J. Anim Sci. 2006. 84:3104-3109. doi:10.2527/jas.2005-607
© 2006 American Society of Animal Science
Voluntary intake and digestibility of reed canarygrass and timothy hay fed to horses1
A. L. Ordakowski-Burk*,2,
R. W. Quinn*,
T. A. Shellem* and
L. R. Vough
1 Departments of *Animal and Avian Sciences and
and
Natural Resource Sciences and Landscape Architecture, University of Maryland, College Park 20742
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Abstract
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Thousands of hectares of timothy (Phleum pretense L.) grown in the Mid-Atlantic region are infected by cereal rust mite (Abacarus hysterix) that causes discoloration and curling of leaves, decreased nutritional quality, and substantial decreases in yield. A decline in production of timothy hay can lower income for hay producers and cause horse owners to search for alternative hays. Low alkaloid reed canarygrass (Phalaris arundinacea L.) hay has potential as an alternative to timothy hay because it grows well in the Mid-Atlantic region, is believed to have a similar nutrient quality to timothy, and is not as susceptible to cereal rust mite. Eleven mature, stalled Thoroughbred geldings (549 ± 12.1 kg) that were exercised daily were used to compare voluntary DMI and apparent nutrient DM digestibility of timothy and low-alkaloid Chiefton variety reed canarygrass hay. Horses were paired by age and BW and randomly assigned to timothy or reed canarygrass hay during a 14-d period to measure voluntary DMI followed by a 4-d period to measure apparent DM digestibility. Both hays met the minimum requirements for DE, CP, Ca, P, K, Fe, and Mn, but they did not meet the minimum requirements for Cu, Zn, and Na for horses at maintenance and averaging 550 kg of BW. Timothy hay seemed to have a lower CP concentration (14.4%) compared with reed canarygrass hay (17.1%) and a more desirable Ca:P ratio at 1.6:1 compared with 0.8:1 for reed canarygrass hay. Horses fed timothy consumed more hay (P <0.001) during the voluntary DMI period compared with horses fed reed canarygrass. Greater voluntary DMI of timothy occurred on d 1, 3, and 5 (P <0.05), but DMI was similar for other days. Apparent DM digestibility was greater in horses fed timothy hay by 9.6% compared with horses fed reed canarygrass hay (P <0.05). Horses fed timothy had greater DM digestibility of ADF (P = 0.001), NDF (P = 0.001), sugar (P = 0.05), and Ca (P = 0.001) but lower apparent DM digestibility of CP (P = 0.012) and crude fat (P = 0.004). Timothy hay was superior in voluntary DMI and apparent DM digestibility compared with low-alkaloid reed canarygrass hay fed to horses.
Key Words: digestibility • hay • horse • reed canarygrass • timothy • voluntary intake
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INTRODUCTION
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Timothy hay is produced on an estimated 34,400 ha in Maryland and is one of the most popular hay species fed to horses in the Mid-Atlantic region of the United States. However, since the late 1980s, cereal rust mite has been infecting timothy in the Mid-Atlantic region, causing discoloration and curling of leaves, decreased nutritional quality, decreased yields up to 70% (Chamberlain et al., 2003
), and a decrease in the income of timothy hay producers. Use of pesticides (e.g., carbaryl) and management techniques including late-fall harvest have decreased the impact of the cereal rust mite; however, resistance to carbaryl is expected to eventually develop. A decline in the production of timothy hay may cause hay producers to grow other forages adapted to the climate of the Mid-Atlantic region, forcing horse owners to find other suitable forage alternatives.
Reed canarygrass shows potential as an alternative hay to timothy hay because it is a tall, leafy, high yielding cool-season perennial grass that grows well in the moist temperate climate and soils of the Mid-Atlantic region, is tolerant to flooding and drought, and has the potential for more summer regrowth (Balasko and Nelson, 2003). Also, newer varieties of reed canarygrass were shown to have equivalent or greater nutrient digestibilities compared with other perennial cool-season grasses (Buxton and Marten, 1989; Buxton, 1990) and have not been reported to be susceptible to the cereal rust mite. In addition, newer varieties of reed canarygrass, such as Chiefton, have lower concentrations of alkaloids (Sheaffer et al., 1990), which should make them more palatable than older varieties.
