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Protein and Mineral Digestibility of Three Pelleted Equine Feeds and Subsequent Nitrogen and Phosphorus Waste Excretion1
The Professional Animal Scientist 22 (2006):341–345
Protein and Mineral Digestibility of Three Pelleted Equine Feeds and Subsequent Nitrogen and Phosphorus Waste Excretion J. A. WILSON,*1 C. W. BABB,† and R. H. PRINCE‡ *Department of Animal Science, †Department of Chemistry, and ‡Department of Mathematics and Computer Science, Berry College, Mount Berry, GA 30149
Abstract This experiment was designed to examine the digestibilities of 3 commercially available equine feeds when fed with Bermudagrass hay, and the N and P waste associated with these types of concentrate feeds. The feeds used were a 12% protein pelleted feed produced by 3 different manufacturers. Nine mature Quarter Horse geldings were used in a 3 × 3 Latin square design. The apparent digestibilities for Ca were 39.02%, 25.47%, and 39.00% for feeds A, B, and C , respectively, with apparent Ca digestibilities of feeds A and C significantly higher (P < .05) than feed B. Apparent digestibility of P was greater (P < .009) for feed A (28.65%, compared with feed B (15.63%) and C (16.08%). There were no differences for apparent CP digestibilities (feed A = 71.19%, feed B = 69.39%, and feed C = 68.37%). The apparent digestibilities for K and Mg were similar between feeds. The P and total kjeldahl N (TKN) in manure was similar among treatment groups. The mean urinary excretion of Ca, P,
1
To whom correspondence should be adddressed: [email protected]
and TKN was similar among feeds. For feeds A, B, and C the TKN results were 1.08%, 1.13 % and 1.10%, respectively. The mean urinary excretion of K and Mg was greater for feed B compared with feeds A and C (P < .05). Data from this study suggest that similar types of equine pelleted feeds may vary slightly in apparent digestibility of nutrients but appear to produce similar amounts of waste products of environmental concern. Key words: equine, apparent digestibility, nitrogen, phosphorus
Introduction The majority of horses today are fed a commercial concentrate feed to supplement the forage portion of their diet. These products are purchased based upon factors such as perceived quality, palatability, and cost. Feeding highly digestible commercial feeds at levels to provide the needed supplementation of nutrients to balance what is provided in the forage is ideal for the horse and should also help to preserve environmental conditions. One of the primary ingredients of concentrate feed is protein, which, when digested, produces by-prod-
uct N in the form of ammonia and organic N (in manure). Of the minerals, Ca and P are of primary concern. Feeds are often supplemented with these minerals in specific amounts and ratios, and some of them will end up in the manure. Although manure can be a source of plant nutrients, it also can contaminate surface and ground water if handled improperly. Two of the primary constituents of horse manure that may cause water quality problems are nitrate and P (Waskom and Davis, 1999). Horse owners often stockpile manure as a management tool, and extreme nitrate loads can develop below an unroofed manure pile (Miner et al., 2000). Excess nitrate in drinking water can be toxic to warmblooded animals, leading to methemoglobinemia (EPA, 2001; Risse, 1999). Over half of all horse operations nationwide report that the application of manure and stall waste on fields is the primary method of on-site disposal (NAHMS, 1998). When manure is land-applied as fertilizer, the application rates are often designed to meet crop N requirements, which cause an excess of P application (Sharpley and Beegle, 2001). An over supply of N
342
and P can end up in ground and surface water resulting in excessive vegetative growth and subsequent water quality degradation, defined as eutrophication. The objectives of this study were to determine 1) the digestibilities of 3 similar, commercially available pelleted equine feeds when fed with Bermudagrass hay, and 2) differences in the N and P concentration of waste associated with the 3 treatment feeds.
Wilson et al.
TABLE 1. Nutrient analysis of Bermudagrass hay.a Analyte
Trial 1
Trial 2
Trial 3
CP (%) P (%) K (%) Ca (%) Mg (%)
12.0 0.19 1.40 0.31 0.25
11.2 0.21 1.70 0.31 0.20
10.6 0.17 1.90 0.26 0.16
a
DM basis.
