J. Anim Sci. 2007. 85:2346-2353. doi:10.2527/jas.2006-848
© 2007 American Society of Animal Science
Endophyte infection level of tall fescue stockpiled for winter grazing does not alter the gain of calves nursing lactating beef cows1
L. E. Curtis and
R. L. Kallenbach2
Division of Plant Sciences, University of Missouri, Columbia 65211
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Abstract
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We examined the effect of endophyte infection level of tall fescue (Festuca arundinacea Schreb.) used for stockpiled forage on the performance of lactating, fallscalving beef cows and their calves. Treatments were endophyte infection levels of 20% (low; SEM = 3.5), 51%, (medium; SEM = 1.25), and 89% (high; SEM = 2.4; 4 replications/treatment). Five cow-calf pairs grazed in each replicate (n = 60 cow-calf pairs/ yr) for 84 d (phase 1) starting on December 2, 2004 (yr 1), and December 1, 2005 (yr 2). After 84 d of grazing each treatment, the cattle were commingled and fed as a single group (phase 2) until weaning in April of each year. Phase 2 allowed measurement of residual effects from grazing stockpiled tall fescue with varying levels of endophyte infection. Pregrazing and postgrazing forage DM yield, forage nutritive value, and total ergot alkaloid concentrations of forage were collected every 21 d during phase 1. Animal performance data included cow BW, ADG, and BCS, as well as calf BW and ADG. Animal performance was monitored during both phases. Endophyte infection did not affect (P = 0.52) apparent intake (pregrazing minus postgrazing forage DM yield) of stockpiled tall fescue, because each cow-calf pair consumed 16 ± 1.7 kg/d regardless of treatment. Cow ADG during phase 1 was –0.47 ±0.43 kg for the low treatment, which was greater (P < 0.01) than either the medium (–0.64 ±0.43 kg) or high (–0.74 ± 0.43 kg) treatments. However, cows that had grazed the high or medium treatments in phase 1 lost –0.43 and –0.57 (±0.24) kg/d, respectively, which was less (P<0.01) BW loss than the cows in the low (–0.78 ± 0.24 kg/d) treatment during phase 2. By the end of phase 2, cow BW did not differ (528 ±27 kg; P = 0.15). Body condition score for cows in the low treatment was greater (P = 0.02) than that of the medium and high treatments at the end of phase 1. Body condition scores did not change appreciably by the end of phase 2, and differences among treatments remained the same as at the end of phase 1 (P = 0.02). In contrast to cow performance, calf ADG was unaffected (P = 0.10) by endophyte level and averaged 0.73 ± 0.07 kg during phase 1 and 0.44 ± 0.04 kg during phase 2. Our data suggest that fall-calving herds can utilize highly-infected tall fescue when stockpiled for winter grazing, with little impact on cow performance and no impact on calf gain.
Key Words: endophyte • fall calving • stockpiling • tall fescue
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INTRODUCTION
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Winter is the most expensive time to feed cattle, especially for fall-calving beef cows. Fall-calving cows are in lactation during winter, and their nutritional demands (NRC, 2000
) are greater relative to spring-calving cows during this same time. Although spring calving is more common in the lower Midwest, some advantages are frequently cited for fall calving. Heat stress reduces reproduction in cattle (De Rensis and Scaramuzzi, 2003) and is mitigated when breeding occurs in December. Marketing advantages are another reason fall calving is gaining popularity (Nelson, 1988).
Several reports indicate that stockpiled tall fescue is an economical feed source for fall-calving herds (Waller et al., 1988; Janovick et al., 2004). More than 90% of tall fescue in the United States (Ball et al., 2002) is infected with the fungal endophyte Neotyphodium coenophialum [(Morgan-Jones and Gams) Glenn, Bacon and Hanlin]. This endophyte produces ergot-like alkaloids that cause a series of animal health disorders collectively known as "fescue toxicosis." Symptoms of fescue toxicosis are generally less severe in cooler temperatures, but the sloughing of the tips of the ears, tails, and even entire hooves does occur during winter months (Chestnut et al., 1991).
