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ANIMAL PRODUCTION |
* Departments of Animal Science and
and
Crop Science, North Carolina State University, Raleigh 27695-7621
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Cattle • Endophytes • Fescue Toxicosis • Festuca arundinacea • Neotyphodium coenophialum • Tall Fescue
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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), has been linked with poor cattle performance (Ball et al., 1993). The endophyte produces ergot alkaloids, which are thought to be the primary causative agents of tall fescue toxicosis. Symptoms of fescue toxicosis include decreased weight gain (Chestnut et al., 1991), decreased feed intake (Aldrich et al., 1993), decreased diet digestibility (Aldrich et al., 1993; Westendorf et al., 1993), decreased plasma prolactin (PRL) concentrations (Aldrich et al., 1993; Emile et al., 2000), increased body temperatures (Rice et al., 1997), and an impaired ability to dissipate heat (Aldrich et al., 1993). The greatest effects on animal performance are seen when ambient temperature exceeds 31°C. MaxQ (Pennington Seed, Inc., Madison, GA) is a nontoxic endophyte (N. coenophialum) that has been inserted into tall fescue. The MaxQ endophyte does not produce ergot alkaloids and was designated as strain AR542 in previous reports (Parish et al., 2003). Grazing studies with several varieties of tall fescue infected with the MaxQ endophyte have shown promising results (Parish et al., 2003), indicating that animal performance characteristics of the nontoxic infected fescue are more similar to endophyte-free (E–) fescue, whereas the agronomic characteristics are more similar to toxic infected fescue. Despite favorable results in recently published studies, additional research needs to be done to evaluate non-toxic infected tall fescue in a variety production scenarios. The objective of this study was to compare and evaluate the effects of toxic endophyte-infected (E+), E–, and nontoxic endophyte-infected (NE; MaxQ) Jesup tall fescue hay consumption on ad libitum intake, water intake, diet digestibility, N metabolism, plasma PRL concentrations, and rectal temperatures under thermoneutral conditions in growing beef steers. Our hypothesis was that E+ fescue would be nutritionally inferior to E– and that NE would have a value closer to Ethan E+. |
Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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) for E+, E–, and NE was 87.5, 4.2, and 94.1%, respectively. Tillers producing ergot alkaloids (determined according to the procedure of Adcock et al., 1997) were 87.5, 4.2, and 3.4% for E+, E–, and NE, respectively.
To optimize hay quality, and minimize toxin concentrations in the E+ known to be related to forage stage of growth and N fertilization rate (Porter, 1995), late-winter N fertilization was minimal (34 kg/ha) and hay was harvested in late April at the late boot stage. Hay was initially packaged into large round bales (1.52 m x 1.52 m, weighing approximately 550 kg) and at approximately 86% DM. After hay was transported to the North Carolina State University Metabolism Unit, it was rebaled into rectangular bales of approximately 20 kg and stored indoors. During the trial, the rectangular bales were sliced to a length of approximately 12.5 cm with a 5600 Van Dale bale processor (J. Starr Industries, Ft. Atkinson, WI) and placed in feed carts for ease of feeding.
Eight Polled Hereford steers (average initial BW 240 ± 9 kg) were used in a replicated, 3 x 3 Latin square design, with an extra steer allotted to each square. The North Carolina State University Animal Care and Use Committee approved care, handling, and sampling of steers (Approval No. IACUC 01-029-A). Steers were obtained from the university herd, trained to lead by halter, and accustomed to close human interaction. Steers were divided into the two squares based on BW. The second square followed the first by 2 wk.
Two weeks before the trial, steers were weighed, de-wormed with Cydectin Pour-on (Fort Dodge Animal Health, Overland Park, KS), and hair coats were clipped to equalize hair coat length among the steers and to facilitate fecal collection during the balance trial. One week before the start of the trial, steers were blocked by BW into two groups and transported to an indoor facility where they were housed in individual tie stalls (115 cm x 178 cm) with individual feeders and metered water cups. Steers were allowed to exercise in an outdoor pen on a regular basis (two to three times per week for 1 h) between collection periods. The experiment was conducted during the summer; however, to minimize heat stress, room temperature was kept at <27°C by use of air conditioning units and fans. Daily high and low room temperatures were recorded at both ends of the barn using AcuRite digital high-low recording thermometers (Cheney Instrument Co., Lake Geneva, WI).
