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Master of Science / Department of Agronomy / Krishna Jagadish / Post-flowering heat stress is one of the major environmental constraints for wheat (Triticum aestivum L.) production in the state of Kansas, where wheat is the most widely grown grain crop. Studies have shown that the optimal temperature for wheat grain development is approximately 21°C. During the grain filling stage for wheat in Kansas, it is fairly common for temperatures to reach more than 30°C and above. These scenarios have resulted in lower productivity and yield in Kansas compared to other regions of the United States. Therefore the objectives of this research project included: phenotyping seven Kansas varieties for post-flowering heat tolerance in a controlled environment growth chamber study as well as in two field experiments, estimation of spike and flag leaf senescence in wheat exposed to post-flowering heat stress, and identifying potential genetic donors for heat tolerance from winter wheat breeding lines and Near Isogenic Lines developed from Kansas State University’s Wheat Breeding Program. To impose heat stress in the controlled growth chambers, plants grown at 25°C were transferred to high day temperature (35°C) chambers ten days after the first sign of anthesis. Under field conditions, custom built “heat tents” were placed over the wheat plots ten days after first flowering and remained until maturity. Plants grown under heat stress exhibited early senescence, indicating a shorter grain filling period compared to the controls. Early-maturing varieties recorded greater percent reductions in grain yield under heat stress. Post-flowering heat stress induced significant reductions in thousand kernel weight, grain number, harvest index, and grain yield. Spike and flag leaves effective quantum yield of PSII was reduced more drastically under growth chamber stress exposure compared to field grown plants. Significant genetic variation in the spike and flag leaf senescence initiation and the differential rate of senescence among the seven tested varieties suggested the potential for considering this trait in breeding programs. Compared to the commercially relevant varieties, breeding lines varied less under heat stress with a few lines recording a greater degree of heat resilience and experienced little to no drop off in heat stress conditions compared to control. The reduced performance under heat stress for the seven varieties highlights the genuine need to explore wider genetic diversity, including wild wheat, to infuse greater resilience into ongoing wheat breeding programs. However, the results observed in the breeding lines indicate that introducing larger genetic diversity may aid in developing greater heat stress resilient wheat varieties for current and future changing climate.

Ventilated capsules (i.e. hygrometry) are widely used to measure time dependent changes in local sweat rate. Despite this, understanding of the reliability (consistency) of local sweat rate is limited to the forearm during mild hyperthermia. Further, extensive regional heterogeneity in sweating may render some regions more reliable than others. Knowledge of reliability has important implications for experimental design, statistical analysis and interpretation, yet it is relatively unknown. The purpose of this study was to determine local sweat rate across various regions of the body and the reliability of these responses, during increasing levels of hyperthermia. On three separate instances, fourteen young men (age: 24 [SD 5] years) donned a whole-body water perfusion suit to raise and clamp esopogheal temperature at elicit low (+0.6°C), moderate (+1.2°C) and high (+1.8°C) levels of heat strain. Local sweat rate was measured at the forehead, chest, abdomen, bicep, forearm, hand, quadriceps, calf, and foot via ventilated capsules (3.8 cm2). Absolute reliability was assessed using coefficient of variation (CV%) which quantifies the amount of error in a given measurement. Relative reliability was evaluated via the intraclass correlation coefficient (ICC); the consistency of an individual’s rank within a group during repeated measurements. At low heat strain, most sites demonstrated acceptable relative (ICC ≥0.70), and moderate absolute reliability (CV <25%). At moderate-heat strain, the abdomen, hand, quadriceps, calf and foot had acceptable relative reliability while the forehead, abdomen, forearm, hand and quadriceps had moderate absolute reliability. At high-heat strain, relative reliability was acceptable at the abdomen, quadriceps, calf, foot and absolute reliability was moderate at the chest, abdomen, forearm, hand, quadriceps, calf and foot. Our findings indicate that reliability of local sweat rate is dependent on both measurement site and level of hyperthermia. Researchers should consider this in their experimental design to increase the likelihood of detecting an effect of an intervention if one exists.