Materials and Methods This study was conducted in accordance with the guidelines of the Berry College Institutional Animal Care and Use Committee. Nine mature stock-type geldings, ranging in age from 8 to 25 yr of age, were randomly assigned treatments within 3 simultaneous 3 × 3 Latin square design experiments to compare digestibilities of 3 equine pelleted feeds (feeds A, B, and C) and N and P content in excretion products. The nutrient digestibilities analyzed were energy, CP, P, Ca, K, and Mg. Each period consisted of an 18-d dietary adjustment period followed by a 4-d total collection period. During the dietary adjustment period, horses were housed in a 92 × 48-m dry lot and housed in individual box stalls (3.05 × 3.05 m) during the collection period. The stalls were set up with 2 rows of stalls, back to back, such that 2 stalls shared a common back wall. The lower portion of the stalls consisted of solid walls, with the top portion containing bar partitions which allowed visual contact among horses. Previous to the start of the experiment, the horses had been used as trail horses, which consisted of light exercise of approximately 1-h rides 3 times/wk. Horses were not exercised for 1 month prior to the start of the experiment. All horses were fed meals twice daily in individual stalls that were the stalls used during the collection periods. The horses were fed the concentrate portion of the
meal first, followed immediately by the hay portion. Horses were given access to fresh, clean water throughout all portions of the study. Horses were fed the treatment feed at 0.8 % BW/d, and Bermudagrass (Tifton 44) hay at 1.2 % BW/d. The BW of horses were measured and recorded every week, and the amount of feed refusal was recorded daily. Treatment feed intakes ranged between 2.0 to 2.5 kg/ d, based on individual BW. Hay intakes ranged between 5.9 and 7.3 kg/d. There were no refusals of either the treatment feed or the hay. Horses were hand-walked twice daily during the collection phases of the project. Body weights ranged from 454 to 636 kg, with average BW of 543 kg. Horses remained healthy throughout the study. There were no incidences of colic or other digestive disorders. Some horses did develop mild edema in the lower leg during the collection phases of the study, but this was resolved within a day of the horses being returned to the dry lot. Hay used was Tifton 44 Bermudagrass hay produced at Berry College, and 10 random core samples from the hay were obtained and composited during each trial period. Crude protein and mineral analysis is shown in Table 1. For each treatment period, 5 random samples of each concentrate feed were composited and sent for analysis. Hay and treatment feeds were analyzed at the Feed and Environ-
mental Water Laboratory at the University of Georgia. At the beginning of each treatment period, horses were fitted with fecal and urine collection bags. Fecal and urine collections were taken every 8 h for 96 h, at which time the bags were emptied. Total feces excreted were collected and weighed. A sample of feces was placed in a freezer bag, identified by horse, period, and treatment, and frozen for later analysis. Total urine volume excreted was recorded, and a 35-mL sample was placed in a 100-mL collection cup. The samples were acidified with 3 N HCl at 3% of volume to prevent Ca precipitation and microbial growth, and then frozen for later compositing and analysis. Urine samples were composited by volume for each horse, period, and treatment combination for analysis at the University of Georgia Animal Feed and Environmental Water Laboratory. Representative samples of feed were analyzed for CP, Ca, P, Mg, Na, Cl (AOAC, 2000), ADF and NDF content, and lignin (Ankom Fiber Analyzer, Macedon, NY). Fecal samples were analyzed for DM, Ca, P, Mg, total N (AOAC, 2000), and GE (Adiabatic Calorimeter, Parr Instrument Co., Moline, IL). Representative samples of urine were analyzed for Ca, Mg, P (AOAC, 2000), and total kjeldahl N (TKN) (Clescerl et al., 1999). Data for nutrient analysis and digestibilities were analyzed using SPSS for Windows (SPSS for Windows, Chicago, IL). The experimental design was a Latin square with feed, horse, and trial as the main factors. Means were tested using a Duncan’s Multiple Range Test.
Results and Discussion The hay used throughout the trial was all from the same cutting. The CP ranged from 9.7 to 11.0%, with an average of 10.3%. The P ranged from 0.15 to 0.19%, with
Digestibility of Three Commercial Pelleted Equine Feeds
TABLE 2. Nutrient analysis of treatment feeds.a Analyte
Feed A
Feed B
Feed C
SEM
CP (%) P (%) K (%) Ca (%) Mg (%) Crude Fat (%)
14.6b 0.89b 0.61b 1.14 0.17b 2.22b
15.9c 0.68c 0.85c 0.94 0.33c 3.73c
15.8c 0.66c 1.0c 0.99 0.28c 3.37c
0.225 0.040 0.074 0.091 0.027 0.460
a
DM basis. Means in rows with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test. b,c
an average of 0.17%. There were no differences in nutrient content of the hay relative to the treatment periods. Nutrient analysis of the 3 treatment feeds is shown in Table 2. Crude protein was higher and P lower (P < 0.05) for feeds B and C compared with feed A. K and Mg were lower (P < 0.05) for feed A compared to feeds B and C. There was no significant difference in Ca among feeds. For feeds A and B, the results for CP, Ca, and P are in agreement with the guaranteed analysis. The CP and P are in compliance with the guaranteed analysis for feed C, but Ca exceeded the maximum percent. Apparent digestibilities for the 3 treatment feeds when fed with Bermudagrass hay are shown in Table 3. Apparent energy digestibility was greater for feeds B and C com-
pared to feed A (P < 0.05). Apparent CP digestibility was not different among feeds. The P digestibility was greater for feed A compared with feeds B and C, and Ca digestibility was lower for feed B compared wiht feeds A and C. Apparent digestibilities of K and Mg were similar between feeds. The difference in energy digestibility may be due to the differences in crude fat between the feeds. Feeds B and C had soy oil as a feed ingredient, leading to a higher crude fat relative to feed A, which did not have oil as a feed component. Both feeds B and C did not meet guaranteed analysis for crude fat, but had significantly greater crude fat content than feed A. The differences in digestibility of Ca and P are likely due to the form of the minerals provided in the feeds and the subsequent bioavai-
TABLE 3. Apparent digestibilities of treatment feeds fed with Bermudagrass hay. Analyte
Feed A
Feed B
Feed C
SEM
Energy (%) CP (%) P (%) K (%) Ca (%) Mg (%)
44.49a 71.2 28.7a 68.2 39.0a 45.8
47.03b 69.4 15.6b 66.1 25.6b 42.8
46.33b 68.4 16.1b 69.6 39.0a 43.2
0.283 0.78 3.31 1.41 3.14 2.57
a,b Means in rows with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test.
