Don Spiers

Immature rats were tested at 2, 7, 11, and 15 days of age to determine steady-state thermoregulatory responses during light (L) and dark (D) phases of the daily cycle. Pups were housed with dams in a vivarium illuminated from 0700 to 1900 h. During each phase tests began approximately 1 h after the change in the light conditions of the vivarium. Duration of each test was approximately 7 h. Rats were tested individually in temperature-controlled cylinders at ambient temperatures (Ta) = 25.0, 30.0, 32.5, and 35.0 degrees C. Both colonic (Tco) and tail skin temperatures of each animal were measured continuously. O2 content of effluent air from each cylinder was determined to provide an estimate of metabolic rate (M). Immature rats, at 2 to 11 days of age, exhibited significant L:D differences in M and Tco. However, no significant L:D differences in these responses were noted at 15 days of age. In every case, nocturnal increases in Tco were associated with a rise in M. L:D differences in Tco response were not attributed to a significant change in total thermal conductance. These data support the conclusion that the immature rat exhibits daily variation in metabolic rate, which is the primary contributor to L:D shifts in Tco.

Rats were tested at 6-7 days of age to determine thermoregulatory responses to microwave exposure (2,450-MHz; continuous wave). Each animal was partially restrained in a cylindrical holder and irradiated at a power density of either 5 or 20 mW/cm2 [specific absorption rate = 0.60 (W/kg)/(mW/cm2)] at a cold ambient temperature (Ta). Following a 1-hour thermal equilibration period, each rat was monitored at 1-min intervals during 1-hour microwave exposure and 1-hour recovery periods. Colonic temperature (Tco), determined with a Vitek probe, and metabolic heat production (M), derived from measures of oxygen consumption, were sampled and recorded during these periods. Tco increased significantly above initial level at both power densities and reached a plateau after 45 min of microwave exposure. Tco doubled with a four-fold increase in microwave intensity. Prior to exposure, M was elevated in response to cold Ta and remained unchanged during exposure at 5 mW/cm2, but decreased 7.2 W/kg during exposure at 20 mW/cm2. The results indicate that the hypothermic rat pup can be effectively warmed by low-level microwave irradiation and is capable of altering metabolism in response to such heating.

Adult rats exhibit rebound hyperthermia within 24 hr following a single injection of ethanol (EtOH). Tests were conducted to determine whether similar changes in thermoregulatory ability occur in the immature rat. Animals were administered saline or EtOH (4 g/kg BW; intraperitoneally) at 2 to 3, 8 to 9, or 14 to 15 days of age. Littermates were handled or left undisturbed with the dams to serve as controls. All rats were tested at 24 or 48 hr post-treatment to measure steady-state colonic temperature (Tco), tail skin temperature and metabolic rate (MR) at both thermoneutral and cold ambient temperatures (Tas). The youngest group exhibited no delayed change in body temperature or MR at 24 or 48 hr post-treatment with EtOH. Likewise, thermoregulatory ability of rats pretreated with EtOH at 8 or 9 or 14 to 15 days of age was not significantly different from controls when tested 24 hr post-treatment at thermoneutral Ta. In contrast, Tco of EtOH-treated rats in the two older age groups was 1 degree C above control level when tested 24 hr post-treatment at cold Ta. This Tco response can be explained by differences in heat transfer to the tail and MR. No altered response to cold Ta was found at 48 hr postinjection, indicating recovery from the EtOH effect. A single injection with EtOH at 2 to 15 days of age results in a change in Tco, which is dependent on postinjection time, age, and Ta.

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.

