Effects of substituting amaranth silage for corn silage on intake, growth performance, diet digestibility, microbial protein, nitrogen retention and ruminal fermentation in fattening lambs

The effect of dietary substitution of corn silage (CS) with amaranth silage (AS) on feed intake, growth performance, digestibility, microbial protein, nitrogen (N) retention and ruminal fermentation was evaluated using 50 Moghani male lambs (initial body weight 28.5 ± 1.9 kg). Five iso-energetic and iso-nitrogenous diets were randomly assigned to the five groups of 10 lambs each in a completely randomized design for a period of 98 days. The diets were offered ad libitum at a forage to concentrate ratio of 40–60 in which CS was replaced by different levels (0, 75, 150, 225 or 300 g/kg of dietary DM) of AS. Diets were offered twice daily (at 08:00 and 17:00 h). Daily feed intake, average daily gain (ADG), in vivo digestibility, rumen fermentation parameters, microbial N supply (MNS) and N retention in the lambs were determined. Increasing dietary level of AS improved feed intake and ADG (P<0.051), but there was no detectable effect on feed efficiency (FE) and diet digestibility. Increasing the proportion of AS in diet increased N retention, MNS and ruminal butyrate (P<0.05) but decreased branched-chain fatty acids. Dietary treatment tended to increase rumen content of total volatile fatty acids (P=0.09). It is concluded that partial substitution of AS for CS, up to 300 g/kg DM, in diet of Moghani lambs had positive effects on feed intake, growth performance, N balance and microbial N, without any effect on FE.