Because fall-calving cows are lactating during winter, they may be more vulnerable than dry cows to fescue toxicosis when grazing stockpiled tall fescue. In addition, little is known about how calf performance is affected when they are nursing dams grazing stockpiled, endophyte-infected tall fescue. Our hypothesis was that fall-calving beef cows grazing stockpiled tall fescue with a low level of endophyte infection would exhibit greater BCS and wean heavier calves than those grazing highly infected tall fescue. Our objective was to examine the effects of endophyte infection level in tall fescue stockpiled for winter grazing on forage yield, nutritive value, total ergot alkaloid concentrations, and subsequent animal performance.
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MATERIALS AND METHODS
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The experimental protocol was reviewed and approved by the University of Missouri Animal Care and Use Committee.
A 2-yr grazing experiment was conducted in 2 phases during the winter and early spring of 2004 to 2005 (yr 1) and 2005 to 2006 (yr 2) at the University of Missouri Forage Systems Research Center near Linneus, Missouri (39°51'N, 93°6'W). During phase 1, cows and calves grazed stockpiled tall fescue for 84 d in the treatments described below. Phase 1 was from December 2 to February 23 in yr 1 and from December 1 to February 22 in yr 2. During phase 2, which immediately followed phase 1, cows and calves were commingled and managed as a single group until weaning in April so that residual effects could be documented. Cows and calves continued to graze stockpiled tall fescue that averaged 53 ± 8.6% endophyte infection at the same location during phase 2. No supplementation, other than free-choice access to a salt-trace mineral block, was given to the cattle during either phase.
Experimental Design and Treatments
The experimental design was a randomized complete block with 3 treatments and 4 replicates. Treatments were tall fescue with endophyte infection levels of 20, 51, and 89% (low, medium, and high, respectively). Stands were established more than 20 yr ago, but endophyte infection status was documented on November 2, 2004, and May 11, 2006, by collecting 25 tall fescue tillers from each pasture and assaying tillers with the immunoblot test described by Hiatt and Hill (1997). The SD = 3.0 percentage units; limit of detection = 50 ng/tiller Endophtye infection levels for individual treatments did not differ between sampling dates (P>0.05).
Pasture Management
The experiment was conducted on a 48-ha block that was divided into twelve 4-ha pastures. The areas used were typical of cool-season, grass-legume pastures in the region, with tall fescue as the predominant species. Orchardgrass (Dactylis glomerata L.) and Kentucky bluegrass (Poa pratensis L.) were subordinate components, as were red clover (Trifolium pratense L.) and birdsfoot trefoil (Lotus corniculatus L.). These components, which together constituted less than 15% of the DM available, were assessed by a modification of the step-point method (Evans and Love, 1957). No difference (P >0.05) in species composition was found among pastures. Soil types were Grundy silt loam (fine, smectitic, mesic Aquertic Argiudolls), Armstrong loam (fine, smectitic, mesic Aquertic Hapludalfs), Lagonda silt loam (fine, smectitic, mesic Aquertic Hapludalfs), and Purdin loam (fine, mixed, superactive, mesic Oxyaquic Hapludalfs). Soil types were determined by using the mapping unit information contained in the Soil Survey of Linn County Missouri (Benham, 1990).
In mid-August, the pastures were uniformly grazed to a height of approximately 8 cm and were then fertilized with 90 kg/ha of N as ammonium nitrate. Soils were sampled and tested annually; lime, phosphorus, and potassium were applied in mid-August according to the recommendations of the University of Missouri Soil Testing Laboratory (Brown and Rodriguez, 1983). After fertilization, pasture growth was allowed to accumulate until early December, when grazing was initiated.
Animal Management
A total of 60 multiparous, crossbred (Gelbvieh, Red Angus, and Angus) cow-calf pairs were stratified by cow BW and age, and by calf age and sex into 12 groups of 5. Calves were born between September 15 and October 15 annually. After stratification, groups were randomly assigned to treatments. Water and trace-mineralized salt blocks were available ad libitum to cows and calves. In early December of both years, a Gelbvieh or a Simmental bull was added to each group to initiate a 45-d breeding season. Each bull passed a breeding soundness examination before the breeding season.
