Journal of Equine Veterinary Science 32 (2012) 579-583
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Voluntary Intake of Four Hay Types by Horses Anne V. Rodiek PhD, Bryn E. Jones BS Department of Animal Sciences and Agricultural Education, California State University, Fresno, CA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 November 2011 Received in revised form 1 February 2012 Accepted 27 February 2012 Available online 30 March 2012
Alfalfa, teff, oat, and wheat hays were fed to eight mature horses to determine voluntary intake of each hay type. After a 2-week adaptation period during which each horse was offered all four hay types each day, a 4-week study was conducted in which two horses were offered each type of hay each week, usually at the rate of 2.2% of initial body weight. Refused feed was collected and weighed the last 5 days of each week to calculate voluntary intake. Horses consumed signiﬁcantly more alfalfa hay than the other hays. Wheat and teff hays were consumed in signiﬁcantly lower amounts than alfalfa, but signiﬁcantly more than oat hay. Across the 5 days during which voluntary intake was measured each week, hay consumption increased each day, reaching levels signiﬁcantly greater than day 1 by day 4, when measured as a percentage of body weight, and day 5 when measured as a percentage of feed offered. Only alfalfa hay, at the amount consumed, met 100% of nutrient requirements for digestible energy, crude protein, lysine, calcium, and phosphorus for horses in maintenance condition. Teff hay met all nutrient requirements except digestible energy. Neither wheat nor oat hays met 100% of any of these nutrient requirements. Alfalfa and teff hays averaged about 12% nonstructural carbohydrate content (NSC), whereas wheat and oats hays contained about 30% NSC. The lower NSC content of the alfalfa and teff hays makes these more suitable for horses with problems related to carbohydrate metabolism or for refeeding starving horses. Published by Elsevier Inc.
Keywords: Horses Hays Voluntary intake Palatability
1. Introduction Because forage is the largest component of the diet of most horses, its quality and acceptability is of high priority to horse owners. Hay not only contributes to meeting the nutrient requirements of horses, but is also an important source of ﬁber or bulk in the diet. Palatability of hay is variable, and factors that inﬂuence palatability may not be discernable by chemical analysis or visual inspection. In the western states, alfalfa hay (Medicago sativa) is widely available and is palatable to most horses. However, the protein and calcium content of alfalfa hay exceeds the nutrient requirements of most classes of horses, and therefore horses can become overweight if fed alfalfa hay
Corresponding author at: Anne V. Rodiek, PhD, Department of Animal Sciences and Agricultural Education, California State University, Fresno, 2415 E. San Ramon Avenue, MS-AS75, Fresno, CA 93740-8033. E-mail address: [email protected]
(A.V. Rodiek). 0737-0806/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.jevs.2012.02.002
generously. Cereal hays, particularly oat (Avena sativa) and wheat (Triticum aestivum) hays, are regionally available, and the nutrient content better matches the energy, protein, and calcium requirements of mature horses. Age of plants at harvest inﬂuences the grain (and therefore the starch) content of cereal hays. High starch content, especially in concert with selective eating of parts of the hay by horses, can result in horses consuming signiﬁcant levels of starch when fed cereal hay. Horses with problems related to carbohydrate metabolism should not be fed forage high in starch or other nonstructural carbohydrates (NSC). Cereal hay is often variably palatable, and visual appraisal does not always indicate palatability. Warm season grasses tend to accumulate lower amounts of NSC and, as such, may be suitable for horses with equine metabolic syndrome, insulin resistance, laminitis, or to those that are overweight. Teff (Eragrostis tef) hay has received much attention as a good hay for horses for these reasons as well as because of its hardy nature,
