Feeding cotton products to cattle

Vet Clin Food Anim 18 (2002) 267–294

Feeding cotton products to cattle Glenn M. Rogers, DVM, MSa,*, Matthew H. Poore, PhDb, Joe C. Paschal, PhDc a Department of Farm Animal Health and Resource Management, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27695, USA b Department of Animal Science, College of Agriculture and Life Sciences, North Carolina State University, Box 7621, Raleigh, NC 27695, USA c Texas Agricultural Extension Service, Texas A&M University, Rt 2, Box 589, Corpus Cristi, TX 78406, USA

Cotton processing results in a variety of co-products and byproducts that might be valuable feed ingredients. These include the products of ginning (gin trash, gin motes, and whole cottonseed), cottonseed processing (delinted cottonseed, cottonseed hulls, cotton linters, and cottonseed meal), and cotton textile milling (cleaning and carding waste, cotton mill sweeps, and cotton mill dust). Table 1 shows the nutrient composition of common cotton products and some standard feeds [1–3]. Whole cottonseed is a good source of protein, energy, and phosphorus. Cottonseed meal is primarily a protein and phosphorus source, and cottonseed hulls, cotton gin trash, and textile mill waste are primarily roughage or fiber sources. Availability and cost of cotton products The average annual harvested cotton acreage from 1991 to 2000 was 13 million acres, with an average annual cottonseed production of 8.5 million tons [4]. Because of their nutritional content, whole cottonseed and other cotton products such as cottonseed hulls, cottonseed meal, cotton gin trash, and cotton textile mill waste are potential feed sources for beef cattle. One important factor that has limited the demand for cotton products in cow/ calf environments is the lack of understanding of how best to feed them, particularly with regard to avoiding gossypol toxicity. This chapter provides guidelines for feeding cotton products properly.

* Corresponding author. Pfizer Animal Health, 138 Rim Rock Road, Aledo, TX 76008, USA. E-mail address: glenn.rogers@pfizer.com (G.M. Rogers). 0749-0720/02/$ - see front matter
2002, Elsevier Science (USA). All rights reserved. PII: S 0 7 4 9 - 0 7 2 0 ( 0 2 ) 0 0 0 2 0 - 8

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Table 1 The nutrient composition of common cotton byproducts and some standard feed ingredients Ingredienta Whole cottonseed Cottonseed hulls Cottonseed meal (41%) Cotton gin trash Cotton textile mill byproducts Alfalfa hay (midbloom) Corn Soybean meal (48%)

Crude Total digestible NEg Nem Calcium Phosphorus protein (%) nutrients (%) (Mcal/lb) (Mcal/lb) (Mcal/lb) (%) 24.4 4.2 45

90 42 75

0.71 0.07 0.53

1.02 0.31 0.81

0.17 0.15 0.20

0.62 0.09 1.16

7 8

44 50

0.03 NAb

0.39 NAb

0.65 0.60

0.12 0.12

18.7

58

0.31

0.56

1.37

0.22

9.8 54

90 87

0.71 0.67

1.02 0.98

0.03 0.29

0.36 0.71

a

Reported on a dry-matter basis. Data not available. Data from Bath D, Dunbar J, King J, Berry S, Olbgrich S. Byproducts and unusual feedstuffs, feedstuffs reference issue and buyers guide. Feedstuffs 2001;73:30, and National Research Council. Nutrient requirements of beef cattle, 7th edition. Washington, DC: National Academy Press. 1996. b

Whole cottonseed In the South, whole cottonseed has been a common feed supplement because of favorable pricing and availability. There are several factors that make whole cottonseed an ideal supplement for brood cows. It is a good source of protein, energy, and phosphorus—three nutrients likely to be deficient in many feeding situations. Although nutrient content is quite consistent, a representative sample should be taken and analyzed for protein, energy, and minerals to guide the feeding program. Analysis of the sample for gossypol and mycotoxins might also be indicated if the feeding rate will be near maximum levels or if mold is evident. Two types of commercial whole cottonseed (WCS) are available: high-lint WCS (‘‘short staple’’) and low-lint WCS (‘‘long staple,’’ Pima seed). On a dry matter basis, low-lint WCS contains about 50 to 100 g/kg less fiber, with higher fat and protein content [5]. The crude protein in cottonseed is true protein, which is better for supplementing high-forage diets than nonprotein nitrogen (urea). The protein in cottonseed is also valuable because it is combined with the fat and encased in the hull, which should provide slow release in the rumen. The energy in cottonseed is primarily from fat, which, if fed at recommended levels, will not interfere with forage digestion, as does the starch in corn. Though the physical form of whole cottonseed can influence the rate of nutrient release, the fact that the fat and protein are bound inside the seed does not alter the amount that can be fed in a complete mixed ration. Feeding whole cottonseed results in a similar nutritional response to feeding the same level of cottonseed hulls, cottonseed oil, and cottonseed meal [6].

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The fat in cottonseed has also been shown to improve reproductive performance, especially in thin cows. This is related to increased circulation of triglycerides and cholesterol, which might aid in steroidogenesis [4]. WCS fat might also reduce metabolic heat production, making it a potentially valuable feed in hot weather [5]. Feeding whole cottonseed An advantage of cottonseed is that it can be fed whole. No grinding is necessary, so handling and equipment costs are decreased. Like all concentrates, cottonseed should be fed in bunks, but it can be fed off sod with good results if the soil is dry. Fig. 1 shows growing heifers being fed whole cottonseed off sod under an electric wire. Some producers prefer to unroll a round bale of high-quality hay and place the cottonseed on top of the hay. This reduces cottonseed waste and gives all of the cattle access to high-quality hay. Because of the high fat content of whole cottonseed, it is wise to limit it to approximately 0.5% of body weight (2.5 kg/day for a 500-kg cow) or 20% of the diet. This provides about 4% fat in the total ration, which is the maximum that can be fed without negatively affecting rumen function [6]. In most situations the total supplement necessary for beef cows will not exceed this amount. An exception would be with first-calf heifers, which might need to be fed a grain supplement in addition to the maximum level of cottonseed to meet their requirements [7]. When using whole cottonseed in a cow/calf operation, producers should take care not to overfeed bulls, developing heifers, and preruminant calves. Because of the potential problems associated with high intake of gossypol, producers should provide plenty of bunk space (45 cm/calf or 60 cm/cow) or spread the cottonseed out so that all animals have adequate access to it. If access is limited, dominant animals might overconsume the cottonseed [8]. For growing cattle it is recommended that whole cottonseed be limited to 0.33% of body weight (2 lb/day for a 600-lb replacement heifer) or 15% of

Fig. 1. Developing heifers being supplemented with whole cottonseed off sod under a temporary electric fence wire.