Stockpiled tall fescue was strip-grazed at a forage DM allocation rate of 11.8% of animal BW every 3.5 d (3.37% of BW/d). Cattle began grazing nearest the water source in each pasture, and every 3.5 d (twice weekly) a temporary electric fence was moved to provide the next allocation of forage. In the event of an ice (>10 mm) or snowstorm (>500 mm accumulation), small square bales of mixed-grass hay were fed until the cattle were able to resume grazing. Over the 2 yr of the experiment, hay was fed for a total of 5 d.
Forage Measurements
Forage pregrazing yield was measured by clipping ten 0.8 x 4.6-m strips to a 2-cm height with a tractor- mounted, flail-type harvester from each pasture before the start of grazing in December. Additional pregrazing harvests were taken from areas not yet allocated for grazing every 21 d throughout phase 1. This sampling scheme provided four 21-d periods within phase 1 annually. At the end of each 21-d period, 12 strips (as described above) were clipped from the area grazed to determine residual forage yield and are referred to as postgrazing yield. Apparent intake (pasture DM disappearance) was calculated from the differences in the pre- and postgrazing harvests (Casler et al., 1998). Pasture utilization was calculated as: [1 – (postgrazing DM yield/pregrazing DM yield)] x 100. Snow on the ground during the second harvest of yr 1 resulted in inaccurate forage DM measurements, and the data were not included in the analysis. Additionally, the forage nutritive value data from this sampling date were omitted.
Grab samples collected from each harvest strip were composited together for a single pasture. This grab sample was then split into 2 aliquots of approximately 300 g each. The first aliquot was analyzed for DM by drying in a forced-air oven for a minimum of 24 h at 90°C. The second aliquot was frozen, freeze-dried, and then ground in a cyclone mill (Udy Corp., Ft. Collins, CO) to pass a 1-mm screen. This sample was used to evaluate forage nutritive value and total ergot alkaloid concentration.
Crude protein and in vitro true digestibility (IVTD) were measured from ground samples with near-infrared reflectance spectroscopy by using the scanning, calibration, and validation methods described by Westerhaus et al. (2004; Table 1). Crude protein for the calibration samples was determined by measuring total N content with a Leco FP-428 nitrogen analyzer (Leco Corp., St. Joseph, MI) and then multiplying N concentrations by 6.25. In vitro true digestibility was determined by a 48-h in vitro digestion, followed by washing with a NDF solution, as described by Spanghero et al. (2003). Ruminal fluid was collected from a cannulated cow offered a forage-based diet. Total ergot alkaloid content was determined by the ELISA method described by Hill and Agee (1994).
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Table 1. Calibration statistics for near-infrared reflectance spectrophotometric determination of CP and in vitro true digestibility (IVTD) content of stockpiled tall fescue
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Animal Measurements
Cow and calf BW were determined at the start and end of grazing stockpiled tall fescue (phase 1), and again at the end of phase 2 when the calves were weaned.Cow and calf BW were taken on 2 consecutive mornings without prior removal from water or pasture. An experienced technician assigned BCS to all cows (1 = emaciated to 9 = obese; Wagner et al., 1988). On April 12 of yr 1 and on April 4 of yr 2, cow pregnancy rates were determined by rectal palpation and ultrasonography.
Statistical Analysis
Forage yield, nutritive value, and total ergot alkaloid content were analyzed as a randomized complete block with 3 treatments and 4 blocks, as described by Steel and Torrie (1980). A split-split plot arrangement of the randomized complete block was used, in which years and blocks were the main plots, endophyte levels (treatments) were the subplots, and periods within years were the subsubplots. Main effects and all interactions were tested. Years and interactions with years were considered random effects, and all others were considered fixed effects. Repeated-measures ANOVA procedures were used to test the effects of treatments and periods. The SAS PROC MIXED (SAS Inst. Inc., Cary, NC) was used, assuming first-order, autoregressive correlation among the repeated measures. Mean separation was performed with Fisher’s protected LSD (alpha = 0.05). Animal performance data, except cow conception, were also analyzed as a randomized complete block with the model described above, except that period was removed from the model. An experimental unit for these measures was a group of 5 cow-calf pairs on each of the 12 pastures. Differences in conception rates between treatments were analyzed by chi-squared analysis using PROC FREQ of SAS (SAS Inst. Inc.).