A.V. Rodiek and B.E. Jones / Journal of Equine Veterinary Science 32 (2012) 579-583
heat tolerance, and capacity for multiple cuttings despite being an annual grass. Promoters of teff hay tout its palatability for horses, but with little scientiﬁc evidence. The goal of this study was to evaluate the horses’ voluntary intake of the following four kinds of hay commonly grown in the western states: alfalfa, oat, wheat, and teff hays. Evaluation of voluntary intake of these four hay types, all grown under similar ﬁeld conditions, may help horse owners choose hays with appropriate palatability and nutrient content as well as understand how palatability may inﬂuence nutrient intakes from these feeds. 2. Materials and Methods 2.1. Horses and Housing This study was conducted in October and November 2010 in central California. Eight nonpregnant mature mares were used in this study. Six Hackney horse and two Quarter horse mares ranged in age from 4 to 18 years and ranged in initial body weight (BW) from 475 to 640 kg. Before the study, the horses were maintained on permanent pasture and were fed alfalfa hay twice daily. In preparation for this study, the eight horses were transferred from pasture and housed in adjacent or opposing (across a barn aisle) individual, partially roofed pipe pens approximately 7 m 13 m in size. The ground in the covered front portion of the pens was covered with rubber mats. Horses received ad libitum water from automatic waterers located at the back of the pens and ate out of deep rubber or galvanized metal tubs. Tubs were placed in the center of the front portion of the pens, under the partial roof, to prevent adjacent horses from sharing feed. 2.2. Experimental Procedures Four types of hay were evaluated: alfalfa, teff, oat, and wheat. All four hay types were grown at the University Farm Laboratory of California State University, Fresno, CA, during the same harvest year under standard production practices. The alfalfa hay was harvested in late summer after several previous cuttings. The teff hay was a second cutting with just more than 30 days of growth since the ﬁrst cutting. Both the wheat and oat hays were fall-sown and grown with irrigation as needed. The horses were fed all of the four experimental hays during a 2-week adaptation period. Each horse received one ﬂake of wheat hay and one ﬂake of alfalfa hay in the morning and one ﬂake of oat hay and one of teff hay in the evening. During this period, neither hay fed nor uneaten hay was weighed. Horses were fed based on their estimated intake, with the goal of offering sufﬁcient hay such that each horse could eat all the hay each horse wanted at each meal. Refused feed was removed, and each pen was cleaned every day at 3:00 PM. The horses were fed a morning meal between 7:00 AM and 8:00 AM and an evening meal between 5:00 PM. and 6:00 PM. This feeding and cleaning schedule continued through the entire study. At the start of the study, after the 2-week adaptation period, the horses were randomly paired so that throughout the study, both horses in a pair ate the same feed during the same period. Each pair of horses was fed
a different hay type each week, (i.e., in each week, one pair of horses ate alfalfa, one pair ate teff, one pair ate wheat, and one pair ate oat hay). The four pairs of horses were fed each hay type through the 4 weeks of the study. At the end of the four experimental periods, all horses had eaten all four different hay types. Each period was 1 week in length, and within each week, hay was offered each day at a rate of 2.2% of the horse’s body as determined by a weight tape. Half the daily hay was fed at the morning feeding (7:00 AM) and half at the evening feeding (5:00 PM). Refused hay was removed daily from the pens at 3:00 PM when pens were cleaned and horses were without feed from 3:00 PM until 5:00 PM. Refused feed was taken out of feeders or picked up off the ground. Some hay was lost if it had become soaked with urine or contaminated with feces. Feeds were changed for the following weekly period at the Friday evening meal. Refused hay was removed but not weighed