343
lablities. The primary Ca supplement in feeds A and C is Ca carbonate, whereas feed B contained several Ca supplements, including Ca pantothenate, dicalcium phosphate, and Ca iodate. Calcium carbonate is generally considered to have an equal or greater bioavailblity compared with other supplemental Ca sources (Soares, 1995a), yet Ca carbonate was equivalent to chelated Ca in absorption of Ca when fed to yearling horses (Highfill et al., 2005). Several factors influence Ca absorption from the gut, and more research is needed to identify the optimum amount and form of Ca supplementation in horses. The variation in P availability from plant products and commercially used P supplements can be quite large. Both feeds A and B listed dicalcium phosphate as a P (and Ca) source, but feed A appeared to supplement it in greater amounts because of its relative position on the ingredients list. The form of dicalcium phosphate (hydrated vs. anhydrous) can affect bioavailability; the hydrated form is generally considered to be more available (Soares, 1995b). Furthermore, the P and Ca compounds and subsequent availabilities will vary with grain products and byproducts in commercial feeds. Because feed labels often list general ingredients, it is difficult to identify the exact grains and specific amounts used. In addition to the forms of these minerals affecting their availability, the ratio of Ca to P can affect availability of both minerals. The ratio of Ca to P varied somewhat among the 3 feeds, with it being 1.3 for feed A, 2.7 for feed B, and 1.5 for feed C. It appears that the form of the minerals in the feeds, the amount fed ,and the different ratio of these 2 minerals contributed to a higher apparent P digestibility in feed A compared with feeds B and C and a lower apparent Ca digestibility in feed B compared with feeds A and C.
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Wilson et al.
TABLE 4. Mean mineral levels in urine samples. Analyte K (ppm) Mg (ppm) Na (ppm) P (ppm) S (ppm) Zn (ppm) TKNc (%) Ca (ppm) Fe (ppm)
Feed A
Feed B
Feed C
SEM
10,272.44 821.93a 743.09 33.44 2,381.89 0.38 1.09 1,866.89 0.45
12,860.78 1094.24b 736.41 9.09 3,043.22 0.41 1.13 1,974.46 0.43
11,909.44 870.74a 727.14 11.46 2,324.67 0.38 1.08 1,620.56 0.51
571.08 53.33 73.46 6.81 190.75 0.03 0.03 122.91 0.05
a,b Means in row with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test. c TKN = total Kjeldahl N.
Differences in urinary mineral concentrations are indicated in Table 4. The only significant difference found among diets was that Mg in feed B was greater than in either feeds A or C. All 3 treatment feeds used Mg oxide as a supplement, and it may be that feed B contained a greater total amount of Mg compared to the other feeds. The urinary mineral data for Ca falls within the range of that reported for mares consuming diets varying in cation-anion balance, and consisting of a foundation pellet fed in combination with grass hay (McKenzie et al., 2003). However, the data for urinary P excretion reported in the current study is less, and the data on urinary Mg excretion is greater. It is likely that the differences in mineral composition of the diets contributed to the differences in urinary excretion of some minerals.
All 3 treatment feeds were measured to have a GE value of 3.83 calories/kg, but the energy digestibility was less for feed A compared with feeds B and C. The feeds were composed of blends of grains and molasses plus vitamins and minerals. The crude fat content varied among feeds, with A, B, and C having guaranteed analyses of 2.5%, 4.5%, and 3.5%, respectively. By analysis, feed C had significantly less fat than feeds A and B (Table 2). Compared to the guaranteed analysis, measured fat in feeds B and C was less, which may be of concern to horse owners who purchase feed (partially) based on fat content. Although there were some differences in apparent digestibility for some of the components of the treatment feeds, no feed appeared to be superior to the other 2. All 3 feeds are considered quality feeds
TABLE 5. P and TKN content of fecal matter (DM basis).a Analyte P (%) TKNb (%) a
Feed A
Feed B
Feed C
SEM
0.85 1.45
0.77 1.52
0.73 1.44
0.04 0.20
Average moisture content of fresh fecal matter is 75%. TKN = total Kjeldahl N.