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the ration. When cottonseed is greater than 15% of the diet dry matter, the animal’s intake, gain, and feed efficiency might be reduced [9]. Fifteen percent of the total diet dry matter also seems to be a practical limit in diets for finishing cattle [10]. Cottonseed has been fed at higher levels to growing cattle with seemingly good results [11], although factors such as changes in energy level of the diet make interpretation difficult. Recommended feeding limits of whole cottonseed for different classes of beef cattle are given in Table 2. Whole cottonseed can be expected to have about the same feed value as a 22% protein mixture of corn and soybean meal in rations in which it is used as a substitute for a high-protein mix (such as with silage-based diets) or with low-quality hay or dormant winter range. The value is about the same as that of corn when protein is not needed, such as with lush winter pastures, high-quality hay, or other high-quality forages. Before purchasing whole cottonseed, producers should evaluate the protein and energy levels of available forages to determine whether energy, protein, or both are needed in nutritional supplements before comparing whole cottonseed with other available feeds [3,12]. Purchasing whole cottonseed The price of whole cottonseed varies dramatically with the season and is especially low in areas with a large cotton crop relative to the availability of seed storage facilities and local demand for feed supplements. During the ginning season whole seed can be purchased as it leaves the gin (gin run seed) at a lower price than when it comes out of the storage facility. This is because stored seed has the added costs of storage and aeration. Aeration of cottonseed is necessary because it is hot when it leaves the gin. When stacked deeply in the storage house, cottonseed retains heat and might spon-

Table 2 Whole cottonseed feeding recommendationsa

Mature cows Bulls (during the breeding season) Young developing bullsb Growing cattle Preruminant calves

% Body weight

% Total diet

kg/animal/day

0.5 0.33 – 0.3 0

20 15 – 15 0

2.3–3.2 2.3–3.2 – 0.7–1.1 0

a A wide margin of safety exists for feeding whole cottonseed to cattle. These are only recommendations. Proper sampling, laboratory analysis, and interpretation of gossypol levels should be performed before wide-scale feeding of whole cottonseed to beef cattle. b Although recommendations have been made for up to 10% whole cottonseed in the diet for young developing bulls, no recommendation is made here. Reasons for this omission include (1) perceptions of potential infertility by purchasers of young bulls, (2) recent research indicating potential reduced fertility in young developing bulls, and (3) the relatively low potential cost savings vs. risk when feeding whole cottonseed at the lower levels previously recommended.

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taneously heat further, especially if there is an elevated level of moisture. This further heating results in damage to the protein, making it unavailable, and eventually might cause spontaneous combustion. Pulling air through the seed removes heat and excess moisture, resulting in a stable product with a prime grade that is suitable for long-distance shipping and long-term storage. Many ginners will price whole cottonseed to move directly to producers to avoid storage costs. Experience indicates that if the purchaser is careful that the gin run cottonseed is not less than 88% dry matter on arrival and is stacked less than 8 feet high, it will cool without continued spontaneous heating. If storage is adequate, this cottonseed will be stable and maintain a high feeding value. Storing and handling whole cottonseed Storage and handling should be considered when making the decision to purchase whole cottonseed. In general, whole cottonseed must be stored in an open shed where it can be protected from rain but where ventilation is adequate to prevent condensation and mold formation. The recommended storage facility is an open shed with the capacity to hold at least as much cottonseed as is expected to be used each year. The floor should be concrete and the roof should have adequate clearance for the type of truck expected at delivery. Large operations should consider constructing a multibay commodity shed that can be used for storage of cottonseed and other byproduct commodities that might be good feed values. Cottonseed should not be stored in grain bins because of difficulties in unloading; augering cottonseed is not possible. The seed should be kept dry, but it should not be covered with or placed on top of plastic because the seed tends to sweat and mold where plastic comes into contact with it. If cottonseed is stored on a dirt floor it will take up moisture. If cottonseed must be placed on a dirt floor, a 3-inch layer of straw or low-quality hay should be laid down first to minimize storage loss and soil contamination during feeding. Cottonseed must be kept dry and free of molds because of the potential negative impact of mycotoxins on health and reproduction [13]. The best method of handling cottonseed depends on the scale of the operation. It can be handled easily in a traditional truck or trailer-mounted feeder in large operations, or in bags or other containers in smaller operations. A process has been developed for coating whole cottonseed with starch. The starch binds short fibers attached to the seed and produces a free-flowing product [14].

Cottonseed hulls Cottonseed hulls are a high-fiber byproduct of processing cottonseed for oil and meal. The hulls are relatively low in nutrient content but they are surprisingly palatable to cattle. In brood cow rations cottonseed hulls are

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a replacement for hay; they might be logical to use during times of hay shortage. Three kilograms of cottonseed hulls can replace 2 kg of averagequality hay. Many commercial preconditioning feeds are based on cottonseed hulls. It is not known why calves choose to eat hulls, but hulls are known to alter the texture of rumen contents [15] and to alter the digestion of other diet ingredients by slowing outflow of particles from the rumen compared with other roughage sources [16]. Cottonseed hulls work well as the only source of roughage in finishing rations for beef cattle because of easy handling and acceptability to cattle, although feed intake is usually increased and feed efficiency is reduced with cottonseed hulls compared with other roughage sources for high-grain diets [17]. Like whole cottonseed, cottonseed hulls should be stored in bulk in an open shed. There is no danger of gossypol poisoning from cottonseed hulls because gossypol is present predominantly in the meat of the cottonseed. Only a trace of gossypol is present in the hulls, and this is because of a small amount of residual meat present in the hulls [8]. Cottonseed meal Cottonseed meal is commonly used as a protein supplement for beef cattle. Because gossypol levels limit its use in swine and poultry rations, it is almost always a less expensive source of protein than soybean meal. When cubed or pelleted, cottonseed meal is also known as cottonseed cake. This is a historical name used to describe the residue of mechanical extraction, which resulted in a cake-like material that had a considerable level of residual oil. The term cake has been retained, although little high-fat cottonseed meal is currently produced. Cottonseed meal can be handled and stored in a manner similar to soybean meal. Cottonseed meal is generally marketed as 41% crude protein meal, although this can vary somewhat by source. To evaluate cottonseed meal as a potential protein source, calculate its cost per pound of crude protein and compare it with other protein sources. The value of protein in cottonseed meal is similar to that of soybean meal for ruminants [18], with 1.2 kg of cottonseed meal (41% crude protein) providing about the same amount of protein as 1 kg of soybean meal (48% crude protein). Cottonseed meal has been produced primarily in three forms: (1) mechanical, (2) prepressed and solvent extracted, and (3) direct solvent extracted. All three forms have similar nutritional value [19,20]. Cotton gin trash (cotton ‘‘burrs’’) When cotton is ginned, it is separated into seed, lint, motes, and gin trash. Cotton gin trash and motes are the lowest-value products that result from this process [21]. Gin trash contains coarse particles of leaf and stem, cotton-

