhulls is as an energy supplement for sheep and/or goats grazing low to moderate quality pasture or consuming similar quality harvested forages. The primary reason to supplement forage-fed animals is to improve performance. Pasture diets are often deficient in energy. Supplemenation may also improve body condition and resilience to internal parasites (worms). Researchers have determined that soyhulls can replace corn as an energy source on a one-to-one basis [10, 19]. If the pasture is low in protein, supplementing with a highly digestible source of fiber may improve forage utilization [19].
If a grassfed designation is required (or desired), soyhulls can be supplemented to grazing animals. The USDA grassfed marketing claim allows supplementation with soyhulls and other fibrous feedstuffs [16]. So long as the animals have access to pasture, there is no limit as to how much soyhulls the livestock can consume. Self-feeding of soyhulls and similar feedstuffs is permissible. If fact, this is a common practice in some pasture finishing operations for beef and sheep.
As a supplement to forage-fed sheep and goats, soyhulls may or may not be more economical as compared to other feedstuffs (or to no supplementation). The economic viability will vary by season, year, farm, and cost and availability of other feedstuffs.
As a replacement
For other small ruminant enterprises, the best use of soyhulls may be as a replacement for some (most or all) of the grain or forage in the diet. Research has shown that soyhulls can replace all of the forage in the diet of ewes and lambs, with no deleterious effects. Pregnant and lactating ewes can be self-fed soyhull-based diets. Lambs can be finished on soyhull-based diets.
For hay. In many geographic areas, hay is an expensive feedstuff. Even if you produce your own hay, it may have a high opportunity cost. Disregarding cost, droughts and other weather conditions may severely limit the availability of hay, especially good quality hay. For these reasons, many producers may want to consider replacing some of the hay in the diet with soyhulls. Accounting for differences in digestibility (TDN), one pound of soyhulls is equivalent to approximately 1.4 pounds of hay.
For grain. If they are a more economical source of energy (TDN, ME), soyhulls can replace some (most or all) of the grain in the diet of sheep and goats. Soyhulls provide a means for forage-based operations to increase the energy density of ewe and doe diets, while still maintaining a grassfed desigination. Without supplemental energy provided by soyhulls and similar fibrous feeds, it can be difficult to meet the nutritional requirements of females nursing multiple offspring. Soyhulls supplementation would make it easier for a female to raise triplets (on pasture) and could offer an alternative to removing the third offspring for artificial rearing.
As a replacement for forage or grain in sheep and goat diets, soyhulls may or may not be a more economical choice than other feedstuffs. Economical viability will vary by season, year, farm, and cost and availability of feedstuffs.
Determining the economics of feeding soyhulls
The decision to include soyhulls in a feeding program for small ruminants should be based largely on economics. Since soyhulls are an energy feed, the cost of energy (TDN) for each feedstuff should be calculated and compared. To do this, all prices must be converted to an equivalent unit, usually pounds (or kilograms). Example: if soyhulls are selling for $180/ton, they have an equivalent price of $0.09/lb: $180/ton ÷ 2000 lbs.
All comparisons (of feed) must also be done on a dry matter basis, as livestock requirements are based on dry matter content of feedstuffs. The cost per pound of dry matter (DM) can be determined by dividing the price per pound by the percent dry matter in the feedstuff. Continuing with soyhulls as an example, the cost per pound of dry matter is $0.10/lb.: $0.09 ÷ 0.90. The cost per pound of TDN is similarly calculated by dividing the dry matter cost by the percent TDN in the feedstuff. For soyhulls, the price per pound of TDN is $0.14/lb: $0.10 ÷ 0.77. Additional calculations can be made to account for feed wastage. If you have to pay to have feed delivered, this should be factored into the initial cost.
The table above compares the cost of TDN for various energy feeds. In the example, soyhulls (bulk delivery) are a more economical source of energy than all feedstuffs except for grain (corn and barley). The bagged soyhulls are a more economical source of energy as compared to the alfalfa and orchardgrass hays. In this scenario, a producer could reduce energy costs by replacing some (most or all) of the hay in the ration with soyhulls. The advantage to soyhulls (and grain) is even greater (as compared to forages) when losses due to feeding and storage are accounted for. The last two columns in the table attempt to quantify the cost(s) of feed/nutrient losses, due to storage and/or feeding method(s).
All producers have a unique situation and need to make their own decisions regarding ration formulation. Not all feedstuffs are available in all geographic locations. Prices of feedstuffs vary by location, year, and season. Whenever feed is put in a bag or mixed with other ingredients to create a complete feed, its cost increases substantially. Delivery costs , handling, storage, and method of feeding are also factors that can affect diet formulation.
Bibliography
[1] 2014 South Dakota State University Sheep Research Report
[2] By-product feeds for meat goats: effects on digestibility, ruminal environment, and carcass characteristics, American Society of Animal Science (2002)
[3] Chemical composition and quality of fresh lamb from rotationally grazed hair and wool x hair lambs as influenced by soyhull supplementation. Journal of Animal Science Abstract (2015).
[4] Determining growth performance of implications on meat goat kids fed soybean hull or corn based pelleted diets. Kansas State University (2015).
[5] The effect of intake level of a soyhulls diet on digestibility in ram lamb and mature non-lactating ewes, Honors Thesis, Cornell University (2009).
[7] Evaluation of distiller's dried grains with solubles, soybean hulls, and corn in diets for growing and finishing meat goats, Kentucky State University (2006)
[8] Feeding soyhulls and dried distiller's grains with solubles to sheep, South Dakota State University (2006)
[9] Nutrient Requirements of Small Ruminants, National Research Council (2007)
[10] Soybean Hulls, Kansas State University (2000)
[11] Soybean hulls an an alternative feed for horses, Animal Industry Report (2004)
[12] Soybean hulls replacing ground corn in diet for early lactation Sannen does: intake, digestibility, milk production, and quality. Revista Brasileira de Zootecnia (2012)
[13] Soyhulls - Ask-a-sheep-vet - Pipestone Vet Clinic
[14] The use of soya bean hulls in rabbit feeding: a review, World Rabbit Science (1999)
[16] United States Standards for Livestock and Meat Marketing Claims, Grass (forage) fed claim for ruminant livestock and meat products derived from such livestock. Agricultural Marketing Service (AMS). Regulations.gov
[17] Using agro-byproducts to improve growth rate of forage-fed hair sheep lambs. Virginia State University. (2014)
[18] Utilization of soybean hulls when fed combination with MDGS in finishing diets (2013)
[19] Utilizing soyhulls in livestock and dairy rations, South Dakota State University (1997)
This article was written in 2015 by Susan Schoenian.