Differences in the mean plasma cholesterol levels of adult White Single Comb Leghorn cockerels were accentuated when a diet containing 10% hydrogenated vegetable oil and 1% cholesterol was fed for six days. The cholesterol levels promoted by the diet were found to be negatively correlated (p 0.05) with the amount of cholesterol excreted by the groups. The differences observed among groups in the rate of elimination of the excess cholesterol from the circulation were not found to be statistically significant. Variation in cholesterol absorption may therefore be responsible, in large measure for differences in the degree of hypercholesterolemia induced, by feeding a diet high in cholesterol. A significant correlation (p 0.01) between the amounts of cholesterol and saponifiable lipids excreted following the feeding of a high-fat, high-cholesterol diet suggests that the amount of dietary fat absorbed may be a major determinant of the amount of cholesterol absorbed. Subjection of cockerels to the feeding of a high-fat, high-cholesterol diet over a prolonged period resulted in an increase in lipid absorption. Cockerels which survived 410 days of feeding maintained throughout the test, a lower mean plasma cholesterol level than nonsurvivors. The blood vessels of survivors compared to nonsurvivors showed little evidence of atherosclerosis. / Land and Food Systems, Faculty of / Graduate

[No abstract available] / Land and Food Systems, Faculty of / Graduate

[No abstract available] / Land and Food Systems, Faculty of / Graduate

[No abstract available] / Land and Food Systems, Faculty of / Graduate

The extent to which egg weight modifies genetic differences in body-weight of the embryo and chick and the correlation between embryonic growth rate and post-hatching growth rate were investigated. This was done by studying the relationships between (1) egg weight and body weight of embryo and chick; (2) strain and body weight of embryo and chick; (3) strain and percentage growth rate of embryo and chick; and (4) the relationship between embryonic growth rate and post-hatching growth rate. This study was conducted on five strains and one strain-cross. Two of the strains were bred for meat, (White Plymouth Rock and White Cornish); two were bred for high egg production, (White Leghorns); and one was an intermediate type, (White New Hampshire). The strain-cross was derived from mating males of one White Leghorn strain with females of the other. Individual egg weights were recorded for over 2,200 eggs. Between nine and eighteen embryos of each category were weighed from each of two incubators from the ninth to the eighteenth day of incubation. Between fifteen and thirty-three chicks of each category were weighed at hatching and at weekly intervals for three weeks. Analyses of variance of embryonic weights, chick weights, and embryonic or chick weights expressed as percentages of egg weight were done. Analyses of variance were also done on embryonic and post-hatching growth rates. Coefficients of correlation (r) between egg weight and embryonic or chick weight and also coefficients of regression of chick weight on egg weight were computed. The correlation between embryonic and post-hatching growth rates was estimated. From the results of the above tests it was concluded that: (1) Differences in embryonic weights among the strains were due to differences in inherent genetic factors; (2) Egg weight exerted a temporary measurable influence on embryonic and chick weight, the effect being greatest at hatching; (3) Differences in post-hatching growth rate among the strains were probably due to differences in nutritional factors which contributed to a more efficient utilization of nutrients by the heavy type chicks; and (4) Approximately 65 per cent of the variation in post-hatching growth rate to three weeks of age was dependent on the variation in growth rate during the nine- to fourteen-day incubation period. The estimate of correlation between growth rate during these two periods was, however, not precise. / Land and Food Systems, Faculty of / Graduate

The crooked toes defect in chicken is an example of an aberrant polymorphic trait associated with inbreeding degeneration. The mechanism governing its expression is a property of balanced genotypes based on obligate levels of heterozygosity. Fixation of the trait was accomplished in California by a selection program combined with inbreeding in a Single Comb White Leghorn flock. The crooked toes line developed from this program was combined, in the present investigation, in crosses with genetically unrelated stock. Strain and breed (New Hampshire) crosses to the crooked toes line were made reciprocally and carried through the F₁, F₂ and backcross generations. Offspring from each cross were mated from the F₁ generation to establish four lines based on reciprocal parental matings. Comparisons were then made to determine the levels of incidence, the degree of phenotypic expression, the association of the trait with fitness and the effects of sex-linkage, maternal environment and inbreeding. Crooked toes were found to be a polygenic trait characterized by semi-dominance and variable penetrance. The trait is associated with a number of modifiers affecting fitness. Inbreeding per se increased incidence, and increased incidence was accompanied by increased expressivity. The behavior of matings between parents with varying degrees of crooked toe incidence was unpredictable. The appearance of the defect is determined to a considerable degree by the presence of a physiological threshold for its expression. An unsuccessful attempt was made to locate marker genes associated with aggregates of crooked toe determining loci. / Land and Food Systems, Faculty of / Graduate

