Alteration of fasting heat production during fescue toxicosis in Holstein steers

Integrative interactomics applied to bovine fescue toxicosis

Bovine fescue toxicosis (FT) is caused by grazing ergot alkaloid-producing endophyte (Epichloë coenophiala)-infected tall fescue. Endophyte’s effects on the animal’s microbiota and metabolism were investigated recently, but its effects in planta or on the plant–animal interactions have not been considered. We examined multi-compartment microbiota–metabolome perturbations using multi-‘omics (16S and ITS2 sequencing, plus untargeted metabolomics) in Angus steers grazing non-toxic (Max-Q) or toxic (E+) tall fescue for 28 days and in E+ plants. E+ altered the plant/animal microbiota, decreasing most ruminal fungi, with mixed effects on rumen bacteria and fecal microbiota. Metabolic perturbations occurred in all matrices, with some plant-animal overlap (e.g., Vitamin B6 metabolism). Integrative interactomics revealed unique E+ network constituents. Only E+ had ruminal solids OTUs within the network and fecal fungal OTUs in E+ had unique taxa (e.g., Anaeromyces). Three E+-unique urinary metabolites that could be potential biomarkers of FT and targeted therapeutically were identified.

Use of Integrative Interactomics for Improvement of Farm Animal Health and Welfare: An Example with Fescue Toxicosis

Rapid scientific advances are increasing our understanding of the way complex biological interactions integrate to maintain homeostatic balance and how seemingly small, localized perturbations can lead to systemic effects. The ‘omics movement, alongside increased throughput resulting from statistical and computational advances, has transformed our understanding of disease mechanisms and the multi-dimensional interaction between environmental stressors and host physiology through data integration into multi-dimensional analyses, i.e., integrative interactomics. This review focuses on the use of high-throughput technologies in farm animal research, including health- and toxicology-related papers. Although limited, we highlight recent animal agriculture-centered reports from the integrative multi-‘omics movement. We provide an example with fescue toxicosis, an economically costly disease affecting grazing livestock, and describe how integrative interactomics can be applied to a disease with a complex pathophysiology in the pursuit of novel treatment and management approaches. We outline how ‘omics techniques have been used thus far to understand fescue toxicosis pathophysiology, lay out a framework for the fescue toxicosis integrome, identify some challenges we foresee, and offer possible means for addressing these challenges. Finally, we briefly discuss how the example with fescue toxicosis could be used for other agriculturally important animal health and welfare problems.

Ruminal motility, reticuloruminal fill, and eating patterns in steers exposed to ergovaline

Fescue toxicosis is problematic for growing steers, causing lower DMI and productivity when fed endophyte-infected (E+) tall fescue. A complete understanding of underlying mechanisms of how fescue toxicosis affects growing steers is lacking. Therefore, the overall objective of this multiexperiment study was to determine whether ruminally dosed ergovaline (ERV) affects rumen motility, rumen contents, and eating patterns. In Exp. 1, an 8-h period to assess ruminal motility began 4 h after feeding by monitoring pressure changes using a wireless system for 21 d. Eight ruminally cannulated steers (283 kg BW) were pair fed with alfalfa cubes (1.5 × NEm) and assigned to endophyte free (E-; 0 μg ERV/kg BW/d) or E+ treatment (20 μg ERV/kg BW/d). Overall, E+ steers had more frequent rumen contractions (Seed P = 0.05 and day of feeding P = 0.02). On days 7 to 9, both treatments showed lower frequencies and E- steers had greater amplitude of contractions (P < 0.001) that corresponded with decreased DMI. In Exp. 2, steers remained in pairs assigned in Exp. 1 (322 kg BW), but reversed seed treatments while increasing ERV levels (titrated 0, 5, 10, 15, and 20 μg ERV/kg BW/d over 57 d). There were no differences between E- and E+ for frequency (P = 0.137) or amplitude of contractions (P = 0.951), but increasing ERV dosage, decreased frequency (P = 0.018) and amplitude (P = 0.005), coinciding with lower DMI. In Exp. 3, 8 steers (589 kg) were pair fed and ruminally dosed 15 μg ERV/kg BW/d, and rumen motility data were collected for 21 d. E- steers showed higher amplitude and lower frequency of contractions than E+ steers with seed (P < 0.001), day (P < 0.001), and seed × day (P < 0.04) effects, but rumen fill was not different between E- and E+ (P > 0.29). Serum prolactin concentrations were lower in E+ steers in Exp. 1 to 3. Eating patterns of pair-fed E- and E+ steers were relatively slower in E+ than E- (Exp. 4) by measuring every 2 h across 24 h. Number of meals were higher in E+ than E- steers, but meal duration and meal size were not different between treatments. Rumen content (DM%) tended to be higher in E+ than in E- when steers were fed once a day (P = 0.07), but there was no difference for rumen content (DM%) when E- and E+ steers were fed 12 times a day (P = 0.13). These results suggest the changes in rumen fill associated with fescue toxicosis may be driven more by changes in feeding behavior and eating pattern rather than by changes in motility.