During a 7-d adaptation to the indoor facility and exercise pen, all steers were fed switchgrass hay and a mineral supplement. During the entire trial, steers were fed a mineral supplement that consisted of a 1:2 mix of dried molasses and a commercial mineral mix (Southern States Cooperative, Richmond, VA; 16.5% Ca, 7.0% P, 24.5% NaCl, 3.5% Mg, 2.0% S, 1.0% K, 70 ppm I, 1,500 ppm Cu, 32 ppm Co, 52 ppm Se, 3,200 ppm Zn, 3,000 ppm Mn, 118,181 IU/kg of vitamin A, 9,091 IU/kg of vitamin D, and 91 IU/kg of vitamin E). The mixture (57 g/d) was offered before the 0900 feeding. Molasses was added to the commercial mineral supplement to aid in rapid and uniform consumption. Water was available at all times, and daily water intake was measured after the 1600 feeding.
Steers were weighed in the morning before feeding on d 1, 15, and 24 of each period. Steers were offered feed ad libitum for 14 d, and feed intake measurements taken on d 10 through 14. Steers were fed at 120% of the previous day’s intake throughout the ad libitum phase. Orts for the previous day were collected at 0830, and hay was offered in two equal portions at 0900 and 1600. Hay and orts were sampled on d 10 through 14, pooled, and then dried in an oven at 105°C to determine ad libitum DMI. These samples were not retained for further analysis. Following the ad libitum phase, hay offered was restricted for 9 d, followed by a 5-d collection phase (d 24 to 28). Hay offered during restriction and collection was based on the steer with the lowest ad libitum DMI (percentage of BW) for that period within square. Hay to be offered during the collection phase was calculated using that lowest percentage of BW DMI and each steer’s BW on d 15.
Before the collection phase, pens were thoroughly scrubbed and washed. Separation boards, designed to allow visual contact among steers, were attached to the pens to minimize cross-contamination of feces between steers. Hair on the underline, hind legs, and two strips across the back of each steer was clipped on d 22 or 23 to minimize matting of fecal material and to allow for secure attachment of the urine harness during the collection phase.
Urine, feces, and orts were collected during the 5-d collection phase. Collections were made at 0800 each morning. Daily grab samples of each hay and the mineral supplement were collected and pooled to represent intake composition. Total orts for the 5-d collection were retained and allowed to air dry, after which they were weighed and a representative sample was taken for laboratory analyses. Urine was collected by aspiration into polypropylene jugs from a urine collection harness as described by Archibeque et al. (2001). Urine jugs contained 400 mL of 6 N HCl daily, which kept urine pH <4 in the jug. For the second and third periods of both squares, an additional 4 L of water was added to each urine jug to prevent a crystal residue from forming, which was observed in the first period of both squares. It was thought that the crystal residue was the result of the combination of a high volume of acid and the small volume of urine at the start of the collection day. Urine was collected daily, volume and weight were recorded, and a representative aliquot (by weight) was retained (5% for the first periods, and 3% for the second and third periods of both squares). Urine pH was measured before collection of an aliquot to verify proper acidification, and all aliquots were pooled for each steer in a given period.
Feces also were collected daily, weighed, and a representative sample was weighed and then dried with forced air at 55°C for 48 h, air-equilibrated, and the DM content was determined. Fecal samples were broken up after 24 h in the oven, and were inspected to ensure they were completely dry after an additional 24 h. After the fifth day of collection, feces attached to the steers and harnesses were removed and collected, steers were removed from the pens, and the pens were thoroughly scraped after applying a small amount of water. Scrapings were included in the final day’s fecal output. Once all fecal samples were dry, they were ground to pass a 2-mm screen in a Wiley Mill (Thomas Scientific, Swedesboro, NJ), and then subsampled and pooled (5% of each day’s DM output) for each steer in a given period.
