Growth performance and N excretion of double muscled Piemontese bulls fed low protein rations with or without the addition of rumen protected conjugated linoleic acid

Growth performance and N excretion of double muscled Piemontese (DMP) bulls were investigated. Forty-eight DMP bulls (LW 279 kg), divided in 4 groups, housed in 12 pens, were fed 2 rations (TMR) differing for crude protein density (diets HP: CP=14.7% DM; diets LP: CP=11.0% DM) and top dressed with 80 g/d of rumen protected CLA ((CLA)) or with 65 g/d of hydrogenated soybean oil ((HSO)). DM intake was measured, weekly and on pen basis, from the weights of feed distributed and orts. Bulls were weighted monthly. Trial lasted 334 d. Data were analysed by ANOVA. Over the whole trial, no effects due to CP, to additive (A) or to CPxA were found on final LW (670 kg), average daily gain (1.187 kg/d), DM intake (8.50 kg/d), and on SEUROP (5.2 points) and cold dressing (67.3%). Interaction CPxA affected (P<0.05) feed conversion ratio and N efficiency. With respect to HP, LP reduced (P<0.01) N excretion from 57 to 40 kg /head. On DMP bulls a reduction of 29% of N excretion can be achieved by using low protein TMR without negative consequence on growth performance and carcass traits.