Using tall fescue in a complementary grazing program for spring-calving beef cows in southern Arkansas1

The Professional Animal Scientist 30 (2014):423–431; http://dx.doi.org/10.15232/pas.2013-01300 ©2014 American Registry of Professional Animal Scientists

Using tall fescue in a complementary grazing

program for spring-calving beef cows in southern Arkansas1 P. A. Beck,*2 PAS, C. B. Stewart,* H. C. Gray,* M. S. Gadberry,† PAS, S. A. Gunter,‡ PAS, C. A. Young,§ and A. A. Hopkins# *Southwest Research and Extension Center, Division of Agriculture, University of Arkansas, 362 Hwy 174 N, Hope 71801; †Cooperative Extension Service, Division of Agriculture, University of Arkansas, 2301 S. University Ave. Rm. 308F, Little Rock 72204; ‡USDA/ARS, Southern Plains Range Research Station, Woodward, OK 73801; §The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401; and #Dow AgroSciences, 1117 Recharge Rd., York, NE 68467

ABSTRACT Over 3 yr, spring-calving beef cows (n = 108, yr 1; n = 72, yr 2 and 3; initial fall BW = 480 ± 8.6 kg, BCS = 5.5 ± 0.07; age = 6 ± 2.6 yr) were allocated by parity, breed composition, and BW to 4.8 ha (n = 6) of warm-season pastures and limit grazed 2.4 ha of tall fescue (Festuca arundinacea) during the winter and spring to determine the effect of endophyte toxicity or clover additions on cow performance (BW, BCS, and reproductive rates) and calf growth. Limit-grazed pastures were nontoxic endophyte-infectThis project was conducted with funding from the University of Arkansas Agricultural Experiment Station, Hatch Project No. AR002265. The authors wish to express their appreciation to Pat Capps and Andy McWilliams of the University of Arkansas Southwest Research Extension Center for technical assistance in completing this project and The Samuel Roberts Noble Foundation for donations of tall fescue germplasm. 2 Corresponding author: [email protected] 1

ed tall fescue (NE) and toxic endophyteinfected tall fescue (TEF), or toxic endophyte-infected tall fescue established with white, red, and crimson clovers (TECL). Calving BCS tended to be less (P = 0.09) for NE than for TEF and TECL but was greater (P = 0.02) for NE than for TEF and TECL in April, before breeding. At weaning, BCS of NE was less (P = 0.05) than TEF and TECL. Pregnancy percentage was greater (P = 0.02) for NE than TEF and TECL and was greater (P = 0.05) for TEF than TECL. Calf BW was unaffected (P ≥ 0.17) by treatment, but weaning BW per cow exposed to a bull was greater (P = 0.02) for NE than TEF and TECL. This experiment indicates that improvements in pregnancy percentages led to increased calf BW at weaning per cow exposed to a bull, an important profitability indicator. Pastures with TECL did not improve cow and calf performance or pregnancy percentages compared with TEF. Key words: beef cow, bermudagrass, clovers, limit grazing, tall fescue

INTRODUCTION Complementary forage systems based on warm-season perennial grasses and cool-season annual grasses have shown promise for maintaining BCS and BW of spring-calving cowherds in the southeastern United States (Hill et al., 1985; DeRouen et al., 1991; Gunter et al., 2002), while reducing the reliance on stored forages and concentrate supplements. Although most cool-season perennial grasses are short lived in the South, tall fescue (Festuca arundinacea Shreb.) infected with the naturally occurring endophyte Neotyphodium coenophialum has the benefit of improved persistence and high nutritive value during the fall and early spring (Beck et al., 2006). Grazing livestock performance is limited by fescue toxicosis (McMurphy et al., 1990; Thompson et al., 1993; Gunter and Beck, 2004). Toxic endophyte tall fescue (TEF) has been responsible for millions of dollars in economic losses (Strickland

424 et al., 2011) because of reduced BW gains, weaning BW, and reproductive rates. Endophyte strains (NE) have been identified that are nontoxic to livestock and bestow tall fescue with the dual advantages of stand persistence and improved animal performance. Research with these selected endophyte tall fescues indicates that this pairing is persistent with improved animal performance in a wide range of environments (Parish et al., 2003; Hopkins and Alison, 2006; Beck et al., 2008). There are relatively few published reports of incorporation of NE tall fescue into cow-calf production systems. Watson et al. (2004) found that cows grazing NE tall fescue from March to September had increased BW, BCS, serum prolactin, and calf weaning BW, yet no differences in calving rate or interval were measured because each year cows were selected from groups that had not been previously exposed to TEF. Caldwell et al. (2013) reported that limited use of NE (25% of pasture area) increased cow BW, BCS, weaning BW, and calving rate in spring-calving herds in tall fescue–based pasture systems in northern Arkansas. The objective of this experiment was to investigate the use of NE or TEF as a forage complement to a warm-season grass pasture system for cow-calf production in the extreme southwestern range of tall fescue adaptation in North America.

