Determinants of bovine thermal response to heat and solar radiation exposures in a field environment.

Continuous exposure of cattle to summer heat in the absence of shade results in significant hyperthermia and impairs growth and general health. Reliable predictors of heat strain are needed to identify this condition. A 12-day study was conducted during a moderate summer heat period using 12 Angus x Simmental (Bos taurus) steers (533 ± 12 kg average body weight) to identify animal and ambient determinations of core body temperature (T(core)) and respiration rate (RR) responses to heat stress. Steers were provided standard diet and water ad libitum, and implanted intraperitoneally with telemetric transmitters to monitor T(core) hourly. Visual count of flank movement at 0800 and 1500 hours was used for RR. Dataloggers recorded air temperature (T(a)), and black globe temperatures (T(bg)) hourly to assess radiant heat load. Analysis was across four periods and 2 consecutive days averaged within each period. Average T(a) and T(bg) increased progressively from 21.7 to 30.3°C and 25.3 to 34.0°C, respectively, from the first to fourth periods. A model utilizing a quadratic function of T(a) explained the most variation in T(core) (R(2) = 0.56). A delay in response from 1 to 3 h did not significantly improve R(2) for this relationship. Measurements at 0800 and 1500 hours alone are sufficient to predict heat strain. Daily minimum core body temperature and initial 2-h rise in T(a) were predictors of maximum core temperature and RR. Further studies using continuous monitoring are needed to expand prediction of heat stress impact under different conditions.

Profile of the bovine acute-phase response following an intravenous bolus-dose lipopolysaccharide challenge.

Our objective was to characterize further the acute-phase response following endotoxin (i.e. lipopolysaccharide; LPS) exposure in the bovine. Nine pure-bred Angus castrated males (i.e. steers; average body weight=299+/-5 kg) were used in a randomized complete block design in environmentally controlled chambers, set at thermoneutral level, to characterize the acute physiological, endocrine, immune, and acute-phase protein responses following an i.v. bolus administration of 2.5 microg of LPS/kg body weight. One day before administration of LPS, all steers were fitted with an indwelling jugular vein catheter for serial blood collection. Blood samples were collected at 30-min intervals from -2 h to 8 h relative to the LPS challenge (time 0), and serum was harvested and stored at -80 degrees C until analyzed for concentrations of cortisol, pro-inflammatory cytokines, and acute-phase proteins. Indicators of thermal status (i.e. rectal temperature, ruminal temperature, respiration rate, sweat rate, and skin temperatures) were measured at 30-min intervals from -1 h to 6 h relative to the challenge. Endotoxin exposure increased (P<0.05) serum concentrations of cortisol, tumor necrosis factor-alpha (TNF-alpha), interleukin 1-beta (IL-1beta), IL-6, interferon-gamma (IFN-gamma), and serum amyloid A. Respiration rate, rectal temperature, and rump skin temperature also were increased (P<0.05) following LPS administration. Endotoxin exposure dramatically decreased ear skin temperature (P=0.002), but tended to increase (P<0.10) ruminal temperature, shoulder skin temperature, and shoulder sweat rate. Serum concentrations of acid soluble protein, alpha-acid glycoprotein, IL-4 and IL-2, and rump sweat rate were not altered (P>0.24) by the challenge. To our knowledge, this report is the most complete characterization of the bovine acute-phase response to a bolus-dose endotoxin challenge conducted under thermoneutral conditions and should provide foundation data for future research.

Effect of ergot alkaloids associated with fescue toxicosis on hepatic cytochrome P450 and antioxidant proteins.

Intake of ergot alkaloids found in endophyte-infected tall fescue grass is associated with decreased feed intake and reduction in body weight gain. The liver is one of the target organs of fescue toxicosis with upregulation of genes involved in xenobiotic metabolism and downregulation of genes associated with antioxidant pathways. It was hypothesized that short-term exposure of rats to ergot alkaloids would change hepatic cytochrome P450 (CYP) and antioxidant expression, as well as reduce antioxidant enzyme activity and hepatocellular proliferation rates. Hepatic gene expression of various CYPs, selected nuclear receptors associated with the CYP induction, and antioxidant enzymes were measured using real-time PCR. Hepatic expression of CYP, antioxidant and proliferating cell nuclear antigen (PCNA) proteins were measured using Western blots. The CYP3A1 protein expression was evaluated using primary rat hepatocellular cultures treated with ergovaline, one of the major ergot alkaloids produced by fescue endophyte, in order to assess the direct role of ergot alkaloids in CYP induction. The enzyme activities of selected antioxidants were assayed spectrophotometrically. While hepatic CYP and nuclear receptor expression were increased in ergot alkaloid-exposed rats, the expression and activity of antioxidant enzymes were reduced. This could potentially lead to increased oxidative stress, which might be responsible for the decrease in hepatocellular proliferation after ergot alkaloid exposure. This study demonstrated that even short-term exposure to ergot alkaloids can potentially induce hepatic oxidative stress which can contribute to the pathogenesis of fescue toxicosis.

Expression profiling of heat stress effects on mice fed ergot alkaloids.