The objective of this study was to evaluate nutrient composition, voluntary DMI, and apparent DM digestibility of timothy and a low-alkaloid reed canarygrass hay to evaluate it as an alternative to timothy hay for horses.
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MATERIALS AND METHODS
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All animal protocols were approved by the University of Maryland’s Institutional Animal Care and Use Committee. Voluntary DMI and digestibility experiments were conducted to assess the value of feeding low-alkaloid reed canarygrass hay in comparison with feeding timothy hay to horses. The experiments were conducted in October and November of 2004.
Horses
Twelve mature Thoroughbred geldings (9.1 ± 0.8 yr; 549 ±12.1 kg of initial BW), housed at the Equine Research Unit in Ellicott City, MD, were used for both experiments. Data collection for 1 horse was discontinued when the horse began stall walking, which made sample collection impossible. Horses were kept in rubber-matted box stalls (3.6 m2) that were bedded lightly with approximately 2.5 cm of pelleted wood fibers (Woody Pet Products Inc., Surrey, British Columbia, Canada) except during the total collection period in the digestibility experiment, in which all bedding was removed.
All horses had routine veterinary medical care, before the beginning of the experiments, that included de-worming (Zimectrin, Bayer Corporation, Shawnee Mission, KS), teeth-floating if needed, and vaccinations if needed (Eastern and Western encephalitis, rabies, rhinopneumonitis, influenza, Potomac horse fever, tetanus, and West Nile). Horses were weighed using a livestock platform scale before and after each experimental period. Horses were walked (1.5 m/s) for 30 min once daily at 1400 or 1440 using an automated 6-horse exerciser (Priefert, Mt. Pleasant, TX), except during the total collection period in the digestibility experiment, during which they were each hand-walked for 10 min/ d to ensure total fecal collection.
Diets
Small square-baled orchardgrass (Dactylis glomerata L.), timothy, and reed canarygrass hays were purchased from local Maryland hay farmers before beginning the study. Orchardgrass hay was fed during the initial acclimation period before the experimental protocol commenced. The orchardgrass, timothy, and reed canarygrass hays were second, third, and second cuttings, respectively, and all were harvested during 2004. All hays were regrowth cuttings and as such had a high leaf to stem ratio. Reed canarygrass and timothy hays were cut in the preboot stage. The reed canarygrass hay was of the low-alkaloid Chiefton variety (Seed Research of Oregon, Corvallis, OR). A visual inspection by the University of Maryland Extension Forage Specialist was performed to ensure that the hays were essentially pure for the desired hay species (L. Vough, personal communication). Random core samples of the hays were taken and submitted in duplicate for nutrient analysis (Dairy One, Ithaca, NY; Table 1). Hay was offered in a rope, hay net that was hung approximately 1.5 m from the ground, and over a wooden box feeder mounted at floor level to catch the orts. Fresh clean water, and salt containing only sodium chloride, were available at all times.
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Table 1. Nutrient composition1 of timothy and reed canarygrass hays fed to mature Thoroughbred geldings during the intake and digestibility experiments
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Voluntary Intake Experiment
Geldings were housed in stalls, fed, and exercised for 1 wk before the beginning of the study to allow for acclimation to the experimental conditions. They were offered fresh clean water twice daily (0730 and 1930) and were fed orchardgrass hay twice daily (0730 and 1930) to meet their maintenance requirement for DE (NRC, 1989). Stalls were cleaned thrice daily (0800, 1400, and 1930). After the acclimation period, horses were paired by age and BW and randomly assigned to reed canarygrass (n = 6) or timothy hay (n = 5). Horses were offered their experimental hay in excess of voluntary intake (~3.2% of BW) during the 14-d voluntary DMI period. The amount of hay consumed and refused was recorded twice daily. Any orts remaining at the morning feeding were weighed, recorded, subtracted from the daily hay intake of the previous day, and then discarded.