The objective of the experiment was to examine the interaction of endophyte-infected tall fescue and environmental temperature on follicular and luteal development and function in beef heifers. Heifers were fed endophyte-free or endophyte-infected tall fescue seed at thermoneutral or heat stress temperatures (n = 6/treatment) 4 wk before and 3 wk after synchronized ovulation. All heifers were subjected to thermoneutral conditions (19 degrees C, 50% relative humidity) from Days -7 to -2; temperature increased incrementally from Days -1 to 0 and cycled between 25 degrees C and 31 degrees C between Days 1 and 20 for heat-stressed heifers. Serum was collected and ovaries monitored every other day after induced luteolysis between Days 1 and 23 or until ovulation. Size and location of follicles >4 mm and corpora lutea were recorded. Serum concentrations of prolactin were reduced in heat-stressed heifers fed infected seed and both heat stress and infected seed decreased total cholesterol. Rectal temperature and respiration rate were greatest in heifers fed the infected seed when exposed to maximal temperatures. Heat stress led to reduced diameter of the corpus luteum and serum progesterone compared with thermoneutral conditions. Progesterone was reduced more so in heifers fed infected seed. The combination of infected seed and heat stress was associated with reduced diameter of the preovulatory dominant follicle, and consumption of infected seed led to fewer large follicles during the estrous cycle. Both stressors led to reduced serum estradiol. Impaired follicle function may explain reduced pregnancy rates commonly observed in heifers grazing infected tall fescue pasture.

Rats were tested at 6-7 days of age to determine thermoregulatory responses to microwave exposure (2,450-MHz; continuous wave). Each animal was partially restrained in a cylindrical holder and irradiated at a power density of either 5 or 20 mW/cm2 [specific absorption rate = 0.60 (W/kg)/(mW/cm2)] at a cold ambient temperature (Ta). Following a 1-hour thermal equilibration period, each rat was monitored at 1-min intervals during 1-hour microwave exposure and 1-hour recovery periods. Colonic temperature (Tco), determined with a Vitek probe, and metabolic heat production (M), derived from measures of oxygen consumption, were sampled and recorded during these periods. Tco increased significantly above initial level at both power densities and reached a plateau after 45 min of microwave exposure. Tco doubled with a four-fold increase in microwave intensity. Prior to exposure, M was elevated in response to cold Ta and remained unchanged during exposure at 5 mW/cm2, but decreased 7.2 W/kg during exposure at 20 mW/cm2. The results indicate that the hypothermic rat pup can be effectively warmed by low-level microwave irradiation and is capable of altering metabolism in response to such heating.

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.

Major improvement in the homeothermic ability of the rat occurs during the first 2 weeks of postnatal development. Changes in thermoregulatory responsiveness to a single injection of ethanol (EtOH) may occur during this period. Immature rats (2-3, 8-9, and 14-15 days of age) were administered either saline or EtOH (2 or 4 g/kg BW; ip) at thermoneutral ambient temperatures (Ta). In one experiment, metabolic rate (MR) and body temperatures (colonic and skin) were recorded for 1-3 hr postinjection. A second experiment determined blood EtOH concentration in rats from the 3 age groups over an 8-hr period following injection of EtOH. 4 g EtOH/kg produced few significant reductions in thermoregulatory function of 2-3 day-old rats, but decreased MR by 16% and colonic temperature by 0.5-0.7 degrees C in 8-15 day-old animals. 2 g EtOH/kg had no effect on 8-9 day-old rats, but reduced MR and colonic temperature in rats aged 14-15 days. In every case, the hypothermic response to EtOH was correlated with a reduction in MR. Back and abdominal skin temperatures decreased with colonic temperature, and tail skin temperature indicated EtOH-induced vasoconstriction in older rats. Blood EtOH concentrations were similar in the three age groups during the first 2 hr postinjection and did not explain differences in metabolic response. The magnitude and duration of thermoregulatory responsiveness to EtOH increases with age in the immature rat.

