Pre- and postweaning performance by cows and calves that grazed toxic or nontoxic endophyte-infected tall fescue pastures1

The Professional Animal Scientist 31 (2015):577–587; http://dx.doi.org/10.15232/pas.2015-01437 ©2015 American Registry of Professional Animal Scientists

P performance re- and postweaning by cows and

calves that grazed toxic or nontoxic endophyte-infected tall fescue pastures1 K. P. Coffey,*2 PAS, W. K. Coblentz,† J. D. Caldwell,‡ R. K. Ogden,† T. Hess,§ D. S. Hubbell III,§ C. P. West,# C. R. Krehbiel,‖ PAS, T. G. Montgomery,** J. A. Jennings,†† and C. F. Rosenkrans Jr.,* PAS *Division of Agriculture, University of Arkansas, Fayetteville 72701; †USDA-ARS, US Dairy Forage Research Center, Marshfield, WI 54449; ‡Purina Animal Nutrition Center, Gray Summit, MO 63039; §Division of Agriculture, University of Arkansas, Batesville 72501; #Department of Plant and Soil Science, Texas Tech University, Lubbock 79409; ‖Department of Animal Science, Oklahoma State University, Stillwater 74074; **Division of Agriculture, University of Arkansas, Monticello 71655; and ††Division of Agriculture, University of Arkansas, Little Rock 72204

ABSTRACT Negative effects on cattle grazing tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] infected with the wild-type endophyte Neotyphodium coenophialum (E+) are well documented, but information about the carryover effects on weaned calves is limited. Our objective was to compare pre- and postweaning performance by spring-calving cows and calves grazing E+ with that by cows grazing a nontoxic endophyte–tall fescue association (NE+). Pregnant Gelbvieh × Angus crossbred cows (n = 1 Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply either recommendation or endorsement by the USDA. 2 Corresponding author: [email protected]

136; 492 ± 19.2 kg of initial BW) were stratified by BW and age and allocated randomly to one of four 10-ha pastures in yr 1 (October 15) and one of eight 10-ha pastures in yr 2 (November 30). Pastures were allocated randomly before establishment to E+ or NE+. Cows remained on their assigned pastures until weaning in yr 2 but were removed from NE+ in the summer of yr 1 because of low forage mass. After weaning, calves grazed bermudagrass [Cynodon dactylon (L.) Pers.] followed by cool-season annual grasses. Cow BW and pregnancy rate, and calf weaning weight and preweaning gain were greater (P < 0.05) from NE+ versus E+. Weaning weight differentials were maintained throughout postweaning production phases, resulting in heavier HCW (P < 0.05) by steers and a tendency for greater (P < 0.10) subsequent calving rates by heifers. Therefore, re-

placing E+ with NE+ may improve preweaning cow and calf performance and heifer reproductive rates, but postweaning gains may not be affected by previous exposure to E+. Key words: tall fescue, novel endophyte, beef calf

INTRODUCTION Cattle consuming tall fescue infected with the wild-type, toxic endophyte Neotyphodium coenophialum (E+) have exhibited a myriad of adverse conditions including reduced DMI (Forcherio et al., 1995; Humphry et al., 2002), poorer cow and calf BW gains (Gay et al., 1988; Peters et al., 1992; Caldwell et al., 2013), and poorer reproductive performance (Gay et al., 1988; Sanson and Coombs,

578 2003; Caldwell et al., 2013) compared with those consuming nontoxic forages. Simply replacing E+ with noninfected tall fescue (E−) seems to be the most logical option, but E− is less persistent than E+, resulting in significant stand losses (Bouton et al., 2002; Vibart et al., 2008). Legumes also have been used successfully, resulting in improved animal gains and reproductive rates (Gay et al., 1988; Waller et al., 1989; Chestnut et al., 1991). However, gain and reproductive rates from cattle grazing E+ pastures with clover were not as great as those from E− pastures, and clover establishment and persistence may be problematic in sites with poorer quality soils (Coffey et al., 2005). In recent years, tall fescue plants were infected artificially with nontoxic novel endophytes. These tall fescue–nontoxic endophyte associations (NE+) maintained their vigor (Bouton et al., 2002; Gunter and Beck, 2004) but did not have detrimental effects on cattle (Parish et al., 2003b; Nihsen et al., 2004; Franzluebbers and Stuedemann, 2006) or sheep (Parish et al., 2003a). To date, limited studies have reported the benefits of grazing NE+ with cow–calf pairs (Watson et al., 2004; Caldwell et al., 2013), and only limited information is available pertaining to postweaning performance by calves weaned from E+ pastures (Brown et al., 1999). The objective of this study was to determine the effects of grazing NE+ compared with grazing E+ on cow performance and pre- and postweaning calf production measurements.

