2009 Annual Report
1a.Objectives (from AD-416)
The long-term objective of this project is to develop an improved understanding of livestock physiology and genetics to enhance the productivity and profitability of meat production from cattle grazing improved temperate pastures while reducing animal stress. Over the next 5 years this project will focus on the following objectives:
Objective 1: Improve grazing animal performance by identifying genes that reduce stress from endophyte-infected cool-season pastures.
Subobjective 1.A. Determine if the tropically adapted Romosinuano breed of cattle is more tolerant of heat stress and fescue toxicosis than Angus cattle.
Subobjective 1.B. Identify genetic markers in cattle tolerant of heat stress and/or fescue toxicosis.
Subobjective 1.C. Determine the role of thermoregulation in tolerance to fescue toxicosis in ruminants.
Objective 2: Enhance nutrient utilization from endophyte-infected cool-season forages through improved understanding and manipulation of the microorganisms of the rumen.
Objective 3: Develop improved cow-calf and stocker management practices for pastures in which endophyte-infected forages dominate.
Subobjective 3.A. Define the effects of ergot alkaloids and lower body condition on cow and/or heifer reproductive performance.
Subobjective 3.B. Define sequences of forages and forage management protocols to enhance the productivity and profitability of cow-calf and stocker cattle grazing temperate pastures.
Subobjective 3.C. Investigate the mechanisms involved in fecal shedding of pathogenic bacteria from ruminants consuming toxic endophyte-infected (wild type) tall fescue (EI-TF).
1b.Approach (from AD-416)
Physiological parameters (respiration rate, skin and rectal temperature, and blood metabolites) of cattle consuming endophyte-free and -infected fescue diets will be compared in environmentally-controlled chambers. Genetic markers of cattle tolerant to heat stress and/or fescue toxicosis will be assessed. Microarray hybridization will be utilized to obtain estimates of gene expression changes due to heat stress and/or fescue toxicosis within breeds of cattle. Replicated field experiments will evaluate cow-calf and stocker management practices and genotypes on novel, endophyte-free or -infected tall fescue pastures to alleviate fescue toxicosis and improve calf production. Ruminal microbes that are capable of degrading ergot alkaloids will be evaluated. In vivo and in vitro studies will be conducted to determine production practices affecting fecal shedding of E. coli and Salmonella.
Genetic marker discovery and validation continues with elements related to heat shock protein 70, prolactin (PRL), cytochrome P450 3A28 (CYP3A28), glucocorticoid receptor, and lactate deyhogenase. Steers were genotyped at the PRL and CYP3A28 genes and assigned in a factorial manner to toxic and non-toxic stockpiled tall fescue pastures. Following a six-month winter/spring grazing trial, steers were finished during a 135 d feedlot phase. Steers grazing the toxic fescue had slower gains and less desirable carcass traits when compared with the non-toxic steers. The PRL polymorphism was not associated with steer traits; however, CYP3A28 polymorphism interacted with forage. Steers with the minor allele at CYP3A28 and grazing toxic fescue, weighed less, had poorer carcass quality, and had elevated concentrations of alkaloid concentrations in their ribfat throughout the finishing phase. Those results suggest that metabolism of ergot alkaloids and their clearance are related to polymorphisms in the cytochrome P450 gene. Our results may have food safety implications. Objectives were to determine the polymorphic nature of the enhancer region of the bovine prolactin (PRL) gene with fertility in beef cows. In the Discovery population, genomic DNA was obtained from purebred Angus, purebred Brahman, Angus x Brahman and Brahman x Angus cows. Cows were assigned to graze either common bermudagrass (CB) or toxic endophyte-infected tall fescue (EI) for their lifetime. Lifetime calving rate, and weight and hip height of calves at weaning during cow lifetime were recorded. In the Validation population, genomic DNA was collected from crossbred Angus cows in either low or moderate body condition (BC) at breeding. Calving rate, diameter of the largest follicle, and Julian calving date were determined. Identification of cows with specific genotypes within the enhancer region of PRL gene can assist beef producers in selection of cows that may have increased fertility. Efforts are being made through examination of a heat-tolerant breed to alleviate signs of fescue toxicosis in a cow-calf herd. Reproduction responses and calf production are being determined among Angus, Romosinuano, and the crossbred cows grazing endophyte-free or infected tall fescue. Pregnancy rates may differ between Angus produced in or near Arkansas and those produced in Florida. Romosinuano cattle show fewer signs of fescue toxicosis. A series of experiments were conducted to evaluate the effects of ergot alkaloids (dihydroergotamine, ergonovine, and ergotamine) on E. coli O157:H7 in both pure and mixed ruminal fluid culture. Ergot alkaloids commonly found in endophyte-infected tall fescue plants reduced E. coli O157:H7 in vitro. Ruminal and/or intestinal populations of E. coli O157:H7 may be influenced in livestock consuming endophyte-infected tall fescue, and these alterations could be due to the presence of ergot alkaloids in fescue plants.