A study was conducted to develop a model for fescue toxicosis using rats fed a diet containing endophyte-infected tall fescue seed (E+). Rats implanted with telemetric transmitters to continuously monitor core body temperature (Tc) and activity were housed at thermoneutrality (21 degrees C) and were fed a diet containing endophyte-free fescue seed (E-). After 2 wk, they were assigned to either E+ or E- diets and initially maintained at thermoneutrality (preheat) for 8 d. They were then exposed to heat stress (31 degrees C) for 22 d, followed by 1 wk of recovery at thermoneutrality (post-heat). Body weight and feed intake were measured daily. Rats receiving the E+ diet showed decreased feed intake (P = 0.001) and weight gains (P = 0.003) during the preheat period. The decrease in Tc from the pre-treatment level was greater in E+ than in E- rats during the preheat (P = 0.001) and postheat (P = 0.001) periods. With heat stress, both groups showed parallel decreases in feed intake. The increase in Tc from pre-heat to heat conditions was greater in E+ vs. E- rats (P = 0.001). Activity level was lower in E+ than in E-rats during heat stress (P = 0.009) and postheat (P = 0.037) periods. These results show that the rat model for fescue toxicosis is extremely useful because many of the observed responses to E+ diet are similar to those noted for cattle, and additional variables that are difficult to measure in cattle, such as activity, can be easily evaluated.

The objective was to determine the effect of a mouse metallothionein/bovine growth hormone transgene on resting metabolic rate (RMR), cold-induced thermogenesis, and beta-agonist stimulated nonshivering thermogenesis in mice. Non-transgenic littermates were used as controls. Open-circuit indirect calorimetry was used to assess RMR and cold-induced thermogenesis in 64 mice. Air temperature in the chamber was set at 31 degrees C for RMR and was decreased to 28, 25, 21, or 17 degrees C to determine cold-induced thermogenesis. Response to the beta-agonist isoproterenol was evaluated by monitoring changes in colonic temperature of 34 mice upon injection of the drug or saline. Despite the fact that RMR tended to be lower in transgenics than in nontransgenics, at 31 degrees C transgenic mice were able to regulate colonic temperature at the same level as nontransgenics, but colonic temperature decreased in transgenics relative to nontransgenics as air temperature was reduced. For each degree decrease in air temperature between 31 and 17 degrees C, nontransgenic mice increased heat production by 1.03 +/- .10 watt/kg, whereas transgenic mice increased it by only .56 +/- .08 watt/kg, indicating that the thermogenic response of transgenics to cold was inferior. The magnitude of the maximal increase in colonic temperature after isoproterenol injection was similar for both groups, but the response was slower in transgenics. We suggest that lean body mass and substrate availability for shivering thermogenesis are reduced in transgenics relative to total body weight, and that they allow colonic temperature to decrease to conserve energy.

Eighty-four Bos taurus crossbred steers were used to investigate effects of level and duration of limit-feeding feedlot cattle in a hot environment. Pens (four/treatment) of steers (seven/pen) were fed feedlot finishing diets and randomly assigned to the following treatments: 1) restricted to approximately 75% of feed consumed when offered ad libitum for 21-d duration (RES21); 2) restricted to approximately 75% of ad libitum for 42-d duration (RES42); and 3) feed offered ad libitum (ADLIB). Tympanic temperatures (TT) were measured via thermistors placed in the ear canal and attached to data loggers. Restricting feed intake for both 21- and 42-d reduced tympanic temperature when compared with ADLIB treatment groups under hot environmental conditions. Temperature reductions exceeded 0.5 degrees C (P < 0.05) depending on time of day. The reduced tympanic temperature is likely due to a reduction in metabolic heat load and/or a concurrent reduction in metabolic rate. Within respective periods, no differences (P > 0.05) were found among treatments for panting or bunching score. However, different proportions of cattle were found to be bunching and panting with ADLIB cattle displaying a greater number of bunched steers that were panting when compared with the other groups. When averaged across diet treatments, dark-colored cattle had the greatest percentage of cattle showing moderate to excessive panting, while light-colored cattle displayed the least panting under thermoneutral climatic conditions. Under hot (mean daily temperature-humidity index >74) conditions, dark-colored cattle tended to bunch more (P = 0.073) and pant more (P < 0.01) than light-colored cattle. Mean TT were 0.2 to 0.6 degrees C (P < 0.05) greater for dark- vs light-colored cattle under hot conditions. Limit-feeding feedlot cattle during early summer is a successful tool for enhancing animal comfort by alleviating the combined effects of high climatic and metabolic heat load.

