Browsing by Subject "Heat Stress"
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Item Adjusting Milk Replacer Intake During Heat Stress and Non-heat Stress as a Means of Improving Dairy Calf Performance(2012-07-16) Chavez, Theresa MarieThe 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.Item Mitigating Heat Stress on Dairy Farms during Three Phases of Production(2009-05-15) Carter, Boone H.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.Item Understanding the Genetic Interactions that Regulate Heat and Drought Tolerance in Relation to Wax Deposition and Yield Stability in Wheat (Tricticum Aestivum L.)(2014-04-08) Huggins, Trevis DWheat (Triticum aestivum L.) has been a major food crop for nearly 8000 years. Breeders continue to face an ongoing battle to produce stress tolerant cultivars that are able to feed a rapidly increasing global population. The ability of varieties to perform similarly in grain yield across various environments is an important trait that is critical to successfully keep up with food demands with decreasingly available arable lands. The work described in this dissertation focused on defining and understanding the genetic interactions of epicuticular wax and high temperature and drought tolerance and its association with yield stability, to better aid breeders in stress tolerance selection. The effect of high temperature on epicuticular wax, yield attributes and yield stability were investigated in a recombinant inbred line population of 180 individuals from a Halberd x Len cross by physiological and molecular techniques. Epicuticular wax offers advantages in protecting the plant from both biotic and abiotic stresses. Under HT conditions, EWL can reduce chlorophyll fluorescence by reflecting excess irradiation and also reduce stomatal conductance, helping to regulate the rate of transpiration. QTL for epicuticular wax with large effects were detected on chromosomes 2A, 2B, 3A, 6B, and 7A. A large effect QTL for epicuticular wax was detected in three field environments on chromosome 2B (QWax.tam-2B.1) with the favorable alleles contributed by Halberd. QTL for yield stability and yield components stability indices with large effects were detected on chromosomes 1A, 1B, 2A, 2B, 3B, 6B, and 7A. A large effect QTL for yield stability was detected by five stability statistics over diverse field environments on chromosome 1B (Qyieldss.tam-1B) with Halberd contributing the favorable alleles. High EWL may promote stable yields but its sensitivity to environmental conditions makes it challenging to definitively point to it as a source of improved stability. Although there were mixed relationships with yield performance and environments, the stability statistics QTL provide strong evidence that genetic variation may be heritable and could have implications for breeding programs targeting a set of environments rather than a single environment.