Rectal temperatures were measured at 1630 each day of the trial using a hand-held digital thermometer (GLA M216TC/H trickle charge with hold thermometer, GLA Agricultural Electronics, San Luis Obispo, CA). During the collection phase, rectal temperatures were also measured at 0930. Rectal temperature data reported are for the 5 d during the collection phase. Jugular venous blood samples were collected in heparinized tubes for each steer before the morning feeding on d 24 and d 28, and at approximately 1500 h on d 26 of each period. Samples were stored on ice until plasma was separated by centrifugation at 10,000 x g for 10 min and frozen for later determination of plasma PRL (d-28 samples) and urea N concentrations (d-24 and d-26 samples.
Chemical Analyses
All hay, ort, and fecal samples were ground in a Wiley Mill (Thomas Scientific, Swedesboro, NJ) to pass a 1-mm screen and stored in sealed plastic containers at room temperature until analyzed. Hay, orts, and feces were analyzed for DM by drying at 105°C overnight in a forced-air oven, and for ash and Kjeldahl N using AOAC (1999) procedures. Neutral detergent fiber, ADF, and 72% sulfuric acid lignin were sequentially determined using the method of Van Soest et al. (1991) in a batch processor (Ankom Technology, Fairport, NY). Hemicellulose was determined as the difference between NDF and ADF, and cellulose was determined as the difference between ADF and the 72% sulfuric acid residue.
In vitro true dry matter digestibility (IVTDMD) of hay samples was determined by a 48-h in vitro fermentation using the Ankom II Daily batch fermenter (Ankom Technology). Vessels contained 1,600 mL of McDougal’s buffer (Tilley and Terry, 1963), and were inoculated with 400 mL of strained ruminal fluid from one steer fed alfalfa hay. After 48 h, the in vitro fermentation was terminated with the NDF procedure in the Ankom 200 fiber analyzer. Samples of mineral supplement were stored in sealed plastic containers at room temperature until analyses for DM and OM for inclusion in digestibility calculations.
Urine and plasma samples were kept at <–4°C until analysis. Urine samples were analyzed for Kjeldahl N using the AOAC (1999) procedure. Plasma and urine samples were analyzed for urea content using the diacetyl monoxime method of Marsh et al. (1957), adapted for use in a Technicon autoanalyzer (Technicon Instruments Corp., Tarrytown, NY). Prolactin concentrations were determined by RIA according to the procedure of Moura and Erickson (1997). Ergovaline content of the hays was determined by the Missouri Veterinary Diagnostic Laboratory using the method of Hill et al. (1993). The limit of detection of ergovaline was 20 ppb.
Statistical Analyses
Statistical analyses of data were performed using ANOVA for a Latin square design and the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The model included the following independent variables: square, animal within square, period, square x period interaction, and treatment. Initially, the model tested for carryover effects from the previous treatment, but carryover was not significant (P > 0.10), so that component was removed from the model. When the overall model showed treatment was significant (P < 0.10), means were separated using the LSD method. Plasma urea N (PUN) concentrations and body temperatures were averaged within steer and period before statistical analysis. Results are reported as least squares means. Data for one steer on the E+ diet for the third period of the first square was not used in the analysis due to an elevated body temperature and a large drop in intake during the collection period.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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). Hemicellulose, lignin, and IVTDMD did not differ among the hays. Average ergovaline concentrations (as-fed) were 120 ppb for E+, 3 ppb for E–, and 0 ppb for NE. Reported concentrations of ergovaline in E+ grass and seed vary widely (Welty et al., 1994; Porter, 1995). Recent reports have shown levels of ergovaline in E+ hay of 220 (Humphry et al., 2002) to 960 ppb (Emile et al., 2000). Although 120 ppb is low compared with some reports, ergovaline concentrations greater than 100 ppb have been associated with adverse effects in animals (T. J. Evans, University of Missouri Veterinary Diagnostic Lab, personal communication). The low level of ergovaline in our E+ hay was probably because it was harvested at an earlier stage of maturity than in many other studies (Emile et al., 2000; Humphry et al., 2002).
