Evaluating the energy and protein requirements for growing Nellore heifers and steers fed two levels of calcium and phosphorus

Abstract Text: An experiment was conducted to evaluate the energy and protein requirements for growing Nellore heifers and steers fed with two levels of calcium and phosphorus. Thirty two Nellore heifers and eighteen Nellore steers were used.  Heifers were divided in four groups. Four animals served as baseline reference animals, four were fed at maintenance  (MAIN) and twenty four received ad libitum (ADLIB) access to feed. The  ADLIB animals were further divided into four groups and assigned to treatments. Treatments were: 1) Ca and P fed at requirements (CaPR) with a 50:50 of roughage:concentrate (R:C) diet; 2) CaPR with at  70:30 R:C diet; 3) 43% of the Ca and 80% of the P requirement (CaPL) with a 50:50 R:C diet; and 4)  CaPL with a  70:30 R:C diet. All steers in this experiment were fed CaPR. Half of the heifers and steers were slaughtered at d 50 and the other animals were slaughtered a d 100 of the feeding period while all MAIN animals were slaughtered at d 100. Total feces and urine were collected from all animals 72 hours prior to slaughter. The net energy (NEm) and metabolizable energy (MEm) requirement for maintenance were obtained by exponentially relating the heat production and the metabolizable energy intake, while the net energy requirements for gain (NEg) were obtained using empty body weight (EBW) and EBW gain (EBG). The net protein requirements for gain (NPg) were estimated according to EBG and retained energy (RE). NEm and MEm were 70.1 and 118 kcal/kg EBW^0.75, respectively. Net protein for maintenance was 1.28 g/kg BW^0.75and NEg and NPg were estimated using the following equations: NEg = 0.053 × EBW^0.75 × EBG^0.6301 and NPg = 137.85 × EBG – 0.05 × RE, respectively. Under the conditions of this experiment, the energy and protein requirements for growth were: NEg = 0.053 × EBW^0.75 × EBG^0.6301 and NPg = 137.85 × EBG – 0.05 × RE, respectively. 

Keywords: energy, protein, sugarcane