b
produced by well-known companies. There were no refusals for any of the feeds, and horses maintained BW and BCS throughout the study. The P and TKN in manure are shown in Table 5. There were no differences in the fecal excretion of N and P relative to the treatment feed consumed by the horses. The percentages of P in manure reported for this study are similar to published data, but the percentages of TKN in manure was less (Western Fertilization Handbook, 1985). Other reports of equine manure characteristics are difficult to use for comparison because that data represents a combination of fresh urine and feces ((ASAE, 2003; Lawrence et al., 2003). Estimates indicate that the amount of livestock waste is 13 times greater than the amount of human sanitary waste generated in the United States (EPA, 2001). The average mature horse produces 2.8 kg feces and 1.6 kg urine per 100 kg of BW daily (Lawrence et al., 2003), or about 20.4 kg of waste each day (EPA, 2001). Because horse owners have not been subjected to strict regulations regarding handling of manure compared to other livestock enterprises, they may not take responsibility of managing this waste in an environmentally sound manner. Over 80% of horse operations in the nation retain manure produced by their horses on-site, and only 11% have manure removed from their property (NAHMS, 1998). More than 50% of horse operations reportedly apply manure and stall waste on fields as a means of on-site disposal (NAHMS, 1998). If manure is applied properly to cropland and pastures, the nutrients in manure can support plant growth and reduce fertilizer costs. In addition, organic matter in manure can enhance soil physical properties and water-holding capacity (Waskom and Davies, 1999). When manure is not managed properly, runoff water from
Digestibility of Three Commercial Pelleted Equine Feeds
dry lots, pastures, and manure storage or compost areas carries pollutants such as N, P, and bacteria into surface waters (Davis and Swinker, 2002).
Implications Results of this study indicate that different commercial pelleted equine feeds, when fed with Bermudagrass hay, produce similar amounts of N and P in manure. Although there were some slight differences in the nutrient composition and apparent digestibility of the feeds, none appeared to be superior relative to reduced excretion of N and P in the waste or maintenance of BW. These results provide additional information for the data base of nutrient content in horse waste. Further research addressing dietary manipulation, physiologic status, and waste management strategies is needed to identify the impact of horse waste on the environment.
Literature Cited AOAC. 2000. Official Methods of Analysis. 17th ed. Association of Official Analytical Chemists, Gaithersburg, MD.
ASAE. 2003. Manure production and characteristics. ASAE Standards. D3841.1 American Society of Agriculture Engineers, St. Joseph, MI. Clescerl, L. S., A. E. Green, and A. D. Eaton. 1999. Standard methods for the examination of water and wastewater. Method 4500B. Nitrogen. 20th ed. Am. Public Health Assoc. Davis, J. G. and A. M. Swinker. 2002. Horse manure management. Colorado State Univ. Cooperative Ext. Bull. 1.219, Fort Collins. EPA. 2001. Managing livestock, poultry, and horse waste to prevent contamination of drinking water. In Source Water Protection Practices Bulletin. EPA-916-F-01-026. United States Environmental Protection Agency. Highfill, J., G. Potter, E. Eller, P. Gibbs, B. Scott, and D. Hood. 2005. Comparative absorption of calcium fed in varying chemical forms and effects on absorption of phosphorus and magnesium. Proc. Equine Sci. Soc. p 37. Tucson, AZ. Lawrence, L., J. R. Bicudo, and E. Wheeler. 2003. Horse manure characteristics literature and database review. In Proc. 9th International Symposium on Animal Agriculture and Food Processing Wastes. p 277. Raleigh, N.C. McKenzie, E. C., S. J. Valberg, S. M. Godden, J. D. Pagan, G. P. Carlson, J. M. MacLeay, and F. D. DeLaCorte. 2003. Comparison of volumetric urine collection versus single-sample urine collection in horses consuming diets varying in cation-anion balance. Am. J. Vet. Res. 64:284. Miner, J. R., F. J. Humenik, and M. R. Overcash. 2000. In Managing Livestock Waste to Preserve Environmental Quality. p 119. Iowa State University Press, Ames.
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NAHMS. 1998. Equine ’98 Study. United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, National Animal Health Monitoring System. Centers for Epidemiology and Animal Health, Fort Collins, CO. Available: http://www.aphis.usda.gov/vs/ceah/ cahm/Equine/equin.htm. Accessed December 2005. Risse, M. 1999. Maintaining water quality in grazing systems. p 65. Proc. Grazing Management Training School, Mount Berry, GA. Sharpley, A., and D. Beegle, 2001. Managing phosphorus for agriculture and the environment. Pennsylvania State University College of Agricultural Sciences, Agriculture Research and Cooperative Extension. Soares, J. H., Jr. 1995a. Calcium bioavailability. In Bioavailability of Nutrients for Animals. C. B. Ammerman, D. H. Baker, and A. J. Lewis, ed, p 95. Academic Press, San Diego, CA. Soares, J. H., Jr. 1995b. Phosphorus bioavailability. In Bioavailability of Nutrients for Animals. C. B. Ammerman, D. H. Baker, and A. J. Lewis, ed. p 257. Academic Press, San Diego, CA. Waskom, R. M., and J. G. Davis. 1999. Best management practices for manure utilization. Colorado State Univ. Cooperative Ext. Bull. 568A, Fort Collins. Western Fertilization Handbook. 1985. Soil organic matter. G.R. Hawkes, K. B. Cambell, A. E. Ludwick, R. M. Millaway, and R. M. Thorup, ed. p143. California Fertilizer Association, Sacramento.