MATERIALS AND METHODS Pasture and Forage Management This study was conducted at the Livestock and Forestry Branch Station located near Batesville, Arkansas (35°49′N, 91°48′W), and the University of Arkansas Institutional Animal Care and Use Committee approved the procedures used (#03017). Gelbvieh × Angus crossbred cows (n = 136; 492 ± 19.2 kg of initial BW)

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were stratified by BW and age and allocated randomly to one of four 10ha pastures in yr 1 and one of eight 10-ha pastures in yr 2 at a stocking density of 1.3 cows per hectare. The pastures were allocated randomly such that half were seeded to E+ and half were seeded to a NE+ association developed at the University of Arkansas by infecting the HiMag tall fescue cultivar with endophyte strain Ark4. Two pastures each of E+ and NE+ were established in October 2003, and 2 additional pastures of each forage were established in October 2004, resulting in 2 experimental units per treatment in yr 1 and 4 experimental units per treatment in yr 2. All pastures received 56 kg of N/ ha in the spring as urea and 45 kg of N/ha in the autumn as ammonium nitrate. Cows confirmed as pregnant via rectal palpation began grazing the experimental pastures on October 15 and November 30 in yr 1 and 2, respectfully. These cows would have been approximately 4 (yr 1) or 5 (yr 2) months in gestation at the time they were added to the experimental pastures. Hay was harvested during the spring from approximately one-third of each pasture for subsequent feeding. During the summer of yr 1, extremely dry conditions resulted in reduced forage mass (<1,000 kg/ha) and forced offering of the winter hay supply during the summer. Once the hay from a particular NE+ pasture was depleted (July 29 on one pasture and September 29 on another pasture), cows were moved to a bermudagrass pasture and offered bermudagrass hay. The bermudagrass pasture was predominantly dormant because of the drought. Cows grazing E+ pastures were fed E+ hay from another location on the research farm and were not removed from their experimental pastures. In all cases, hay was offered for ad libitum consumption. The amount of hay offered to cows above that produced on the particular replicate was quantified by weighing 6 bales from each hay type and multiplying the number of bales offered by the average weight of the 6 bales.

Early autumn rainfall stimulated forage growth and all cows were returned to their respective pastures on October 6, 7 d before weaning. This resulted in cows from NE+ pastures being removed from their respective pastures for either 69 or 7 d, depending on the particular replication. During yr 2, forage mass was adequate, and cows remained on their assigned pastures until their calves were weaned.

Cattle Management and Measurements Cow weight and BCS were evaluated at the beginning of the trial, immediately before the start of the calving season, and at weaning without prior removal from pasture or water. Calving rates were determined as the proportion of cows actually giving birth to a calf the following spring, and calving interval was determined as the difference between the actual calving dates. Cows that did not calve were not included in the calving-interval data set. Hair scores of the cows also were estimated at weaning using a 5-point scale where 1 represents no rough, discolored hair; 3 represents rough, discolored hair on 50% of the cow body; and 5 represents rough, discolored hair on >90% of the cow body. Cows were vaccinated against 7 clostridial strains (Alpha-7; Boehringer Ingelheim Animal Health Inc., St. Joseph, MO) approximately 2 wk before the onset of calving. Cows also were vaccinated against infectious bovine rhinotracheitis, bovine virus diarrhea, parainfluenza, bovine respiratory syncytial virus, and 5 strains of Leptospira (Elite 9; Boehringer Ingelheim Animal Health Inc.) and were treated for internal parasites with moxidectin (Cydectin; Fort Dodge Animal Health, Fort Dodge, IA) approximately 28 d before the start of the breeding season. An Angus × Gelbvieh bull that passed a breeding soundness examination according to the guidelines of the Society of Theriogenology (Hopkins and Spitzer, 1997) approximately 4

Cow and calf pre- and postweaning performance on tall fescue

wk before the initiation of breeding was added to each pasture replicate on May 10 of each year and remained in the assigned pasture for the entire 60-d breeding season. Cows that lost their calves were replaced with a primiparous heifer and calf at the time bulls were added. These heifers were added to maintain equal grazing pressure across pastures but were not included in the cattle performance data set because they were not on the forages until immediately before the start of the breeding season. Calf BW were measured at birth, at the start and end of the breeding season, and at weaning in early October (October 12 and October 10 in yr 1 and 2, respectively) without prior removal from pasture and water. Calves were weaned using a lowstress weaning program where they were gathered; vaccinated against 7 clostridial strains (Alpha-7; Boehringer Ingelheim Animal Health), infectious bovine rhinotracheitis, bovine virus diarrhea, parainfluenza, bovine respiratory syncytial virus, Haemophilus somnus, and 5 strains of Leptospira (Elite 9-HS; Boehringer Ingelheim Animal Health); and treated for internal parasites with moxidectin (Cydectin; Fort Dodge Animal Health). Calves then were placed directly across an electric fence from their dams for 14 d. Blood samples were collected at the time of initial vaccination via jugular venipuncture into tubes with EDTA for whole blood hemograms (Vacutainer product no. 366643, Becton Dickinson Co., Franklin Lakes, NJ). After the 14-d fence-line weaning, calves were gathered and revaccinated, blood was collected as described above, and then calves were moved to a new location and placed on bermudagrass pastures. Blood hematology profiles were determined using a Hema Vet multispecies hematology system (CDC Technologies Inc., Oxford, CT). Calves were moved to cool-season annual pastures during the late fall, winter, and early spring. Heifers grazed annual ryegrass (Lolium multiflorum Lam.) until breeding in

early May. Steers grazed winter wheat (Triticum aestivum L.) until transport to feedlot facilities. In yr 1, steers were transported to the Oklahoma State University feedlot facility near Stillwater, Oklahoma, on March 8 and penned by preweaning pasture group. In yr 2, steers were transported to a commercial feedlot near Scott City, Kansas, on March 19 and penned together in one feedlot pen. Heifers were moved to bermudagrass pastures and commingled for mating. All heifers from yr 1 were mated to one sire, whereas heifers in yr 2 were divided equally across previous treatments and mated to 2 sires.

