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Four studies were conducted in the Texas Panhandle during the summer of 2007 to evaluate methods for cooling cattle in three phases of production (unweaned calves in hutches, weaned heifers on pasture and lactating cows). Unweaned calves (n = 20) housed in polyethylene hutches, covered with reflective aluminum and bubble film insulation, were compared to calves (n = 18) in similar, un-insulated hutches. Mean thermal heat index (THI) for the trial was 71.9 ± 5.5 (SD). Insulation treatment did not affect body weight gain (P > 0.044). Insulation affected interior hutch temperature, calf body temperature, and respiration rate (P < 0.05), indicating insulation may moderate temperature extremes within the hutch. Weaned heifers (n = 55) on pastures with shade were compared to similar heifers (n = 62) in pastures without shade. Mean THI for the trials was 70.8 ± 6.2 (SD). Shade treatment increased body temperature (P = 0.03) and decreased body weight gain. The effect of shade on foraging behavior was dependant on THI. Shade use by heifers was dependant on THI and wind speed. Heifers utilized shade when THI was above 72, especially when wind speed was low. Feed bunk attendance was compared among pens (n = 3) of lactating cows where the feed bunk was equipped with water sprinklers that sprayed the backs of cows and pens (n = 2) without feed bunk sprinklers. Mean THI for the trial was 70.8 ± 5.7 (SD). Feed bunk sprinklers mediated the affect of elevated THI on decreasing bunk attendance, but overall bunk attendance was not different among treatments. Lactating dairy cows, cooled with water sprinklers and fans three times each day in the holding pen prior to milking, were compared with similar cows cooled in the holding pen by fans only. Mean THI for the trial was 69.9 ± 5.3 (SD). Body temperature, milk yield and somatic cell count were not different among treatments. Sprinkled cows had lower milk fat and total protein than control cows. Sprinkling cows in the holding pen when THI is less than 70 may negatively affect milk production.

Fission yeast Srk1 kinase is essential for cellular responses to extracellular stimuli. It is activated downstream of the MAPK Spc1 and participates in controlling mitotic entry by directly phosphorylating and inhibiting Cdc25 phosphatase during the normal cell cycle and also in response to osmotic stress. Following phosphorylation, Cdc25 is exported out of the nucleus. Heat stress caused by a temperature shift from 25°C to 36°C, which is within the normal temperature tolerance of fission yeast, temporarily inhibits nuclear division in wildtype cells. The same response is seen in cells deleted for the Pyp1 and Pyp2 phosphatases which normally serve to down regulate the Spc1 stress response. I have shown that the transient block in nuclear division caused by temperature shifts within the physiological range does not occur in srk1- cells but instead there is a stimulation of mitosis and cell division in response to the heat stress. This pattern of mitotic stimulation is phenocopied in cdc25-9a cells where nine putative Srk1 phosphorylation sites on Cdc25 are changed to alanine. Cells lacking srk1, however, display the same cell cycle progression pattern as the wildtype cells in response to osmotic stress. This experiment clearly distinguishes separate pathways for these two stress responses. Also, Cdc25 is found to be phosphorylated after a mild heat stress and seems to be exported out of the nucleus. These data indicate that Srk1 kinase plays the central role in regulating mitotic entry in response to mild heat stress by negatively regulating the Cdc25 tyrosine phosphatase. Thus my work highlights the role of Srk1 kinase in cell cycle regulation and is consistent with the Spc1 MAPK cascade linking the G2/M transition to extracellular stress. This response to mild heat stress is important because temperature sensitive mutants are frequently used in fission yeast research and this work shows that a temperature shift from 25°C to 36°C, which is within the physiological growth range, can trigger a stress response. / Thesis (Master, Biology) -- Queen's University, 2011-07-28 09:34:52.164

