Abstract:
Dietary effects on circulating concentrations of some blood metabolites were assessed in Holstein-Friesian cows in early lactation. Thirty-two lactating cows were randomly assigned to receive four diets differing in dry matter intake (DMI) and metabolizable energy (ME) density, namely low dry matter and metabolizable energy (LL), low dry matter and high metabolizable energy (LH), high dry matter and low metabolizable energy (HL), high dry matter and high metabolizable energy (HH), and concentrations of some blood metabolites determined. At the end of the 5-week study, the level of insulin-like growth factor-I (IGF-I) was higher (P < 0.001) in cows on diet HH than those on diets HL, LH, or LL. The glucose concentration was higher (P < 0.001) in cows on HH and LH than those on HL and LL diets, while those of non-esterified fatty acid (NEFA) were similar in cows on the four dietary treatments. Cows fed HL and LL diets recorded higher (P < 0.001) beta-hydroxybutyrate (BHB) concentrations than those on the HH or LH diets. Urea concentration was higher (P < 0.001) in cows on LL than that of their counterparts on the other diets. IGF-I was positively correlated (P < 0.01) with glucose, but negatively related with BHB (P < 0.01) and urea (P < 0.05). Glucose was negatively correlated with BHB (P < 0.01) and urea (P < 0.05). NEFA was negatively correlated with urea (P < 0.05) while BHB was positively correlated with urea (P < 0.01). The levels of metabolites in the blood can reflect the nutritional status of cows during early lactation.