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. The overall high temperatures ranged from 26.8 to 27.3°C, and the overall low temperatures ranged from 21.4 to 22.6°C. Although the study was conducted during the summer, hay is most often fed in the winter when the effects of heat stress are not a concern. By keeping the environmental temperature <27 °C, the potential effect of heat stress on the dependent variables was limited, making results more applicable to most hay feeding situations.
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reported heat dissipation via skin vaporization for steers on E+ tall fescue diets (ergovaline = 285 ppb) housed at 32°C was lower than for steers fed E– tall fescue, whereas at 22°C skin vaporization was similar for the two treatments. Burke et al. (2001) reported heifers on an E+ diet (ergovaline = 1,900 ppb) under heat stress (4-h daily exposure to a maximum daily temperature of 31°C) had decreased feed intakes, reduced serum PRL concentrations, increased respiration rates, and increased rectal temperatures compared with steers on an E– diet. In our study, water intake, urine output, and rectal temperatures did not differ among diets (Table 3). The absence of severe heat stress or the low level of ergovaline in this study may explain these observations. Emile et al. (2000) reported no difference in body temperature and little difference in performance in heifers or lambs fed E+ or E– fescue hay in cool conditions. The greatest effects on animal performance for animals on E+ tall fescue have been seen when the temperature exceeds 31°C, although the endophyte can have an effect at any temperature (Parish et al., 2003), including fescue foot and sloughed tail switches that usually occur in cold weather (Ball et al., 1993).
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) were lower (P < 0.05) for steers on the E+ diet compared with the E–diet, but not different from those of steers on the NE diet. These findings agree with the results of other studies (Chestnut et al., 1991; Aldrich et al., 1993), in which cattle on E+ diets had lower PRL concentrations than those on E– diets. Parish et al. (2003), however, reported that PRL was lower in cattle grazing E+ compared with either E– or NE tall fescue. Their differences, however, were more dramatic than those reported here, where PRL concentrations for NE were intermediate between the E+ or E– diets. This may be due to the more controlled environment in our study, or due to differences in toxin concentrations. These differences also might be due to the shorter nature of this Latin square design in contrast to the longer grazing trials of Parish et al. (2003).
Ad libitum (d 10 to 14) DMI and ad libitum DMI as a percentage of BW were substantially (>10%) higher for the E– and NE hays compared with the E+ hay (Table 4). Aldrich et al. (1993) reported lower DMI as a percentage of BW for steers on an E+ tall fescue diet (4.51%) than for steers on an E– tall fescue diet (4.79%). Goetsch et al. (1987) also reported lower DMI (P < 0.05) as a percentage of BW as the dietary level of E+ hay increased.
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for their digestion phase, where intake was restricted to a fixed percentage of BW. In contrast, Goetsch et al. (1987) allowed ad libitum DMI during their digestion studies.
Apparent DM and CP digestibilities were less (P < 0.05) for the E+ hay than for the E– and NE hay (Table 5). Apparent OM digestibility was less (P < 0.05) for E+ than for E– hay, and tended (P = 0.07) to be lower for E+ than for NE hay. Similar studies where DMI was equalized among diets also have reported lower DM (Fiorito et al., 1991; Aldrich et al., 1993; Westendorf et al., 1993), OM (Aldrich et al., 1993; Hannah et al., 1990), and CP (Westendorf et al., 1993) digestibility for ruminants on E+ diets vs. those on E– diets. These observations contrast those of Goetsch et al. (1987), where digestibility actually increased in diets containing increasing levels of E+ hay, probably because digestibility was determined at ad libitum DMI, and DMI decreased as E+ hay in the diet increased. In our study, IVTDMD (Table 1) results suggested that the three hays would be expected to be similar in digestibility, but in vivo digestibility was actually substantially less for E+ than for E– or NE hay.
