Author : Le Trong Trung

Summary : Response to varying levels of energy and protein in corn silage-based complete rations was studied using 24 crossbred (Holstein X Red Sindhi) yearling dairy heifers. A 2 x 3 factorial in a randomized-complete-block experiment was used involving two energy levels (E1= 69 percent total digestible nutrients (TDN), E2=72 percent TDN); and three levels of protein (P1= 9 percent crude protein (CP), P2= 11 percent, and P3= 13 percent CP). The feeding trial consisted of a two-week preliminary period and an experimental period which allowed the heifers sufficient time to reach 250 kg liveweight or more. Using the Tilley and Terry method (1963), as modified by Barnes (1967), the in vitro dry matter digestibility progressively improved (P<.05) as the energy concentration increase at all levels of protein. On the other hand, at low-energy level, protein content did not significantly affect the digestibility which was found significantly higher (P<.01) at high-energy level in favor of 13 percent CP over 9 percent CP. No significant differences were found in daily dry matter (DM) and TDN intakes while daily protein intake significantly increased (P<.01) as the protein level increased. The two levels of energy did not significantly change the average daily gain (ADG) of the heifers. On the other hand, the ADG significantly (P<.05) increased from 0.60 kg to 0.70 kg as the protein levels increased from 9 to 11 percent CP. The ADG could be predicted from daily nutrient intakes by the regression equation: ADG = 0.1094 - 0.2688 Dm + 0.4803 TDN + 0.4075 CP. Body weight (BW) increase in body weight was found linear for the heifers in all groups, from 144 to 250 kg. BW could be estimated from hearth girth (HG) and body length (BL) using the equation: BW = -421.93 + 2.38 HG + 2.47 BL. As the level of either energy or protein was increased (but not beyond 11 percent), feed conversion significantly (P<.05) improved. The most efficient ratios were 6.9 and 7.03 kg DM/kg gain at 72 percent TDN and 11 percent CP, respectively. For...