Forage Measurements and Sample Collection Unless cattle were being fed hay, pastures were evaluated monthly for quantity and quality of available forage by walking each pasture in a zigzag pattern to ensure random but representative sampling of each pasture (Sollenberger and Cherney, 1995). Forage mass was estimated at 5 locations per hectare using a disk meter (Bransby et al., 1977), and samples for forage quality analyses were gathered at those locations by clipping forage to a 2.5-cm stubble height with hand shears. At the completion of sampling of each pasture, forage samples were placed in plastic bags and submerged under ice immediately. Samples were transported to a conventional freezer (−20°C) and stored a minimum of 2 h, they were then transported on ice and stored in an ultralow freezer (−80°C) pending lyophilization. Disk meters were calibrated by clipping forage directly underneath the disk meter with hand shears to a 2.5-cm stubble height in 5 locations representing a variety of disk meter heights. These samples were dried under forced air at 50°C to a constant weight, and the resulting weight was converted to kilograms per hectare and regressed against the disk meter heights to develop calibration equations. The average disk meter height

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for each pasture was then used to estimate the average available forage for each pasture. After lyophilization, forage samples were ground through a 1-mm screen using a Wiley mill (Arthur H. Thomas Co., Swedesboro, NJ) and analyzed for IVDMD by the batch culture procedures outlined by ANKOM Technology Corp. (Fairport, NY; Vogel et al., 1999) and for total N by rapid combustion (AOAC International, 1998; AOAC Official Method 990.03; Elementar Americas Inc., Mt. Laurel, NJ). Forage CP was estimated by multiplying the N concentration by 6.25. Ergovaline concentrations were determined using a modified HPLC procedure (Moubarak et al., 1993) on samples gathered in May and June. All values were corrected to a DM basis based on drying a subsample of the ground forage overnight at 105°C. Tall fescue basal coverage was estimated in the spring before the initiation of grazing of each newly established pasture the ensuing autumn. A minimum of 2 trained personnel walked each entire pasture and estimated the proportion of each drill row with viable tall fescue forage. Estimates before the initial grazing of the experimental pastures were 80 and 83% continuous drill-row coverage for NE+ and E+, respectively. Forage species frequency and basal cover were determined in November before the initiation of grazing in yr 1 and 2 and after grazing in yr 2 by a modified step-point procedure (Owensby, 1973). Twenty observations were recorded per hectare. The proportion of perennial and annual forages were categorized as (1) tall fescue; (2) other cool-season perennials consisting of rescuegrass (Bromus catharticus Vahl), orchardgrass (Dactylis glomerata L.), and Kentucky bluegrass (Poa pratensis L.); (3) other cool-season annuals consisting of cheat (Bromus secalinus L.), little barley (Hordeum pusillum Nutt.), and annual ryegrass; (4) other warm-season perennials consisting of bermudagrass, goosegrass [Eleusine indica (L.) Gaertn.], and johnsongrass

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Figure 1. Monthly forage mass averaged across forage type and year in pastures grazed by cow–calf pairs. Forage types were Neotyphodium coenophialum–infected tall fescue (E+) or tall fescue infected with a nontoxic novel endophyte (NE+). The forage type or forage type × sampling date interaction was not detected (P ≥ 0.66). The least significant difference for mean comparisons between dates was 195.9.

[Sorghum halepensis (L.) Pers.]; (5) other warm-season annuals consisting of crabgrass [Digitaria sanguinalis (L.) Scop.] and giant foxtail (Setaria spp.); (6) clovers consisting of white clover (Trifolium repens) and hop clover (Trifolium agrarium); and (7) broadleaf weeds consisting primarily of horse nettle (Solanum carolinense L.) and wooly croton (Croton capitatus Michx.).