MATERIALS AND METHODS Animal Management and Forage Management All procedures in the following experiments were approved by the University of Arkansas Institutional Animal Care and Use Committee (protocol #12043). This research was conducted at the University of Arkansas Southwest Research and Extension Center in southwestern Arkansas (latitude: 33°40′4″N, longitude: 93°35′24″W, elevation 107 m). The objective of this experiment was to determine the effect of endophyte toxicity and clover addition to

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tall fescue pastures used as a limitgrazed complement to warm-season grass pastures. Replicate tall fescue pastures (n = 2/treatment) were randomly assigned to treatment and established to NE (cv. Texoma MaxQII, infected with the AR584 endophyte, Pennington Seed Inc., Madison, GA); TEF (cv. Texoma, Noble Foundation, Ardmore, OK), tall fescue managed with commercial fertilizer N sources; or TEF established with (TECL) clovers [white (Trifolium repens cv. Regal Graze, Cal/West Seeds, Woodland, CA, 3 kg/ha seeding rate), red (Trifolium pratense cv. Kenland; Allied Seed LLC, Murfreesboro, TN, 7 kg/ha seeding rate), and crimson (Trifolium incarnatum cv. Dixie, 14 kg/ha seeding rate)] planted in September of yr 1 of the experiment. Over 3 yr, beef cows (n = 108, yr 1; n = 72, yr 2 and 3; initial fall BW = 480 ± 8.6 kg; BCS = 5.5 ± 0.07; age = 6 ± 2.6) grazed 4.8 ha (n = 6) warm-season grass pastures in the summer and fall and were fed warmseason grass hay and limit grazed 2.4 ha of tall fescue in the winter and spring. Cows were allowed access to tall fescue paddocks for 8 h/d for 2 d/wk in December and January, 3 d/ wk in February, and 4 d/wk in March and were given ad libitum access to tall fescue paddocks in April, May, and early June. Access to tall fescue and tall fescue clover paddocks by cows was restricted through the summer to 2 periods of flash grazing for approximately 1 wk in July and August to remove warm-season grass forage mass. Calves were allowed creep access to respective tall fescue and tall fescue clover pastures at all times during the experiment. Tall fescue pastures were fertilized with P and K to meet soil test requirements for moderate level of production annually in September, and bermudagrass pastures were fertilized with P and K to meet soil test requirements for moderate level of production annually in May (Espinoza et al., 2006). Nitrogen (56 kg of N/ha as ammonium nitrate) was applied to bermudagrass pastures in May and June each summer (112 kg of total N/ha). All tall fescue

pastures were fertilized with N at a rate of 56 kg of N/ha in September, whereas only NE and TEF received N (56 kg of N/ha) each year in March. Cow BW and BCS (1 to 9 point scale, 1 = thin and 9 = obese; Richards et al., 1986) were collected (unshrunk) in November (following weaning), January (before calving), April (following the calving season and before bull turnout), and October (at separation of calves from dams for weaning). At each weighing, cows were gathered from pastures at 0700 h, separated from calves and weighed, reunited with their calf, and returned to pastures within 5 h. Within 24 h of birth, calves were weighed to determine birth BW, navels were treated with iodine, and male calves were castrated. Calf BW were also collected (unshrunk) in April and October (weaning). Cows were of predominantly English breeding (75% Angus or Hereford) with some Bos indicus and Continental (Simmental) influence. Cows were assigned to treatments based on parity, breed composition, and BW by randomly assigning cows within each parity, breed type, and BW group to pastures. In yr 1, cows were stocked at 2.5 cow-calf units per total system hectare (3.6 cow-calf units/ha of bermudagrass). Because of limited forage production during yr 2 and 3, cow stocking rate was decreased to 1.6 cow-calf units per total system hectare (2.5 cow-calf units/ha of bermudagrass). The reduction in stocking rate was conducted by removing of all cows that were not pregnant, failed to raise a calf to weaning, or were in excess of 10-yr of age. Cows originally allocated to each pasture remained on pasture throughout the 3-yr experiment (except cows removed between yr 1 and 2) unless culled for reproductive failure or failure to wean a live calf. Cull cows were replaced with second-parity cows of similar breeding to maintain similar stocking rates among pastures. Cows from each group were exposed to an Angus bull that had passed a breeding-soundness examination for natural service during May and June. Cows calved during a

