Between April 2006 and February 2008, metabolic profile, milk constituents and plasma long chain fatty acids (LCFA) profiles were assessed every 8 week intervals on individual blood and milk samples from thirty five dairy cows (27 Simmental and 8 Holstein Friesian cows, with lactation number from 1 to 6) selected from a dairy herd. Body condition score (BCS) and back fat thickness (BFT) were done at the same day of blood sampling as well. Assessment of the variability of blood metabolites, milk composition and body condition in relation to the influences of lactation stage, season of the year and parity of was the main objective of this study.
Stage of lactation (early up to 100 day, mid from 100 to 200 day, late from 200 to 300 day in milk and dry cows) markedly influenced blood metabolites including plasma long chain fatty acids, milk composition and body condition in both Simmental and Holstein Friesian (HF) dairy cows. All studied blood metabolites are significantly influenced by stage of lactation except serum phosphorus, zinc, short chain carnitine and from milk metabolites milk fat, milk fat:protein quotient no lactation stage effect was noted in Simmental cows. However, in Holstein cows serum GGT, bilirubin, calcium, Mg, Cu, Zn, Milk fat:protein quotient, plasma free, short chain, and total carnitine showed no significant differences in relation to stage of lactation. There were significant increases in serum glucose, urea, milk protein (p<0.001), milk urea with the advancement in lactation in both breed. Milk fat increased significantly in HF and numerically in Simmental cows with the progress of lactation. Both serum total cholesterol and serum bile acids were significantly higher during the whole lactation (early, mid and late lactation) and lower in dry Simmental cows however cholesterol was higher in mid lactation and lower in early and dry cows in HF cows. A significant increase was noted for both BCS and BFT in late lactation and dry cows in both Simmental and HF cows. Furthermore, there were substantial decreases in serum ßHBA, AST, total protein, bilirubin, Mg with the progress of lactation in Simmental cows, while, ßHBA decreased with the advancement of lactation and AST activity decreased in dry period in HF cows. Plasma total and free L¿carnitine significantly increased in dry than lactating Simmental cows and not affected in HF cows.
Dairy cows / blood profile / lactation stage / number of lactation / season / milk constituents / body condition