Digestibility Experiment
The digestibility experiment immediately followed the voluntary intake experiment using the same geldings and following the same housing and exercising procedures previously described. Horses were maintained on their experimental hay fed in the voluntary DMI experiment but were fed 2.2% of their BW daily, which was divided equally and fed in 2 meals (0730 and 1930) for a 5-d period to allow for acclimation to the dietary level before the beginning of the total fecal collection. Horses were fed slightly above their maintenance requirement for DE (2.2% of BW) to ensure BW loss did not occur. Orts were collected daily, weighed, and discarded to allow for calculation of daily hay intake.
After the acclimation period, total collection of feces was performed for 4 d following the methods of Ordakowski et al. (2001). Manure was removed thrice daily (0800, 1400, and 2000) for calculation of total daily fecal output. Before removing feces from the stalls, a subsample (approximately 0.2 kg) of feces was obtained from the ground for each horse, placed in a collection bag, weighed, and placed aside to be weighed with the remaining feces collected that day. The remaining feces were collected into 88-L plastic containers lined with plastic bags that were closed throughout the day to maintain the moisture content of the manure. Subsamples of feces were dried in a forced-air oven and ground through a 0.5-mm screen in a Cyclone Mill (UDY Corp., Fort Collins, CO), composited, mixed thoroughly, and another subsample was submitted in duplicate for nutrient analysis (Dairy One Inc.) for each horse over the 4-d total collection period. Dry matter was determined by dividing the weight of the hay or feces after drying by the wet weight of the hay or feces as sampled. Apparent DM digestibility was calculated using the mean daily DMI and the mean daily fecal DM output (FO) using the equation: DM digestibility = (DMI – FO)/DMI.
Statistical Analysis
Data are presented as means ±SE. Data were analyzed using a mixed-model procedure (SAS Inst. Inc, Cary, NC). Comparisons of voluntary DMI and digestibility of nutrients were made using repeated measures with day, diet, and day x diet in the model. Comparisons of BW changes during the voluntary DMI experiment were performed using diet, day, and diet x day in the model. Correlations between voluntary DMI and DM digestibility and BW were evaluated using diet in the model. Comparisons among means were tested at the 5% level of significance.
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RESULTS
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Voluntary Intake Experiment
Horses consumed more timothy hay than reed canarygrass hay over the 14-d voluntary DMI period when expressed as kg of DM/d, % BW, or g/kg of BW0.75 (P <0.001; Table 2). There was a main effect of day (P = 0.01; Figure 1), but no diet x day interaction was observed. Horses fed timothy consumed more hay than horses fed reed canarygrass on d 1 (P = 0.02), 3 (P = 0.04), and 5 (P = 0.02) during the study. Horses fed either hay increased BW during the voluntary DMI period (P <0.03; Table 2); however, increases in BW gain were more pronounced for horses fed timothy hay (P <0.01). There was no significant correlation between final BW and voluntary DMI (r2 = 0.001; P = 0.93).
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Figure 1. Average voluntary DMI (kg/d) by Thoroughbred geldings fed timothy (TIM; n = 5) or reed canarygrass hay (RC; n = 6). There was a main effect of diet (P <0.05) and day (P <0.01). *Denotes difference between diets within day (P <0.05).
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Digestibility Experiment
Apparent nutrient DM digestibilities of timothy and reed canarygrass hay are shown in Table 3. Apparent DM digestibility was greater for horses consuming timothy compared with horses fed reed canarygrass hay (P = 0.003). Horses fed timothy also had greater apparent digestibility of ADF (P = 0.001), NDF (P = 0.001), and sugar (P = 0.05), but lower apparent digestibility of CP (P = 0.012) and crude fat (P = 0.004). Horses fed timothy hay had greater apparent digestibility of Ca than those fed reed canarygrass (P = 0.001). Apparent DM digestibility of nonstructural carbohydrates, starch, and P, Mg, K, Fe, Zn, Cu, and Mn did not differ between hays. There was no correlation between initial BW of horses and apparent DM digestibility of hays (r2 = 0.010; P = 0.76).
