Commercial laying hens are heavily selected for increased egg production, but little selection has occurred for resistance to extreme temperatures. The objective of the experiment was to determine the effects of a daily cyclic heat stress (HS) on performance, body temperature, egg quality, nitrogen corrected apparent metabolizable energy, and blood chemistry in laying hens at acute and chronic time points. In total, 407 pure line laying hen pullets (18 wk) were sourced from Hy-Line International and housed individually for the duration of the experiment. Feed intake, egg production, and body weights were significantly decreased while egg weight and feed efficiency increased due to HS exposure. All egg quality parameters except yolk weight were decreased by HS exposure, including Haugh unit, eggshell and albumen weights. Egg yolk weights were increased over the first 2 wk of HS before falling. Blood chemistry was affected by HS resulting in respiratory alkalosis likely caused by increased respiration and evaporative cooling. There was a decrease in the PCO2, an increase in pH and a reduction in iCa in the blood within 4 to 6 hours of HS when compared to pre-HS levels. The data indicate that the hens were negatively affected by HS and the response was different for acute and chronic time points. At the acute time point the changes to the hen's physiology were caused by altered blood chemistry, but after chronic exposure, the low feed intake seemed to influence the responses. / Master of Science / High environmental temperatures can cause laying hens to become heat stressed, including reduced egg production, egg quality, and body weight, and in some cases increased mortality. Two mechanisms to reduce heat production and increase heat dissipation are reduced feed intake and increased respiration rate during heat stress. The reduced feed intake can result in insufficient nutrients to maintain egg production and increased respiration rate can change the blood chemistry, reducing ionic calcium and ultimately causing thinner eggshells. The most efficient way to reduce the negative effects of heat stress is by avoidance through controlling the environmental temperature, however, above certain temperatures cooling methods fail. If heat stress conditions are reached, it is important to understand the genetic ability of the hen to minimize the negative consequences of elevated temperature. Therefore, the effects of a four-week heat stress were determined with a focus on hen performance, egg quality, and blood chemistry parameters in laying hens. Some parameters such as blood pH and ionized calcium, shell weight, and body temperature were negatively affected within four to six hours while others, such as shell thickness, Haugh unit, and egg production took longer to be affected. By the end of the experiment blood pH returned to pre-heat stress levels but feed intake was significantly reduced over the 4 wk HS period. This could indicate that the laying hens began to acclimate to the high environmental temperatures but were not able to completely overcome the negative effects.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/73369 |
| Date | 02 November 2016 |
| Creators | Barrett, Nathaniel W. |
| Contributors | Animal and Poultry Sciences, Persia, Michael E., Schmidt, Carl J., Dalloul, Rami A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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