Interaction of ergovaline with serotonin receptor 5-HT2A in bovine ruminal and mesenteric vasculature

Ergot alkaloids from endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum) induce vasoconstriction. Previous work has shown that serotonin receptor subtype, 5HT2A, is present in bovine ruminal (R) and mesenteric (M) vasculature, plays a role in vasoconstriction, and could be influenced by ergot alkaloids. To determine the influence of ergot alkaloids on 5HT2A, the vasoactivity of an agonist selective for 5HT2A, (4-bromo-3,6-dimethoxybenzocyclobuten-1-yl) methylamine HCl (TCB-2), was evaluated using bovine ruminal and mesenteric arteries and veins (RA, RV, MA, MV) that were exposed to ergovaline (ERV) prior to or during the TCB-2 additions. Ruminal and mesenteric blood vessel segments were collected, cleaned, and cut into 2- to 3-mm cross-sections. Vessel segments were incubated in Krebs-Henseleit buffer containing 0, 0.01 or 1 µM ERV for 2 h prior to TCB-2 dose response or exposed to ERV concentrations simultaneously during TCB-2 dose response. For the dose response portion of the study, vessels were suspended in a multimyograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of TCB-2 every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference. Analysis of variance was evaluated separately for each vessel and each ERV exposure experiment using the mixed models procedure of SAS for effects of TCB-2 and ERV concentrations. All blood vessels with previous ERV exposure had significantly lower contractile responses to TCB-2 (P < 0.01). All blood vessels with simultaneous exposure to 1 µM ERV had higher (P < 0.01) contractile responses at lower concentrations of TCB-2. Simultaneous ERV addition at 1 × 10-4 M TCB-2 did not affect contractility of RV, MA, MV (P > 0.05), but decreased contractility of RA (P < 0.01). These results indicate that ergopeptine alkaloid exposure influences contractility of bovine ruminal and mesenteric blood vessels through serotonin receptor subtype 5HT2A by acting as both an agonist and antagonist. Additional work is needed to determine if ergot alkaloids like ERV simply occupy receptor binding sites competitively, or influence receptor internalization to cause the observed divergent responses.

Ergovaline, an endophytic alkaloid. 2. Intake and impact on animal production, with reference to New Zealand

On the basis of published reports, the daily intake of the alkaloid ergovaline from the consumption of endophyte-containing ryegrass in New Zealand ranges from 0.008 to 0.287 mg ergovaline/kg LW0.75.day. Most of the reports are based on the use of standard endophyte-containing ryegrass and, thus, it is difficult to disassociate the impact of ergovaline consumption from that of lolitrem B. However, physiological effects of ergovaline consumption, such as reduced circulating prolactin concentration, vasoconstriction and elevated core temperature, have been detected at fairly low ergovaline intake, whereas decreased feed intake, liveweight gain and milk production have not generally been observed in animals at an intake below 0.07 mg ergovaline/kg LW0.75.day. Intakes above this value represent only 17% of published values. There are insufficient data to suggest a threshold ergovaline intake associated with heat stress with animal-welfare implications. The relationship between published ergovaline intake and the corresponding ergovaline concentration in pasture is poor (R2 = 0.48), but on average an intake of 0.07 ergovaline/kg LW0.75.day is associated with an ergovaline concentration in ryegrass of 0.70 mg/kg DM. About 16–18% of published ergovaline concentrations in ryegrass pasture exceed this value. The ergovaline concentration in ryegrass is greater in the basal parts of the plant than in the leaf and during the late summer–autumn than in spring. Animals grazing in the lower sward horizons (horizontal grazing plane) are more at risk of high ergovaline intake, although the reduction in grazing intake induced by grazing at low pasture height aids in limiting ergovaline intake. As pasture growth rates decline in late summer, supplementary feed may be used to maintain stocking rate and, if such feeds have zero ergovaline concentration, they serve to dilute the mean dietary ergovaline intake. Ergovaline-containing ryegrass pastures are widely used in New Zealand. It appears that farmers consider the risks of depressed animal production on these pastures to be less than the benefits ergovaline bestows through its deterrent effect of specific insect attack and thus greater survival and pasture persistence.