Statistical Analysis All statistical analyses with the exception of calving rates were performed using PROC MIXED of SAS (SAS Institute Inc., Cary, NC). Forage mass and chemical composition data were analyzed with effects of FORAGE, SAMPLING DATE, and their associated 2-way interactions included in the model. Year was considered a random effect, and sampling date was considered to be a repeated measure. Forage species composition data were analyzed with effects of FORAGE, year, and their interaction included in the model. Year was considered a repeated measurement. Cow and calf perfor-

mance measurements were analyzed with effects of FORAGE, CALF SEX, SIRE OF CALF, and the CALF SEX × FORAGE and SIRE × FORAGE interactions included in the initial model for calf measurements. SIRE OF CALF affected (P < 0.01) all calf performance measurements but did not interact (P ≥ 0.08) with forages. However, 13 different sires were represented in the data set, and they were not distributed evenly among FORAGE and SEX OF CALF, resulting in nonestimated least squares means for overall forage effects. Therefore, sire effects and the interaction of sire were removed from the model for both cows and calves. Year was considered a random effect because cows were reallocated to pastures each year. Calf hemogram values were analyzed with effects of FORAGE, CALF SEX, SAMPLING DATE, and their interaction included in the model. SIRE OF CALF and the interaction of sire with forage type were originally included in the model but were removed because of nonestimated least squares means due to uneven representation of the 13 sires across forages and sex of calf. Year was considered a random effect

and sampling date was considered a repeated measurement. The group of animals within a pasture was considered the experimental unit for each of the above measurements to compare forage effects. Postweaning calf performance data were sorted and analyzed within sex of calf because the heifers were retained for breeding and steers were shipped to feedlot facilities. CALF SIRE was included in the model along with FORAGE effects, and year was treated as a random effect. Cow and heifer pregnancy rates and percentage of steers grading USDA Choice were analyzed by Chi-squared using the PROC FREQ of SAS. All data are reported as least squares means. Statistical differences were designated at P < 0.05 and statistical tendencies at 0.05 < P < 0.10.

RESULTS AND DISCUSSION Pastures and Forage Measurements Forage mass differed (P < 0.01) across sampling dates but was not affected by forage (P = 0.66) or the forage × sampling date interaction (P = 0.99). Therefore, forage mass is averaged across years and tall fescue types within each sampling date in Figure 1. Forage mass followed typical patterns observed for cool-season forages. Pastures were dominated by tall fescue (Table 1). The proportion of tall fescue did not differ (P = 0.47) between NE+ and E+ pastures, but the percentage of other cool-season perennials tended (P = 0.08) to be greater in NE+ pastures. Year effects were noted (P < 0.05) for basal cover, other warm-season perennials, and broadleaf weeds. It has long been accepted that N. coenophialum infection benefits tall fescue plants through increased tolerance of pests, drought, and overgrazing, resulting in greater forage persistence (Hoveland, 1993). However, toxins produced by wild-type N. coenophialum have also been blamed for substantial reductions in numerous

Cow and calf pre- and postweaning performance on tall fescue

Table 1. Forage species composition in tall fescue pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) and grazed by spring-calving cow–calf pairs Forage Item, %

E+

NE+

SE

Basal cover Tall fescue Other cool-season perennials2 Other cool-season annuals3 Other warm-season perennials4 Other warm-season annuals5 Clovers6 Broadleaf weeds7

28.2 78.5 1.4 9.3 4.7 3.1 0.1 2.8

29.4 81.6 4.1 8.3 2.9 1.7 0.1 1.5

2.46 2.90 0.92 2.60 1.67 0.83 0.08 0.63

 

Effect1 Y NS f NS Y NS NS Y

Y = year effect (P < 0.05); f = forage effect (P < 0.10); NS = not different statistically (P > 0.10). 2 Included rescuegrass (Bromus catharticus Vahl), orchardgrass (Dactylis glomerata L.), and Kentucky bluegrass (Poa pratensis L.). 3 Included cheat (Bromus secalinus L.), little barley (Hordeum pusillum Nutt.), and annual ryegrass (Lolium multiflorum Lam.). 4 Included bermudagrass [Cynodon dactylon (L.) Pers.], goosegrass [Eleusine indica (L.) Gaertn.], and johnsongrass [Sorghum halepensis (L.) Pers.]. 5 Included crabgrass [Digitaria sanguinalis (L.) Scop.] and giant foxtail (Setaria spp.). 6 Included white clover (Trifolium repens L.) and hop clover (Trifolium agrarium L.). 7 Included horse nettle (Solanum carolinense L.) and wooly croton (Croton capitatus Michx.). 1

measurements of animal performance (Paterson et al., 1995; Roberts and Andrae, 2004; Waller, 2009). Introduction of new or “novel” endophytes that produce no ergot alkaloids were shown to improve plant persistence but not reduce animal performance (Bouton et al., 2002; Franzluebbers and Stuedemann, 2006). However, there is considerable variability in the symbiosis between specific endophytes and tall fescue cultivars (Bouton et

al., 2002), necessitating evaluation of each such endophyte–tall fescue cultivar association. In the present study, neither the year effect nor the year × forage type interaction was detected (P = 0.16 and 0.49, respectively) for the percentage of tall fescue in the experimental pastures. This is indicative that NE+ was as persistent as E+ after 2 yr of grazing. Forage concentrations of CP and IVDMD differed across sampling

Table 2. Forage CP, IVDMD, and ergovaline concentrations in tall pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) and grazed by spring-calving cow–calf pairs Forage Item

E+

NE+

SE

CP, g/kg IVDMD, g/kg Ergovaline, μg/kg

162 689 492

167 709 57

3.7 21.1 134.9

1

 

Effect1 D D, f F

D = date effect (P < 0.05); F, f = forage effect (P < 0.05 and 0.10, respectively).