Protein and Mineral Digestibility of Three Pelleted Equine Feeds and Subsequent Nitrogen and Phosphorus Waste Excretion J. A. WILSON,*1 C. W. BABB,† and R. H. PRINCE‡ *Department of Animal Science, †Department of Chemistry, and ‡Department of Mathematics and Computer Science, Berry College, Mount Berry, GA 30149
Abstract This experiment was designed to examine the digestibilities of 3 commercially available equine feeds when fed with Bermudagrass hay, and the N and P waste associated with these types of concentrate feeds. The feeds used were a 12% protein pelleted feed produced by 3 different manufacturers. Nine mature Quarter Horse geldings were used in a 3 × 3 Latin square design. The apparent digestibilities for Ca were 39.02%, 25.47%, and 39.00% for feeds A, B, and C , respectively, with apparent Ca digestibilities of feeds A and C significantly higher (P < .05) than feed B. Apparent digestibility of P was greater (P < .009) for feed A (28.65%, compared with feed B (15.63%) and C (16.08%). There were no differences for apparent CP digestibilities (feed A = 71.19%, feed B = 69.39%, and feed C = 68.37%). The apparent digestibilities for K and Mg were similar between feeds. The P and total kjeldahl N (TKN) in manure was similar among treatment groups. The mean urinary excretion of Ca, P,
1
To whom correspondence should be adddressed: [email protected]
and TKN was similar among feeds. For feeds A, B, and C the TKN results were 1.08%, 1.13 % and 1.10%, respectively. The mean urinary excretion of K and Mg was greater for feed B compared with feeds A and C (P < .05). Data from this study suggest that similar types of equine pelleted feeds may vary slightly in apparent digestibility of nutrients but appear to produce similar amounts of waste products of environmental concern. Key words: equine, apparent digestibility, nitrogen, phosphorus
Introduction The majority of horses today are fed a commercial concentrate feed to supplement the forage portion of their diet. These products are purchased based upon factors such as perceived quality, palatability, and cost. Feeding highly digestible commercial feeds at levels to provide the needed supplementation of nutrients to balance what is provided in the forage is ideal for the horse and should also help to preserve environmental conditions. One of the primary ingredients of concentrate feed is protein, which, when digested, produces by-prod-
uct N in the form of ammonia and organic N (in manure). Of the minerals, Ca and P are of primary concern. Feeds are often supplemented with these minerals in specific amounts and ratios, and some of them will end up in the manure. Although manure can be a source of plant nutrients, it also can contaminate surface and ground water if handled improperly. Two of the primary constituents of horse manure that may cause water quality problems are nitrate and P (Waskom and Davis, 1999). Horse owners often stockpile manure as a management tool, and extreme nitrate loads can develop below an unroofed manure pile (Miner et al., 2000). Excess nitrate in drinking water can be toxic to warmblooded animals, leading to methemoglobinemia (EPA, 2001; Risse, 1999). Over half of all horse operations nationwide report that the application of manure and stall waste on fields is the primary method of on-site disposal (NAHMS, 1998). When manure is land-applied as fertilizer, the application rates are often designed to meet crop N requirements, which cause an excess of P application (Sharpley and Beegle, 2001). An over supply of N
342
and P can end up in ground and surface water resulting in excessive vegetative growth and subsequent water quality degradation, defined as eutrophication. The objectives of this study were to determine 1) the digestibilities of 3 similar, commercially available pelleted equine feeds when fed with Bermudagrass hay, and 2) differences in the N and P concentration of waste associated with the 3 treatment feeds.
Wilson et al.
TABLE 1. Nutrient analysis of Bermudagrass hay.a Analyte
Trial 1
Trial 2
Trial 3
CP (%) P (%) K (%) Ca (%) Mg (%)
12.0 0.19 1.40 0.31 0.25
11.2 0.21 1.70 0.31 0.20
10.6 0.17 1.90 0.26 0.16
a
DM basis.