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seed, lint, boles, and soil. Gin motes are similar to gin trash, except motes contain more usable fiber and immature cottonseed and less leaf, stem, boles, and soil than does cotton gin trash. As its name indicates, cotton gin trash has been generally considered to be a waste product because of a lack of readily available feed market for the material. Gin motes are usually marketable to specialized gins that re-gin them to produce usable fiber and a waste product similar to textile mill waste. At some gins the motes are included in the gin trash, increasing its feeding value. Composition of gin trash from a variety of published sources is shown in Table 3. Note the variability in composition, which illustrates the importance of analyzing for nutrients until composition from a given source is understood. Cotton gin trash was sampled from 21 cotton gins in Georgia and analyzed for potential chemical residues. No significant levels of chemicals were found except for the defoliant S,S,S-tributyl phosphorotrithioate (DEF). Values for DEF ranged from 0 to 25.6 ppm, with an average value of 4.49 ppm. There is no defined tolerance for DEF levels in cotton gin trash, but the tolerance level in cottonseed hulls is 6 ppm. Caution should be taken when developing a feeding program with cotton gin trash, but if feeding is short-term to cattle not destined for slaughter for an extended time (ie, beef brood cows prior to calving) there is not a high risk of problems [22]. Gins in the United States produce approximately 2.8 million tons of cotton gin waste annually [23]. With growing environmental awareness and regulations, the disposal of cotton gin trash is a concern because of its slow rate of decomposition. Cotton gin trash has long been used as a feed ingredient, but its low quality, coarse texture, and low bulk density have limited its use. It can also contain substantial chemical residues, which should be considered before it is incorporated into a feeding program, especially for cattle being fed for slaughter. A recent Oklahoma case involved the death of 18 of 48 cattle that consumed disulfton-treated cottonseed that was disposed in cotton gin trash. Disulfoton is an organophosphorus insecticide. One example of its use is the Table 3 Composition of cotton gin trash, % Reference

N

CP

ADICP

ADF

Calcium

Phos

Ash

NCSU, CEFSa Bath et al [1] NCSU summaryb Stewart et al [22] Hill et al [27,28] Axe et al [91] Lalor et al [92]

2 – 8 35 2 1 6

16.6 7.4 12.2 11.7 14.4 10.3 7.8

5.03 – 6.51 4.40 – – –

57.6 46.0 65.0 – 63.8 67.8 –

0.84 0.65 1.01 0.90 – 2.32 –

0.30 0.15 0.22 0.20 – 0.29 –

15.5 5.9 10.9 11.1 10.5 20.9 13.0

Abbreviations: ADF, acid detergent fiber; ADICP, acid detergent insoluble crude protein; CP, crude protein; N, number of independent analyses. a Center for Environmental Farming Systems (Poore, unpublished). b North Carolina gins, 1996–1997.

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impregnation of seed grain to control insect damage during storage, planting, and germination. Disulfton and the fungicide captan are the active ingredients of Di-Syston (Bayer Corporation, Kansas City, MO). Use of this product has significantly declined in recent years [24]. Cotton gin trash has nevertheless been used in feedlot rations in which roughage costs are high, and it is a fairly accepted ingredient in some Western feedlots. Its use in feeding brood cows has been limited because of the difficulty in handling the bulky material and the high rate of refusal if the material is offered in large amounts. The low bulk density problem—which restricts transportation—can be solved by putting cotton gin trash into large modules, bales, or cubes for transport to local beef producers. There has been considerable interest in the chemical treatment of gin trash to improve its feeding value. Processes such as ozonization and treatment with sodium hydroxide have proven to be effective in increasing digestibility [21,25]. Although chemical treatment seems to have potential in small studies, a commercial system with the ability to process large amounts has not been developed. In Israel, where much work has been done with chemical treatment, the current focus for using cotton gin trash and cotton straw is to provide it to animals in a large quantity and allow them to pick through and eat the palatable components (~50% of the material). The refused material is then removed and composted for later use as a fertilizer or mulch [26]. Cotton gin trash has been evaluated as a winter feed for dry beef cows. Cows were housed in a dry lot and fed all the gin trash they could consume with or without a small amount of corn (1.4 kg/head daily). Intake of the cotton gin trash was low during the first 10 days, but then increased rapidly; the cows consumed an average of 12.7 kg/head of cotton gin trash dry matter over a 55-day period. Cows fed only cotton gin trash lost some weight and body condition over this 55-day period while those supplemented with corn maintained weight and condition. The researchers concluded that cotton gin trash was a viable feed for dry brood cows if supplemented with additional concentrate or forage sources [27]. When the same workers fed cotton gin trash to growing cattle with increasing levels of corn, there were dramatic associative effects on digestibility of the fiber in cotton gin trash, resulting in a conclusion that cotton gin trash had little potential for highlevel feeding to growing cattle [28]. Two of the authors of this paper (GMR and MHP, unpublished) have used cotton gin trash successfully as a winter feed for dry beef cows in North Carolina. Over a 2-year period at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, half of the mature brood cow herd was fed cotton gin trash with some supplemental hay (~4.5 kg/head daily) until 2 weeks before calving (49 days in year 1, 42 days in year 2). The remaining half of the herd was fed hay ad libitum. Cotton gin trash was compacted into modules at a local cotton gin and transported to the pastures. Access to modules was restricted by a single strand of electric ‘‘polywire’’ and cows were allowed to sort through the gin trash—resulting in about 75% utiliza-

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tion—before the wire was moved allowing access to more of the module (Fig. 2). In year 1 the cows had excellent body condition (average initial score 6.2), so no supplemental feed was offered either group. During year 2 the cows were in marginal body condition (average initial score 5.2), so all cows received 1.1 kg whole cottonseed daily as a supplement. In the first year, cows on each wintering system gained weight (0.23 kg/day) and lost body condition (
0.5 score), while during the second year both groups gained weight (1.1 kg/day) and improved in body condition (+0.5 score). There were no significant differences between the groups. Because the cotton gin trash was provided to the farm free of charge (a common practice near gins in North Carolina) there was a savings of approximately $25 per cow, a significant amount in the budget of a beef cow. The mixing of whole cottonseed and cotton gin waste has shown promise as an alternative to cotton gin waste alone. In a Mississippi study the mixture was heated and compressed to form chips that were handled easily with feed handling equipment. The nutritional value of the mixture was good, free gossypol content was reduced, and chemical residue problems associated with gin trash alone were reduced [23]. If a cotton gin is nearby, low-cost cotton gin trash might be readily available. In such cases veterinarians, nutritionists, and producers should discuss the possibility of using cotton gin trash as a feed source. This cotton byproduct has potential as a winter feed for dry cows, a partial replacement for hay or pasture, and a roughage source in high-concentrate diets for feedlot cattle. Other cotton byproducts When cotton is processed, several types of byproducts are formed, which are essentially short-fiber cotton. These products include cotton gin motes, cotton linters from cottonseed processing, and cotton textile mill waste resulting from the processing of raw cotton for spinning. These products have a similar feeding value, about the same as average-quality hay [29].

Fig. 2. Brood cows eating cotton gin trash from a module. Note the temporary electric wire being used to restrict access to the module by the cows.