Heat stress (HS) induces hyperinsulinemia and hypoglycemia in lactating dairy cows. We hypothesized that γ-aminobutyric acid (GABA) participates in the regulation of this altered glycemic state as it is produced by the pancreatic beta cells and has a stimulatory effect on pancreatic secretion of insulin. Multiparous lactating Holstein cows (n=6; 63.33±2.35 DIM, 3.17±0.40 lactations) were placed in environmentally controlled rooms for four experimental periods: 1) thermoneutral (TN; d 1-5; 18±4°C), 2) TN + hyperinsulinemic-hypoglycemic clamp (HHC; d 6-10), 3) heat stress (HS; d 16-20; 33±4°C), and 4) HS + euglycemic clamp (EC; d 21-25). Cows were milked twice daily, and blood samples were collected once daily via coccygeal venipuncture into heparinized evacuated tubes. Plasma GABA concentrations were determined using a competitive ELISA. The data were analyzed in two ways. The first analysis included data from all treatment periods and yielded no period-based differences in plasma GABA concentrations. In this analysis, plasma GABA was lowly correlated to plasma insulin concentrations (r = -0.29, P<0.01). The second excluded data from HHC and EC periods so that GABA concentrations during TN were directly compared to concentrations during HS. In this analysis, plasma GABA concentrations tended to be higher in TN than HS (16.31±2.14 vs 13.80±2.15 ng/ml, respectively, P = 0.06). Milk production was moderately correlated with plasma GABA (r=0.42, P<0.01) and the average plasma GABA during TN and HS was moderately correlated to baseline glucose levels for those periods (r=-0.57, P=0.05). Furthermore, the percent change in plasma GABA was strongly correlated with the percent change in plasma glucose from TN to HS (r=-0.95, P<0.01). Plasma GABA was again lowly correlated to plasma insulin concentrations (r = -0.35, P = 0.01). While these analyses are not indicative of causality, the results suggest that GABA is involved in the regulation of the altered glycemic state observed during HS. More research is needed to determine its precise role in heat-stressed lactating dairy cattle. / Master of Science / Heat stress causes large annual financial losses for the dairy industry and presents potential welfare issues for dairy cows when they can no longer cope appropriately with their environment. As climate change continues, the intensity and duration of heat stress experienced by dairy cows will increase which will cause the effects of heat stress on the dairy industry, as well as on the wellbeing of dairy cows, to become more significant. For this reason, it is important to understand the physiological processes underlying a cow's adaptive response to heat stress to improve future farm management in a changing climate. It is well documented that heat stressed dairy cows experience an increase in plasma insulin concentrations, as well as a concurrent decrease in plasma glucose concentrations. It is not well understood how or why these changes occur, but ɣ-aminobutyric acid (GABA) is known to be secreted from the same cells that secrete insulin and to have effects on the secretion of insulin, as well as on concentrations of glucose in the blood through effects on pancreatic glucagon secretion. This work began the process of determining the physiological mechanism behind these changed concentrations by determining how plasma GABA changes during heat stress in lactating dairy cows and how those changes are related to other physiological changes observed during heat stress. It was determined that plasma GABA tends to decline during heat stress and is significantly related to milk production, as well as blood glucose concentrations. While these results cannot be taken without more research to imply cause, they do support the idea that GABA plays a role in coordinating the altered glycemic state observed in heat stressed dairy cattle and would be an interesting research target in the future.