Materials and Methods This study was conducted in accordance with the guidelines of the Berry College Institutional Animal Care and Use Committee. Nine mature stock-type geldings, ranging in age from 8 to 25 yr of age, were randomly assigned treatments within 3 simultaneous 3 × 3 Latin square design experiments to compare digestibilities of 3 equine pelleted feeds (feeds A, B, and C) and N and P content in excretion products. The nutrient digestibilities analyzed were energy, CP, P, Ca, K, and Mg. Each period consisted of an 18-d dietary adjustment period followed by a 4-d total collection period. During the dietary adjustment period, horses were housed in a 92 × 48-m dry lot and housed in individual box stalls (3.05 × 3.05 m) during the collection period. The stalls were set up with 2 rows of stalls, back to back, such that 2 stalls shared a common back wall. The lower portion of the stalls consisted of solid walls, with the top portion containing bar partitions which allowed visual contact among horses. Previous to the start of the experiment, the horses had been used as trail horses, which consisted of light exercise of approximately 1-h rides 3 times/wk. Horses were not exercised for 1 month prior to the start of the experiment. All horses were fed meals twice daily in individual stalls that were the stalls used during the collection periods. The horses were fed the concentrate portion of the
meal first, followed immediately by the hay portion. Horses were given access to fresh, clean water throughout all portions of the study. Horses were fed the treatment feed at 0.8 % BW/d, and Bermudagrass (Tifton 44) hay at 1.2 % BW/d. The BW of horses were measured and recorded every week, and the amount of feed refusal was recorded daily. Treatment feed intakes ranged between 2.0 to 2.5 kg/ d, based on individual BW. Hay intakes ranged between 5.9 and 7.3 kg/d. There were no refusals of either the treatment feed or the hay. Horses were hand-walked twice daily during the collection phases of the project. Body weights ranged from 454 to 636 kg, with average BW of 543 kg. Horses remained healthy throughout the study. There were no incidences of colic or other digestive disorders. Some horses did develop mild edema in the lower leg during the collection phases of the study, but this was resolved within a day of the horses being returned to the dry lot. Hay used was Tifton 44 Bermudagrass hay produced at Berry College, and 10 random core samples from the hay were obtained and composited during each trial period. Crude protein and mineral analysis is shown in Table 1. For each treatment period, 5 random samples of each concentrate feed were composited and sent for analysis. Hay and treatment feeds were analyzed at the Feed and Environ-
mental Water Laboratory at the University of Georgia. At the beginning of each treatment period, horses were fitted with fecal and urine collection bags. Fecal and urine collections were taken every 8 h for 96 h, at which time the bags were emptied. Total feces excreted were collected and weighed. A sample of feces was placed in a freezer bag, identified by horse, period, and treatment, and frozen for later analysis. Total urine volume excreted was recorded, and a 35-mL sample was placed in a 100-mL collection cup. The samples were acidified with 3 N HCl at 3% of volume to prevent Ca precipitation and microbial growth, and then frozen for later compositing and analysis. Urine samples were composited by volume for each horse, period, and treatment combination for analysis at the University of Georgia Animal Feed and Environmental Water Laboratory. Representative samples of feed were analyzed for CP, Ca, P, Mg, Na, Cl (AOAC, 2000), ADF and NDF content, and lignin (Ankom Fiber Analyzer, Macedon, NY). Fecal samples were analyzed for DM, Ca, P, Mg, total N (AOAC, 2000), and GE (Adiabatic Calorimeter, Parr Instrument Co., Moline, IL). Representative samples of urine were analyzed for Ca, Mg, P (AOAC, 2000), and total kjeldahl N (TKN) (Clescerl et al., 1999). Data for nutrient analysis and digestibilities were analyzed using SPSS for Windows (SPSS for Windows, Chicago, IL). The experimental design was a Latin square with feed, horse, and trial as the main factors. Means were tested using a Duncan’s Multiple Range Test.
Results and Discussion The hay used throughout the trial was all from the same cutting. The CP ranged from 9.7 to 11.0%, with an average of 10.3%. The P ranged from 0.15 to 0.19%, with
Digestibility of Three Commercial Pelleted Equine Feeds
TABLE 2. Nutrient analysis of treatment feeds.a Analyte
Feed A
Feed B
Feed C
SEM
CP (%) P (%) K (%) Ca (%) Mg (%) Crude Fat (%)
14.6b 0.89b 0.61b 1.14 0.17b 2.22b
15.9c 0.68c 0.85c 0.94 0.33c 3.73c
15.8c 0.66c 1.0c 0.99 0.28c 3.37c
0.225 0.040 0.074 0.091 0.027 0.460
a
DM basis. Means in rows with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test. b,c
an average of 0.17%. There were no differences in nutrient content of the hay relative to the treatment periods. Nutrient analysis of the 3 treatment feeds is shown in Table 2. Crude protein was higher and P lower (P < 0.05) for feeds B and C compared with feed A. K and Mg were lower (P < 0.05) for feed A compared to feeds B and C. There was no significant difference in Ca among feeds. For feeds A and B, the results for CP, Ca, and P are in agreement with the guaranteed analysis. The CP and P are in compliance with the guaranteed analysis for feed C, but Ca exceeded the maximum percent. Apparent digestibilities for the 3 treatment feeds when fed with Bermudagrass hay are shown in Table 3. Apparent energy digestibility was greater for feeds B and C com-
pared to feed A (P < 0.05). Apparent CP digestibility was not different among feeds. The P digestibility was greater for feed A compared with feeds B and C, and Ca digestibility was lower for feed B compared wiht feeds A and C. Apparent digestibilities of K and Mg were similar between feeds. The difference in energy digestibility may be due to the differences in crude fat between the feeds. Feeds B and C had soy oil as a feed ingredient, leading to a higher crude fat relative to feed A, which did not have oil as a feed component. Both feeds B and C did not meet guaranteed analysis for crude fat, but had significantly greater crude fat content than feed A. The differences in digestibility of Ca and P are likely due to the form of the minerals provided in the feeds and the subsequent bioavai-
TABLE 3. Apparent digestibilities of treatment feeds fed with Bermudagrass hay. Analyte
Feed A
Feed B
Feed C
SEM
Energy (%) CP (%) P (%) K (%) Ca (%) Mg (%)
44.49a 71.2 28.7a 68.2 39.0a 45.8
47.03b 69.4 15.6b 66.1 25.6b 42.8
46.33b 68.4 16.1b 69.6 39.0a 43.2
0.283 0.78 3.31 1.41 3.14 2.57
a,b Means in rows with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test.