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Cotton gin motes and cotton linters As indicated earlier, gin motes are generally re-ginned to produce linters and a waste product. Linters are used in high-quality papers and explosives, and for other specialized purposes. They are usually unavailable for cattle feed. Cotton textile mill byproduct Cotton textile mill byproduct contains short cotton fibers, residual seeds, fragments of stems and leaves, and other foreign materials cleaned from cotton when it is processed into yarn. Primary yarn mills are common across the southern region of the country, especially in the Southeast. The waste produced by these plants generally consists of (1) stem, leaf, and cottonseed fragments cleaned from the baled lint; (2) short fibers removed during the carding process; (3) dust cleaned from the mill air; (4) waste yarn and slivers (long strands ready for spinning) produced during spinning because of untangling and re-setting of the equipment; and (5) foreign materials discarded on the spinning floor. Traditionally, all these materials have been combined and disposed of in solid waste landfills; only recently have they been considered as potential cattle feed. Many mills now combine the cleaning waste, short fiber, and dust into a cotton textile mill byproduct. In addition, they combine the waste yarn, slivers, and trash into a product called sweeps. Sweeps are undesirable as a feed because the long strands of yarn can cause choking. Moreover, sweeps might contain metal objects such as screws and nails that were thrown on the floor of the spinning room. Cotton textile mill byproduct has a nutrient value comparable to medium-quality grass hay, with protein averaging 8% and estimated total digestible nutrients of approximately 50% to 60% (Table 1) (M.H. Poore; unpublished data, 1995). Several studies have shown cotton textile mill byproduct to be an acceptable ingredient in feed [9,29,30]. In a study of growing beef heifers, cotton textile mill byproduct was similar to sorghum silage when included as 20% (dry basis) of the diets [9]. In digestion studies with steers, cotton textile mill byproduct had a digestibility similar to low-quality fescue hay and high-quality bermudagrass hay [29,30]. Until more is known about cotton textile mill waste it is recommend that mature cows be limited to 10 lb/day of the material, and that stocker calves be limited to 20% of their diet. Cattle should not be fed the material for 28 days before slaughter. Recent research suggests that much higher levels of cotton textile mill byproduct can be safely fed to animals with relatively low nutritional requirements, such as wintering dry cows [30]. This material is generally available in 700-lb bales or in 2- to 3-inch pellets (briquettes). Cotton textile mill byproduct can be fed in round bale feeders (Fig. 3). Cows sometimes need to be encouraged to eat the material with dry or wet molasses or silage on the surface of the bale. Once the cows begin to consume it, palatability is usually not a problem.

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Fig. 3. Brood cows eating cotton textile mill byproduct in large bales from a common round bale feeder.

Often the cotton textile mill byproduct is pressed into large pellets, or briquettes, because of problems of reduced landfill space in many communities. These briquettes have been successfully fed to cows when the pressure on the briquette-making machine is lowered to the point where the briquettes barely hold together. This results in a product that is both easy to handle and palatable for the cattle. The loose briquettes are also ideal for mixing in a total mixed ration wagon, as they will break up well if added as the first ingredient. One concern with cotton textile mill byproduct has been the possibility of chemical residues. Before 1993 substantial levels of arsenic were found in waste from plants that purchased cotton from regions in which arsenic acid was used as a defoliant. Because arsenic acid was removed from the market as a defoliant, arsenic contamination is no longer a great concern. While cases with low levels of certain chemical residues such as malathion have been observed, none of the reported cases have led to a great concern for feeding, especially considering standard use levels. Cotton textile mill byproduct should be approached with caution as a feed. Although it has been safe and effective in studies conducted in North Carolina [9,29,30], it is not yet an accepted feed ingredient, and liability regarding its use might be high. Many mills providing the material require the producer to sign a liability release form. In this case, the liability for losses directly related to feeding the material can come to bear on the person providing nutritional consulting services to the beef producer. This is the case with any unrecognized feed ingredient, and care should be taken to ensure a safe feeding program [3]. Gossypol Utilization of cotton products in cow/calf environments has been somewhat limited, partially because of the fear of the toxic effects of gossypol.

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The remainder of this chapter will focus on the potential toxic effects of gossypol in diets containing cotton products. Gossypol is a yellow pigment present in glands throughout the cotton plant. The highest gossypol concentrations occur in the seeds and roots. These glands are grossly visible as small, dark spots scattered throughout the tissue of the cottonseed kernel (meat). Gossypol is chemically classified as a polyphenolic binapthyl dialdehyde. The gossypol content of cottonseed might be affected by the species and variety of the cotton plant [31]. Climatic conditions have also been demonstrated to have an influence on gossypol levels. A direct relationship exists between high rainfall areas and gossypol content, whereas an inverse relationship has been observed between areas with higher average temperatures and gossypol content [31]. Other factors affecting the gossypol content of cottonseed include regional soil conditions, water supply, amount and composition of fertilizer applied, and any major changes in plant growth during the vegetative period [31,32]. Although much variability in gossypol content exists, gossypol content of seed from commercial varieties grown throughout the cotton belt has not changed appreciably in the last 50 years [33]. Whole cottonseed was evaluated from eight varieties in 13 different locations in the 1950s with a gossypol range from 0.39% to 1.7% [31]. In the 1970s a mean gossypol content of 1.32% (range 0.59–2.35%) was found in cottonseed kernels (whole seed without the linters and hulls) [34]. The mean amount of gossypol in kernels from 1977 to1989 was 0.89%, and the range was 0.64% to 1.19% [20]. Cottonseed is composed of kernel (65%), linters (9%), and hull (26%) [20]. Whether or not laboratories report free gossypol values as a percentage of the whole cottonseed or as a percentage of the kernel alone is of utmost importance in interpreting the laboratory analysis. Gossypol exists in two forms, free and bound. The free form is toxic, whereas the bound form is usually considered nontoxic because it is not released in the rumen. Dilution and slowed absorption help detoxify gossypol in the rumen [35–38]. Some researchers suggest that bound gossypol can be converted to free gossypol in the gastrointestinal tract, however [32,39– 43]. If this is correct, there are serious implications in terms of accurately determining gossypol toxicity potential. Free gossypol is that part of the total gossypol in cottonseed that is soluble in 70% acetone. Bound gossypol levels are calculated by subtracting the free value from the total value. Virtually all of the gossypol in whole seed is in the free state, so free gossypol and total gossypol values for whole cottonseed should be almost identical [31]. Significant variation in the free and total gossypol reported for whole cottonseed is suggestive of artifacts created during laboratory analysis. When feeding cottonseed meal it might be appropriate to analyze only for free gossypol. Gossypol exists naturally as a mixture of two stereoisomers because of the restricted motion about the bond that joins the two napthalene groups

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of the molecule [44]. These isomers are referred to as (+) and (
) gossypol. The (
) isomer seems to have the greatest biological activity and is responsible for toxic effects, including infertility in bulls [44]. Researchers are only now beginning to understand certain factors involved in rumen detoxification and the level of availability of gossypol from cottonseed products processed by different methods. For this reason, current methods of evaluating diet safety by measuring free gossypol levels might be misleading [44]. Diet seems to play an important role in the development of gossypol toxicity. High- concentrate rations increase the chances for gossypol toxicosis. This is perhaps because of the faster rate of passage and lower ruminal pH, which allow gossypol to pass through the rumen unbound [45]. Most reported cases of gossypol toxicosis in ruminants have involved animals on a predominantly concentrate ration high in cottonseed meal [46]. Apparently, animals can tolerate higher levels of free gossypol in whole cottonseed than in cottonseed meal. The gossypol in whole cottonseed is possibly released more slowly because more time is spent in the rumen than with cottonseed meal [8]. Another reason for this slower release is that some cottonseed remains unbroken after chewing, resulting in a more gradual gossypol release as cottonseeds are ruminated. Commercial processing of cottonseed into cottonseed meal disrupts pigment glands, leading to the release of free gossypol and binding with other seed components. The extent and type of binding can vary with the particular processing method. Higher temperatures and pressures involved in the expeller and prepress-solvent and expander-solvent procedures leave much lower levels of gossypol in the meal than does the direct-solvent procedure. Cottonseed meal usually contains 0.8% to 1.4% total gossypol. Representative values for free gossypol content in cottonseed meal processed by different methods include (1) screw pressing (0.05%) [11], (2) prepressed-solvent extraction (0.05%), (3) expander-solvent extraction (0.13%) [44], and (4) direct-solvent extraction (0.30%). During screwpress extraction most of the free gossypol binds to sulphurcontaining amino acids, which lowers the nutritional value of the protein. Solvent extraction methods produce cottonseed meal with higher quality protein but increase the free gossypol content [47]. Most direct-solvent cottonseed processing plants have converted to the expander-solvent process, making currently available cottonseed meals much less likely to cause gossypol toxicity problems [44]. Additionally, storage of cottonseed meal has little effect on the free gossypol content [31]. While nonruminants and preruminants are particularly sensitive to gossypol, adult ruminants are relatively resistant. In spite of this, extremely high intakes of free gossypol (>24 g/day) in direct-solvent cottonseed meal have been shown to overwhelm the ability of the mature dairy cow’s rumen to detoxify gossypol [36,43]. It should be noted that this level was achieved by feeding more than 9 kg/day of direct-solvent cottonseed meal, a level that far exceeds prudent standard industry recommendations. Cows in one study