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60-d period in February and March, and calves were weaned during the initial week of October each year. Pregnancy status was determined for cows via rectal palpation by an experienced veterinarian at the time of weaning. Pregnancy percentage was calculated as the number of cows pregnant divided by the number of cows exposed to the bull times 100. Throughout the experiment cows had ad libitum access to a salt-andmineral mixture designed to meet requirements of grazing beef cows. The mineral mixture (Sunbelt Custom Minerals Inc., Sulfur Springs, TX) contained 14% Ca and 7% P from CaCO3 and Ca2PO4, 5% Mg from MgO, and 14% NaCl, as well as vitamins (661,500 IU/kg vitamin A, 221 IU/kg vitamin E, and 66,150 IU/kg vitamin D) and trace minerals (1,000 mg/kg Mn from MnSO4, 2,355 mg/ kg Fe from FeSO4, 1,250 mg/kg Cu From CuSO4, 3,000 mg/kg Zn from ZnSO4, 20 mg/kg Co from CoCO3, and 25 mg/kg I from ethylenediamine dihydroiodide). Pastures were sampled at midmonth throughout the grazing season for each forage type. Bermudagrass pastures were sampled monthly beginning in May through October each year. Tall fescue paddocks were sampled beginning in December through May of each year. Forage mass in each pasture was estimated using a calibrated rising-plate meter with 20 sampling points per pasture (Michell and Large, 1983). Calibration samples were collected by clipping all forage within a single 0.1-m2 frame in each pasture at each sampling to 2.5-cm stubble height with hand shears. Clipped calibration samples were dried to a constant weight under forced air at 50°C. Dry weights of these clippings were used to relate forage mass (kg of DM/ha) to plate height within each treatment using linear regression for forage mass prediction. Forage mass prediction equations for the rising-plate data were generated using the regression procedure of SAS (SAS Institute Inc., Cary, NC) using the clipping data for each collection period. The regres-

sion of rising-plate reading on clipped DM yield resulted in equations that explained 87% of variation (P < 0.01) in forage mass (kg/ha) for tall fescue and 78% of variation (P < 0.01) in forage mass for bermudagrass. To estimate quality of forage consumed by cattle, forage samples were collected to be representative of diets consumed by grazing cows from all pastures by clipping forage to mimic forage selected by grazing cows. Stand counts of tall fescue and clover within respective paddocks were conducted each year in early June using the step-point method (Owensby, 1973). The presence of clover in stand counts conducted in TECL pastures was used to determine the requirement for reseeding of clovers the following fall.

Laboratory Analysis Forage samples collected for nutrient analysis were dried to constant weight at 50°C in a forced-air oven and ground to pass a 2-mm screen (Thomas A. Wiley Laboratory Mill, Model 4, Thomas Scientific, Swedesboro, NJ) for analysis using near infrared reflectance spectroscopy (Feed & Forage Analyzer model 6500, FOSS North America, Eden Prairie, MN). The CP calibration equation had an SE of calibration of 0.92, an SE of cross validation of 0.93, and R2 of 0.96. The NDF calibration equation had an SE of calibration of 2.63, an SE of cross validation of 2.73, and R2 of 0.95. The ADF calibration equation had an SE of calibration of 1.66, an SE of cross validation of 1.70, and R2 of 0.93. At the beginning of the study, tall fescue tillers in each paddock were tested for endophyte infection rates using a PCR-based screen with markers that distinguish each endophyte (Takach et al., 2012; Takach and Young, 2014).

Statistical Analysis Cow BW and BCS data were analyzed as a repeated measure experiment using the mixed procedure of SAS with a variance components

covariance structure. Pregnancy percentage was analyzed using the glimmix procedure of SAS. Year was used as repeated measure because the cows used in this experiment remained on pastures for the 3-yr period, and there was potential for carryover effects of fescue toxicosis or adaptation to fescue toxins over time to affect cow and calf performance differently across years of the study. Pasture within year was the experimental unit, individual cow or calf was the sampling unit, and pasture within treatment was the subject. Models for analysis of cow performance indicators (calving date, BW, and BCS) and calf performance (BW) included cow age, forage treatment, year, and the year × treatment interaction. Treatment least squares means were separated using the contrasts 1) TEF and TECL versus NE and 2) TEF versus TECL. As per convention, statistical differences were declared with P ≤ 0.05, and tendency was declared with P > 0.05 and ≤0.10. Forage mass and forage nutritive value were analyzed as a completely randomized design with a split plot. Month within year was in the subplot. The main effects of forage treatment and month along with the effects of treatment × month interaction were tested with the interaction of year and pasture in the random statement. Because of significant (P ≤ 0.04) year effects and year × treatment and year × treatment × month interactions, forage mass and nutritive quality were analyzed by month within year using pasture within treatment in the random statement. Least squares means of forage mass and nutritive value were separated using the predicted differences option in SAS. Statistical differences were declared with P ≤ 0.05, and tendency was declared with P > 0.05 and ≤0.10.