Tall fescue toxicosis continues to be a major syndrome in temperate climates of the world in terms of economic loss to animal producers. Studies with forage-fed animals over the past three decades have provided insight concerning the pathophysiological effects of the alkaloids present in tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] infected with the fungal endophyte Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin. To provide the reader a general understanding of the overall problem, we present a detailed discussion of the clinical signs of fescue toxicosis, the proposed toxicants, and projected solutions to this costly disease condition of ungulates. We also explore the physiological mechanisms proposed to be involved in the expression of the syndrome. Finally, we offer our suggestions for future research efforts in this arena and the potential impact of these approaches. [PLEASE NOTE: PRINT VERSION IS AVAILABLE AT https://portal.sciencesocieties.o...

Ethanol has been shown to induce a hypothermia in rats maintained in air at 26 degrees C. The objective of the present study was to assess the metabolic responsiveness of ethanol-treated rats to administration of isoproterenol, a beta-adrenoceptor agonist, and to assess whether ethanol per se, or the hypothermia accompanying its administration, contribute to changes in beta-adrenergic responsiveness. In the present study, administration of ethanol (3 g/kg, i.p.) reduced both colonic temperature (Tco) and rate of oxygen consumption (metabolic rate) of rats maintained at 26 degrees C to levels below those of saline-treated controls within 20 min after treatment. Maximal decreases in both parameters occurred within approximately 40 min. Administration of isoproterenol (50 micrograms/kg, s.c.) 10 min after treatment with either ethanol or saline was accompanied by an increase in the metabolic rates of both groups, although the magnitude of the increase in the ethanol-treated group was l...

Ethanol has been shown to induce a hypothermia in rats maintained in air at 26 °C. The objective of the present study was to assess the metabolic responsiveness of ethanol-treated rats to administration of isoproterenol, a β-adrenoceptor agonist, and to assess whether ethanol per se, or the hypothermia accompanying its administration, contribute to changes in β-adrenergic responsiveness. In the present study, administration of ethanol (3 g/ kg, i.p.) reduced both colonic temperature (Tco) and rate of oxygen consumption (metabolic rate) of rats maintained at 26 °C to levels below those of saline-treated controls within 20 min after treatment. Maximal decreases in both parameters occurred within approximately 40 min. Administration of isoproterenol (50 μg/kg, s.c.) 10 min after treatment with either ethanol or saline was accompanied by an increase in the metabolic rates of both groups, although the magnitude of the increase in the ethanol-treated group was less than that of controls. ...

Fescue toxicosis affects wild and domestic animals grazing fescue pasture infected with the endophytic fungus Neotyphodium coenophialum. Signs of fescue toxicosis include increased core body temperature and respiration rate and decreased milk yield and reproductive performance. Laboratory mice also exhibit symptoms of fescue toxicosis, as indicated by reduced growth rate and reproductive performance. Mice were used to study the effects of fescue toxicosis on hepatic gene expression. Twenty-seven mice were randomly allocated to a diet containing either 50% endophyte-infected (E+; 6 ppm ergovaline) or endophyte-free (E-) fescue seed for 2 wk under thermoneutral conditions. Liver genes differentially expressed due to fescue toxicosis were identified using DNA microarray. A 2-stage ANOVA of microarray data identified 36 differentially expressed genes between mice fed E+ and E- diets. Another analysis method, significance analysis of microarray, identified 9 genes as differentially expre...

Twenty-six lactating Holstein cows (90 d of lactation) were blocked according to milk production, parity, and days of lactation for assignment to one of two dietary treatments. Diets included a control diet with no supplemental niacin and a diet supplemented with increasing concentrations of niacin (12, 24, or 36 g/d per cow over three consecutive 17-d periods. Cows were housed in a covered free-stall barn and were fed and milked twice daily. Mean maximum air temperatures and temperature-humidity indexes were 28.5, 31.4, and 25.2 degrees C and 79.6, 85.1, and 75, respectively, for the three periods. Rectal temperature was measured with a rectal probe, tail and rump temperatures by infrared thermometry, and respiratory rate by visual observation. Measurements were made daily at 0800, 1600, and 2200 h. Rectal temperature was not affected by treatment. Comparison of skin temperatures for control cows and cows fed niacin showed higher temperatures at the tail (34.0 vs. 33.7 degrees C at...

