Effects Of Modified Insulin Resistance On Glucose And Fatty Acid Metabolism During Late Gestation In Dairy Cattle
In dairy cattle, insulin resistance of peripheral tissues during the transition from pregnancy to lactation is a normal adaptation to spare glucose for the gravid uterus and mammary gland. Exaggerated insulin resistance, a potential factor in overfed dry cows, may contribute to excess mobilization of adipose tissue in early lactation. The objectives were to determine the mechanism by which an insulin sensitizing agent (2,4-thiazolidinedione; TZD) and plane of nutrition (PON) can affect the metabolic health of transition cows. In experiment one, plasma leptin and tumor necrosis factor-[alpha], and adipose tissue peroxisome proliferator activated-[gamma] (PPAR[gamma]) mRNA were increased by prepartum TZD administration. The effects of PON and feed deprivation on insulin responses were measured in experiment two via glucose tolerance test (GTT) and hyperinsulinemic-euglycemic clamp (HEC) techniques. Cows subjected to high and low PON and then subjected to feed deprivation had different responses in glucose and lipid metabolism as measured by both GTT and HEC. The effects of feed deprivation were much greater than PON. Cows deprived of feed had much slower clearance of glucose during GTT, suggesting greater insulin resistance. Following feed deprivation, cows had greatly attenuated insulin response to GTT. In the final experiment, the effects of both PON and TZD were investigated using GTT, insulin challenge (IC), and adipose tissue mRNA analysis. There were differential effects of PON on glucose and fatty acid metabolism such that cows fed a lower PON had smaller glucose but larger NEFA responses following GTT. The only significant interactions of PON and TZD administration were that plasma NEFA responses were most dramatic for cows treated with TZD and fed lower PON. While TZD administration or diet did not affect fatty acid synthase, leptin, TNF[alpha], or adiponectin mRNA expression, the higher energy level diet increased mRNA of PPAR[gamma] and lipoprotein lipase. It is possible that these effects and interactions of diet and TZD would be more dramatic closer to the time of calving. Results from GTT and IC indicate that PON and insulin-sensitizing agents affect glucose and lipid metabolism during the dry period, which may have implications for the transition period.
Dairy cattle; Insulin; Thiazolidinedione
Overton, Thomas R
Qi, Ling; Bauman, Dale Elton; Boisclair, Yves R; Long, Qiaoming
Ph. D., Animal Science
Doctor of Philosophy
dissertation or thesis