RESULTS AND DISCUSSION Forage DM Yield and Nutritive Quality The endophyte infection levels ranged from 91.7 to 100.0% for both

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NE and TEF pastures and were determined to be specific for the desired endophyte strain. The tall fescue sampled from TEF and TECL pastures exhibited mean ±SD infection rates of 95 ±3.1%, and tall fescue sampled from NE exhibited mean ±SD infection rates of 97 ±2.0%. Stand counts of the tall fescue in limit-grazed pastures indicate that tall-fescue pastures persisted well throughout the 3-yr experiment.

Stand counts indicate stands of NE were 85 ±11%, 83 ±15%, and 76 ±13% tall fescue in yr 1, 2, and 3, respectively; TEF were 89 ±12%, 86 ±14%, and 86 ±14% tall fescue in yr 1, 2, and 3, respectively; and TECL were 75 ±10%, 64 ±12%, and 55 ±17% tall fescue in yr 1, 2, and 3, respectively. Stand counts of clover contribution in TECL were 15 ±4%, 20 ±9%, and 7 ±3% of the tall-fescue pasture in

Table 1. Effect of novel endophyte tall fescue or toxic endophyte tall fescue managed with fertilizer or clover on forage DM yield and chemical composition during yr 11 Item DM yield, kg/ha  December2  January2  April2  May2  July3  August3  September3 CP, %  December2  January2  April2  May2  July3  August3  September3 ADF, %  December2  January2  April2  May2  July3  August3  September3 NDF, %  December2  January2  April2  May2  July3  August3  September3

TECL  

1,162 911 1,562 2,147 1,515 2,188b 1,605   14.6 16.0 19.2 18.5 13.9 16.9 22.1   27.4 24.7 26.1 32.9 33.9a 30.2 28.1   45.0 41.7 45.4 56.7 62.0 60.4 59.6

TEF  

1,578 1,452 1,518 2,099 1,314 1,793a 1,262   16.0 14.1 18.0 18.9 13.2 18.8 22.7   26.3 27.1 26.1 32.2 37.7b 28.6 27.5   45.0 44.8 48.5 57.0 64.5 59.1 58.5

NE  

1,372 1,188 1,549 1,425 1,625 1,515a 1,606   16.4 13.5 15.8 19.8 15.2 17.2 20.3   26.0 28.3 30.3 31.2 34.5a 31.8 29.4   45.8 46.5 53.5 55.2 62.0 59.9 61.0

SE  

139.9 161.1 157.6 202.5 391.2 115.4 123.4   1.4 1.5 0.9 0.7 0.5 1.3 0.5   1.7 1.9 1.7 1.5 0.7 2.0 0.7   1.7 2.7 1.8 1.9 1.1 2.7 1.1

P-value  

0.26 0.21 0.98 0.14 0.86 0.05 0.19   0.65 0.55 0.18 0.48 0.14 0.61 0.17   0.82 0.50 0.29 0.72 0.05 0.59 0.27   0.93 0.52 0.11 0.78 0.31 0.94 0.15

Least squares means with differing superscripts differ (P ≤ 0.05). Treatments were cows limit grazed in the winter and spring: 1) nontoxic endophyte tall fescue (NE), 2) toxic endophyte tall fescue (TEF), or 3) toxic endophyte tall fescue with interseeded clovers (TECL). 2 Tall fescue. 3 Bermudagrass. a,b