Fescue toxicosis affects wild and domestic animals consuming ergot alkaloids contained in tall fescue forage infected with the endophytic fungus, Neotyphodium coenophialum. When animals are consuming infected fescue (E+) forage during periods of elevated ambient temperatures (summer), a range of phenotypic disorders collectively called summer slump is observed. It is characterized by hyperthermia, with an accompanying decrease in feed intake, growth, milk yield, and reproductive fitness. Laboratory mice also exhibit symptoms of fescue toxicosis at thermoneutral (TN) temperature, as indicated by reduced growth rate and reproductive fitness. Our goal was to characterize the differences in gene expression in liver of mice exposed to summer-type heat stress (HS) and E+ when compared to mice fed E+ at TN temperature. Mice were fed E+ diet under HS (34 +/- 1 degrees C; n = 13; E+HS) or TN conditions (24 +/- 1 degrees C; n = 14; E+TN) for a period of 2 weeks between 47 and 60 days of age. Genes differentially expressed between E+HS versus E+TN were identified using DNA microarrays. Forty-one genes were differentially expressed between treatment groups. Expressions of eight genes were measured using quantitative real-time PCR. Genes coding for phase I detoxification enzymes were upregulated in E+HS mouse liver. This detoxification pathway is known to produce reactive oxidative species. We observed an upregulation of genes involved in the protection against reactive oxidative species. Key genes involved in de novo lipogenesis and lipid transport were also upregulated. Finally, genes involved in DNA damage control and unfolded protein responses were downregulated.

Development and testing of a high-density cDNA microarray resource for cattle.

A cDNA microarray resource has been developed with the goal of providing integrated functional genomics resources for cattle. The National Bovine Functional Genomics Consortium's (NBFGC) expressed sequence tag (EST) collection was established in 2001 to develop resources for functional genomics research. The NBFGC EST collection and microarray contains 18,263 unique transcripts, derived from many different tissue types and various physiologically important states within these tissues. The NBFGC microarray has been tested for false-positive rates using self-self hybridizations and was shown to yield robust results in test microarray experiments. A web-accessible database has been established to provide pertinent data related to NBFGC clones, including sequence data, BLAST results, and ontology information. The NBFGC microarray represents the largest cDNA microarray for a livestock species prepared to date and should prove to be a valuable tool in studying genome-wide gene expression in cattle.

Thermoregulatory response of dairy cows fed ergotized barley during summer heat stress.

Claviceps purpurea infects the seed heads of cereal grains and grasses and produces ergopeptine alkaloids that cause hyperthermia and agalactia in cattle during periods of heat stress. A field experiment was undertaken to examine the effects of ergopeptine alkaloids found in barley on thermal status of dairy cattle during periods of heat stress. Production end points were also measured to identify the effect of the change in thermal status. Contaminated barley screenings containing known levels of ergopeptine alkaloids were fed to lactating Holstein cattle (10 microg total ergopeptine alkaloids/kg BW/day) for 10 days during summer heat stress. Air temperature increased 14.4 C during the first 8 days of treatment and then declined the same during the last 2 days. Extreme daily values for rectal temperature and respiration rate, using averages of all animals, showed maximum increases of 2.3 C and 56.8 breaths/minute, respectively, during this period. Group afternoon milk production decreased 2 kg/day during the heat stress period, with no measurable change in feed intake. A greater level of hyperthermia occurred in cattle consuming the diet with ergopeptine alkaloids, with only marginal symptoms of ergot toxicosis reflected in feed intake and milk production. Therefore, the ergopeptine alkaloid dose used in this study represents a level for minimal induction of the ergot toxicity response.

Whole-blood concentrations of glutathione in cattle exposed to heat stress or a combination of heat stress and endophyte-infected tall fescue toxins in controlled environmental conditions.

OBJECTIVE: To determine whether cattle exposed to heat stress alone or heat stress while consuming endophyte-infected fescue (EIF) have lower whole-blood (WB) concentrations of glutathione (GSH). ANIMALS: 10 Simmental cows. PROCEDURE: Cows were sequentially exposed to thermoneutral (TN; 2 weeks; 18 C, 50% relative humidity [RH]), heat stress (HS; 2 weeks; alternating 4-hour intervals at 26 and 33 C; 50% RH), and heat stress while consuming EIF (10 microg of ergovaline/kg/d; 2 weeks, HS + EIF). Blood samples were collected after each period and tested for GSH and oxidized glutathione (GSSG) concentrations. RESULTS: Feed consumption was similar when data were analyzed for time points at which WB concentrations of GSH or GSSG were determined. However, significant effects of treatment, cow, days exposed to heat, cow-by-treatment interaction, and treatment-by-days exposed to heat interaction were detected when data were considered simultaneously. Mean +/- SD hematocrit for TN, HS, and HS + EIF were 35.3+/-3, 33.3+/-2, and 37.1+/-3%, respectively. Mean WBGSH concentrations for TN, HS, and HS + EIF were 3.2+/-0.65, 2.7+/-0.62, and 2.4+/-0.56 mmol/L of RBC, respectively. Reduced WBGSH concentrations were associated with reduced feed intake during the later part of each heat period. CONCLUSIONS AND CLINICAL RELEVANCE: Decreased GSH and increased GSSG concentrations were evident during heat stress, especially when cattle consumed EIF These were associated with reduced feed intake during heat stress. Heat stress, reductions in feed intake, and thermoregulatory effects of EIF may induce oxidative stress in cattle.