Fescue toxicosis is a condition that afflicts livestock grazing endophyte-infected tall fescue and is particularly detrimental to pregnant mares. A two year evaluation study of a novel endophtye-infected cultivar, AGRFA-144 (A-144), did not induce fescue toxicosis in late-term pregnant mares. All mares delivered viable foals except in E+ group which had two viable foals, one stillborn-dystocia and one compromised foal which was euthanized at 72 h pp. Serum P4 concentrations were similar among A-144, NE+, and E- mares (p>0.05). Foal BW and foal/placental weight ratios were similar for A-144, NE+, and E- (p>0.05). Foal serum P4 was similar on 1 d and 2 d in all groups, but was lower (p = 0.049) in the A-144 group than the E- foals on day 0. Neutrophil/lymphocyte ratios were similar (~5:1) in all foals on d 0 and 2. IgG values were similar (p>0.05) among A-144, NE+, and E-.

A wild-type endophyte (Neotyphodium coenophialum [(Morgan-Jones & Gams) Glen Bacon & Hanlin]) that infects tall fescue [Lolium arundinaceum (Schreb.) Darbysh. = Schedonorous arundinaceum (Schreb.) Dumort.] imparts tolerances to moisture, heat, and grazing stresses, but also produces ergot alkaloids that adversely affect performance and physiology of cattle. Novel endophytes, developed by AgResearch Ltd. NZ, can sustain fescue persistence and productivity, but do not produce toxic ergot alkaloids. University of Kentucky Plant Breeder, T. D. Phillips Ph.D, developed a tall fescue experimental population (KYFA9301) for the upper transition zone. A 2-yr grazing experiment was conducted with steers to evaluate steer performance and physiology, and forage quality and productivity of KYFA9301 infected with AR584 novel endophyte (AR584) compared with KY31 wild-type endophyte (KY31), endophyte-free KYFA9301 (EF9301) and AR542-‘Jesup’ (MaxQ). Fescue-endophyte combinations were assigned to 1.0-ha pastures in a randomized complete block design with three replications. Pastures were grazed with variable stocking (four testers) from 6 May to 23 July 2008 (76 d), and 2 April to 25 June 2009 (84 d). Shrunk bodyweights were taken at initiation and termination of grazing each year. Average daily gains among MaxQ, AR584, and EF9301 were similar and were greater (P < 0.10) than KY31. Rectal and skin temperatures were collected three times each year at approximately days 28, 56, and study completion, along with blood collection for serum prolactin assay. Rectal and skin temperatures among AR584, MaxQ, and EF9301 were similar and were lower (P < 0.10) than KY31. Serum prolactin concentrations were similar among the three nontoxic varieties and higher (P < 0.10) than KY31. Forage collections were taken at 2 week intervals throughout the study each year and nutritive quality analysis were conducted through wet chemistry to determine forage acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), and In-Vitro Dry Matter Digestibility (IVDMD). Nutritive analyses indicated no differences between fescue-endophyte combinations with the exception of EF9301 having higher ADF concentrations (P = 0.031) than KY31 during the dry year of 2008. Results indicated steer performance and physiological responses for KYFA9301, with and without AR584 were enhanced compared to KY31 and similar to those for MaxQ.