1

yr 1, 2, and 3, respectively. Clover contribution to stands in TECL was targeted to be between 15 and 20% (Gunter et al., 2012). Because stand counts indicated adequate levels of clover in both yr 1 and 2, clovers were not reseeded into pastures, clovers may have not produced adequate seed in the spring of yr 2, or clovers were unable to persist through the summer in yr 2, which are likely explanations for the low population of clovers in yr 3. Forage mass (kg of DM/ha) and nutritive quality are presented by year in Tables 1, 2, and 3. In yr 1, (Table 1) there were no differences in (P ≥ 0.11) forage mass, CP, ADF, or NDF among treatments. Although forage mass in TECL was numerically less (P = 0.21) than NE or TEF in January, the legumes established in TECL were able to adequately replace synthetic N used in TEF and NE. The forage mass in NE was numerically less (P = 0.14) than TECL and TEF in May, which may be an indication of reduced DMI by grazing cow-calf pairs in TEF and TECL often observed with toxic endophyte tall-fescue pastures (Strickland et al., 2011). Crude protein during yr 1 ranged between 13 and 22% for all treatments, which is well within the required range for cows at all stages of production (NRC, 1996). Neutraldetergent-fiber content did not differ (P ≥ 0.11) among treatments during the first year of the experiment. Using the equations developed for Arkansas tall fescue (Davis et al., 2002) and bermudagrass, tall fescue ranged between 60 and 65% TDN and bermudagrass ranged between 65 and 82% TDN, indicating digestibility of forages would not be limiting to performance of beef cows at any level of production based on NRC (1996) requirements. In yr 2 (Table 2), at the initiation of limit grazing in December there were no differences (P = 0.39) in forage mass among treatments. Yet in January, TEF had greater (P = 0.03) forage mass than either TECL or NE, which indicates either lower production or greater DMI by beef cows.

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Table 2. Effect of novel endophyte tall fescue or toxic endophyte tall fescue managed with fertilizer or clover on forage DM yield and chemical composition during yr 21 Item DM yield, kg/ha  December2  January2  February2  March2  April2  May2  June3  July3  September3 CP, %  December2  January2  February2  March2  April2  May2  June3  July3 ADF, %  December2  January2  February2  March2  April2  May2  June3  July3 NDF, %  December2  January2  February2  March2  April2  May2  June3  July3

TECL  

1,549 1,008a 810 849 1,179 1,359 2,195 1,858 1,437   13.4 15.6a 20.9 14.9 16.7 15.6 13.0 11.3   28.9 30.3 24.8 31.0 30.1 31.9 35.7 37.3   50.6 54.5 48.1 55.4 60.6 65.7 72.7 72.0

TEF  

NE

1,768 1,478b 911 1,060 1,496 2,446 1,825 1,470 1,333   15.3 16.0a 28.7 17.5 19.9 13.5 14.4 16.5   26.9 30.3 18.3 29.3 30.3 35.3 33.5 32.6   47.2 53.8 39.9 53.6 52.5 67.7 69.5 68.2

 

1,839 937a 845 849 1,223 1,513 1,709 1,534 1,278   14.4 18.6b 29.7 14.8 18.9 12.1 12.6 10.7   29.4 27.9 17.7 32.6 29.6 36.3 35.9 38.5   50.7 51.2 39.3 59.2 56.2 68.2 72.4 72.8

SE  

127.1 115.4 57.9 57.2 169.0 390.0 302.1 418.2 304.8   0.6 0.4 3.5 1.1 1.0 0.9 1.0 3.3   1.4 1.2 2.8 1.5 3.0 1.9 0.9 3.0   1.4 1.2 4.0 2.4 3.1 2.0 0.9 1.9

P-value  

0.39 0.08 0.53 0.12 0.46 0.25 0.56 0.80 0.93   0.21 0.01 0.30 0.31 0.22 0.14 0.52 0.48   0.49 0.38 0.28 0.40 0.99 0.28 0.30 0.44   0.27 0.28 0.35 0.37 0.32 0.67 0.15 0.30

Least squares means with differing superscripts differ (P ≤ 0.05). Treatments were cows limit grazed in the winter and spring: 1) nontoxic endophyte tall fescue (NE), 2) toxic endophyte tall fescue (TEF), or 3) toxic endophyte tall fescue with interseeded clovers (TECL). 2 Tall fescue. 3 Bermudagrass.

ranged between 83% in the spring and 58% in the fall at weaning and would not be expected to be deficient (NRC, 1996) for the stage of production for cow-calf pairs at the time of sample collection. In yr 3 (Table 3), forage mass did not differ (P ≥ 0.29) among tallfescue pastures until late spring (May) sampling, at which time the NE pastures tended to have less (P = 0.06) forage mass than TECL or TEF. Low levels of forage mass in bermudagrass pastures during July and August may have become limiting to DMI of cows and calves, which would have reduced animal performance during the midsummer sample collection periods. Crude protein did not differ (P ≥ 0.19) among treatments at any time during yr 3 of this experiment. In May, TECL had less (P < 0.01) ADF and NDF than either TEF or NE. In May the calculated TDN of TECL (66.6%) was 6.5 percentage units more than TEF and NE. There were no other differences (P ≥ 0.17) in ADF or NDF at any other sampling period during yr 3. The lack of differences in forage mass and stand persistence between TEF and NE is similar to previous research comparisons between TEF and NE tall fescues reported in the studies by Beck et al. (2009) and Hopkins and Alison (2006). Forage nutritive value of tall fescue in the current study is also in agreement with previous research (Parish et al., 2003; Beck et al., 2006; Beck et al., 2009).