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RESULTS AND DISCUSSION
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Stockpiled Tall Fescue Forage
Forage Yield.
Stockpiled tall fescue DM yield had year by treatment interactions (P <0.05), but all other interactions were not significant (P >0.05); therefore, forage DM yield data were averaged over periods by year for each treatment. During yr 1, DM yield of tall fescue in the high treatment averaged 4,910 ± 142 kg/ ha, which was greater (P <0.01) than the medium (4,378 ± 142 kg/ha) and low (4,054 ± 142 kg/ha) treatments (Figure 1). Similarly, during yr 2 the high treatment yielded 4,976 ± 95 kg/ha, which was greater (P = 0.02) than the medium (4,627 ± 95 kg/ha) and low (4,651 ± 95 kg/ha) treatments (Figure 1). Similar to the data reported by Fribourg and Bell (1984) and Kallenbach et al. (2003), over the course of phase 1, tall fescue DM yield declined by 18% in yr 1 (P <0 0.01) and 11% in yr 2 (P <0.001). Kallenbach et al. (2003) reported 20% greater stockpiled DM yield for endophyte-infected tall fescue compared with endophyte-free tall fescue. Our data support their finding that endophyte infection enhanced the autumn growth of tall fescue.
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Figure 1. Dry matter yield of stockpiled tall fescue before grazing in pastures with 3 endophyte infection levels [20 (low), 51 (medium), and 89% (high)]. Data are means of 4 harvests during yr 1 and 5 harvests during yr 2. Year 1 represents December 2004 to February 2005, and yr 2 represents December 2005 to February 2006. Error bars represent 2 times the SE. Within a year, bars without a common letter differ (P <0.05).
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Forage Nutritive Value.
Year by period interactions were detected (P <0.05) for all measures of nutritive value; therefore, data were presented by year and period. Endophyte infection level did not affect (P = 0.34) the CP concentration of stockpiled tall fescue in either year or IVTD in yr 2 (P = 0.11). However in yr 1, IVTD for the low treatment was 74.0%, which was greater (P = 0.002) than the medium and high treatments (data not shown). Crude protein concentration of stockpiled tall fescue declined by less than 1 percentage unit during phase 1 in yr 1; during yr 2, CP was close to 13% at every sampling period (Table 2). For yr 1 and 2, IVTD concentrations of the stockpiled tall fescue started at 77.4 and 80.9%, respectively, and by late February declined by 8.8 and 4.7 percentage units (Table 2). These relatively small changes in forage nutritive values detected over the winter suggest a relatively constant forage quality that satisfied the CP and energy requirements for lactating beef cows (NRC, 2000).
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Table 2. Crude protein and in vitro true digestibility (IVTD) of tall fescue for each harvest during phase 1 of yr 1 (2004–2005) and yr 2 (2005–2006)1
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Total Ergot Alkaloid Concentrations.
For total ergot alkaloid concentrations, interactions with year were not observed (P >0.05); thus, data were combined over years. Total ergot alkaloid concentrations for the high treatment started at 918 ng/g and declined to 450 ng/ g between early December and late February (Figure 2). Similar to the high treatment, the medium treatment declined by 52% during phase 1, ending at 168 ng/g (Figure 2). The low treatment contained almost no ergot alkaloid at each sampling date, even though standing forage had an endophyte infection level of 20%. Similar to the findings of Kallenbach et al. (2003) with ergovaline, the total ergot alkaloid concentration declined at faster rates than did IVTD or CP. Because the total ergot alkaloid concentration declined relatively quickly during phase 1, implications can be drawn. Producers could use pastures with low levels of endophyte infection first and then move to pastures with greater infection levels in late winter. This strategy would at least minimize ergot alkaloid consumption. To accomplish this management, however, endophyte testing of tall fescue pastures would have to be implemented.
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Figure 2. Total ergot alkaloid concentration of stockpiled tall fescue from pastures with 51 (medium) and 89% (high) endophyte infection. Data were averaged across 2 yr and are presented by day of phase 1. Error bars represent 2 times the SE. Day 0 represents December 2, 2004, and December 1, 2005. Data from pastures with 20% endophyte infection (low) were not plotted because all points were at or near zero.
