Date of Award

12-1999

Document Type

On-Campus Dissertation

Degree Name

Master of Science (MS)

Program

Epidemiology

Research Advisor

Elizabeth A. Tolley, Ph.D.

Committee

Andrew J. Bush, Ph.D. Timothy D. Mandrell, D.V.M. Linda A. Toth, D.V.M., Ph.D.

Abstract

This study was part of a long-term investigation of the effects of genotype on growth and reproduction in cattle grazing endophyte-infected (Neotyphodium coenophialum) tall fescue (Festuca arundinacea Schreb.) pastures (E+ fescue) with those grazing bermudagrass [Cynodon dactylon (L.) pers.] pastures (BG). Cattle grazing E+ fescue appear to have a higher prevalence of fat necrosis than do cattle grazing other forages. Thus, we hypothesized that factors in E+ fescue may be associated with changes in lipid metabolism as reflected in altered levels of circulating total cholesterol. Furthermore, different genotypes and various physiologic states of the animal, as well as the vegetative stages of the forage, may exaggerate or mitigate any such effects. Blood samples were obtained from 453 F1 Angus (AA), Brahman (BB), and reciprocal-cross (AB and BA) progeny, as well as the original P1 Angus and Brahman dams. Blood samples from steers were collected as weanlings through 14 mo. Heifers were sampled from weaning through their second-calf production stage. The F1 heifers were bred to Polled Hereford bulls and 135 F2 calves were sampled at weaning. Additionally, for their fifth calf crop the original P1 Angus and Brahman cows were bred to Beefmaster (BM) and Brahman (BB) bulls to produce 76 F1 calves of varying Brahman percentage. Data were used to evaluate the main and interaction effects of forage environment, genotype, and, if appropriate, calf crop, gender, and lactation on total cholesterol and lipoproteins. Generally, blood cholesterol levels of AB, BA, and BB F1 heifers were similar to each other over time. Grazing either E+ fescue or BG pastures, AA had lower blood cholesterol levels compared with the other genotypes. Grazing E+ fescue pastures lowered blood cholesterol levels in AA, but not the other genotypes, compared with grazing BG pastures. Lactation resulted in higher cholesterol levels in all genotypes. The association between the partial regression on rate of gain and serum cholesterol depended on ages and physiological states of the cattle, as well as season of the year and vegetative stages of the plant. Similar responses occurred among P1 Angus and Brahman cows, Hereford-sired F2 weanlings and Brahman- and Beefmaster-sired F1 weanlings. In general, these results support the hypotheses that (1) the consumption of E+ fescue may be associated with changes in circulating total serum cholesterol levels, and (2) genotypic differences and physiologic states of the animal, as well as vegetative stages of the forage, may exaggerate or mitigate these effects.

DOI

10.21007/etd.cghs.1999.0101

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