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were fed a 150 g/kg WCS diet supplying 23 g/day of free gossypol for 4 weeks; they did not exhibit signs of gossypol toxicity [48]. Clinical signs of gossypol toxicosis Since gossypol toxicosis is similar in presentation to other diseases of an infectious, parasitic, or nutritional nature, a clinical diagnosis is rarely made. Likewise, a specific diagnostic test is not currently available. A presumptive diagnosis can be made when calves present with these clinical signs: dyspnea, decreased growth rate, anorexia, weakness, gastroenteritis, and a history of exposure to cottonseed products at higher than recommended levels. Abdominal distention and terminal convulsions have been reported to occur after the development of subtle signs [36,42,49]. Some calf deaths related to gossypol toxicosis have been attributed to pulmonary edema [50]. Gossypol toxicosis seems to have a cumulative effect [42]. Surviving calves have been reported to remain unthrifty and have poor haircoats and distended abdomens throughout life [51]. The highest death losses have been reported in bottle calves whose starter rations and creep feeds contained cottonseed meal that had a high gossypol content as their protein source [52]. Clinical signs of gossypol toxicity in mature cattle include decreased dry matter intake, decreased milk production, panting, elevated heart rate, ruminal stasis, severe abomasitis, conception failures, hemoglobinuria, and sudden death [36,43,46,53,54]. Signs are exacerbated when cattle are stressed, such as by high temperatures or by physiological or nutritional factors [36,44,53]. Decreased hematocrit and hemoglobin concentrations have been reported in calves and mature cattle experiencing gossypol toxicosis [36,43,52]. Additionally, increased erythrocyte fragility and increased clotting time have been reported [36,43]. Gossypol interferes with the normal oxygen exchange in ruminant erythrocytes, thus increasing fragility [36]. Vitamin E supplementation (2000–4000 IU/day) decreases the detrimental effect of gossypol on erythrocyte osmotic fragility [55]. One study reported that an elevation in serum sorbitol dehydrogenase (SDH) was the most consistent clinical finding in young calves that were fed a high concentration of cottonseed meal [56]. The mean SDH for dying, hospitalized, and clinically healthy calves fed a high concentration of cottonseed meal was 277 units/L, 34 units/L, and 45 units/L, respectively. The mean SDH for healthy calves not fed cottonseed meal was 18 units/L. In one investigation, an elevated serum potassium concentration (11.9 and 7.6 mm/L) and a decreased chloride concentration (89 and 86 mm/L) were reported in two calves that had gossypol toxicosis [32]. Postmortem findings Gossypol is a cardiotoxin, although the mechanism of the cardiac toxicity is unclear [56]. Necrosis of cardiac musculature occurs over time. Destroying

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cardiac musculature can interfere with the conduction system, resulting in either lesions associated with congestive heart failure or no observable lesions [52]. Some investigators have noted degenerative changes histologically in the myocardium [36,37,42,47,54]. Another investigator typically found only minimal changes in the cardiac muscle in calves that died suddenly, even in calves that had severe thoracic and peritoneal fluid transudation [56]. In most deaths caused by gossypol toxicity, enlarged, flabby, pale hearts with marked ventricular dilatation can be found [35,37,42,51,54,57]. Areas of myocardial degeneration are sometimes present [42]. A list of differential diagnoses for heart failure in cattle includes monensin toxicosis, lasolacid toxicosis, selenium deficiency, and senna toxicity. Generalized edema is a common postmortem lesion. Large amounts of straw-colored fluid of a high-protein content are consistently found in the thoracic and peritoneal cavities and pericardial sac [35,47,56,58]. Subcutaneous edema has been reported to be prominent throughout the ventral cervical and thoracic region [35,36]. One researcher observed froth-filled tracheobronchial trees in calves that succumbed to gossypol toxicosis [43]. Abomasitis with marked edema and hyperemia has also been observed [43,54]. Congestion and interlobular edema of the lungs, a swollen, congested, nutmeg liver, and gastroenteritis are all lesions that have been reported in calves [35–37,42,43,47]. In some cases the mucosa of the jejunum appeared thickened and hyperemic [43]. The most consistent histological finding with gossypol toxicosis is hepatic centrilobular fatty change and necrosis [36,37,42,54,56]. One researcher reported that there were no anatomical differences between the liver lesions of animals dying after their access to high dietary cottonseed meal had ceased for up to 30 days versus the lesions of those animals dying much earlier [56]. There was no evidence of hepatic insult (ie, hepatocyte regeneration or fibrosis) or of a chronic process. This finding is of interest because of the necessity for relatively long-term feeding (70+ days) of the excessive cottonseed meal and the occurrence of fatal cases for up to 30 days after withdrawal of cottonseed meal from the diet. The nature of the liver lesions combined with the severe vascular leakage in body cavities and heart dilatation in calves late in an outbreak suggest that cardiac insufficiency might be an important physiological event in the death of animals and contributes to the hepatic necrosis [32,56]. Sixteen hundred lightweight Holstein feeder calves died after consuming a ration containing 25% cottonseed meal with 10,000 ppm free gossypol in the cottonseed meal. Nutmeg livers and enlarged flabby hearts were reported at necropsy. Histopathology revealed lesions consistent with a cardiotoxin [59]. Reproductive effects During the 1930s and 1940s men in certain areas of rural China experienced infertility that was later associated with gossypol ingestion. Raw