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dates (P < 0.01) but were not affected (P ≥ 0.90) by the forage × sampling date interaction (Table 2). Forage concentrations of CP did not differ (P = 0.42) between E+ and NE+, but forage IVDMD tended (P = 0.08) to be greater from NE+ compared with E+. Others reported greater concentrations of CP and in vivo DM and ADF digestibilities from NE+ compared with E+ hay (Matthews et al., 2005), or no differences in concentrations of IVDMD, but greater concentrations of CP in Jesup tall fescue pasture samples with a nonergot alkaloid–producing endophyte compared with the same variety with the wild-type ergot alkaloid–producing endophyte (Parish et al., 2003a). Concentrations of ergovaline were not different (P = 0.17) across sampling dates, and the concentrations were not affected (P = 0.20) by the forage × sampling date interaction. Ergovaline was detected in both NE+ and E+ pastures, but the concentrations (57 and 492 μg/kg, respectively) were much greater (P < 0.01) from E+ pastures than from NE+ pastures.

Preweaning Cow–Calf Performance Cow performance measurements and the amount of hay offered to the different groups of cows are shown in Table 3. As mentioned previously, hay harvested from each pasture was offered during the summer in yr 1 because of atypical dry conditions. Cows on NE+ depleted their hay supplies earlier than those on E+ and were removed from their pastures earlier (one pasture removed July 29, the other removed September 3), resulting in those cows being offered 823 kg more hay, numerically, (P = 0.20) than those on E+. Cow weight and BCS at the beginning of the calving and breeding seasons were not different (P ≥ 0.45) between NE+ and E+, but cow BW at the end of the breeding season tended (P = 0.07) to be greater from NE+. Cows grazing NE+ were 53 kg heavier (P = 0.01) at weaning and tended (P = 0.08) to have a greater

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Table 3. Performance by cows grazing tall fescue pastures with either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) Forage Item Hay offered,2 kg/cow Cow BW, kg  Initial   At calving   At breeding   At end of breeding   At weaning Cow weaning efficiency,3 % BCS4  Initial   At calving   At breeding   At end of breeding   At weaning Cow hair score5 Calving rate, % Calving interval, days

E+

NE+

SE

955   486 547 513 503 456 46.2   6.2 6.8 6.0 5.8 5.4 3.1 44.7 371

1,778   482 562 548 561 509 47.2   6.2 6.8 6.0 5.9 5.7 1.2 85.1 368

5.6   19.3 15.1 21.6 18.6 30.6 1.52   0.06 0.57 0.06 0.12 0.14 0.20   3.39

 

Effect1 NS NS NS NS f F NS F×X f×x NS NS f F F NS

NS = effects of forage or sex of calf were not different (P > 0.10); F, f = forage effect (P < 0.05 and 0.10, respectively); F × X, f × x = forage by sex of calf interaction (P < 0.05 and 0.10, respectively). 2 Hay offered represents the quantity of hay offered to cows after the hay harvested from a specific pasture was fed. This occurred in yr 1 only. 3 Calf weaning weight expressed as a percentage of cow BW at weaning. 4 Body condition scores were estimated on a 9-point scale where a BCS of 6 is described as having no distinct visible bone structure, the transverse processes can be felt with firm pressure, the hindquarters appear plump and full, and there is sponginess over foreribs and around tail head representing fat deposits. 5 Hair scores were measured on a scale of 1 to 5 where 1 represents no rough, discolored hair; 3 represents rough, discolored hair on 50% of the body; and 5 represents rough, discolored hair on 100% of the body. 1

BCS at weaning than those grazing E+. However, cow efficiency expressed as calf weaning weight as a percentage of cow BW at weaning did not differ (P = 0.38) between forages. Body condition scores at the end of breeding were not different (P = 0.31) between forages. Hair scores estimated at weaning were greater (P < 0.01) from E+ than from NE+ cows; those grazing E+ averaged having rough, discolored hair on 50% of their body, whereas those on NE+ exhibited little to no rough, discolored hair on their body. Calving rates from E+ were 47.5% lower (P < 0.01) than from cows grazing NE+ pastures. Calving interval, however, did not differ (P = 0.68) between forages.

At a BCS of 6.8 at the start of the calving season, and a BCS of 6.0 at the start of the breeding season, cows grazing both forages should have been cycling and had high reproductive rates based on previous research with cows consuming nontoxic forages (Selk et al., 1988; Lake et al., 2005). Therefore, differences in pregnancy rates observed in this study were likely due to tall fescue toxicosis independent of BCS. Others have reported reductions in calving rates in cows grazing E+ pastures (Gay et al., 1988; Waller et al., 1989; Caldwell et al., 2013), even when precalving and prebreeding BCS were maintained at approximately 6 (Sanson and Coombs, 2003). In a previous study (Watson et al., 2004),

