Call number: LD2668 .T4 1985 S336 / Master of Science

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Bovine mammary glands respond to infection by foreign pathogens such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) through changes in gene expression. Monitoring the gene expression profiles will contribute to better understanding of the pathology of mastitis, and provide important selective markers for future animal breeding programs. Using cultured bovine mammary duct epithelial cells and somatic cells from infected bovine mammary glands, this study first examined the existence of Toll Like Receptors in these two systems. In cultured duct epithelial cells stimulated with E. coli LPS, both TLR 4 and 2 mRNA up regulation was detected at 2h-72h and 12h-48h respectively. For S. aureus LTA TLR 2 mRNA was up regulated at 48 and 72h whereas for TLR 4 mRNA expression up regulation was detected at 24, 48, and 72h in comparison to the Oh (p<0.05). In the case of PGN, an abundant structural component of S. aureus, the expression of TLR 2 mRNA was significant (p<0.05) at 72h whereas TLR 4 mRNA expression increased at 24, 48, and 72h. The expression of these receptors was also monitored in milk cells from cows infected with either E. coli or S. aureus. However, results obtained from the milk cells were inconclusive due to the high individual variability. Afterwards, differential gene expression profiles were monitored by the Differential Display Polymerase Chain Reaction technique in the cultured duct epithelial cells in response to E. coli and S. aureus structural components. A total of 6 candidate fragments were identified for E. coli LPS induction, whereas only one fragment was identified for S. aureus LTA induction. After LTA induction, a specific band was found to be up regulated and confirmed to be GCP-2, a chemokine involved in neutrophil recruitment. In contrast, PGN induction resulted in no change in GCP-2 levels. In different preparations of cultured duct epithelial cells both GCP-2 and IL-8 were confirmed by real time PCR to be up regulated by LTA with a significance of (p<0.01) when compared to the control cells. In the case of the E. coli identified bands, a different approach is necessary to potentially confirm the origin of these fragments. Further large scale screening of the GCP-2 and IL-8 genes in dairy cattle is necessary to test for their potential use as targets to differentiate the mastitis resistant from the mastitis prone cows.

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.

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Fifteen calves of two sires were fed endophyte infected (E + ) fescue seed to quantify differences in susceptibility to fescue toxicosis among sire groups. One of the sires, a Polled Hereford, had a commercial reputation of producing calves with less severe symptoms of tall fescue toxicosis than their contemporaries. The control sire, also a Polled Hereford, had unknown merit with regard to offspring susceptibility to fescue toxicosis. The study was divided into five phases, two in which endophyte-infected fescue seed was included in the diet (phases two and four) and three in which fescue seed was not in the diet (phases one, three, and five). All calves were treated similarly and given the same opportunities for water, shade and socialization. Susceptibility to fescue toxicosis was measured by appetite (amount of feed consumed per day per unit of metabolic body weight), serum prolactin, cholesterol, and alkaline phosphatase concentrations, ability to maintain homeotherny (afternoon minus morning rectal temperature), ability to dissipate core body heat (afternoon minus morning surface temperature), and heat-transfer inefficiency (afternoon rectal minus afternoon surface temperatures). Appetite was decreased by the E + fescue seed, but the sire groups did not differ in their response to or recovery from E + fescue seed. The E + fescue seed caused prolactin to decrease (P < .0001) but the sire groups did not differ in their responses to addition or withdrawal of E + fescue seed from the diet. Cholesterol levels were lower overall (P < .001) when the E+ fescue seed was fed, and the sire groups recovered from the fescue toxicity at different rates (P < .001). Alkaline phosphatase concentrations were lower during the phases when E + fescue seed was fed; calves from the control sire were less resistant to the E + fescue seed effects than the Missouri calves (P < .0001). Ability to maintain homeothermy was reduced by the E + fescue seed, but the reduction did not differ between sire groups. Surface temperature changes and heat-transfer inefficiencies were not indicative of fescue toxicosis in this study. It was concluded that serum cholesterol and serum alkaline phosphatase concentrations may be accurate indicators of differences among paternal half sib groups of cattle in susceptibility to fescue toxicosis. / Master of Science