An experiment was designed to test the hypothesis that enthalpy could be used as an indicator of the suitability of the environment for growing poultry. Growth-rates and body weights of the birds were used as a measure of their performance under different enthalpy conditions. The experiment tested three enthalpy treatments, ranging from 29.3 to 33.3 BTU/lb of air, each treatment being replicated three times. Male University of British Columbia New Hampshire chickens from nine hatches (120 birds per hatch) were used. They were grown from hatch to seven weeks of age in three groups. Two of the groups were raised from hatch to three weeks of age in controlled environment brooders. The third group was raised in a non-controlled environment in a floor pen, and used as a check or control group. The results of the analyses indicated that further study would be necessary before enthalpies in the range studied could be used to predict environmental conditions for poultry. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Male progeny of 15 sires each mated to 2 dams from the University of British Columbia's New Hampshire flock were reared in 2 environmental treatments, an environment chamber or a standard floor pen. Birds reared in the chamber were transferred to the floor at 3 weeks of age where they were reared with the birds of the floor treatment to 7 weeks of age. Six experiments were conducted involving a total of 339 birds. Individual body weights were recorded for the progeny at hatch and at weekly intervals until 7 weeks of age. Chamber temperatures were started at 95°F for experiment 1 and 90°F for experiments 2-6 and reduced 3°F every 3 days to 3 weeks. Relative humidity was held constant at 50%. Birds on the chamber treatment were heavier at 7 weeks of age than birds raised on the floor from hatch to 7 weeks. This difference was attributed to the high 1-3 week growth rate of chamber reared birds. Using multiple linear regression techniques the 1-3 and 3-7 week growth periods were found to be the important periods in accounting for the variability in 7-week weight for the floor and chamber birds respectively. Heritability estimates of body weight based on σ²s for floor and chamber birds were found to be high (0.82) and relatively the same between the 2 environmental treatments from hatch to 2 weeks of age. They diverged to 0 and 1 by the 5th week for the floor and chamber, respectively. The high heritability based on σ²s for chamber reared birds at the time of transfer was attributed to an increase in selectable genetic variance due to stress. The effect of stress after transfer was reflected in low growth rates during the 3-4 week period. Average 1-week weight, average 1-3 week growth rate and average 3-7 week growth rate were regressed on the heritability (based on σ²s) of 7-week body weight. For floor reared birds the early growth period was the important period in accounting for variability in heritability of 7-week weight while for chamber birds the 3-7 week growth period was the most meaningful period. It was concluded that the environment controls the variability of weekly growth rate and changes the importance of these growth periods in accounting for the genotypic variability in 7-week weight. In a theoretical selection program based on 7-week weight the percentage of progeny each sire contributed to the selected population depended upon the environment in which the progeny were reared. However a small number of sires were able to maintain their percentage contribution in both environments. For the floor treatment more selected birds had an above average 1-3 week growth rate than 3-7 week growth rate. For the chamber treatment more selected individuals had an above average 3-7 week growth rate than 1-3 week growth rate. Although growth rate from 1-3 weeks of age raised the mean 7-week weight of chamber birds, it was the individual’s ability to grow under the stress conditions which placed it in the selected population. Birds which were below average with respect to 1 or 2 of the traits, 1-week body weight, 1-3 week growth rate and 3-7 week growth rate were present in the population of birds which had been selected on the basis of 7-week body weight. The percentage of selected individuals carrying any particular combination of these traits depended upon the environment in which the birds were reared. It was concluded that selection based on individuals which were above average with respect to all 3 of the aforementioned traits as well as 7-week weight would improve the selection response when compared to selection based upon 7-week weight alone. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.