Graduate Thesis Or Dissertation
 

Genetic studies of reproductive and biochemical traits in turkeys (Meleagris gallopavo) divergently selected for semen ejaculate volume

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  • The genetic control of changes in unselected traits of Wrolstad Medium White turkeys divergently selected for semen ejaculate volumes (SEV) for 16 generations (G) was studied. Genetic parameters were estimated in G 10 to 14 for embryonic mortality (EM), the incidence of pipped eggs, and for total plasma cholesterol (PC) and high density lipoprotein cholesterol (HDLC) in 16-week old birds of G 15. An attempt at determining enzyme polymorphisms in the two lines was performed in G 16. A multivariate discriminant analysis procedure was established in an attempt to classify birds as low or high SEV based on fertility and incubation records in G 10 and 12. It was determined that a more reliable, yet flexible method of estimation of variance components for heritability of embryonic mortality in turkeys is a likelihood procedure. The mean heritability estimates were -.03 and .10 for embryonic mortality in the early (Days 1- 10) and late (Days 21-28), respectively. Estimates of heritability for the incidence of pipped eggs were .21 and .08 in the low and high lines respectively. Since there were no line differences (P>.05) for PC and HDLC, data was pooled from low and high SEV lines and h² was computed to be -.03 and .26, respectively. Genetic correlation among PC, HDLC, and 16 week body weight (BW) varied from .05 between PC and HDLC, .13 PC and BW and -.34 HDLC and BW. No polymorphisms were observed for the enzymes examined in the present study. The discriminant function developed to categorize birds as low or high volume semen producers, had a moderate (.55) to high (.75) hit ratio for classification of birds as low or high volume producers in G 10 and 12. It was concluded that divergence in unselected traits, embryonic mortality and the incidence of pipped eggs, in the low and high SEV lines had a negligible additive genetic control. Cholesterol, though a major intermediate in the biosynthesis of steroid hormones, in turkeys at 16 weeks of age is not a suitable biochemical marker for SEV. Although genetic control in turkeys appears to be negligible for PC, there is a moderate and significant hereditary influence on HDLC. With a misclassification rate of .30-.40, fertility and incubation records, as demonstrated here can be used to classify birds as low or high volume semen producers.
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