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). These results agree with those of Aldrich et al. (1993), who reported lower OM digestibility but similar NDF digestibility for cattle on E+ compared with E– diets. However, decreased fiber digestibility by ruminants fed E+ compared with E– also has been reported (Hannah et al., 1990; Westendorf et al., 1993; Humphry, et al., 2002).
The E+ diet of Aldrich et al. (1993) contained an ergovaline concentration of 285 ppb; however, Hannah et al. (1990) and Westendorf et al. (1993) had E+ diets with much higher concentrations of ergot alkaloids. Humphry et al. (2002), who fed hay with 220 ppb ergovaline, showed a difference in fiber digestibility in one experiment but not in another with the same hay. It is thought that the differences in digestibility noted with E+ and E– tall fescue could be due to an array of factors that include ergovaline concentration consumed (Hannah et al., 1990), hay quality (Emile et al., 2000), environmental temperature (Emile et al., 2000), level of feed intake (Goetsch et al., 1987), and altered ruminal flow kinetics (Hannah et al., 1990).
Nitrogen intake was higher (P < 0.01) for steers fed E– and NE hays compared with those fed the E+ hay (Table 5). Fecal and urinary N excretion (g/d) did not differ among diets. Nitrogen retained (g/d) was less (P <0.01) for the E+ hay than for the E– and NE hays. Nitrogen retained as a percentage of N intake was lower (P < 0.01) for E+ hay than for E– or NE hay, as was N retained as a percentage of N digested (P < 0.05).
Our results are similar to those of Fiorito et al. (1991), who reported that N retained (g/d) and N retained as a percentage of N digested were greater (P < 0.10) for E– vs. E+ tall fescue hays. Humphry et al. (2002) reported no differences in N retained and N retained as a percentage of N intake between E+ and E– fescue hay; however, the E+ hay in their study was 1.5 percentage points higher in CP than the E– hay (8.1 vs. 6.6% CP, respectively), and DMI was quite low (1.2% of BW), resulting in a very low N retention. In our study, the E+ hay was slightly lower in CP than the E– and NE hays (Table 1), which could have had a small influence on N retention in addition to the lower DMI and lower diet digestibility on the E+ hay.
Plasma urea N, urine urea N output, and urea N as a percentage of urinary N (UUN) were not influenced by treatment (Table 6). It has been suggested that PUN is a good indicator of the balance between N and energy availability in forage-fed ruminants (Hammond et al., 1994). It also has been suggested that UUN is closely related to protein intake relative to animal requirements (Archibeque et al., 2001; Huntington et al., 2001). Both PUN and UUN reported in this trial were marginally low for cattle on all- or high-forage diets (Taniguchi et al., 1995; Archibeque et al., 2001; Huntington et al., 2001), suggesting that the CP level of the hay was marginal relative to energy value. These results indicate that there were no major differences in N metabolism induced by presence of either type of endophyte, and suggest that higher N retention for E– and NE hays was related more to lower digestibility rather than to postabsorptive effects on N metabolism.
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Several researchers have studied the time necessary to alleviate the effects of endophyte on metabolic processes. Aiken et al. (2001) showed that prolactin increased and stabilized, and that body temperature returned to normal levels within 3 d of removal from E+ fescue. Lusby et al. (1990) showed that body temperatures normalized within 6 d of removal from E+ fescue. Stuedemann et al. (1998) studied the time necessary for clearance of ergot alkaloids from the body. Within 2 d of removal from E+ fescue, urinary excretion of ergot alkaloids fell to levels not different from steers grazing E– fescue within 3 d. These reports suggest that the length of adaptation chosen for the current trial was adequate for steers to overcome most, if not all, of the toxic effects of E+ fescue before measurements on E– or EN fescue were made.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Current address: Embrex, P.O. Box 13989, Research Triangle Park, NC 27709-3989.
3 Correspondence: Box 7621 (phone: 919-515-7798; fax: 919-515-9061; e-mail: Matt_Poore{at}ncsu.edu).
Received for publication September 22, 2004. Accepted for publication January 26, 2005.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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