Corticosteroid Induced Changes in Plasma Amino Acids and Thyroid Activity in Dairy Cows Treated Early or Late During Lactation

Abstract

The effect of a single injection of flumethasone (6α, 9α-difluoro-16α-methyl-11β, 17α, 21-triol-l, 4-pregnadien-3, 20-dione) or dexamethasone TMA (9α-fluoro-16α-methyl-11β, 17α, 21-triol-l, 4-pregnadien-3, 20-dione 21-trimethylacetate) at their optimal clinical doses, for ketosis treatment (2.5 and 15mg) on the plasma amino acid pool and on thyroid function was studied in dairy cows early and late in lactation.Both corticosteroids temporarily increased most amino acid in the plasma. Quality and quantity of the responses were significantly dependent upon the steroid administered and stage of lactation. Flumethasone superseded dexamethasone TMA in mobilizing glucogenic amino acids. Significantly more amino acids, taurine, serine, glutamine, glycerine, valine, methionine, isoleucine, leucine, tyrosine and phenylalanine were found early in lactation.Simultaneously, there were nearly uniform increases in total plasma iodine and protein bound iodine for 12 to 24 hours, followed by decreases 36 to 72 hours after injection, which were more pronounced early in lactation. The total plasma iodine mobilizing effect of flumethasone lasted about 12 hours longer in both stages of lactation. There were significant differences in total plasma and protein bound iodine base levels between stages of lactation, being highest post-partum.