Holstein (n = 12) and Guernsey (n = 6) calves, housed in hutches, were used to evaluate the complex relationships among external environment, housing microclimate, and thermal status of calves. The study was conducted during the summer; 9 calves were housed in hutches under supplemental shade, and 9 calves were maintained in hutches under direct sunlight. Environmental and calf temperatures were measured twice daily at 0700 and 1500 h, which included determinations of air temperature, inner and outer surface temperatures of the hutch, rectal and skin temperatures of the calf, and respiration rate. Outer and inner surface temperatures of the hutch were lower under supplemental shade. Hutch air temperature was highly correlated with inner surface temperature and therefore was lower in the shaded environment. During the p.m. period, when heat stress was highest, calves housed in a shaded hutch environment had lower skin temperatures and respiration rates than did unshaded calves. Body ...

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.

A study was conducted to evaluate the influence of Ascophyllum nodosum (Tasco) on rectal temperature, respiration rates, and in situ NDF disappearance in cattle exposed to elevated ambient temperature. Twenty-four Angus crossbred steers (average BW= 300.6 ...

Rats at thermoneutral ambient temperature (Ta) exhibit change in thermoregulatory response to ethanol (EtOH) from 2 to 15 days of age. In the present study, rats at 2-3, 8-9, and 14-15 days of age were administered either saline or EtOH (4 g/kg b.wt.;IP) using two different routines to determine EtOH effect on specific cold defense mechanisms. Injection of EtOH in the first routine occurred after exposure to cold Ta, to determine effect on maintenance of cold thermogenesis. EtOH-induced metabolic depression increased from 3 to 8 days of age, with little change after this time. Injection of EtOH in the second routine was at thermoneutral Ta, followed at 20 min postinjection by rapid exposure to cold Ta to determine effect on activation of cold thermogenesis. EtOH-treatment delayed onset of cold thermogenesis at 2-3 and 14-15 days of age, and completely eliminated 8-9-day-old response to cold Ta. Rats exposed to cold Ta at 2-3 days of age exhibited a slower rate of EtOH absorption and lower blood EtOH concentration than rats in the older groups, to explain some age differences in EtOH response.

Several thermoregulatory responses (i.e., colonic temperature, tail-skin temperature, rate of oxygen consumption) were measured in the rat following acute administration of either saline or 3 g ethanol/kg BW i.p. at ambient temperatures (Ta) of 17, 25, and 32 degrees C. The magnitude of the ethanol-induced, hypothermic response was inversely related to Ta, with the decrease in colonic temperature (Tco) at 120 min postinjection ranging from 0.1 degree C at Ta 32 degrees C to 3.2 degrees C at Ta 17 degrees C. Depression of rate of oxygen consumption (heat production) was a major factor contributing to ethanol-induced hypothermia, with no observed differences in heat loss as assessed by differences in the responses of tail skin temperature. Thermoregulatory responses were also measured following acute administration of ethanol at Ta 25 degrees C and immediate exposure to either Ta 32 or 17 degrees C. The increase in Tco of ethanol-treated rats was delayed compared to controls following exposure to 32 degrees C. In addition, tail skin temperature and rate of oxygen consumption of treated rats were significantly lower. The delayed rise in Tco is most likely the result of a reduction in rate of oxygen consumption. When administered ethanol at Ta 25 degrees C and then exposed to Ta 17 degrees C, the rats exhibited a significant recovery from the metabolic depression that characterized the administration of ethanol during exposure to Ta 17 degrees C. This was most likely related to differences in the clearance of ethanol from blood. The results of this study are consistent with the suggestion that the physiologically significant inhibitory effect of acute administration of 3 g ethanol/kg BW on thermoregulatory responses of rats is manifested at the level of heat production rather than heat loss and that the effect is exacerbated by a reduction in Ta.