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cottonseed oil was commonly ingested and was later found to be the source of the gossypol-linked spermatogenesis suppression [60]. Gossypol apparently inhibited enzyme activity that was involved in metabolic regulation of spermatozoa [61,62]. In one study 10% of men remained sterile for an average of 4 to 5 years after gossypol consumption ceased, suggesting that infertility in men was only partially reversible [62]. Reproductive effects of gossypol in the ruminant are a topic of considerable controversy. Females are relatively resistant to reproductive effects [63,64]. A New Mexico study demonstrated that long-term feeding (431 days) of whole cottonseed (15% of total diet and 1300 ppm total gossypol) beginning at 3 months of age had no detectable deleterious effects for heifers in the onset of puberty or the pregnancy rate [65]. There are apparently no long-term effects on the reproductive performance of cows that survive gossypol toxicosis [43]. Negative effects on male bovine reproduction have been well documented. Reductions in sperm motility caused by mitochondrial damage to sperm tails, depression in spermatogenesis caused by damage to germinal epithelium, and testicular damage have been reported [63]. Aplasia of the mitochondrial helix is considered to be essentially pathognomonic for gossypol spermatoxicity [66]. Gossypol effects on male bovine reproduction are dose and time dependent. In one study yearling beef bulls were fed a gossypol-containing diet for 2 months, which resulted in seminiferous tubules with larger lumens, decreased wall thickness, and a reduced number of cell layers [67]. After then feeding the same bulls a gossypol-free diet for 2 months, improvement in the previously mentioned histological characteristics was observed. This finding indicates that gossypol-induced fertility effects in bulls are at least partially reversible [67]. The time period used to evaluate the positive reproductive effects of the gossypol-free diet corresponds with the 6- to 8-week period necessary for creating mature spermatozoa from primordial cells. There are no reported data showing impaired breeding caused by recommended levels of supplementation of range bulls with cottonseed meal or whole cottonseed. In post-pubertal ruminant males fed cottonseed meal or whole cottonseed diets containing gossypol (~3.2 or 32 g/day, respectively), single ejaculates showed no consistent differences in sperm concentration, motility, or morphologic abnormalities under light microscopy compared with those animals fed a gossypol-free diet [68]. In previous reports, the sperm quality and quantity of postpubertal bulls and rams that were fed diets containing gossypol also appeared normal [69–71]. Breeding soundness examination scores based on the Society of Theriogenology system do not appear to be significantly reduced because of gossypol [72]. The scrotal circumference measurement does not vary, and morphologic changes might not be detectable by standard light microscopy procedures. An Australian study concluded that the feeding of whole cottonseed at levels up to 19.8 g free gossypol per head daily had no effect on fertility. These workers suggested that the variability seen in the effects of gossypol

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on ruminant health and performance might be caused by the presence of binding agents in the rumen. Binding of free gossypol by lysine, calcium, iron, sodium, and potassium could have resulted in the variable effects seen in gossypol toxicity studies [73]. Gossypol seems to be more damaging to reproductive function in young ruminant males near puberty than in mature males. Young bulls in one study were fed a diet consisting of 60 mg/kg free gossypol/head/day (16 g/ bull/day) in whole cottonseed, 6-mg/kg free gossypol/head/day (1.8 g/bull/ day) in cottonseed meal, or no gossypol (soybean meal supplement) from weaning through puberty (196 days) [74]. The bulls fed the whole cottonseed in this study had lower body weight gain and reached puberty at an older age than bulls fed cottonseed meal or soybean meal. Because puberty was reached at similar body weights and scrotal circumferences, however, delayed puberty in the bulls fed whole cottonseed might have been because of a lower energy balance and not gossypol per se. In this study, gossypol did not appear to reduce sperm quality or quantity at puberty under light microscopy [74]. Four of eight young Brahman bulls in one study were fed 8.2 g (3000 ppm) of free gossypol per day from cottonseed meal for 11 weeks [75,76]. The percentage of normal spermatozoa was lower (P < 0.01) in the treated than in the control group beginning in week five. Abnormal sperm— detected using differential interference phase optics—primarily involved the midpiece. These midpiece abnormalities appeared to be the cause of decreased sperm motility. No cases of infertility have been reported in bulls with this type of midpiece abnormality, however. The percentage of ‘‘live’’ spermatozoa in the gossypol-treated bulls in this study was not affected despite significant reductions in the number of spermatozoa that were morphologically normal. This indicates that gossypol can have deleterious effects on certain sperm structural components, particularly the midpiece, without destroying sperm membrane viability [75,76]. The testicle seems to be more sensitive to gossypol than are other organs [77]. In one study testicular morphology was affected in bulls that were fed high levels of gossypol [74]. In a Florida study cottonseed meal was fed to Holstein bulls at a concentration that provided 14 mg free gossypol/kg/day from 6 to 16 months of age. Increased sperm abnormalities, decreased sperm production, and an adverse affect on some aspects of sexual behavior were reported. Vitamin E feeding (4000 IU/bull/day) throughout the study to one treatment group reversed the negative effects of gossypol on reproductive measurements [78]. The female ruminant seems to be relatively insensitive to the antifertility effect of gossypol; however, in vitro data indicate some inhibition of embryonic development and ovarian steroidogenesis [63,64]. A diet containing dietary free gossypol greater than 10 g/day or 20 g/day was fed to postpubertal heifers or mature cows, respectively, for 1 to 2 months. Although increased erythrocyte fragility was detected in both groups, no detrimental

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effects on growth rates, body condition scores, or reproductive parameters were found [79]. These amounts of dietary free gossypol were in excess of those used in typical production schemes. These data are difficult to interpret because both cottonseed meal and whole cottonseed were used in each ration, and both provided a different proportion of free gossypol in the diet. The high lipid content in whole cottonseed exerts a positive effect on female bovine reproduction. One study suggests that low-level progesterone elevations caused by the high lipid content of a 30% whole cottonseed diet might lead to an earlier onset of estrous cyclicity [4]. A Texas study in which pregnant Brahman cows and heifers were fed diets containing various levels of free gossypol (0, 2, or 4 g/hd/day) for 90 days prepartum and 112 days postpartum compared calf development and cow performance parameters. By 96 to 105 days after calving a greater number (P < 0.05) of cows consuming the diets containing 2 or 4 g free gossypol experienced luteal activity and a greater number (P < 0.10) had conceived by 112 days postpartum. Some aspects of calf skeletal development and vitamin metabolism were impaired, although long-term performance of cows and calves was not affected [80]. Laboratory analysis When should cottonseed be tested for gossypol? Nutritionists, veterinarians, and producers should be conscious of the potential risk resulting from feeding animals gossypol-containing feeds. In some situations cottonseed meal or whole-seed feeding might be at a low enough level that there is a very low risk of gossypol poisoning. In these situations it might not be cost effective to test for gossypol. When lower prices for cottonseed products occur it becomes increasingly common for producers to feed at the upper end of recommended use levels. In this situation a gossypol analysis might be useful to prevent cases of gossypol toxicosis. Knowing the gossypol level might allow increasing cottonseed feeding levels above those normally recommended. Veterinarians and consulting nutritionists might recommend routine testing of cottonseed and cottonseed byproducts to protect against liability and to interpret production problems that might occur. Obtaining a representative sample For an analysis of gossypol to be meaningful a representative sample of the cottonseed is necessary. Cottonseed might not be sampled as easily as grains or forages because standard sampling equipment might not be effective. To sample, take at least 20 grab samples from the cottonseed pile at various locations and depths. A hand posthole digger can be used to dig to various locations in the pile to obtain these samples. Place the subsamples in a plastic trash can and mix well before removing about 0.5 kg to be submitted to the gossypol testing laboratory. Another 0.5 kg sample should be submitted for nutrient analysis.

