Effects of endophyte-infected tall fescue seed and red clover isoflavones on rumen microbial populations and physiological parameters of beef cattle1,2

Abstract

Lolium arundinaceum [(Darbyshire) tall fescue] toxicosis is responsible for substantial beef production losses in the United States, due to its negative effects on reproduction, growth, and feed efficiency. These effects are consequences of toxic alkaloids within tall fescue. Interseeding legumes, such as Trifolium pratense (red clover), into pastures has been shown to mitigate a portion of these effects. Clovers contain isoflavones, which may play a role in tall fescue toxicosis mitigation. The present study utilized 36 Angus steers to determine the effects of daily supplementation with a red clover-isolated isoflavone feed additive on physiological symptoms of tall fescue toxicosis and the rumen microbial environment over a 21-d period. Angus steers were initially stratified based upon their single nucleotide polymorphism genotype at the DRD2 receptor. Treatments were then randomly assigned in a 2 × 2 factorial arrangement within a completely randomized design, where treatment factors consisted of tall fescue seed type (endophyte-infected tall fescue seed vs. endophyte-free tall fescue seed) supplemented with and without the isoflavone additive. Steers that consumed endophyte-infected tall fescue seed had lower serum prolactin concentrations (P = 0.0007), average daily gain (ADG; P = 0.003), final body weight (BW; P = 0.004), and feed efficiency (P = 0.018) when compared with steers that consumed endophyte-free tall fescue seed. Serum insulin-like growth factor-1 (IGF-1) tended to be reduced with supplementation of isoflavones (P = 0.06) but was unaffected by seed type (P ≥ 0.10) and seed by treatment interaction (P ≥ 0.10). Isoflavones reduced serum glucose levels (P = 0.023), but neither seed type, isoflavones, or their interaction affected serum urea nitrogen (SUN), nonesterified fatty acids (NEFA), or insulin (P ≥ 0.10). Volatile fatty acid concentrations, dry matter intake (DMI), ruminal pH, and overall feeding behaviors were also unaffected by seed type or isoflavone treatments (P ≥ 0.10). Twenty-eight ruminal bacteria taxa shifted as a result of seed type or isoflavone treatment (P < 0.05). In this experiment, feeding isoflavones to Angus cattle did not completely mitigate all symptoms of fescue toxicosis. However, dose–response trials may aid future research to determine if dietary supplementation with isoflavones alleviates fescue toxicosis symptoms and promotes livestock growth and performance.

Rumen and Serum Metabolomes in Response to Endophyte-Infected Tall Fescue Seed and Isoflavone Supplementation in Beef Steers

“…The rumen microbiome is crucial for providing nutrients needed by the host for energy requirements and muscle development. As the microbiome has previously been shown to be affected by consuming endophyte infected tall fescue [12,23], the metabolites and other products produced by the rumen microorganisms may be altered, potentially contributing to reductions in growth and feed efficiency. The metabolites produced by the rumen microorganisms are a result of the richness of the rumen microbiome.…”

“…Experimental design, animal treatments, and sample collection methods have been previously described in Melchior et al [12]. Briefly, this study used 36 purebred Angus steers of approximately eight months of age weighing 250 ± 20 kg from Ames Plantation in Grand Junction, TN.…”

“…Briefly, this study used 36 purebred Angus steers of approximately eight months of age weighing 250 ± 20 kg from Ames Plantation in Grand Junction, TN. Steers were transported to the Plateau Research and Education Center (PREC) in Crossville, TN for the trial, as previously described [12]. Steers were allowed a 10 d acclimation period to the diet formulated to provide 11.57% crude protein and 76.93% total digestible nutrients (DM basis).…”

“…The GrowSafe System© (GrowSafe Systems Ltd., Calgary, AB, Canada) was used to monitor feed intake. Prior to the beginning of the trial, steers were genotyped for the DRD2 receptor gene, which can influence cattle's response to fescue toxicity [12]. Using this information, the study was blocked on DRD2 genotype, implementing a randomized complete block design.…”

“…Isoflavones act as an agonist on the β-adrenergic receptors present on blood vessels to promote vasodilation [10], reversing the effects of ergot alkaloid induced vasoconstriction. Additionally, isoflavones act as a natural antibiotic selective against hyper-ammonia-producing bacteria (HAB) and some cellulolytic and amylolytic bacteria [11,12]. The reduction of ammonia levels as a result of less HAB in the rumen allows more amino acids to be absorbed and used by the ruminant, while altered celluloytic and amylolytic bacteria can influence the production of volatile fatty acids for energy.…”