This 2-yr experiment evaluated productivity of wild-type, endophyte-infected tall fescue (E+) and novel endophyte-infected tall fescue (NE) summer stockpiled (SS) pastures and the performance of fall-calving beef cow/calf pairs stocked on each cultivar. Fescue cultivars used were KY-31 and MaxQ for E+ and NE treatments, respectively. Pregnant Simmental x Angus cows (128 total, 64 each yr) were stratified by BW, BCS, and expected calving date and then allotted to 1 of 10 pasture groups within each yr (20 groups total, 10 per treatment). Forage growth was stockpiled from April until the initiation of strip-grazing on August 31 of 2017 and 2018. Cows grazed treatment pastures for 52 d from 23 ± 14 d prepartum to 29 ± 14 d postpartum, and calved on treatment pastures. Forage quadrats were clipped from the grazed and ungrazed portions of each pasture to determine weekly forage mass. Total ergot alkaloid (TEA) concentrations were analyzed for all pastures at the beginning of the experiment and every subsequent 2 wk for E+ tall fescue. Cow BW was recorded on 2 consecutive d and BCS determined at the start and end of the experiment. In yr 2, ultrasound 12th rib fat thickness (FT) was measured at the beginning and end of the treatment period Milk production was estimated using the weigh-suckle-weigh technique at 29 ± 14 d postpartum. Initial TEA concentrations for NE (Yr. 1 = 112 µg/kg; Yr. 2 = 632 µg/kg) were decreased (P ≤ 0.01) compared to E+ (Yr. 1 = 1831 µg/kg; Yr. 2 = 2903 µg/kg). TEA concentrations for E+ pastures did not differ (P < 0.23) by sample date. However, average TEA concentrations were greater for yr 2 than yr 1(P ≤ 0.01). Fescue cultivars were not different (P ≥ 0.06) in forage CP, Ash, Ether Extract, and grazed or ungrazed forage mass. However, differences were observed (P ≤ 0.02) for ADF, NDF, and TDN by fescue cultivar. Cow BW, BCS, and FT at the beginning and end of grazing were not different (P ≥ 0.41) by treatment. Milk production was greater (P < 0.01) for cows grazed on E+. Calving date, calf BW, calf ADG were not different (P ≥ 0.65) by treatment. Neither AI nor overall conception rates differed (P ≥ 0.23) between cultivars. Performance of fall-calving cows pre-exposed to E+ was not hindered when grazed on E+ relative to NE in a SS system. / Master of Science / Wild-type, endophyte-infected tall fescue (E+) is the predominant forage of use for producers within the southeastern United States. Endophyte-infected tall fescue gained notoriety due to its drought and pest resistance as well as climate adaptability. These advantages are the result of a symbiotic relationship with an endophytic fungus that has been shown to decrease in animal performance through the production of toxic ergot alkaloids. Development of improved fescue cultivars provided producers with an alternative forage, known as novel endophyte-infected tall fescue (NE), that maintains the agronomic advantages noted with E+ fescue without negative impacts on animal gain and reproductive performance. In adopting NE tall fescue, producers are faced with the financial challenge of renovating existing stands of E+ with NE fescue; leaving pastures unusable during times of normal grazing behavior. This constraint has highlighted the need to explore forage utilization and strategies that can extend the grazing period that do not require the significant cost of total renovation with NE. Fall stockpiled tall fescue has provided producers an option to extend grazing from late November through February when pasture growth ceases and hay supplementation is normally needed. However, a 60 to 90 d period between summer and fall stockpiled grazing leaves producers looking for an additional strategy to provide standing forage for their herds. Summer stockpiling (SS), is a novel grazing strategy that bridges summer and fall stockpiled grazing through proper accumulation of 25 % of total pasture to help extend producers grazing season. The objective of the current experiment is to evaluate both E+ and NE SS pastures and its effect on animal performance, forage availability, and nutritive value. Cow BW and BCS were measured at the initiation, conclusion, and before artificial insemination. Calf BW and ADG were assessed 48 h post-calving and at weaning. Ungrazed and grazed forage mass was collected weekly, while measurements of ADF, NDF, CP, TDN, ether extract, and ash were measured every 2 weeks. After a 52 d treatment period, forage mass was similar across both cultivars, with ADF, NDF, and TDN favoring E+ tall fescue. Additionally, animal performance across both E+ and NE pastures were similar, however increased milk production was observed for cows grazed on E+. This experiment helps shed light on the concept of strategic renovation. Strategic renovation can be best utilized by producers who are interested in maximizing pasture utilization through rotationally grazing E+ and NE tall fescue pastures. By following this renovation strategy, proper allocation of NE tall fescue during times of enhanced ergotism and E+ tall fescue during low thresholds will develop a more specific rotation thus decreasing renovation costs for producers when ergotism is lowest.

Kentucky 31 tall fescue (KY31) infected with the common toxic endophyte strains of Epichloё coenophiala produces toxic alkaloids that improve plant vigor, but cause numerous adverse effects in grazing animals. Researchers developed a variety of KY31 containing an alternative strain of E. coenophiala, termed novel endophyte (NE). Adverse health effects in mares have not been evaluated. Experiments in this thesis tested the hypothesis that the NE pasture does not cause adverse effects typically associated with KY31. Specific aims were to: 1) compare forage ergovaline concentrations between KY31 vs NE pastures; 2) evaluate palmar artery diameters in mares grazing KY31, NE, or orchardgrass-bluegrass (OGBG) pastures; 3) determine mare serum prolactin, estradiol, and progesterone concentrations associated with ingesting each pasture type over time; and 4) measure foaling outcomes, including percentage of live foals, foal birth weights, and foal growth rates. In 2015, six nonpregnant mares grazed KY31, six pregnant mares grazed NE and six pregnant mares grazed OGBG pastures. In 2016, eighteen mares were used; six mares grazed each pasture type. Study results showed that ergovaline did not appear to be produced by NE. Novel endophyte pasture did not have negative effects on palmar artery diameter, reproductive hormones, or foaling outcomes.