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Cow and Calf Performance
Apparent Intake and Pasture Utilization of Cow-Calf Pairs.
Apparent DMI of stockpiled tall fescue was 2 kg/d greater for yr 1 compared with yr 2. However, there were no year by treatment interactions (P >0.05); thus, data were averaged across years. In addition, apparent DMI was unaffected (P = 0.33) by endophyte infection level, with apparent DMI remaining constant across all treatments at 16 ± 1.7 kg/d for each cow-calf pair (data not shown). Pasture utilization averaged 76% in yr 1, which was greater (P = 0.01) than the 63% measured in yr 2, but endophyte infection level did not influence (P = 0.25) pasture utilization (data not shown). These year differences in apparent DMI and pasture utilization were attributed to differences in weather: yr 1 was a wet winter, whereas yr 2 was a dry winter with temperatures usually above average (Figure 3). When cattle are wet, metabolic rates increase to regulate body temperature (NRC, 2000). As a result, DMI and passage rate increase, which increases the heat increment (NRC, 2000).
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Figure 3. Air temperature and precipitation during phase 1 for yr 1 (2004 to 2005) and yr 2 (2005 to 2006) in comparison with the 30-yr means.
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Cow Performance.
All measures of animal performance were greater (P <0.05) for yr 2 than for yr 1. However, there were no year by treatment interactions (P >0.05); thus, animal performance data were averaged across years. Cows averaged 610 ± 4 kg at the start of phase 1 (Table 3). At the end of phase 1, cows in the low treatment had lost 39 kg each compared with 54 and 63 ± 36 kg/cow for the medium and high treatments, respectively (P = 0.04). Additionally, BCS of cows in the low treatment was greater (P <0.02) than those of the medium and high treatments at the end of phase 1 (Table 3). Although cow BW and BCS declined in all treatments during phase 1 (P <0.01), the low treatment primarily showed the limitations of forage quality, because total ergot alkaloid concentrations were nil (Figure 2
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Table 3. Body weight, ADG, and BCS of cows grazing stockpiled tall fescue with endophyte infection levels of 20 (low), 51 (medium), and 89% (high)1
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The medium and high treatments were more complex because limitations of both forage quality and ergot alkaloids were at play. Sleper and West (1996), Kallenbach et al. (2003), and Oliphant (2005) have suggested that the concentrations of alkaloids are lower in stockpiled tall fescue compared with samples taken during the growing season. Our data suggest that the total ergot alkaloid concentrations in tall fescue fields with endophyte infection levels of 51% or greater were still high enough to negatively influence the BW and BCS of lactating cows grazing stockpiled forage during winter.Waller et al. (1988) compared a leader-follower system, in which fall-calving cows grazed after their calves, with a conventional system, in which cows and calves grazed simultaneously. They found that fall-calving cows grazing stockpiled tall fescue after their calves likely consumed more endophyte-infected tall fescue and had lower ADG than cows that did not follow their calves.
During phase 2, cows that had grazed the high or medium treatments during phase 1 lost less (P <0.01) BW than did cows in the low treatment. It seems likely that cows in the low treatment during phase 1 were introduced or reintroduced to ergot alkaloids, albeit at levels considered low (Tor-Agbidye et al., 2001). This sudden switch during phase 2 likely influenced their intake, and thus BW, more than the cows that had been acclimated to the infected tall fescue in phase 1. Porter et al. (1990) documented that steers grazing endophyte-free tall fescue for 6 wk, and then switched to 100% endophyte-infected tall fescue for 8 wk, lost more BW in the 8 wk following the switch than those that grazed only 100% endophyte-infected tall fescue for the entire 14 wk. We contend that cows grazing in the low treatment likely responded in a similar manner during phase 2. At the end of phase 2 (weaning) BW of all cows did not differ (528 ± 27 kg; P = 0.15; Table 3) among treatments. Body condition scores did not change appreciably (P >0.05) between the end of phase 1 and phase 2, and the BCS of cows in the low treatment was greater (P = 0.02) than the BCS of cows in the medium and high treatments (Table 3).