calving rates did not differ (94% for both forages) when E+ was compared with a different tall fescue–nontoxic endophyte association (AR542) than the one used in this experiment (HM4). However, in that study, cows were placed on their assigned pastures at the end of March, bulls were added April 1, and the breeding season was 75 d. Furthermore, those cows either grazed endophyte-free tall fescue or were offered endophyte-free hay before allocation to their assigned pastures. In the present study, cows were allocated to the experimental pastures in the fall and remained on their assigned pastures throughout the spring and subsequent 60-d breeding season, which began with bull introduction on May 10. This resulted in longer exposure of the cows to tall fescue toxins on E+ pastures before introduction of bulls in the present study, and the cattle on E+ pastures were likely exposed to greater heat stress during the breeding season than cows in the previous study (Watson et al., 2004). Calving rate data from the current study are similar to those reported recently (Caldwell et al., 2013) where similar breeding times and breeding season length were used in a 3-yr study in which cows grazed NE+ or E+ throughout the entire year. It is also noteworthy that calving interval did not differ between cows grazing NE+ and those grazing E+ in the present study. By observation of calving date records and assuming a 285-d gestation interval, no cows were bred successfully after June 20 of either year although the bulls remained in their assigned pastures until July 15. This cessation of breeding during periods of higher ambient temperature may be due to reduced semen quality of the bulls (Looper et al., 2009), impaired follicular function (Mahmood et al., 1994; Burke et al., 2001), or some combination of both. Average calf birth date, birth weight, and BW at the start of the breeding season (Table 4) were not different (P ≥ 0.33) among forages. However, by the end of the breeding season, calves grazing NE+ tended (P = 0.06) to be heavier (14 kg) than

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Cow and calf pre- and postweaning performance on tall fescue

Table 4. Preweaning growth performance by calves grazing tall fescue pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) before weaning Forage Item Birth date Birth weight, kg Calf BW, kg   At beginning of cow breeding2   At end of cow breeding   At weaning Age at weaning, d BW gain, kg Daily gain, kg

E+

NE+

March 5 38   115 159 209 217 169 0.78

March 7 38   119 173 240 219 193 0.95

SE

  Effect1

2.1 1.7   5.4 4.3 20.1 0.5 24.0 0.077

NS X NS f, X F, X NS F, f × x F

NS = effects of forage or sex of calf were not different (P > 0.10); X = sex of calf effect (P < 0.05); F, f = forage effect (P < 0.05 and 0.10, respectively); f × x = forage by sex of calf interaction (P < 0.10). 2 The breeding season began on May 10 of each year making the calves approximately 2 mo of age at this time. 1

those grazing E+. Actual weaning BW and calf gain from birth to weaning were greater (P < 0.05) from NE+ compared with E+. Sire of calf affected each of these measurement (P < 0.01; data not shown), but the sire × forage interaction either tended to

or did not affect these measurements (P ≥ 0.08). The difference in weaning weights between calves weaned from NE+ and those weaned from E+ pastures observed in this study (31 kg) were similar to those observed by others

comparing E+ and E− (Gay et al., 1988) or E+ and NE+ (Caldwell et al., 2013) but somewhat greater than differences between calves weaned from E+ compared with that of calves weaned from other nontoxic forages (Peters et al., 1992; Sanson and Coombs, 2003; Watson et al., 2004). Preweaning daily gain differences between NE+ and E+ in our study were similar to those reported from weaned heifers (Franzluebbers and Stuedemann, 2006) or suckling calves (Watson et al., 2004) but less than those from pubertal heifers (Drewnoski et al., 2009). Low levels of ergovaline were detected in the NE+ pastures. The source of the ergovaline is uncertain, but it is likely from a low level of rogue E+ plants that germinated from residual seed. However, based on the animal performance measurements reported in the present study, it is likely that the low level of ergovaline detected in the NE+ samples was not sufficient to adversely affect performance by cow–calf pairs. Problematic for those considering replacement of E+ with NE+ based on cow performance, however, was the deficit of forage during the

Table 5. Hemogram measurements at weaning and 14 d postweaning from calves grazing tall fescue pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) until weaning Item1

E+, wean

NE+, wean

E+, postwean

NE+, postwean

SE

Total white blood cells, 103/μL Neutrophils, 103/μL Lymphocytes, 103/μL Neutrophil:lymphocyte Monocytes, 103/μL Eosinophils, 103/μL Basophils, 103/μL Total red blood cells, 106/μL Hemoglobin, g/dL Hematocrit, % MCV, fL MCH, pg MCHC, g/dL Platelets, 103/μL

8.8 1.9a 6.1 0.5 0.8 0.1 0.1 10.3 12.6 37.1 36.1 12.3 34.1 587

9.2 2.0a 6.2 0.5 1.0 0.1 0.1 10.0 12.4 36.2 36.4 12.5 34.3 621

9.6 1.4b 7.2 0.3 0.9 0.0 0.1 10.1 12.4 36.7 36.5 12.4 33.9 622

10.2 2.0a 7.1 0.4 1.0 0.0 0.1 9.8 12.3 36.0 36.7 12.6 34.2 626

1.16 0.49 0.74 0.06 0.06 0.02 0.02 0.63 0.91 2.55 0.44 0.18 0.15 98.7

 