343
lablities. The primary Ca supplement in feeds A and C is Ca carbonate, whereas feed B contained several Ca supplements, including Ca pantothenate, dicalcium phosphate, and Ca iodate. Calcium carbonate is generally considered to have an equal or greater bioavailblity compared with other supplemental Ca sources (Soares, 1995a), yet Ca carbonate was equivalent to chelated Ca in absorption of Ca when fed to yearling horses (Highfill et al., 2005). Several factors influence Ca absorption from the gut, and more research is needed to identify the optimum amount and form of Ca supplementation in horses. The variation in P availability from plant products and commercially used P supplements can be quite large. Both feeds A and B listed dicalcium phosphate as a P (and Ca) source, but feed A appeared to supplement it in greater amounts because of its relative position on the ingredients list. The form of dicalcium phosphate (hydrated vs. anhydrous) can affect bioavailability; the hydrated form is generally considered to be more available (Soares, 1995b). Furthermore, the P and Ca compounds and subsequent availabilities will vary with grain products and byproducts in commercial feeds. Because feed labels often list general ingredients, it is difficult to identify the exact grains and specific amounts used. In addition to the forms of these minerals affecting their availability, the ratio of Ca to P can affect availability of both minerals. The ratio of Ca to P varied somewhat among the 3 feeds, with it being 1.3 for feed A, 2.7 for feed B, and 1.5 for feed C. It appears that the form of the minerals in the feeds, the amount fed ,and the different ratio of these 2 minerals contributed to a higher apparent P digestibility in feed A compared with feeds B and C and a lower apparent Ca digestibility in feed B compared with feeds A and C.
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Wilson et al.
TABLE 4. Mean mineral levels in urine samples. Analyte K (ppm) Mg (ppm) Na (ppm) P (ppm) S (ppm) Zn (ppm) TKNc (%) Ca (ppm) Fe (ppm)
Feed A
Feed B
Feed C
SEM
10,272.44 821.93a 743.09 33.44 2,381.89 0.38 1.09 1,866.89 0.45
12,860.78 1094.24b 736.41 9.09 3,043.22 0.41 1.13 1,974.46 0.43
11,909.44 870.74a 727.14 11.46 2,324.67 0.38 1.08 1,620.56 0.51
571.08 53.33 73.46 6.81 190.75 0.03 0.03 122.91 0.05
a,b Means in row with differing superscripts differ (P < 0.05) according to Duncan’s Multiple Range Test. c TKN = total Kjeldahl N.
Differences in urinary mineral concentrations are indicated in Table 4. The only significant difference found among diets was that Mg in feed B was greater than in either feeds A or C. All 3 treatment feeds used Mg oxide as a supplement, and it may be that feed B contained a greater total amount of Mg compared to the other feeds. The urinary mineral data for Ca falls within the range of that reported for mares consuming diets varying in cation-anion balance, and consisting of a foundation pellet fed in combination with grass hay (McKenzie et al., 2003). However, the data for urinary P excretion reported in the current study is less, and the data on urinary Mg excretion is greater. It is likely that the differences in mineral composition of the diets contributed to the differences in urinary excretion of some minerals.
All 3 treatment feeds were measured to have a GE value of 3.83 calories/kg, but the energy digestibility was less for feed A compared with feeds B and C. The feeds were composed of blends of grains and molasses plus vitamins and minerals. The crude fat content varied among feeds, with A, B, and C having guaranteed analyses of 2.5%, 4.5%, and 3.5%, respectively. By analysis, feed C had significantly less fat than feeds A and B (Table 2). Compared to the guaranteed analysis, measured fat in feeds B and C was less, which may be of concern to horse owners who purchase feed (partially) based on fat content. Although there were some differences in apparent digestibility for some of the components of the treatment feeds, no feed appeared to be superior to the other 2. All 3 feeds are considered quality feeds
TABLE 5. P and TKN content of fecal matter (DM basis).a Analyte P (%) TKNb (%) a
Feed A
Feed B
Feed C
SEM
0.85 1.45
0.77 1.52
0.73 1.44
0.04 0.20
Average moisture content of fresh fecal matter is 75%. TKN = total Kjeldahl N.