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DISCUSSION
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Although comparisons of nutrient composition of hays (Table 1
) could not be determined statistically, a comparison of nutrient concentrations was necessary to gain insight into its feeding value and to identify whether any differences observed could have had biological relevance to voluntary DMI and apparent DM digestibility. Both hays met minimum requirements for DE, CP, Ca, P, K, Fe, and Mn, but they did not meet minimum requirements for Cu, Zn, and Na for horses at maintenance averaging 550 kg (NRC, 1989). The main differences in nutrient composition between the timothy and reed canarygrass hays were that timothy seemed to have a lower CP concentration (14.4 vs. 17.1%, respectively), a Ca:P ratio more near the ideal of 2:1 (1.6:1 vs. 0.8:1, respectively), and a greater Fe concentration (144.5 vs. 78.5 ppm, respectively). There also appeared to be a greater concentration of nonstructural carbohydrates in the timothy hay compared with the reed canarygrass hay, but differences were not as pronounced.
Voluntary DMI of forage is a function of its chemical, physical, and morphological characteristics as well as its digestibility (Van Soest, 1965). Mean voluntary DMI of timothy hay was greater than the reed canarygrass hay in our study over the 14-d experimental period; however, differences were most pronounced during the first week on d 1, 3, and 5 (Figure 1). Two weeks of collection for the voluntary DMI experiment was used to ensure the data collected would be truly representative of intake. The collection period length was longer than used in previous voluntary intake studies in horses (Darlington and Hershberger, 1968; Crozier et al., 1997; La Casha et al. 1999). In our study, voluntary DMI of timothy hay was similar to amounts reportedly eaten by horses when fed timothy at different stages of maturity for 10 d (Darlington and Hershberger, 1968).
There may have been other factors that influenced the voluntary DMI of reed canarygrass and timothy hay over the 14-d collection period. First, the reed canarygrass hay had a lower apparent DM digestibility, which was determined in the digestibility experiment. The difference in digestibility may have resulted in less material leaving the gut, thus increasing the bulk fill. An increase in gut fill in horses fed reed canarygrass hay may have caused the horses to feel satiated longer, thus reducing the likelihood of them consuming more hay. However, a lower digestibility is usually associated with an increased mean retention time (Drogoul et al., 2000; Medina et al., 2002). A more likely explanation might have been the influence of the low concentration of alkaloids in the reed canarygrass hay on voluntary DMI. Alkaloids are bitter tasting organic bases containing N and usually O that occur especially in seed plants. Older varieties of reed canarygrass contained greater concentrations of alkaloids, including gramine alkaloids, which resulted in low palatability when fed to livestock (Marten, 1985). Newer varieties of reed canarygrass tested in field studies were reported to have lower levels of alkaloids (Sheaffer et al., 1990). Despite being low-alkaloid varieties of reed canarygrass, Palaton and Vantage hays were consumed in lower amounts when fed to lambs compared with timothy and tall fescue hays (Narasimhalu et al., 1995).
Dry matter digestibility of forage is an important attribute to consider when feeding horses because it reflects the nutritive value of the forage and helps predict the performance of the animal. We found that the reed canarygrass hay was not as digestible as timothy hay when fed to horses. The DM digestibility of timothy hay was greater by approximately 6% than previously observed when timothy hay of similar maturity was fed to geldings (Vander Noot and Gilbreath, 1970). Nutrient digestibility of forages fed to horses is influenced by several factors including nutrient content and plant maturity, the latter being positively correlated to fiber content (Darlington and Hershberger, 1968). It is difficult to ascertain why the reed canarygrass hay had a lower apparent digestibility considering that nutrient composition, with the exception of CP and Fe, did not appear to differ. Plant maturity itself was unlikely to be a factor causing the difference in hay digestibility because both hays were regrowth cuttings with little to no presence of seed heads. Timothy hay yielded greater DM digestibility of NDF and ADF, which may indicate that the fiber in the timothy hay was more fermentable. Reed canarygrass with its longer, wider leaf had a larger particle size, which has been found to increase the mean retention time through the hindgut of the horse, thus reducing digestibility of the forage (Drogoul et al., 2000; Medina et al., 2002; Van Weyenberg et al., 2006).