Heat stress (HS) causes significant losses to the U.S. swine industry in several production and health areas including efficient lean tissue accretion. Perturbations in skeletal muscle metabolism may participate in this defect. The study objectives were to examine the cellular bioenergetic profile in skeletal muscle of piglets subjected to thermal stress in utero and/or during postnatal life. To accomplish this, 96 offspring from 14 sows were prenatally exposed to 1 of 4 environmental treatments involving thermal neutral (TN, 25°C) or HS conditions (cyclical 28-34°C). Sows exposed to TN or HS throughout gestation are denoted TNTN and HSHS, respectively whereas sows heat-stressed for the first or second half of gestation are denoted HSTN and TNHS, respectively. At 14 weeks of age, offspring were exposed to one of two postnatal thermal environments, constant TN (21°C) or HS (35°C) for 24 hrs (acute study) or 5 weeks (chronic study). Pigs were sacrificed after treatment and longissimus dorsi skeletal muscle samples collected for molecular analyses. Differences (p<0.05) were observed in protein abundance of p-4eBP1 and total Rs6 and gene expression of Cox5B, CytB, EEF2, HK2, MURF, ND1, PGC-1α, SDHA, and TFAM during the acute heat stress study. Differences (p<0.05) were observed in protein abundance of 4eBP1, total Akt, and p-Rs6 and gene expression of CytB, MURF, and PGC-1α during the chronic heat stress study. These data indicate that acute postnatal HS alters skeletal muscle metabolism, which may favor a reduction in mitochondrial respiration and protein synthesis potentially via the mTOR pathway. / Master of Science

The US dairy industry loses approximately $1.2 billion due to heat stress related production losses annually. It was formerly believed that heat-stressed lactating dairy cattle produce less milk because they consume less feed. It has since been established that the reduction of feed intake is only responsible for about 50% of the reduced milk yield in HS cows. It is believed that HS increases gastrointestinal permeability (GIP), resulting in microbial components leaking from the lumen of the gastrointestinal tract into underlying tissue and stimulating an immune response. The immune response is suspected to alter overall metabolism, and milk production specifically, by diverting nutrients away from the mammary gland and other non-essential processes to support immune system activation. Topics examined herein focus on identifying markers to assess gastrointestinal permeability and the influence of heat stress on GIP and nutrient metabolism. The first study utilized an in vitro rumen fermentation system to determine if lactulose, sucralose, and D-mannitol could persist in an in vitro rumen culture. Lactulose could not be quantified in the rumen fluid matrix, D-mannitol was rapidly degraded, and sucralose concentrations did not change after 48 h of incubation, establishing sucralose as an indigestible marker in mature ruminants. The second study utilized a pair feeding design to directly assess the effect of HS on GIP, milk yield, and immune activation by lipopolysaccharide (LPS). HS cows (n=7) were exposed to a temperature-humidity index (THI) value of 74-80 for 4 d. The pair-fed thermoneutral cows (PFTN, n=8) were exposed to a constant THI of 64 with their intake matched to the HS cows. HS lowered milk yield without altering GIP, measured using orally dosed sucralose as a permeability marker, or eliciting an LPS related immune response. Jejunal mucosal scrapings were harvested from each cow, tight junction proteins were quantified, and no differences were detected. Lack of treatment responses in GIP marker recovery and tight junction protein abundance indicate that increased GIP may not be a driving force behind production losses in HS dairy cows. The third study focused on energy substrate utilization during HS with the objective of determining if tissue-level energy substrate metabolism could be influencing glucose sparing mechanisms. Metabolic flexibility of skeletal muscle, liver, and mammary tissue was assessed after 4 d of HS. It was determined that HS reduced skeletal muscle metabolic flexibility and did not alter liver and mammary metabolic flexibility. This indicates that skeletal muscle has a greater dependency on glucose as an energy substrate, which may decrease the pool of glucose available for lactose synthesis in lactating cows. Finally, the last study had the objective of assessing branched-chain amino acid (BCAA) requirements during HS. BCAA are oxidized for ATP synthesis in extrahepatic tissues and provide precursors for the biosynthesis of non-essential amino acids. They are also taken up by the mammary gland at a rate greater than what they are used in milk protein. Taken together, it was hypothesized that BCAA requirements may be increased during HS. BCAA entry rates into blood were assessed using a stable isotope approach and a 4-pool model. No differences were detected in daily entry rates or flux rates between pools indicating no change in requirements. When considering the results of all studies, reductions in milk yield are likely a result of altered macronutrient metabolism but