Energy-protein intake and its effect on blood metabolites of high-producing dairy cows

Abstract

Forty-six multiparous Israeli Holstein cows were used to evaluate the effect of three dietary concentrate levels (50, 65 and 80%) and two crude protein (CP) levels (17 and 21%) in dry matter (DM), on blood metabolites. Cows were divided into six dietary treatments in a 2 × 3 factorial design. Rations were fed ad libitum for the first 5 wk of lactation. Milk yield and feed intake were recorded daily, while milk composition and plasma metabolites were determined weekly. Raising the concentrate levels in the diet led to increased net energy (NE) intake (P < 0.01), and decrease milk fat percent (P < 0.0001); Cows tended to gain more weight and the negative energy balance declined (P < 0.0001) in group 80% concentrate relative to the other two groups. High-CP in the diet elevated protein intake (P < 0.001) without affecting the cows' performance. Increasing the energy intake by raising the concentrate level from 50 to 65 and 80% in the diet, lowered (P < 0.05) the plasma nonesterified fatty acid (NEFA) and 3-hydroxybutyrate (3-OHB) levels and raised the glucose level (P < 0.05) in the 80% concentrate group. The high-CP diet raised the level of 3-OHB (P < 0.01), while plasma levels of NEFA, glucose and cholesterol remained unchanged. No difference was found between winter (December–April) and summer (May–November) in overall average of DM and NE intake. However, 4% FCM, milk fat percentage and milk protein yield were higher (P < 0.05) in winter than summer. This elevation was accompanied by a rise in NEFA (P < 0.06) and total α-amino nitrogen (P < 0.05). It was concluded that plasma parameters determined were found to reflect the dietary status of dairy cows in early lactation; winter conditions encourages lypogenesis and supply of metabolites needed for milk production. Key words: Energy-protein, dairy cow, season, blood metabolites