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Choosing a laboratory Many laboratories analyze samples of cottonseed and cottonseed byproducts for gossypol. Most laboratories use the official spectrophotometric method of the American Oil Chemists Society (AOCS) and will analyze for both free and total gossypol content. Because it seems that the level of total gossypol is the most important measurement for whole cottonseed, the expense of performing free gossypol analysis in addition to total is probably not warranted. If only free gossypol is analyzed, problems that occur in sample preparation could result in misleading recommendations. Cottonseed meal only needs to be analyzed for free gossypol. A laboratory should be chosen that is certified by the AOCS or the Association of Official Analytical Chemists (AOAC) for gossypol analysis. Interpreting results Gossypol levels reported from laboratories and in the literature must be closely monitored to ensure that proper comparisons are made. Four critical concerns in evaluating laboratory results are (1) whether the gossypol level reported is from the kernel or whole seed, (2) whether the level reported is free or total gossypol, (3) whether the level is reported on an ‘‘as-received’’ or a ‘‘dry matter’’ basis, and (4) whether the sample is a straight cottonseed product or a mixed feed. Commercial testing laboratories generally report free gossypol as a percentage of the kernel (meat) only on an as-received basis. The weight of linters and hulls must be considered to calculate levels in whole seed (usually 35% of gin-run whole seed) [20]. In mixed feed samples the potential exists for interactions between free gossypol and other feed ingredients. This binding effect can result in lower reported free gossypol values than might actually be in the feed. In addition, the value for gossypol concentration in whole cottonseed reported by the laboratory should be converted to the concentration in the total diet. An example calculation is shown in Table 4. Recommendations for feeding gossypol There is little reason for concern about gossypol poisoning when cottonseed meal and whole cottonseed are fed at levels that are sufficient to provide recommended levels of protein for mature cattle diets [81]. Much of the gossypol research in the past has emphasized feeding high levels to demonstrate a gossypol toxicity effect. Defining safe recommendations based upon lowerlevel feeding, such as is commonly employed in practical field conditions, has received inadequate attention. Recommended safe levels (based upon research and field experience) for gossypol in diets containing cottonseed meal or whole cottonseed are given below and summarized in Table 5. Preruminants Diets containing free gossypol from cottonseed products should be avoided in preruminants [63]. Cottonseed meal should not be fed to young

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Table 4 Converting total gossypol content of whole cottonseed to gossypol content of total diet Assumptions Animals Dry, spring-calving mature beef cows (average wt 1150 lb) 120-day supplementation period Body condition score: 5–6 Daily nutrient requirements Net energy maintenance (Mcal)

Net energy gain (Mcal) 0

11.74 Feed analysis Feed

Coastal Bermuda medium-qualitya Whole cottonseeda

Crude protein (lb) 0.86

Dry Net energy Net energy Crude mater (%) maintenance gain (Mcal/kg) protein (%) (Mcal/kg) 90 0.93 0.39 6.0 92

2.41

1.69

23.9

Intake 2.2% of body wt Total 25.3 lb dry-matter basis Average-quality roughage (Bermuda grass; 90% dry matter) Whole cottonseed (92% dry matter) Total

Dry matter (kg) As fed (kg) 10.25 11.38 1.26 11.50

1.36 12.75

Diet 10.7% whole cottonseed in total diet (as fed) Laboratory analysis 1.2% total gossypol (kernel or meat basis) Calculations Step 1. Convert gossypol value to whole-seed basis by multiplying reported value by 0.65. (The meat portion of cottonseed is about equal to 65% of the total seed.) Note: Assume for this calculation that gossypol present in the hulls is negligible. 1.2  0.65 ¼ 0.78% Step 2. Multiply % in whole seed by the % cottonseed in the total diet (10.7% of total diet). 0.78  0.107 ¼ 0.0835% Step 3. Multiply by 10,000 to convert to parts per million. 0.0835  10,000 ¼ 835 ppm a Data from National Research council. Nutrient requirements of beef cattle, 6th edition. Washington, DC: National Academy Press. 1984.

calves as part of a liquid diet [42]. When a young ruminant drinks milk, the esophageal groove closes and causes most of the liquid to bypass the rumen and go directly into the omasum. This prevents detoxifying free gossypol regardless of rumen development. Results of research in North Carolina to

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Table 5 Maximum safe level for free gossypol in the total dieta

Preruminants Growing steers and heifers Young developing bulls Mature bulls (during breeding season, ~120 d) Mature cows

Cottonseed meal (ppm)

Whole cottonseed (ppm)

100–200 200 150 200 600

100–200 900 600 900 1200

a

The reason for the difference in gossypol effect between cottonseed meal and whole cottonseed is poorly understood. Possibly the gossypol in whole cottonseed is released more slowly. More research is needed to gain a better understanding of this phenomenon. This table was developed from historical recommendations [48] and known safe feeding levels common used in the cattle industry [8,9,38,81,85,86].

determine the safe level of dietary free gossypol for young calves indicate that the maximum level is 100 ppm, as is suggested for swine [35]. This level could also be expressed as less than 140 mg/cwt/day or less than 3.1 mg/kg/day. Recent work by Risco and colleagues found that a diet containing 200 ppm free gossypol was safe in Holstein bull calves from 1 to 120 days of age [38]. A recent South African study confirmed the safety of up to 200 mg free gossypol in Holstein and Jersey calves from 14 days to 3 months of age [82]. In one study, twenty-four of 57 calves (7–15 weeks of age) that were fed a diet containing 33% cottonseed meal and 100 to 220 ppm free gossypol died. The deaths continued for 4 weeks after withdrawal of cottonseed meal from the diet [47]. Cottonseed meal with 400 mg free gossypol/kg of diet dry matter (DM) was associated with the death of four of ten calves in a Florida study. These studies confirmed earlier work by Risco, which reported that 400 mg free gossypol/kg of diet can be toxic to calves [38]. A common concern pertaining to beef herds in which whole cottonseed is used to supplement cow feed during the winter is the relative risk of gossypol intoxicating nursing calves that consume variable amounts of whole cottonseed during this winter supplementation period. The risk varies between spring and fall calving herds. Spring calving herds are at a low risk because most calves are born after the typical supplementation period. In fall calving and year-round calving herds higher levels of risk for nursing calves theoretically exist. Calves nursing from cows that are fed recommended levels of whole cottonseed as a winter supplement (<0.5% body weight) have not been observed to consume enough whole cottonseed to result in gossypol toxicosis [83]. Furthermore, gossypol is not excreted in significant quantities in milk [36]. Bulls Feeding recommended levels of cottonseed products (<4 lb/head/day of expander-processed meal, 4 lb/head/day of screw-processed meal, or 5 lb/