Some stallions are expected to perform athletically and breed contemporarily. Athletic activity has the potential, especially during the summer months, to induce thermal stress to the testes, resulting in reduced reproductive capability due to decreased sperm quality and libido. There is concern in the horse industry about what level of exercise, if any, affects the reproductive capability of a stallion. Thermal stress associated with training and exercise may impact sperm quality and the future reproductive capability of the stallion. The goal of this study was to determine the effect of strenuous exercise on stallion sperm quality. The objectives were to measure changes in body and scrotal temperatures following strenuous exercise and sperm quality following strenuous exercise. Miniature Horse stallions (n = 7), implanted with subdermal thermosensory devices in the subcutaneous neck and scrotal tissue, were assigned to treatment group based on age and semen quality. Exercising stallions (EX; n = 3) were exercised 4 d/wk for 90 min for 12 wk, while non-exercising stallions (CN) were tied in the shade. Semen was collected from stallions for 5 consecutive days every 4 wk to evaluate semen quality (raw, 24 h and 48 h cooled). Subcutaneous scrotal (SQST), rectal (RT) and neck (NT) temperatures were recorded along with heart rate. Spermatozoa data were normally distributed; therefore, they were subjected to parametric analysis by repeated measures (wk) using the PROC MIXED procedure (SAS v 9.1; SAS Inst. Inc., Cary, NC). Model included treatment (CN or EX), time (wk 0, 4, 8, or 12), and stallion as the subject of the repeated measures. Compared to the CN group, EX stallions had elevated temperatures (avg RT 39.27 vs 37.07 degrees, NT 39.77 vs 37.44 degrees C, and SQST 34.90 vs 33.40 degrees C; P < 0.0001). There was no difference in sperm quality between treatment groups (P > 0.05). In this study, strenuous exercise in Miniature Horse stallions, did not affect sperm quality. This suggests that anecdotal reports of reduced sperm quality in stallions in training may have other causes other than elevated scrotal and body temperature. While previous studies have illustrated that prolonged insulation of the testes reduces semen quality, strenuously exercising stallions for up to 90 min under hot and humid ambient conditions may not be harmful to spermatogenesis.

The current thesis examined local and whole-body heat loss responses during heat stress at rest, exercise and/or pharmacological stimuli as a function of increasing age. The first study examined the effects of age on whole-body heat loss and heat storage during passive exposure to conditions representative of the upper temperature extremes in Canada. The results demonstrate that the cumulative change in body heat content after 2 h of rest was significantly greater in older adults in a hot-dry (older: 212±25; young: 131±27 kJ, P=0.018) and hot-humid (older: 426±37; young: 317±45 kJ, P=0.037) condition. The second study evaluated the maximal capacity of whole-body evaporative heat loss as a function of age and aerobic fitness. The findings demonstrate that whole-body evaporative heat loss was significantly lower in middle-aged untrained (Ex2: 426±34; Ex3:497±17 W) and older (Ex2: 424±38; Ex3: 485±44 W) compared to young (Ex2: 472±42; Ex3: 558±51 W) and middle-aged trained (Ex2: 474±21; Ex3: 552±23 W) males at the end of the last two exercise bouts (P<0.05). The third study assessed the maximal capacity of whole-body evaporative heat loss in females and found that whole-body evaporative heat loss was significantly lower (P=0.002) in the older (Ex2: 343±39 W; Ex3: 389±29 W) compared to the young (Ex2: 383±34 W; Ex3: 437±36 W) females at the end of the second and third exercise-induced heat loads of 325 and 400 W, while no differences were observed during recovery (P=0.693). The fourth study examined nitric oxide-dependent sweating during exercise/rest cycles in young and older adults. We showed that nitric oxide-dependent sweating during short bouts of exercise in the heat is observed in young males, but not in older adults. The fifth study examined: 1) the extent to which peripheral factors (i.e., sweat gland and skin vasodilatory function) contribute to the postexercise suppression of heat loss; and 2) whether age-related differences exist in the mechanisms modulating postexercise heat loss. The findings demonstrate that there were no differences in sweat rate between the no exercise resting condition and a postexercise condition at either an acetylcholine (ACh) or methacholine (MCh) site for the young (ACh: P=0.992 and MCh: P=0.710) or older (ACh: P=0.775 and MCh: P=0.738) adults. However, older adults had a lower sweating response for both the no exercise resting condition (ACh: P=0.049 and MCh: P=0.006) and postexercise condition (ACh: P=0.050 and MCh: P=0.029) compared to their younger counterparts. Taken together, the current thesis shows true age-related impairments in the ability to dissipate heat exist during both a passive and exercise-induced heat stress over a certain heat load threshold. Specifically, older adults have an impaired ability to dissipate heat compared to young adults during rest in hot-dry and hot-humid conditions. Additionally, middle-aged untrained and older adults have a reduced capacity to dissipate heat at an exercise-induced heat load of ≥400 W for males and ≥325 W for females, which becomes more pronounced at as the level of heat load increases. However, the age-related impairment in heat loss can be attenuated by maintaining a high level of aerobic fitness. Furthermore, age-related impairments in sweating may be associated with age-related reductions in nitric oxide-mediated sweating. However, there does not appear to be age-related differences in the modulation of heat loss postexercise.