Ergovaline, an endophytic alkaloid. 1. Animal physiology and metabolism

Ergovaline is an ergot alkaloid found in some endophyte-infected ryegrasses and it has been implicated in the expression of ergotism-like symptoms of grazing livestock, as well as in the protection of the plant against invertebrate predation and abiotic stresses. These selection pressures have resulted in a conflict between the needs of the pasture for persistence and the needs of the animal for production. Ergovaline has not been well studied in terms of animal physiology until recently. There are several putative mechanisms that limit the bioavailability of ergovaline, ranging from microbial biotransformation to post-absorptive hepatic detoxification. Although there are mechanisms that protect the animal from ergovaline exposure, tissues are very sensitive to ergovaline, indicating that ergovaline is very potent and that small quantities have the potential to cause noticeable physiological effects. The range of physiological effects, including decreased circulating prolactin, vasoconstriction and increased susceptibility to heat stress are all linked to the interaction of ergovaline with biogenic amine receptors found throughout the body. This review will focus on understanding the variation of ergovaline concentration in terms of bioavailability, the myriad of hurdles a molecule of ergovaline must overcome to cause an effect, what the ergovaline-induced effects are in New Zealand livestock and how this relates to the potency of ergovaline.

Activities and Effects of Ergot Alkaloids on Livestock Physiology and Production

Consumption of feedstuffs contaminated with ergot alkaloids has a broad impact on many different physiological mechanisms that alters the homeostasis of livestock. This change in homeostasis causes an increased sensitivity in livestock to perturbations in the ambient environment, resulting in an increased sensitivity to such stressors. This ultimately results in large financial losses in the form of production losses to livestock producers around the world. This review will focus on the underlying physiological mechanisms that are affected by ergot alkaloids that lead to decreases in livestock production.

Effect of fescue toxicosis on whole body energy and nitrogen balance, in situ degradation and ruminal passage rates in Holstein steers

This study was designed to examine alteration of ruminal kinetics, as well as N and energy balance during fescue toxicosis. Six ruminally cannulated Holstein steers (bodyweight (BW) = 217 ± 7 kg) were weight matched into pairs and pair fed throughout a crossover design experiment with a 2×2 factorial treatment structure. Factors were endophyte (infected, E+ vs. uninfected, E−) and feeding level (1100 (L) or 1800 (H) kJ/kG BW.75). During each period, after 8 days of feeding level adaptation, animals were ruminally dosed twice daily with ground fescue seed for the remainder of the period. One steer per pair was dosed with ground endophyte infected fescue seed (E+), the other with ground endophyte free fescue seed. In situ degradation of ground alfalfa was determined on Days 13–16. Total faecal and urinary collections were performed on Days 17–21, with animals placed into indirect calorimetry head-boxes during Days 20 and 21. Heat production (HP) was calculated using the Brower equation. Retained energy (RE) was calculated as intakeE – (faecalE + urinaryE + gaseousE + HP). Liquid and particulate passage rates were evaluated using Cr:EDTA and iADF respectively on Days 22 and 23. There was no difference (P > 0.9) in dry matter intake (DMI)/kg.75 between endophyte treatments, and DMI/kg.75 was different (P < 0.01) between H and L intake by design. Animals on H feeding had higher (P < 0.01) water, N and energy intakes. Energy and N excretion, as well as retained DE, ME, RE, and HP were higher (P < 0.03) for H versus L. There was no difference in retained N, DE, ME, or HP (P > 0.15) between endophyte treatments. Neither rate nor extent of in situ degradation was altered by intake level or endophyte treatment (P > 0.3). DM percentage and DM weight of rumen contents were increased (P < 0.01) by E+ dosing. Particulate passage increased (P = 0.0002) during H intake and decreased (P = 0.02) with E+ dosing. Ruminal liquid passage decreased (P < 0.03) with H feeding, while liquid flow rate tended to be reduced (P < 0.14) with E+ dosing. Total VFA concentration increased with both H feeding (P < 0.01) and E+ dosing (P < 0.0001). Despite these differences, the N and energy balance data indicate that the reductions in weight gain and productivity seen during fescue toxicosis are primarily due to reduced intake.