a,b 1

There were no other differences (P ≥ 0.12) in forage mass for the duration of the experiment in the second year. Crude protein content of NE was greater than TEF or TECL during January (P = 0.01), yet CP did not differ (P ≥ 0.14) among treatments the remainder of the experiment in yr

2. As observed in yr 1, there were no differences (P ≥ 0.15) in detergentfiber content throughout the second year of the experiment. Crude protein would not be expected to be deficient (NRC, 1996). Total digestible nutrients calculated from CP and detergent-fiber content (Davis et al., 2002)

Cow Performance Although there were differences among years (P < 0.01) for all factors examined, there was no year × forage treatment interactions (P ≥ 0.10) for cow performance; thus, cow performance data are presented across years in Table 4. Cow BW did not differ (P ≥ 0.18) among treatments throughout the experiment. Body condition score tended (P = 0.09) to be less for NE than TEF and TECL at calving but was greater (P = 0.02) for NE than TEF and TECL in April before breeding, and TEF tended (P = 0.08)

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Table 3. Effect of novel endophyte tall fescue or toxic endophyte tall fescue managed with fertilizer or clover on forage DM yield and chemical composition during yr 31 Item DM yield, kg/ha  January2  February2  March2  May2  June3  July3  August3  October3 CP, %  January2  February2  March2  May2  June3  July3  August3  October3 ADF, %  January2  February2  March2  May2  June3  July3  August3  October3 NDF, %  January2  February2  March2  May2  June3  July3  August3  October3

TECL  

1,148 986 1,346 1,355 1,010 648 932 1,276   21.9 20.2 23.5 18.2 14.0 12.4 12.5 14.5   12.8 21.9 16.8 25.3a 34.5 48.0 40.0 33.4   38.3 49.4 42.6 55.2a 66.8 70.9 68.8 69.8

TEF  

NE

1,205 730 1,720 1,298 1,204 803 861 1,049   24.3 24.4 24.3 15.3 16.3 13.0 12.5 12.4   10.6 19.3 16.2 30.8b 30.8 51.0 41.0 35.2   35.3 46.2 39.8 61.3b 63.5 70.4 67.7 71.6

 

1,025 1,118 1,197 840 1,256 622 813 900   22.9 21.1 20.7 14.0 14.4 10.8 11.3 14.1   12.8 22.2 19.3 32.7c 32.4 49.2 51.3 35.8   37.1 48.9 44.3 64.0b 64.5 71.4 65.0 74.0

SE  

327.6 162.7 193.3 99.9 187.1 106.8 207.0 222.9   1.7 1.8 1.1 1.3 0.8 6.2 0.7 1.2   1.5 1.3 1.0 0.4 1.2 4.1 1.5 2.2   1.8 0.9 1.6 0.5 0.9 1.5 1.0 1.4

P-value  

0.93 0.36 0.29 0.06 0.66 0.51 0.92 0.55   0.64 0.36 0.19 0.20 0.25 0.43 0.43 0.51   0.62 0.35 0.22 <0.01 0.24 0.52 0.28 0.75   0.57 0.17 0.28 <0.01 0.17 0.40 0.30 0.24

Least squares means with differing superscripts differ (P ≤ 0.05). Treatments were cows limit grazed in the winter and spring: 1) nontoxic endophyte tall fescue (NE), 2) toxic endophyte tall fescue (TEF), or 3) toxic endophyte tall fescue with interseeded clovers (TECL). 2 Tall fescue. 3 Bermudagrass. a–c 1

to have greater BCS than TECL. At weaning in October, BCS of cows grazing NE was less (P = 0.05) than TEF and TECL. Even though these changes in BCS among treatments were observed, the average BCS of the cows in this experiment was in the upper 5 to low 6 ranges, so minimal

effect on reproduction would be expected (Richards et al., 1986). Peters et al. (1992) found that cows grazing toxic endophyte-infected tall fescue in Missouri had reduced milk production and lost more BW and BCS compared with cows grazing endophyte-free tall fescue or orchard-