This thesis sought to evaluate whether the impairments in nitric oxide (NO)-dependent cutaneous vasodilation and sweating observed in older adults during exercise in the heat stem from age-related increases in oxidative stress and/or arginase activity. Furthermore, we assessed whether changes in the sensitivity to NO at the level of the end-organ (i.e., cutaneous vasculature and sweat gland) also contribute. A total of 20 young (age, 23 ± 3 yrs) and 28 older (age, 63 ± 7 yrs) males completed one of two intermittent exercise protocols that consisted of two 30-min bouts of semi-recumbent cycling in the heat (35˚C) at a rate of metabolic heat production of 500 (protocol I; 11 young, 19 older) or 400 (protocol II; 9 young, 9 older) W. Each exercise bout was followed by a 20-min recovery period. During each protocol, local cutaneous vascular conductance (CVC; laser-Doppler flowmetry/mean arterial pressure) and sweat rate (SR, ventilated capsule) were continuously measured at four forearm skin sites. In protocol I, each forearm skin site was continuously perfused via intradermal microdialysis with either: 1) lactated Ringer’s serving as a control (Control); 2) 10 mM NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor; 3) 10 mM ascorbate (Ascorbate), a non-selective antioxidant or 4) a combination of 10 mM ascorbate and 10 mM L-NAME (L-NAME + Ascorbate). In protocol II, the Ascorbate and L-NAME + Ascorbate skin sites were replaced with 5 mM Nω-hydroxy-nor-Arginine + 5 mM S-(2-boronoethyl)-L-cysteine to inhibit arginase activity (Nor-NOHA+BEC) and 1 µM sodium nitroprusside, a nitric oxide donor (SNP). In the young adults during protocol I, CVC was reduced relative to Control at L-NAME (both P<0.01) and L-NAME + Ascorbate (both P≤0.03) but similar to Control at Ascorbate (both P≥0.26). In the older adults, CVC was reduced from Control during both exercise bouts at L-NAME (both P≤0.02) but not Ascorbate (both P≥0.09) or L-NAME + Ascorbate (both P≥0.15). While L-NAME (both P<0.04) and L-NAME + Ascorbate (both P<0.04) attenuated SR in the younger adults during exercise (no effect of Ascorbate; both P≥0.36), no differences between Control and any treatment site were observed in the older adults (P=0.42). However, correlational analysis revealed a moderate negative correlation between between VO2peak and the change in SR from control at the Ascorbate site during both exercise bouts (-0.55≤r≤-0.54; both P=0.02) exercise. Furthermore, the change in SR from Control at L-NAME + Ascorbate was also found to be negatively correlated with VO2peak in the second (r=-0.54; P=0.02) but not first (r=-0.42; P=0.08) exercise bout. In protocol II, CVC was reduced from Control at L-NAME in the young and older adults during both (both P<0.01) and the first (P=0.05) exercise bout, respectively. Furthermore, SR was reduced from Control in the young (both P≤0.03) but not older (P=0.28) adults at the L-NAME skin site. However, no influence of Nor-NOHA+BEC or SNP was observed in either age group for both CVC (all P≥0.38) and SR (P=0.28). This thesis demonstrates that age-related increases in oxidative stress influence cutaneous vasodilation during exercise via mechanisms independent of NO. Furthermore, the current findings suggest an effect of oxidative stress on NO-independent SR in older adults but that secondary factors (i.e., aerobic fitness and/or physical activity level) may play a modulatory role. Finally, the results of this thesis demonstrate that, during exercise in the heat, neither elevated arginase activity nor changes in the sensitivity of the thermoregulatory end-organs to NO effect the CVC and SR responses in older adults.