further work is needed to confirm that hypothesis. Understanding the physiology behind HS related production losses is the first step in developing mitigation strategies. / Doctor of Philosophy / Heat stress (HS) is a global issue that compromises dairy cattle welfare and reduces milk production. On average the US dairy industry loses approximately $1.2 billion due to heat stress related production losses annually. With the global population expected to exceed 9 billion by 2050, strategies to mitigate HS related production losses are needed. Although cows exposed to HS conditions eat less food, that only explains about 50% of the production losses. It is hypothesized that the other 50% of milk yield losses is at least partially caused by increased gastrointestinal permeability (GIP), which elicits an immune response. Questions examined herein primarily focus on quantification of physiological and metabolic responses to HS. The objective of the first study was to identify a marker to assess GIP we could give orally to cows and detect in their urine. Commonly used GIP markers used in monogastric are carbohydrates, which have the potential to be fermented in the rumen. Sucralose was identified as a suitable marker due to its resistance to degradation in the rumen. The next study focused on measuring physiological responses of lactating dairy cows when exposed to HS conditions. Under the conditions of our experiment, HS decreased dry matter intake and milk yield without increasing GIP or inducing an immune response. It was determined that the reduction in dry matter intake was responsible for 66% of the reduced milk yield with the other 34% being associated with physiological changes other than increased GIP. The next study focused on how HS impacts the ability of skeletal muscle, mammary, and liver tissue to utilize glucose or palmitic acid as an energy substrate. The ability to switch between energy substrates is called metabolic flexibility. It was found that HS lowered the ability of skeletal muscle because it was unable to utilize fat as an energy source. Mammary and liver tissue exhibited no change in metabolic flexibility. The final study focused on how HS changed branched-chain amino acid (BCAA) plasma entry rates into plasma. An in vivo stable isotope method and a 4-pool mathematical model was used to predict how BCAA moved between pools which corresponds to the rate of protein turnover. Under the conditions of this experiment, no differences in BCAA entry rates were observed. Overall, results indicate altered energy substrate metabolism independent of immune activation stemming from altered GIP may be a driving factor in HS related production losses. Overall, this work contributes to understanding of HS biology and questions the established belief that increased GIP resulting in immune activation is responsible for about 50% of production losses.

Cooling systems used to reduce heat stress in dairy operations require high energy, water usage, or both. Steady increases in electricity costs and reduction of water availability and an increase in water usage regulations require evaluation of passive cooling systems to cool cows and reduce use of water and electricity. A series of experiments were conducted to evaluate the use of heat exchangers buried as components in a conductive system for cooling cows. In the first experiment six cows were housed in environmentally controlled rooms with tiestall beds, which were equipped with a heat exchanger and filled with 25 cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per each kind of bedding material) constituted a control group (water off), and the other 4 (2 sand and 2 dried manure) used water at 7°C passing through the heat exchangers (water on). The experiment was divided in 2 periods of 40 d, and each period involved 3 repetitions of 3 different climates (hot and dry, thermo neutral, and hot and humid). Each cow was randomly assigned to a different treatment after each repetition was over. Sand bedding remained cooler than dried manure bedding in all environments and at all levels of cooling (water on or off). Results from this experiment demonstrated that bed temperatures were lower and heat flux higher during the bed treatment with sand and water on. We also detected a reduction in core body temperatures, respiration rates, rectal temperatures, and skin temperatures of those cows during the sand and water on treatment. Feed intake and milk yield numerically increased during the bed treatment with sand and water on for all climates. No major changes were observed in the lying time of cows or the composition of the milk produced. The efficiency of conductive cooling as a heat abatement technique in dairy production is highly correlated with the distance between the cooling system and the skin of the cow and the type of bedding material used. A second experiment was conducted to identify possible improvements in the utilization of conductive cooling for cooling cows. Heat exchangers buried 12.7 cm below the surface as components in a conductive system ware evaluated in this study. Six cows were housed in environmentally controlled rooms with tie-stall beds, which