on Saturdays and Sundays; on the last 5 days of each weekly period (Monday afternoon through Friday afternoon), refused hay was weighed to determine voluntary intake of the previous 22 hours. On the rare occasion when a horse consumed all of its offered feed from the previous two feedings, the amount of hay offered was increased to 2.5% of BW for the following morning feeding. This was done to ensure that horses were fed ad libitum during 22 hours of each day. Hay samples were taken each week as random grab samples, as hay was weighed for each feeding and were combined at the end of the four experimental periods. The hay samples were analyzed at a commercial laboratory (Equi-analytical, Ithaca, NY; Table 3). Voluntary dry matter intakes (feed offeredefeed refused during a 22-hour period, i.e., 5 PM of the previous day until 3 PM of each day when pens were cleaned and refused feed was removed) were calculated as a percentage of BW of the horses and also as percentage of feed offered that was consumed. Nutrient intakes were calculated based on dry matter intakes and nutrient composition of the feeds. Nutrient intakes were compared with nutrient requirements of adult horses in high maintenance condition, as described by the 2007 Nutrient Requirements of Horses . 2.3. Statistical Analysis The measured parameters, voluntary dry matter intake as a percentage of BW and voluntary dry matter intake as a percentage of hay offered, were evaluated by analysis of variance (PROC GLM, SAS Institute Inc., Cary, NC) as a randomized complete block with three main effects: hay type, period, and day within period. Horses were considered as the replicates and the source of random error. Tukey’s mean separation test was used to determine differences between means within the main effects. Differences were considered signiﬁcant with P < .05. 3. Results Voluntary dry matter intake, measured as a percentage of BW, was signiﬁcantly affected by period, day, and hay type. Voluntary dry matter intake, measured as a percentage of feed offered, was signiﬁcantly affected by day and feed type, but not by period.
A.V. Rodiek and B.E. Jones / Journal of Equine Veterinary Science 32 (2012) 579-583 Table 1 Means and standard errors of voluntary dry matter intake by horses fed alfalfa, teff, oat, or wheat hay
DMI, % of BW DMI, % of feed offered
1.71 .05a 87.2 2.0a
1.37 .06b 70.9 2.6b
1.03 .06c 54.8 2.8c
1.43 .04b 75.5 2.0b
BW, body weight; DMI, dry matter intake. a,b,c Within rows, means with different superscripts differ (P < .05).
Voluntary dry matter intake was signiﬁcantly greater for alfalfa hay than for the other hay types. Voluntary dry matter intakes of teff and wheat hays were similar and were signiﬁcantly greater than that for oat hay (Table 1). Voluntary dry matter intake increased each day within all periods combined between days 1 and 5 (Table 2). Intake increased signiﬁcantly over day 1 by day 4 and day 5 for intakes measured as percentage of BW and percentage of feed offered, respectively. Voluntary dry matter intake was higher in periods 3 and 4 than in periods 1 and 2 when measured as percentage of BW but not when measured as percentage of feed offered. The nutrient compositions (dry matter basis) of the four hays fed are shown in Table 3. Nutrient intakes as a percentage of nutrient requirements, based on nutrient content of the hays and voluntary dry matter intakes of each hay type, are shown in Fig. 1. Only alfalfa hay exceeded nutrient requirements for digestible energy (DE), crude protein (CP), lysine, calcium, and phosphorus. Teff hay exceeded all nutrient requirements except for DE, whereas neither oat nor wheat hay met nutrient requirements for any of the nutrient requirements shown. Nutrient requirements were determined as those for horses in high maintenance . Carbohydrate intakes, based on chemical composition of the hays and voluntary dry matter intakes of each hay, are shown in Fig. 2. Total NSC consumption, calculated as water-soluble carbohydrate (WSC) and starch , and based on voluntary intakes, were 822, 1,043, 1,662, and 2,174 g for alfalfa, teff, oat, and wheat hays, respectively.
