Effect of Hypobaric Hypoxia on Ascites Resistant and Susceptible Lines and Their Reciprocal F1 Crosses. 1. Pro- Duction Parameters and Ascites Mortality. Effect of Hypobaric Hypoxia on Ascites Resistant and Susceptible Lines and Their Reciprocal F1 Crosses. 2. Gut

s of papers 23 with ascites syndrome, reciprocal F1 crosses of the RES and SUS lines were produced. One objective of this multidisciplinary trial was to determine the effects of hypobaric hypoxia on gut development in the pure-line RES, pure-line SUS, and the reciprocal F1 crosses (RS, SR). Four hundred and eighty vaccinated, pedigreed broiler chickens (40 groups of 12 birds) were randomly assigned to cages in either a hypobaric chamber (simulated 2900 m above sea level) or a matching local altitude chamber (390 m above sea level). On Day 42, specimens of duodenum and distal ileum were collected from five chickens in each line at each altitude. Each sample of intestine was cut open longitudinally at the antimesenteric attachment. Sections were fixed, cut (5 μm) and stained with hematoxylin and eosin. From these stained sections, 10 measurements of villus height were made at random from different parts of each tissue slide using a reticle (100 mm divisions) placed in the eyepiece of the microscope. There were significant effects on gut development due to both altitude and genetic line. Villus height (mm) of the duodenum and ileum were greater across all lines at local altitude compared to the hypobaric chamber (P = 0.0001). Similar morphometric increases were observed in pure-line RES and F1 crosses when compared with pure-line SUS at local altitude (P = 0.0001). This study suggests that birds selected for ascites resistance also exhibit improved gut development and this improvement is maintained in their reciprocal crosses. Additionally, hypobaric hypoxia alone results in a significant reduction in gut development across all lines. This work was supported in part by the U.S. Poultry & Egg Association Project # 285 and Cobb-Vantress, Inc.