were equipped with a heat exchanger and filled with 12.7 cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per bedding material type) constituted a control group (water OFF), and the other four (two sand and two dried manure) used water at 7°C passing through the heat exchangers (water ON). The experiment was divided into two periods of 40 days and each period involved three repetitions of three different climates hot dry (HD), thermo neutral(TN) and hot humid (HH). Each cow was randomly assigned to a different treatment after each repetition was over. The sand and water on treatment was the most efficient treatment under heat stress conditions (humid or dry heat). Cows in stalls with the sand and water on treatment demonstrated lower rectal temperatures, respiration rates, skin surface temperatures and core body temperatures compared to the other three treatments. Additionally, the sand and water on treatment increased milk yield and resting time of cows under heat stress. Also, the sand and water on treatment had the lowest bed surface temperatures and highest heat exchange compared to the other treatments. From these two experiments we confirm that heat exchangers are a viable heat abatement technique that could reduce the heat load of heat stressed cows; however, this system should be paired with additional cooling systems (e.g. fans and or misters) to most efficiently reduce the negative effects of heat stress on dairy production. Additionally, Sand was superior to dried manure as a bedding material in combination with heat exchangers. To make further recommendations of the use of heat exchangers in commercial dairy farm, a third study was developed. Based on the data obtained in the previous experiments, a comprehensive energy balance was developed to fully understand conductive cooling in two different environments (HD and HH), two bedding materials (sand and dried manure) and two depths between cows and the heat exchangers (25 vs. 12.5 cm). The energy balance estimates indicated that sand is the most efficient bedding material when utilized as bedding material with conductive cooling in both hot dry and hot humid environments. In the hot-dry environment there was an increase in the conductive heat exchanged with the reduction in bedding depth to 12.5 cm, however this did not result in a reduction in the heat storage of cows. In the hot-humid environment when heat exchangers were placed 12.5 cm from the top of the bed there was an increase in both the conductive heat loss and heat storage of cows when compared to 25 cm. Additionally, results demonstrated that the efficiency of heat exchangers as measured by heat flux was improved when heat exchangers were at a depth of 12.5 cm. The sensibility analysis indicated that a reduction in the depth and/or an increase in the thermal conductivity of both bedding materials would maximize conductive heat exchange. These results should be utilized as recommendations for the utilization of heat exchangers and conductive cooling in commercial dairy farms. Evaporative cooling is widely used in dairy farms located in arid environments. Even though, these cooling systems have been shown to effectively reduce the heat stress of lactating dairy cows, a growing shortage of water and rising cost of electricity compromise its future usage. An experiment was developed to compare two evaporative cooling systems, their interaction with lactating dairy cows and their usage of natural resources. The efficacy of 2 evaporative cooling systems (Korral Kool, KK, Korral Kool Inc., Mesa, AZ; FlipFan dairy system, FF, Schaefer Ventilation Equipment LLC, Sauk Rapids, MN) was estimated utilizing 400 multiparous Holstein dairy cows randomly assigned to 1 of 4 cooled California-style shade pens (2 shade pens per cooling system). Each shaded pen contained 100 cows (days in milk = 58 ± 39, milk production = 56 ± 18 kg/d, and lactation = 3 ± 1). Production data (milk yield and reproductive performance) were collected during 3 months (June–August, 2013) and physiological responses (core body temperature, respiration rates, surface temperatures, and resting time) were measured in June and July to estimate responses of cows to the 2 different cooling systems. Water and electricity consumption were recorded for each system. Cows in the KK system displayed slightly lower respiration rates in the month of June and lower surface temperatures in June and July. However, no differences were observed in the core body temperature of cows, resting time, feed intake, milk yield, services/cow, and conception rate between systems. The FF system used less water and electricity during this study. In conclusion, both cooling systems (KK and FF) were effective in mitigating the negative effects of heat stress on cows housed in arid environments, whereas the FF system consumed less water and electricity and did not require use of curtains on the shade structure. Results of this research indicate that effective use of conductive cooling in combination with efficient evaporative cooling systems offer opportunities to reduce both water and electricity consumption on dairy farms under both hot dry and hot humid environments.