4. Discussion As expected, horses consumed more alfalfa than the other hay types. A preference among horses for alfalfa over other hay types has been shown in other studies [3,4]. In a review of literature on voluntary food intake by horses, Cuddeford  summarized several studies on voluntary dry matter intake of different types of hay, and reported that in almost all studies in which alfalfa hay was compared with
other types of hay, alfalfa hay was found to be consumed at the highest levels. Wheat and teff hays were consumed to a lesser extent than alfalfa hay, but to a greater extent than oat hay. Staniar et al.  reported dry matter intakes of teff hay between 1.5% and 1.8% for hay harvested at late-heading and boot stages, respectively. These intakes are greater than those found in this study (1.37% of BW). In this study, DE, CP, ADF, and NDF were 2.2 Mcal/kg, 19.7%, 29.7%, and 57.2%, respectively, whereas in the study by Staniar et al., the DE content was estimated at 1.9 Mcal/kg, and CP, ADF, and NDF values ranged from 7.5% to 16.4%, 41.5% to 35.7%, and 70.8% to 68.1%, respectively, for the late-heading and boot stages of harvest. Teff fed in the present study was higher in protein and lower in ﬁber than in the study conducted by Staniar et al. The protein concentration of the teff hay in this study was high, whereas the ADF and NDF values seemed to be consistent with values reported for teff hay grown and harvested in ﬁeld trials in Oregon . The inﬂuence of these different nutrient compositions on intake by the horses is not known. The different intakes of oat and wheat hay were signiﬁcant, but the cause of the preference for the wheat hay is not clear. Chemical composition of the oat and wheat hays was not much different with respect to DE (2.35 vs. 2.28 Mcal/kg), CP (both 8.7%), ADF (31.1 vs. 33.0%), or NDF (51.2 vs. 53.9%), respectively. The oat hay was higher than the wheat hay in WSC (24.8 vs. 17.5%) but lower in starch (4.7 vs. 12.9%). It appeared, by observation, that the wheat hay had more grain in it (reﬂected as the higher starch content) than the oat hay. Perhaps, while in search of the wheat grain, the horses consumed a greater amount of wheat hay, in total, compared with the oat hay. There appears to be no clear predictor among chemical components of voluntary feed intake by horses of different forages . Stimulation by sight, smell, and texture of feed as well as other factors such as time of day and social facilitation may play a more important role in meal size than in energy status, which may be more important for long-term feed intake . Edouard et al.  reviewed data on dry matter intakes of 21 horses fed 45 different types of forage and concluded that a weak positive relationship existed between ﬁber content (NDF) and dry matter intake in grass hays. However, no such relationship was found for alfalfa hay. The NDF content of the grass hays in this study (51.2%, 53.9%, and 57.2% for the oat, wheat, and teff hays, respectively) did not correspond to the order of voluntary intakes. Although oat hay was consumed at a lower level than wheat or teff hay, wheat hay, with its somewhat lower NDF, was consumed to a greater, although not signiﬁcantly, level than teff hay. The relatively small differences in NDF content of the grass hays in this study, perhaps, are not
Table 2 Means and standard errors of voluntary dry matter intake by horses for ﬁve consecutive daysa (hay types and periods combined)
DMI, % of BW DMI, % of feed offered
1.27 .07b 66.6 3.5b
1.36 .07b,c 71.0 3.4b,c
1.40 .07b,c 72.0 3.2b,c
1.43 .07c 74.7 3.3b,c
1.47 .07c 76.2 3.2c
a Days 1-5 indicate ﬁve consecutive days of each week (Monday through Friday) after a 2-day (Saturday and Sunday) adaptation period to the new feeds offered each of the 4 weeks of the study. b,c Within rows, means with different superscripts differ (P < .05).
A.V. Rodiek and B.E. Jones / Journal of Equine Veterinary Science 32 (2012) 579-583
Table 3 Nutrient compositiona of alfalfa, teff, oat, and wheat hays Nutrient
DE (Mcal/kg) CP (%) Estimated lysine (%) ADF (%) NDF (%) WSC (%) ESC (%) Starch (%) NFC (%) NSC (%) Ca (%) P (%)
2.54 23.0 1.17 28.4 36.1 10.2 7.1 2.0 29.0 12.2 1.21 .29
2.20 19.7 .69 29.7 57.2 10.7 7.5 1.3 13.9 12.0 .44 .38
2.35 8.7 .31 31.1 51.2 25.8 11.8 4.7 29.5 30.5 .32 .21
2.28 8.7 .37 33.0 53.9 17.5 11.1 12.9 27.5 30.4 .26 .19
DE, digestible energy; CP, crude protein; ADF, acid detergent ﬁber; NDF, neutral detergent ﬁber; WSC, water-soluble carbohydrate (mono- and disaccharides and some polysaccharides, mainly fructan); ESC, ethanolsoluble carbohydrate (mono- and disaccharides); NFC, nonﬁber carbohydrate, calculated as 100% (CP% þ NDF% þ fat % þ ash%); NSC, nonstructural carbohydrate, calculated as WSC þ starch. a Dry matter basis.