The estimated daily DMI of CP was greater than the daily recommendation for horses at maintenance (NRC, 1989), but the CP concentration in reed canarygrass (17.1%) was nearly 3% units greater than that in timothy hay. Darlington and Hershberger (1968) found that the digestibility of CP was related to the CP concentration of the forage. We found the same to be true with the greater concentration of CP in the reed canarygrass hay resulting in a greater digestibility of CP in horses fed the reed canarygrass compared with timothy hay. Crozier et al. (1997) also found a greater digestibility of CP when hays with increasing concentrations of CP were fed to geldings.
There has been increasing interest in the nonstructural carbohydrate concentration in equine feeds over the last decade because of the belief that high nonstructural carbohydrate diets increase the risk of metabolic conditions in horses (Ralston, 1996; Valentine et al., 2001; Treiber et al., 2005). The sugar analysis performed in our study includes all monosaccharides, disaccharides, and fructans. The starch analysis performed on our study includes amylose and amylopectin. The forage analysis indicated that the percentages of nonfiber component, nonstructural carbohydrates, sugar, and starch in our hays were within normal ranges reported by Dairy One (Ithaca, NY) in their Feed Composition Library. The slightly greater digestibility of sugars by horses fed timothy hay might have also contributed to the greater apparent DM digestibility observed.
Both groups of horses had negative values for crude fat digestibility. It is not uncommon to find negative values for apparent digestibility of nutrients when they are in low concentration in the diet, especially in diets comprised mainly of roughages (Schneider and Flatt, 1975). The negative value usually indicates a greater endogenous loss of the nutrient in question compared with its intake due to the conversion of carbohydrates to fats.
Timothy hay had a more desirable Ca:P ratio at 1.6:1 compared with 0.8:1 of reed canarygrass hay (Table 1). Calcium to phosphorous ratios less than 1:1 can be detrimental to Ca absorption, and we found a lowered apparent Ca digestibility in this study. It is unknown whether the Ca:P ratio observed here is typical for the Chiefton variety because no published reports exist describing the nutritional content of Chiefton reed canarygrass. Similar concentrations of CP, but a greater Ca:P ratio (1:5:1), was reported for vegetative Chiefton reed canarygrass by the company that produces the seed (Seed Research of Oregon, Corvallis, OR). The greater P concentration in our reed canarygrass hay may be more related to the hay production practices of the local grower we purchased the hay from rather than the normal nutrient characteristics of the forages. If it is common for Chiefton reed canarygrass to have a lowered Ca:P ratio, forage, grain, supplements, or a combination of these should be added to the diet of horses to balance the ration to provide a more ideal Ca:P ratio. All other nutrients investigated did not differ in apparent digestibility between the forages.
In summary, both hays were of good nutritional quality and met most of the nutrient requirements for horses at maintenance. Timothy hay was superior to the Chiefton variety of low-alkaloid reed canarygrass hay in voluntary DMI and apparent digestibilities. Additional studies are needed to 1) confirm the average protein and Ca:P ratio in low-alkaloid varieties of reed canarygrass hay, 2) compare low-alkaloid reed canarygrass hay with other grass hays (e.g., orchardgrass) that grow well in the Mid-Atlantic region.
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IMPLICATIONS
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Chiefton reed canarygrass hay can be fed to horses in place of timothy hay, keeping in mind that reed canarygrass hay may be consumed at a lower rate, is not as digestible, and has a high crude protein concentration and a lower calcium to phosphorous ratio than the ideal. Further studies on the feeding value of low-alkaloid varieties of reed canarygrass compared with other grass hay species would be valuable to the horse industry.
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Footnotes
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1 This research was supported in part by a grant from the Maryland Horse Industry Board. The authors thank the staff at the Central Maryland Research and Education Center for their assistance during the study and Larry Douglass for assistance with statistical analysis. 
2 Corresponding author: amyburk{at}umd.edu
Received for publication October 20, 2005.
Accepted for publication May 10, 2006.
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Abstract
INTRODUCTION