grass. In agreement with the results of Peters et al. (1992), Watson et al. (2004) found beef cows grazing nontoxic endophyte-infected tall fescue had a greater BW and BCS than cows grazing toxic endophyte-infected tall fescue, whereas Coblentz et al. (2006) observed similar results with beef cows grazing endophyte-free tall fescue or orchardgrass compared with TEF pastures in northern Arkansas. Calving date (P ≥ 0.51) was not affected by treatment. Average calving date was Julian d 58 (February 28), which was close to the midpoint of the calving season. Although the average calving date was similar across treatments, pregnancy percentage was 18 percentage units greater (P = 0.02) for NE than the average of TEF and TECL. Pregnancy percentage was also 16 percentage units greater (P = 0.05) for TEF than TECL. Although cows were not tested for objective symptoms of fescue toxicosis, the cows in TEF and TECL were observed to exhibit signs of heat distress (panting, loitering near water sources, and so on) during the late spring to early summer (May and June) breeding season. Thus, it appears that exposure to tall fescue toxins before and during breeding may affect reproductive performance during the subsequent early summer breeding season. In agreement with the current research, it has been reported that fescue toxicosis caused moderate to severe reduction in pregnancy percentages of 8 to 39% (Strickland et al., 2011), although this is not consistent throughout the literature (Drewnoski et al., 2009; Strickland et al., 2011). In contrast with other studies, Drewnoski et al. (2009) reported that pregnancy percentages of heifers grazing toxic endophyte-infected or nontoxic endophyte-infected, or endophyte-free tall fescue did not differ. In a comparison of TEF and NE tall fescues, Watson et al. (2004) reported that neither calving rate nor calving interval were affected by tall fescue toxins, which may be expected because cows with previous exposure to tall-fescue toxins were excluded from the analysis.

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Table 4. Effect of limit grazing of tall fescue toxicity status and legumes on performance of spring-calving cows1 Contrast3 Item BW, kg  November  January  April  October BCS  November  January Calving  April  October Calving date Pregnant,%4

NE

TEF

TECL

SE

Interaction2

NE vs. TEF and TECL

TEF vs. TECL

  503 527 499 496   5.9 5.8 5.7 6.1 5.7 59 80

  511 538 502 501   5.9 5.9 5.9 6.0 5.9 57 70

  515 536 504 515   5.9 5.9 5.9 5.9 5.9 57 54

  5.2 5.7 5.7 8.3   0.05 0.08 0.06 0.02 0.06 2.4 4.0

  0.47 0.93 0.30 0.46   0.29 0.20 0.17 0.80 0.16 0.40 0.16

  0.18 0.23 0.59 0.32   0.58 0.32 0.09 0.02 0.05 0.51 0.02

  0.60 0.74 0.92 0.29   0.99 0.99 0.92 0.08 0.49 0.81 0.05

Treatments were cows limit grazed in the winter and spring: 1) nontoxic endophyte tall fescue (NE), 2) toxic endophyte tall fescue (TEF), or 3) toxic endophyte tall fescue with interseeded clovers (TECL). 2 Year × forage treatment interaction. 3 Least squares means for treatments were separated using the following contrast statements: NE compared with mean of TEF and TECL; and TEF compared with TECL. Statistical differences were declared with P ≤ 0.05, and tendency was declared with P > 0.05 and ≤0.10. 4 Percentage of cows determined to be pregnant by rectal palpation at weaning. Pregnancy percentage was calculated as the number of cows pregnant divided by the number of cows exposed to the bull times 100. 1

Caldwell et al. (2013) indicated that the effect of tall-fescue toxins on cow BW, BCS, caving rate, and calving interval was influenced by calving season. Calving rate of spring-calving cows entirely on toxic tall fescue was 44%, whereas calving rate of fall calving cows entirely on toxic tall fescue was 90% (Caldwell et al., 2013), indicating a dramatic effect of fescue toxicosis on reproductive efficiency of spring-calving cowherds.

Calf Performance Calf-performance-traits measured differed (P < 0.01) among years, but there were no year × forage treatment interactions (P ≥ 0.10); thus, calf preweaning performance data are presented across years in Table 5. Calf BW at birth, in April, and at weaning in October was unaffected by treatment (P ≥ 0.17), which indicates that milk production by the dams in this experiment was likely not affected by the fescue toxins as has commonly