large enough to display a true relationship between NDF and intake. All measures of soluble carbohydrate (WSC, ethanolsoluble carbohydrate, and starch) were highest for the cereal grains compared with alfalfa and teff. Calculated as WSC plus starch, the content of NSC of the alfalfa, teff, oat, and wheat hays were 12.2%, 12.0%, 30.5%, and 30.4%, respectively. The intake of NSC at the voluntary hay intakes found in this study shows that horses consumed 822, 1,043, 1,662, and 2,174 g of NSC when they ate teff, alfalfa, oat, and wheat hays, respectively. It has been recommended that insulin-resistant or obese horses be fed forages that contain less than 10% NSC . In this study, none of the hay types contained less than 10% NSC, although both the alfalfa and teff hays (about 12% NSC) were notably lower than the cereal hays (about 30% NSC). Both alfalfa and teff hays should be preferred over cereal hays for rehabilitation of starving horses, as the low NSC content of these will elicit a reduced insulin response and be less likely to produce hypotonic concentrations of minerals in the circulation and the deleterious effects seen in refeeding syndrome . Across all hays, hay intake increased on subsequent days throughout each experimental week. No signiﬁcant interaction was found between day and hay type, indicating that
Fig. 2. Daily intakes (grams) of starch, ethanol-soluble carbohydrate (ESC), water-soluble carbohydrate (WSC), and nonstructural carbohydrate (NSC, calculated as WSC þ starch) by alfalfa, teff, oat, and wheat hays based on average intake of each hay and average body weight.
this trend was common across all hays. An explanation for this trend is not clear. It may be that the horses became more accustomed to each feed as the days of consumption progressed. It may be that long-term controls of intake, such as energy status, resulted in increased consumption over time . If each period of consumption had been longer, a steady-state voluntary dry matter intake more likely would have been reached, which would have provided a better understanding of how well each feed met the nutrient requirements. Based on DE content of each hay type, horses would have to have consumed 1.43%, 1.65%, 1.54%, and 1.59% of BW of alfalfa, teff, oat, and wheat hays, respectively, to meet the DE requirement of horses in high maintenance. Only alfalfa hay, at its level of intake, met the DE requirement of horses in maintenance in this study. Both alfalfa and teff hays exceeded nutrient requirements for CP, lysine, calcium, and phosphorus. Neither oat nor wheat hay met nutrient requirements for these nutrients. Whether nutrient requirements would have been met after more days on each feed, assuming horses would continue to increase intakes of each hay, is not known. As shown in other studies, horses preferred alfalfa hay over grass hays. Teff hay was well accepted, especially in comparison with cereal hays. The ability of both alfalfa and teff hay to exceed nutrient requirements, while at the same time supplying only low levels of NSC, may make both hays valuable for horses that are insulin resistant. Claims by teff promoters regarding good acceptance by horses appear to be supported by this study. The increasing level of intake on subsequent days in each week of the trial may be evidence of the horse’s evolution as a versatile consumer of a variety of forages, eating to meet its energy needs.
Fig. 1. Percentage of nutrient requirements met by alfalfa, teff, oat, and wheat hays based on average intake of each and average body weight. Nutrient requirements for high maintenance were set at 100% (from the Nutrient Requirements of Horses, 2007 ). DE, digestible energy; CP, crude protein; LYS, lysine.
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