b
produced by well-known companies. There were no refusals for any of the feeds, and horses maintained BW and BCS throughout the study. The P and TKN in manure are shown in Table 5. There were no differences in the fecal excretion of N and P relative to the treatment feed consumed by the horses. The percentages of P in manure reported for this study are similar to published data, but the percentages of TKN in manure was less (Western Fertilization Handbook, 1985). Other reports of equine manure characteristics are difficult to use for comparison because that data represents a combination of fresh urine and feces ((ASAE, 2003; Lawrence et al., 2003). Estimates indicate that the amount of livestock waste is 13 times greater than the amount of human sanitary waste generated in the United States (EPA, 2001). The average mature horse produces 2.8 kg feces and 1.6 kg urine per 100 kg of BW daily (Lawrence et al., 2003), or about 20.4 kg of waste each day (EPA, 2001). Because horse owners have not been subjected to strict regulations regarding handling of manure compared to other livestock enterprises, they may not take responsibility of managing this waste in an environmentally sound manner. Over 80% of horse operations in the nation retain manure produced by their horses on-site, and only 11% have manure removed from their property (NAHMS, 1998). More than 50% of horse operations reportedly apply manure and stall waste on fields as a means of on-site disposal (NAHMS, 1998). If manure is applied properly to cropland and pastures, the nutrients in manure can support plant growth and reduce fertilizer costs. In addition, organic matter in manure can enhance soil physical properties and water-holding capacity (Waskom and Davies, 1999). When manure is not managed properly, runoff water from
Digestibility of Three Commercial Pelleted Equine Feeds
dry lots, pastures, and manure storage or compost areas carries pollutants such as N, P, and bacteria into surface waters (Davis and Swinker, 2002).
Implications Results of this study indicate that different commercial pelleted equine feeds, when fed with Bermudagrass hay, produce similar amounts of N and P in manure. Although there were some slight differences in the nutrient composition and apparent digestibility of the feeds, none appeared to be superior relative to reduced excretion of N and P in the waste or maintenance of BW. These results provide additional information for the data base of nutrient content in horse waste. Further research addressing dietary manipulation, physiologic status, and waste management strategies is needed to identify the impact of horse waste on the environment.
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ASAE. 2003. Manure production and characteristics. ASAE Standards. D3841.1 American Society of Agriculture Engineers, St. Joseph, MI. Clescerl, L. S., A. E. Green, and A. D. Eaton. 1999. Standard methods for the examination of water and wastewater. Method 4500B. Nitrogen. 20th ed. Am. Public Health Assoc. Davis, J. G. and A. M. Swinker. 2002. Horse manure management. Colorado State Univ. Cooperative Ext. Bull. 1.219, Fort Collins. EPA. 2001. Managing livestock, poultry, and horse waste to prevent contamination of drinking water. In Source Water Protection Practices Bulletin. EPA-916-F-01-026. United States Environmental Protection Agency. Highfill, J., G. Potter, E. Eller, P. Gibbs, B. Scott, and D. Hood. 2005. Comparative absorption of calcium fed in varying chemical forms and effects on absorption of phosphorus and magnesium. Proc. Equine Sci. Soc. p 37. Tucson, AZ. Lawrence, L., J. R. Bicudo, and E. Wheeler. 2003. Horse manure characteristics literature and database review. In Proc. 9th International Symposium on Animal Agriculture and Food Processing Wastes. p 277. Raleigh, N.C. McKenzie, E. C., S. J. Valberg, S. M. Godden, J. D. Pagan, G. P. Carlson, J. M. MacLeay, and F. D. DeLaCorte. 2003. Comparison of volumetric urine collection versus single-sample urine collection in horses consuming diets varying in cation-anion balance. Am. J. Vet. Res. 64:284. Miner, J. R., F. J. Humenik, and M. R. Overcash. 2000. In Managing Livestock Waste to Preserve Environmental Quality. p 119. Iowa State University Press, Ames.
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NAHMS. 1998. Equine ’98 Study. United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, National Animal Health Monitoring System. Centers for Epidemiology and Animal Health, Fort Collins, CO. Available: http://www.aphis.usda.gov/vs/ceah/ cahm/Equine/equin.htm. Accessed December 2005. Risse, M. 1999. Maintaining water quality in grazing systems. p 65. Proc. Grazing Management Training School, Mount Berry, GA. Sharpley, A., and D. Beegle, 2001. Managing phosphorus for agriculture and the environment. Pennsylvania State University College of Agricultural Sciences, Agriculture Research and Cooperative Extension. Soares, J. H., Jr. 1995a. Calcium bioavailability. In Bioavailability of Nutrients for Animals. C. B. Ammerman, D. H. Baker, and A. J. Lewis, ed, p 95. Academic Press, San Diego, CA. Soares, J. H., Jr. 1995b. Phosphorus bioavailability. In Bioavailability of Nutrients for Animals. C. B. Ammerman, D. H. Baker, and A. J. Lewis, ed. p 257. Academic Press, San Diego, CA. Waskom, R. M., and J. G. Davis. 1999. Best management practices for manure utilization. Colorado State Univ. Cooperative Ext. Bull. 568A, Fort Collins. Western Fertilization Handbook. 1985. Soil organic matter. G.R. Hawkes, K. B. Cambell, A. E. Ludwick, R. M. Millaway, and R. M. Thorup, ed. p143. California Fertilizer Association, Sacramento.