Pigs exposed to elevated ambient temperatures exhibit reduced average daily gain, alterations in muscle and fat deposition during growth phases, and decreased overall health. Negative aspects of gastrointestinal (GI) function, integrity and permeability also result from hyperthermia. Saccharin-based artificial sweeteners have the potential to ameliorate the negative effects of heat stress (HS) by increasing GI GLP-2 production while capsicum oleoresin has been shown to reduce inflammatory response. Study objectives were to examine the effects of two artificial sweeteners, neohesperidin dihydrochalcone and saccharin, in combination with capsicum oleoresin (TakTik Sweet Heat , Pancosma, SA) on growth performance of pigs. Forty-eight pigs (12 weeks of age, 47.3 ± 7.6kg) were assigned to six treatments: thermal neutral conditions (21°C) fed ad libitum with (TN+) or without supplement (TN-), heat stress (35°C) fed ad libitum with (HS+) or without supplement (HS-), and thermal neutral conditions pair-fed to HS intake with (PFTN+) or without supplement (PFTN-). Dietary supplementation began 2 days prior to the 3-day environmental treatment period. Body weight was recorded on day -1 and day 3 relative to start of environmental treatment. Body temperature (BT) and respiration rate (RR) were measured thrice daily and feed intake (FI) were recorded daily. Blood samples were collected on day -1 and day 3 to determine metabolite profiles and immune response. Following sacrifice, sections of duodenum, ileum, and colon were collected for histology. Pigs in HS conditions had increased average BT and RR (~2.7-fold) compared to TN and PFTN groups (P<0.01). Irrespective of day, HS+ animals had increased respiration rates when compared to HS- animals (P<0.04). Heat stress decreased FI compared to TN groups. Regardless of treatment, supplement increased feed efficiency by 0.12kg (P<0.04). Circulating glucose concentration tended to decrease in HS+ and PFTN+ pigs compared to non-supplemented treatments (P=0.1). Circulating insulin increased in HS compared to PFTN (P<0.04), but did not differ from TN. Lymphocyte count tended to be decrease in HS compared to PFTN and TN (P=0.052). Monocyte count increased during HS compared to PFTN (P=0.01), but HS and TN did not differ. Supplement increased basophil count (P<0.03), irrespective of treatment. Ileal villus height tended to decrease during HS and PFTN compared to TN (P<0.08). Duodenal and colon villus height nor duodenal, ileal and colon crypt cell depth did not differ between groups. Overall, TakTik Sweet Heat supplementation increases pig feed efficiency and may improve immune response. / Master of Science

This study was done to examine the effects of supplementing electrolytes to heat stressed transitioning cows on dry matter intake (DMI), milk yield (MY), and blood metabolites. Overall, 104 Holstein and Jersey cows were utilized from August to September, 2012, and from August to November, 2013. Control (CON) cows were fed standard TMR and E+ cows received the same TMR plus 170 g of Bovine BlueLite. The DMI, MY and composition, rectal temperature, and respiration rate were monitored daily; while blood metabolites, body weight, condition score and frame size (withers height, hip height, and heart girth) were measured weekly. The DMI, MY and composition were not different among treatments. Health condition, body change, and blood chemistry were not affected by treatment. Electrolyte supplementation did not have any negative effects on performance of dry and lactating cows, but showed positive potential for alleviation of heat stress in the present study.

10 pp. / Upland cotton is vulnerable to heat stress during the summer monsoon season in the low desert of Arizona. The primary impact of heat stress is a reduction in fruit retention which can reduce overall lint yields, delay crop maturity and reduce lint quality. This bulletin provides a general overview of cotton heat stress as it pertains to Arizona production systems.

Purpose: This study aimed to expand our knowledge of the underlying mechanisms of orthostatic tolerance. First, cerebral perfusion was compared with reductions in orthostatic tolerance between normal thermic and heated conditions. The researchers' hypothesized that subjects with the greatest reduction in orthostatic tolerance will experience the largest drop in cerebral blood flow. Additionally, ANG II was measured in order to identify if during passive heating, the elevation in plasma ANG II is negatively correlated with heat-stress induced reductions in orthostatic tolerance. Lastly, orthostatic tolerance changes during the simulated hemorrhage between heat stress and normal thermic conditions will be compared to fitness level, measured by VO2 max. Results and Conclusion: Cerebral perfusion, as indexed by middle cerebral artery blood velocity, was reduced during heat stress compared with normothermia (P [less than] 0.001); however, the magnitude of reduction did not differ between groups (P = 0.51). In the initial stage of LBNP during heat stress (LBNP 20 mmHg), middle cerebral artery blood velocity and end-tidal PCO2 were lower; whereas, heart rate was higher in the large difference group compared with small difference group (P [less than] 0.05 for all). In opposition to the hypotheses, the large differences in tolerance to a simulated hemorrhage during normothermic and heat stress conditions are not solely related to the degree of heat stress-induced reduction in cerebral perfusion. Also, an individual's level of cardiorespiratory capacity (fitness) and/or the degree of heat stress-induced increase in plasma ANG II does not reliably predict the level of reduction in tolerance to a simulated hemorrhage challenge when heat stressed. / text