Effect2 D F, F × D D d f D f, D NS NS NS NS NS f NS

Means within a row without a common superscript letter differ (P < 0.05). MCV = mean corpuscular volume; MCH = mean corpuscular hemoglobin; MCHC = mean corpuscular hemoglobin concentration. 2 F, f = forage effect (P < 0.05 and 0.10, respectively); D, d = effect of sampling date (P < 0.05 and 0.10, respectively); F × D = forage by sampling date interaction (P < 0.05). a,b 1

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first year of the study. Because E+ and NE+ pastures were established simultaneously, this difference was not due to stand age considerations. These results are likely a combination of greater consumption of the NE+ forage (Matthews et al., 2005) resulting in lower carrying capacity of the NE+ pastures (Franzluebbers and Stuedemann, 2006) because forage production was not different between tall fescue infected with high- versus low-alkaloid-producing endophytes in previous work (Hill et al., 2002).

Hemogram Measurements Although concentrations of total white blood cells did not differ (P = 0.52) between calves grazing NE+ and those grazing E+ at weaning and 14 d postweaning, the forage type × sampling date interaction affected (P < 0.05) concentrations of neutrophils (Table 5). Concentrations of neutrophils were lower (P < 0.05) from E+ calves sampled 14 d postweaning compared with E+ calves sampled at weaning or with NE+ calves sampled

Table 6. Postweaning performance and carcass measurements from steers previously grazing tall fescue pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) Forage Item No. of observations Steer BW, kg   At weaning   End of 14-d weaning period   On winter annuals   At shipping   At shipping (shrunk)   At feedlot   At end feedlot (full)   At end feedlot (shrunk) Gain, kg   Weaning to shipping Daily gain, kg   During 14-d weaning period   Weaning to winter annuals   On winter annuals   Weaning to shipping   Feedlot (using unshrunk BW)   Feedlot (using shrunk BW) Days on feed DMI,2 kg/d G:F,2 kg/kg Carcass   HCW, kg  DP   Rib fat, mm   LM area, cm2   USDA Yield grade   Marbling score3   % USDA Choice

E+

NE+

SE

34   208 219 228 326 313 322 584 561   118   0.70 0.31 0.93 0.79 1.72 1.79 137 10.4 0.165   355 63.3 11 87.1 2.6 37 57

41   249 262 264 363 349 351 623 598   108   0.95 0.09 0.92 0.76 1.76 1.84 136 10.8 0.160   381 63.7 16 89.0 2.6 37 46

    20.9 19.0 17.7 29.3 28.1 26.0 24.3 23.3   52.2   0.174 0.109 0.399 0.351 0.073 0.053 27.0 0.53 0.0034   15.1 0.40 4.4 3.94 0.29 2.3  

  Effect1

F, S F, S F, S F, S F, S F, S F, S F, S NS NS F NS NS NS NS NS NS NS F, S NS s NS S S NS

F = forage effect (P < 0.05); S, s = effect of calf sire (P < 0.05 and 0.10, respectively); NS = effects of forage or calf sire were not different (P > 0.10). 2 Feedlot DMI and feed conversion were only measured in yr 1. 3 Scores: 30 = Slight0; 40 = Small0. 1

at weaning and 14 d postweaning. Concentrations of monocytes, basophils, and corpuscular hemoglobin tended (P ≤ 0.10) to be greater from calves weaned from NE+ compared with those from E+. No other hemogram measurements differed (P ≥ 0.27) between forages. In all instances, the differences observed were small, and all values were within normal reference ranges (Oliver et al., 2000). It is therefore unlikely that these tendencies explained animal production differences observed in this study. Concentrations of total white blood cells, lymphocytes, and basophils were greater (P < 0.05) on the postweaning sampling date compared with those at weaning, and concentrations of eosinophils were greater (P < 0.05) at weaning than at 2 wk after weaning. No other sampling date effects (P ≥ 0.11) or forage type × sampling date interactions (P ≥ 0.27) were detected.

Postweaning Calf Performance When the data were sorted by sex of calf for postweaning evaluations, steers weaned from NE+ were 41 kg heavier (P < 0.01) at weaning, 43 kg heavier (P < 0.01) at the end of the 14-d fence-line weaning, 36 kg heavier (P < 0.01) when placed on winter annuals, and 37 kg heavier at the end of the feedlot period (Table 6). Daily gains were greater (P < 0.01) from E+ compared with NE+ during a grazing period on bermudagrass pasture between the time fence-line weaning was completed and when the steers were placed on winter annual forages. However, daily gains did not differ (P ≥ 0.16) between preweaning forage treatments during any other segment of the postweaning period. Likewise, daily DMI in the feedlot and G:F did not differ (P ≥ 0.37) between preweaning forage treatments during yr 1 (data not shown). Therefore, it is apparent that steers weaned from E+ pastures did not compensate during the postweaning periods for reduced growth before weaning. Numerous studies have reported compensatory gain by yearling steers during a feedlot period following

