Thesis (M.Sc.)--University of Alberta, 1997. / Submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Master of Science, Department of Agricultural, Food and Nutritional Science. Also available online.

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Lactating cows with cannulae in the rumen and proximal duodenum were used in two 4 X 4 Latin square experiments to evaluate biohydrogenation, flow rates, and digestibility of dietary fatty acids in the gastrointestinal tract. In the first experiment, four cows were fed diets with 0% supplemental fat, 3% tallow, 3% partially hydrogenated tallow, or 3% tallow coated with casein and corn syrup solids. Fatty acid intake and flow to the duodenum increased with fat supplementation. Total tract apparent fatty acid digestibility was reduced by partially hydrogenated tallow. Apparent digestibility of C_18:0 in the small intestine quadradically decreased (R²=.86) as C_18:0 flow to the intestine increased. Fat supplementation increased milk production and decreased milk protein percent but did not affect milk fat percent or 3.5% FCM. Fat supplementation increased C_18:0 and C_18:1 and lowered C_12:0 and C_14:0 concentrations in milk fat. In the second experiment, four lactating Holstein cows were fed diets with 0% supplemental fat, 3% partially hydrogenated fatty acids, 1.5% fish oil plus 1.5% stearic acid, or 1.5% soybean oil plus 1.5% partially hydrogenated soybean oil. Fish oil decreased DM intake. Fish oil and soybean oil reduced biohydrogenation of C_18:1 + C_18:2 + C_18:3 in the rumen from 65% (control) to 28% and 55%, respectively, and increased trans C_18:1 flow from the rumen 4-fold. Milk fat percent was decreased by fish oil and soybean oil. Milk fat percent across treatments linearly decreased with amount (g/d) of trans C_18:1 flowing to the duodenum (R²=.92) and percent trans C_18:1 in milk fat (R²=.94). / Master of Science

Extensive emphasis on selection for milk yield with minimal attention to the animals' functional performance has increased the yield of North American dairy cattle. The high intensity of selection for production traits such as milk yield, protein yield and fat yield has also brought about a rapid increase in genetic relationships among animals. In dairy cattle, correlated response to selection for milk yield includes fertility and susceptibility to diseases. Although the high producing cows have greater net profit, they also have higher mammary and discarded milk costs associated with high production. Long-term genetic selection against clinically diagnosed diseases might be useful to diminish their incidence. The Scandinavian countries have incorporated the health traits into their selection indices. Canadian breeding programs realize the need to consider traits other than the yield in selection decisions. The objective of this study was to determine the genetic variability of various clinically diagnosed health traits. Data from 171 herds of the Ontario milk-recording program were used. These herds are collaborating with the University of Guelph (Dr. David Kelton) to record health traits. A major impediment to estimating heritabilities for the majority of the disorders was that the progeny group size per sire was not large enough to enable detecting a significant difference among sires. Hence, heritability estimates were not obtained for all the health disorders included in the study. The progeny group size per sire has to be increased such that there are at least 5 cases per progeny group to enable detecting a difference among sires. Heritability estimates for retained placenta and displaced abomasum in the first lactation were 0.067 and 0.212 respectively. The heritability estimate of cystic ovaries in the second lactation was 0.092. In the third lactation, the heritability estimate of mastitis was 0.10 whereas retained placenta had a heritability of 0.25.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 44-49). Also available on the World Wide Web.

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