Graduate Thesis Or Dissertation

 

Analysis of laying house mortality in a line of single comb white leghorns Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s1784p44k

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  • The Oregon State University Production Line of Single Comb White Leghorns was under selection for increased henhoused egg production from 1947 through 1972. Since henhoused egg production is directly related to mortality, mortality would be expected to decrease over the years if selection was effective. To determine if the mortality had decreased and to gain a comprehensive view of the problem that mortality presents, the laying house mortality during a 23 year period, 1950 through 1972, was analyzed. Analysis of percent mortality in the flock between 20 and 68 weeks of age showed a decrease of slightly over fourtenths of a percent per year, about 10 percent during the entire period studied, or a 50 percent decrease from the original level. The average length of life in the laying house increased by about 16 days during the 23 year period. At 70 percent production this translates to 11 extra eggs in a 48 week laying period. Mortality was lowest in the early part of the laying year and reached its peak when the birds were between 57 and 60 weeks of age. Over three-fourths of the production time lost due to mortality occurred in the first half of the laying year. Leukosis claimed more of the flock than any other disease and most of the deaths from this disease occurred in the early part of the laying year. Marek's disease and non-leukotic tumors appeared to follow the same pattern as leukosis over the years. Other important diseases included dysfunctions of the urinary and digestive systems, vascular debilities, and cannibalism.
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