No description available.

Occupationally induced heat-related illnesses (HRI) can play a huge part in the lives of employees working within outdoor kitchens. According to the National Institute for Occupational Safety and Health [NIOSH] (2016), “exposure to heat can result in injuries, disease, reduced productivity and death”. When working in outdoor environments, it is important to limit exposure time of direct sun or heat as well as to stay properly hydrated. One way to ensure limited occupational heat exposure is by measuring the Heat Index of the worker's environmental conditions. The purpose of this study is to determine whether there was a difference between the indoor and outdoor Heat Index measurements among various kitchens. Multiple locations within eight, freestanding, take-away service kitchens were sampled over a period of three days. A 3M QUESTemp 46 Heat Stress Monitor was used to sample the outdoor and indoor environmental conditions, specifically capturing the indoor Heat Index measurements. The outdoor Heat Index was reported with meteorological data from Weather Underground linked to the National Weather Service. Multiple statistical analyses were performed to understand and explore the relationships between or among the difference of indoor to outdoor Heat Index measurements, as well as kitchen production levels and forced air ventilation. The results showed that higher production kitchens had a significantly greater increase in Heat Index compared to low production and high production kitchens with forced air ventilation. Due to the small sample size of this study, it is recommended that future efforts to compare indoor and outdoor Heat Index measurements for kitchens include a larger sample size of both kitchens and locations.

The objective of this study was to evaluate the effects of heat stress and varying levels of milk replacer on dairy calf performance. Holstein bull calves ≤ 2 d of age were randomly assigned housing, outside under a covered area, heat stress (HS), or inside a controlled environment, non-heat stress (NHS), to test for heat stress effects on growth. Calves were also assigned to one of three feeding strategies: increasing amounts of milk replacer from 1.1% body weight (BW) to 1.5% BW (INC), constant at 1.1% BW (CON), or decreasing from 1.6% BW to 1.2% BW (DEC), adjusted weekly, commencing on day 9 of feeding and ending on day 40. Milk replacer amounts were adjusted twice weekly after weighing. Calves had ad libitum access to commercial starter feed and water. Starter intake, water intake, and fecal score (1 to 4) were recorded daily. Respiration rates and rectal temperatures were recorded twice daily at 0600h and 1800h. Average daily gain was greater (P < 0.01) for NHS (0.79 ± 0.03 kg/d) compared to HS (0.66 ± 0.03 kg/d) The NHS calves consumed more starter (P < 0.01) than HS (1.77 vs 1.16 ± 0.06 kg/d. Water consumption averaged 3923 ± 105 mL/d for HS which was greater (P < 0.01) than NHS (2338 ± 105 mL/d). No significant differences were observed among the feeding treatment groups for weight gain (P = 0.73). Milk replacer levels had a significant impact (P < 0.01) on the amount of calf starter consumed with CON consuming the most (1.64 ± 0.07 kg/d), followed by INC (1.44 ± 0.07) and DEC consuming the least (1.34 ± 0.07 kg/d). Water intake was also significantly impacted by milk replacer levels (P < 0.01). Calves in the DEC group consumed the least amount of starter, and consumed more water (3657 ± 129 mL/d) than both INC calves (3119 ± 129 mL/d) and CON calves (2614 ± 129 mL/d). Overall, housing has an impact on growth in neonatal dairy calves; however, milk replacer levels did not impact growth of the calves.