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grazing E+ pastures (Coffey et al., 1990; Lusby et al., 1990; Cole et al., 2001). However, others reported that postweaning weight gains by calves weaned from E+ did not differ from those weaned from bermudagrass pastures (Brown et al., 1999). Therefore, calf age or time during the calf growth cycle in which they are exposed to tall fescue toxins may affect the severity of response and the recovery from tall fescue toxins. Hot carcass weights were heavier (P = 0.01) from calves weaned from NE+ than from those from E+ pastures, which is in agreement with previous research (Brown et al., 1999) with calves weaned from E+. However, HCW from yearling steers previously grazing E+ pastures were not different from those grazing nontoxic pastures (Coffey et al., 1990; Cole et al., 2001) because of the compensatory gain achieved during the subsequent feedlot period by calves previously grazing E+. Other carcass measurements in the present study did not differ (P ≥ 0.36) between NE+ and E+ steers, which is in agreement with previous research with weaned calves (Brown et al., 1999) and yearling steers (Coffey et al., 1990; Cole et al., 2001). Heifer weights at weaning tended (P = 0.07) to be heavier from NE+ compared with E+ (Table 7). This tendency was only maintained (P ≤ 0.09) through the time heifers were placed on winter annual forages. The differential in BW of heifers between those weaned from NE+ and those weaned from E+ were not as extreme as those observed from steers. Specifically, heifers weaned from NE+ were 18 kg heavier (P = 0.07) at weaning, 19 kg heavier (P = 0.07) at the end of the 14-d fence-line weaning, 15 kg heavier (P = 0.09) when placed on winter annuals, and 10 kg heavier (P = 0.33) at breeding. Daily gains did not differ between heifers weaned from E+ versus NE+ during any postweaning phase. It is not readily apparent why heifers might respond less severely to tall fescue toxins than steers. Others have reported reduced gains by

heifers (Mahmood et al., 1994; Emile et al., 2000) offered E+ compared with those offered nontoxic forages. However, the negative effects of E+ on weanling heifers were greater than on yearling heifers (Mahmood et al., 1994). Also, the response of steers to strict estrogenic implants (avg. of 0.18 kg/d; Brazle and Coffey, 1991; Beconi et al., 1995) was slightly greater than the response to combination progesterone–estradiol implants (avg. 0.10 kg/d; Coffey et al., 1992; Aiken et al., 2001), possibly implicating hormonal profile differences between steers and heifers as mitigating factors in response to tall fescue toxins. Calving rates by heifers weaned from NE+ were 41% greater (P < 0.01) than from those weaned from E+ pastures, but calving dates did not differ (P = 0.88) between heifers weaned from NE+ versus those weaned from E+. Negative effects of consuming E+ diets immediately before, or at the time of, breeding on reproductive performance by heifers and cows is well documented (Gay et al., 1988; Waller et al., 1989; Burke et al., 2001). However, exposure of the heifers in this study to E+ ceased at

weaning, and they were grown on other nontoxic forages following weaning until well beyond the breeding season. The poor reproductive performance by the heifers exposed to E+ pastures only during late prepartum or early postpartum calfhood development has not been reported previously but raises serious questions about the severity of exposure to tall fescue toxins during these phases of development.

IMPLICATIONS Based on the improvements observed in calf growth and weaning weight, combined with dramatic improvements in not only cow reproductive rates, but those by heifers weaned from tall fescue pastures, novel endophyte technology could provide much-needed relief from tall fescue toxicosis throughout the entire tall fescue region. However, further evaluations are needed to determine plant vigor and persistence under continual year-round grazing for more years, and to determine how time of exposure to tall fescue toxins affects subsequent heifer reproductive rates so that adequate economic evaluations can be

Table 7. Postweaning performance by heifers previously grazing tall fescue pastures containing either the wild-type toxic endophyte (E+) or a nontoxic novel endophyte (NE+) Forage Item No. of observations Heifer BW, kg   At weaning   End of 14-d weaning period   On winter annual   At breeding Daily gain, kg   During 14-d weaning period   Weaning to winter annuals   On winter annuals   Weaning to breeding Heifer calving rate, % Heifer calving date

E+ 39   208 217 256 362   0.63 0.47 0.90 0.73 64.1 March 1

NE+ 32   226 236 271 372   0.62 0.44 0.90 0.70 90.6 March 2

SE

17.6 16.9 6.0 7.5   0.167 0.130 0.040 0.071   4.0

 

Effect1

f, S f, S f, S S s S NS NS F NS

F, f = forage effect (P < 0.05 and 0.10, respectively); S, s = calf sire effect (P < 0.05 and 0.10, respectively); NS = effects of forage or calf sire were not different (P > 0.10).

1

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conducted. No carryover effects of tall fescue toxins were observed in steers beyond the exposure period, making it unjustified to discount the price paid for these calves; producers simply have to accept that those calves will reach market at a lower finishing weight.

ACKNOWLEDGMENTS This work was partially supported by the University of Arkansas Division of Agriculture and by USDAARS Specific Cooperative Agreement 6227-21310-008-38S through the Dale Bumpers Small Farm Research Center, Booneville, Arkansas.

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