Ergot alkaloids dihydroergotamine, ergonovine, and ergotamine and growth of Escherichia coli O157:H7 in vitro: Escherichia coli O157:H7 (toxic E. coli) is one of the most common agents of foodborne illness in humans. Ergot alkaloids have been used in modern medicine to control migraine headaches and induce uterine contractions during childbirth. How ergot alkaloids in endophyte-infected tall fescue affect growth of toxic E. coli is unknown. ARS scientists from Booneville, Arkansas, and College Station, Texas, and personnel from the University of Arkansas conducted a series of laboratory experiments to evaluate the effects of ergot alkaloids on growth of toxic E. coli. Ergot alkaloids reduced growth of toxic E. coli, suggesting that populations of toxic E. coli may be reduced in livestock consuming endophyte-infected tall fescue. Addition of ergot alkaloids to the diets of feedyard cattle prior to harvest may increase food safety, ultimately improving human health.
Milk production and quality of Angus or Romosinuano cows grazing endophyte-free or -infected tall fescue: Calf growth is often reduced in response to decreased milk production in cow-calf production utilizing endophyte-infected tall fescue and costs the beef industry millions of dollars annually. Use of a tropically adapted Bos taurus beef breed, Romosinuano, that is more thermo-tolerant may allow for a tolerance to fescue toxins and improve calf production on tall fescue. Scientists from USDA, ARS Booneville, Arkansas, and Brooksville, Florida, determined that milk production was similar between cows grazing the endophyte-free and -infected tall fescue, but greater in Angus than Romosinuano cows. However, calf weights were similar. While Romosinuano cows showed no signs of heat stress when grazing tall fescue during summer months, subclinical signs of fescue toxicosis still existed but would not be apparent at the sale barn. These results provide information on potential genetics for cow-calf production on endophyte-infected tall fescue, which could recuperate losses to the cattle industry in association with fescue toxicosis.
Caldwell, J.D., Coffey, K.P., Coblentz, W.K., Jennings, J.A., Hubbell III, D.S., Kreider, D.L., Looper, M.L., Rosenkrans Jr, C.F. 2009. Performance by fall-calving cows grazing tall fescue pastures with different proportions stockpiled. Forage and Grazinglands [serial online]. doi:10.1094/FG-2009-0312-01-RS.
Aiken, G.E., Strickland, J.R., Looper, M.L., Bush, L.P., Schrick, F.N. 2009. Hemodynamics are Altered in the Caudal Artery of Beef Heifers Fed Different Ergot Alkaloid Concentrations. J. Anim Sci..2009; 87: 2142-2150
Looper, M.L., Edrington, T.S., Rosenkrans, C.F. 2009. Influence of body condition and forage type on prevalence of Escherichia coli O157:H7 and Salmonella in grazing beef cattle. Letters in Applied Microbiology. 49:361-365.
Looper, M.L., Edrington, T.S., Callaway, T.R., Rosenkrans, C.F. 2009. Fate of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry applied to soil surrounding tall fescue. Letters in Applied Microbiology. 48:513-516.