been cited in the literature and associated with reductions in prolactin production (Peters et al., 1992; Strickland et al., 2011). Although treatment differences varied among years (year × treatment interaction, P < 0.01), the effect of fescue treatment across all 3 yr of the experiment indicates large effects of TEF on the weaning BW per cow exposed to a bull (Table 5). Cows grazing NE produced 40 kg more (P = 0.02) weaning BW per cow exposed to a bull than TEF and TECL, whereas TEF produced 33 kg more (P = 0.05) weaning BW per cow exposed than TECL. The effect of limit grazing tall fescue on weaning BW per cow exposed by year of the experiment is presented in Figure 1. In the first and second years of the experiment, NE tended to produce more (P ≤ 0.08) weaning BW per cow exposed than TEF and TECL, which do not differ (P ≥ 0.38). Yet in the third year of the experiment, NE produced more (P ≤ 0.05) weaning BW per

cow exposed than TEF and TECL, whereas TEF produced more (P = 0.01) weaning BW per cow exposed than TECL. Because weaning BW per cow exposed to a bull is calculated based on both calf BW at weaning and pregnancy percentage, seemingly minor changes for these factors could possibly have large effects on this important economic indicator. Research from southern Arkansas has shown the inclusion of clovers in cool-season pastures to increase weaning BW per cow exposed to a bull (Gunter et al., 2012). This later research mentioned was conducted with fall-calving cows grazing wheat (Triticum aestivum L.) and annual ryegrass (Lolium multiflorum Lam.) pasture compared with similar pasture including red clover (Trifolium pretense L.). Based on the difference between this research and that of Gunter et al. (2012), it seems that changes in weaning BW per cow exposed to a bull as a result of clover inclusion might be dependent on the species of grass that the clovers are

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Table 5. Effect of limit grazing of tall fescue toxicity status and legumes on preweaning performance of springborn calves1 Contrast3 Item BW, kg  Birth  April  Weaning WW per cow exposed4

NE  

37 88 217 175

TEF  

37 92 221 152

TECL  

38 90 219 119

SE  

1.2 1.2 2.6 7.2

Interaction2  

0.45 0.17 0.49 <0.01

NE vs. TEF and TECL  

0.83 0.17 0.45 0.02

TEF vs. TECL  

0.66 0.32 0.68 0.05

Treatments were cows limit grazed in the winter and spring: 1) nontoxic endophyte tall fescue (NE), 2) toxic endophyte tall fescue (TEF), or 3) toxic endophyte tall fescue with interseeded clovers (TECL). 2 Year × forage treatment interaction. 3 Least squares means for treatments were separated using the following contrast statements: NE compared with mean of TEF and TECL; and TEF compared with TECL. Statistical differences were declared with P ≤ 0.05, and tendency was declared with P > 0.05 and ≤0.10. 4 Calf BW at weaning for all cows exposed to bull for breeding. 1

interseeded in or the calving season the forage system is imposed on. In contrast with the results of this research, Peters et al. (1992) reported that cows grazing exclusively on toxic endophyte tall fescue weaned lighter calves than cows grazing nontoxic forages, which was associated with reduced milk production. Watson et al.

(2004) similarly found calves reared on TEF pastures had reduced rate of BW gain and were lighter at weaning than calves from nontoxic endophyteinfected tall-fescue pastures. Coblentz et al. (2006) found that replacing TEF with either endophyte-free tall fescue or orchardgrass increased weaning BW and calf ADG.

IMPLICATIONS The results of this experiment indicate that NE did not improve BW gain or BW at weaning of cows or calves compared with TEF or TECL. However, NE improved pregnancy percentages, leading to increased calf BW weaned per cow exposed to a bull during the breeding season. Weaning BW yield per cow maintained on a ranch is an important indicator of enterprise profitability. Including clovers in TEF pastures did not improve calf performance, pregnancy percentages, or calf BW weaned per cow exposed to a bull compared with TEF. Hence, in the productions systems explored in this experiment, it seems that the most efficacious technology to adapt would be NE tall fescue, and increases in efficiency would be expected to result from increased calf BW weaned per cow exposed to a bull.

LITERATURE CITED Beck, P. A., S. A. Gunter, K. S. Lusby, C. P. West, K. B. Watkins, and D. S. Hubbell. 2008. Animal performance and economic comparison of novel and toxic endophyte tall fescues to cool-season annuals. J. Anim. Sci. 86:2043–2055.

Figure 1. Weaning BW per cow exposed to a bull by year for cows limit grazing nontoxic endophyte tall fescue (NE), toxic endophyte tall fescue (TEF), or toxic endophyte tall fescue with interseeded clovers (TECL) during the winter and spring. Columns within year with differing letters (a–c) differ (P < 0.05).

Beck, P. A., S. A. Gunter, and J. M. Phillips. 2006. Evaluation of supplementation programs for growing cattle grazing tall fescue. Prof. Anim. Sci. 22:325–333.

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