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head/day of whole cottonseed) should not pose a problem for bull fertility when mature bulls are fed with cows during the breeding season, assuming that the cottonseed is well distributed and fed on a daily or every-other-day basis [8,84]. Concurrent feeding of Vitamin E might reverse negative reproductive effects when gossypol is fed at higher than recommended levels [78]. The relative risk of bull exposure to excessive free gossypol varies with the timing of the breeding season. With spring calving herds the breeding season follows the usual supplementation period, so minimal risk is present. With herds calving in the fall or on a year-round basis, young developing bulls in particular could be at risk in situations in which excessive amounts of whole cottonseed or cottonseed meal are fed to the cow herd. Growing calves (excluding pre-ruminants) Whole cottonseed should be limited to 15% of the total diet for growing cattle [9,85]. This feeding level should normally result in a gossypol level below the maximum recommendation of 900 ppm [9,86]. Cows Commercial beef cows that receive cottonseed meal as a protein source in mixed feed or cottonseed meal or whole cottonseed as a supplement are unlikely to be in danger of toxicosis. A mature beef cow in a production environment will not usually receive enough cottonseed meal or whole cottonseed to tax the rumen’s gossypol detoxification abilities. Recommended maximum levels of whole cottonseed or cottonseed meal per day have been reported to be 1.6 to 2.7 kg [37]. Other investigators have suggested that safe levels vary from 2.3 to 3.6 kg of whole cottonseed/head/day for mature dairy cows [53,84,86]. This level should normally be below the maximum gossypol recommendation of 1200 ppm for adult cattle [86]. Alternative processing methods Pelleting of whole cottonseed, although not a common procedure, is one mechanism for decreasing the toxicity of gossypol. Cottonseed glands are ruptured by the heat and pressure produced during the mechanical action of pelleting or extruding. In one study, pelleting reduced free gossypol by as much as 70% in whole cottonseed and by 48% in cottonseed meal [48]. Pelleting or extruding increases the percentage of positive gossypol isomers [87]. Although pelleting might reduce free gossypol in whole seed, this practice might be contraindicated because of increased cost, potential rancidity problems after prolonged storage, and an increased rate of fat release. Recommended levels of cottonseed supplementation Whole cottonseed generally should be limited to 15% to 20% of the total diet (dry matter) of cattle with a functioning rumen. Young developing bulls

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should probably be restricted to 10% or less. When using combinations of cotton products, combined concentrations of gossypol must be considered. A high intake of protein, calcium, or iron seems to protect against gossypol toxicity [88,89]. The summary of a 1991 symposium on managing gossypol in cottonseed products states ‘‘There has been no work done which indicates that the result of feeding cottonseed meal or whole cottonseed at the usual levels of supplementation to the beef breeding herd results in a measurable decrease or even a nonsignificant decrease in salable calf crop. There is evidence indicating alterations in tissues, and in some measures of reproductive performance that are not related to actual calf crop percentage, but there has not been a controlled experiment done which would indicate that whole cottonseed or cottonseed meal at traditionally fed levels of supplementation results in a lower calf crop.’’ [20]

Special concerns Small producers might experience toxicosis or feed-related deaths that are not recognized as such. Although it might not be economically feasible to sample individual sacks of feed for gossypol, producers and veterinarians should be aware that the potential exists for gossypol toxicosis to occur after feeding commercially prepared and packaged feeds. Special feed such as ‘‘calf starter ration’’ could contain toxic gossypol levels. Currently, batches of whole cottonseed and cottonseed meal are not routinely tested for free or total gossypol levels. Consequently, knowledgeable recommendations are difficult to make, particularly when any of these products are included in pre-ruminant diets. There are no specific laws that deal with gossypol levels in livestock feed. The question of who is responsible when these toxicities occur is controversial. From a public health standpoint, gossypol consumption by food animals is of little consequence. The toxin is not found in muscle, and it is unlikely that a person would eat enough liver or kidney over a sufficient period of time to result in toxicosis. Cottonseed flour has been investigated as a food source in various parts of the world where cotton is grown. There is some concern that in certain developing countries protein shortages might lead to higher amounts of cottonseed products in human diets [90].

Summary Despite the potential for gossypol toxicosis (particularly in pre-ruminants) and risk factors associated with impaired fertility in bulls, cottonseed products offer a safe alternative feed for cattle producers when fed at recom-

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mended levels. Beef producers seeking to lower production costs should consider using cotton byproducts in their feeding programs. If carefully incorporated, cotton byproduct feeds can reduce feed costs while maintaining or increasing the level of cattle performance. Cottonseed meal will remain a standard protein supplement for beef cattle throughout the country. Whole cottonseed has much potential for Southern producers near cotton gins if it is purchased in a timely fashion and fed according to recommendations. Cotton gin trash, cottonseed hulls, and cotton textile mill waste also have potential economic benefits, especially to producers located near cotton and cottonseed processing facilities. References [1] Bath D, Dunbar J, King J, Berry S, Olbgrich S. Byproducts and unusual feedstuffs. Feedstuffs reference issue and buyer’s guide. Feedstuffs 2001;73:30. [2] National Research Council. Nutrient requirements of beef cattle. 7th edition. Washington DC: National Academy Press; 1996. [3] Rogers GM, Poore MH. Alternative feeds for reducing beef cow feed costs. Vet Med 1994;89:1073–84. [4] Williams GL. Modulation of luteal activity in postpartum beef cows through changes in dietary lipid. J Anim Sci 1989;67:785–93. [5] Arieli A. Whole cottonseed in dairy cattle feeding: a review. Anim Feed Sci Technol 1998;72:97–110. [6] Moore JA, Swingle RS, Hale WH. Effects of whole cottonseed, cottonseed oil or animal fat on digestibility of wheat straw diets by steers. J Anim Sci 1986;63:1267. [7] Poore MH. Whole cottonseed should be explored by Carolina cattle producers. Carolina Cattle Connection 1995;40:. [8] Lusby K, Herd D, Randel RD. ‘‘Recommendation statement’’ on feeding cottonseed and cottonseed meal to beef cattle in Texas and Oklahoma. Cattle research with gossypol containing feeds. Memphis, TN: National Cottonseed Products Association; 1991. p. 93–6. [9] Poore MH. Whole cottonseed in sorghum-silage based diets for developing heifers. J Anim Sci 1994;72:382. [10] Preston RL, Bartle SJ, Rule DC. Effect of whole cottonseeds in cattle finishing diets. Texas Tech University Agricultural Sciences Technical Report No. T-5 1989;22:263. [11] Calhoun MC, Huston JE, Ueckert DN, et al. Performance of yearling heifers fed diets containing whole cottonseed. Texas Agricultural Experiment Station. Beef Cattle Research in Texas, Progress Report 1990;4839:75. [12] Poore MH, Harvey RW, Spears JW. Forage needs for beef cattle in North Carolina. In: Production and utilization of pastures and forages in North Carolina, Vol. 305. North Carolina Agricultural Research Service Technical Bulletin; 1995. p. 85–90. [13] Washburn SP, Whitlow LW, Hagler WM Jr. Effects of moldy cottonseed on reproduction in beef and dairy heifers. Biodeterioration Research 1994;4:121. [14] Bernard JK, Calhoun MC, Martin SA. Effect of coating whole cottonseed on performance of lactating dairy cows. J Dairy Sci 1999;82:1296–304. [15] Moore JA, Poore MH, Swingle RS. Influence of roughage source on kinetics of digestion and passage, and on calculated extents of ruminal digestion in beef steers fed 65% concentrate diets. J Anim Sci 1990;68:3412. [16] Goetsch AL, Owens FN, Doran BE. Whole or ground corn and different roughage sources in high concentrate diets for beef heifers. Okla Agr Exp Sta Res Rep 1986;MP-118:154.

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