Contrary to the finding of Chestnut et al. (1991) that visual signs of tall fescue toxicosis are less severe in cool weather, 4 cows in the high treatment were diagnosed with "fescue foot" during yr 1 and 2. These cows remained on test for the entire study, except that in yr 2, 1 cow lost an entire hoof and became so lame that she had to be euthanized in mid-February. Despite these symptoms, cow conception was unaffected by endophyte infection level (P = 0.76). Even with clinical symptoms of fescue toxicosis during the 84 d of phase 1, the natural service conception rate was 93% across all treatments. This is despite the fact that total ergot alkaloid concentrations were as great as 900 ng/g during the breeding season (Figure 2). In summarizing several reproductive studies, Porter and Thompson (1992) reported that conception rates decreased by 3.5% for each 10% increase in endophyte infection for spring-calving herds. However, tall fescue toxicosis amplifies the symptoms of heat stress (Porter and Thompson, 1992). Because fall-calving cows are rebreeding during early winter, the effects of endophyte infection on cow pregnancy rates may be less because there is minimal heat stress.
Calf Weight and Gain.
In contrast to BW of cows, calf BW were unaffected by endophyte level. Average daily gain and BW of calves were 0.73 ± 0.07 kg (P <0.10) and 170 ± 2 kg (P = 0.14), respectively, at the end of phase 1 (Table 4). At the end of phase 2, calves averaged 197 ± 3 kg (P = 0.49). In a similar study, Waller et al. (1988) found that the gain of nursing calves was not affected when their dams grazed endophyte-infected tall fescue (30 to 50% endophyte-infected) during winter. Our data, along with this earlier report, showed that renovation of endophyte-infected pastures was unlikely to increase the BW of calves weaned in April from fall-calving beef herds.
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Table 4. Body weight and ADG of nursing calves when their dams grazed stockpiled tall fescue with endophyte infection levels of 20 (low), 51 (medium), and 89% (high)1
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In a review article, Paterson et al. (1995) concluded that decreased milk production was a common effect of cows grazing endophyte-infected tall fescue. Although we did not directly measure milk production in this study, Rutledge et al. (1971) showed that a dam’s milking ability describes 66% of the variation in calf weaning weight. Furthermore, Peters et al. (1992) found that cows grazing endophyte-infected tall fescue during spring and summer produced 25% less milk, and as a result, their calves had lower weaning weights than cows grazing endophyte-free tall fescue or or-chardgrass. Because there was no difference (P = 0.49) in calf weaning weight between treatments, it is possible that the dam’s milking ability was unaffected by grazing stockpiled, endophyte-infected tall fescue. Another possibility is that cows grazing in the medium and high treatments had decreased DMI and, because pasture utilization rates were equal among treatments, calves could have consumed more forage to make up for this difference in cow DMI. However, calves in the high treatment would have had to consume tall fescue with appreciable ergot alkaloid concentrations to make up the differences in BW compared with those in the low treatment.
The ergot-like alkaloids in endophyte-infected tall fescue stockpiled for winter grazing decreased by approximately 50% from December through February; however, the weight loss and body condition of lactating beef cows was still influenced by endophyte infection level. Nursing calves on the other hand, did not show changes in ADG or weaning weight based on the endophyte infection level of the stockpiled tall fescue their dams consumed. Based on our results for calf gain and weaning weight, renovation of endophyte-infected tall fescue pasture would not be needed if the forage is to be stockpiled for winter grazing. Our results also reiterate the importance of knowing the endophyte infection level of tall fescue pastures. If cattle producers have fields with different levels of endophyte infection, cattle could graze less toxic pastures in early winter and then be moved to pastures with greater levels of endophyte infection later in winter. This strategy takes advantage of the decline in toxic alkaloids in pastures with a greater level of endophytes. This procedure should help minimize the BW loss of lactating cows on stockpiled tall fescue and reduce the need for winter supplementation.
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Footnotes
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1 This material is based on work supported by the USDA under Cooperative Agreement No. 58–6227–3–016. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the USDA. This research was supported in part by the Missouri Agricultural Experiment Station. 
2 Corresponding author: kallenbachr{at}missouri.edu
Received for publication December 29, 2006.
Accepted for publication May 2, 2007.
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Abstract
INTRODUCTION
