Influence of dietary feeding different levels of mixed potato-wheat straw silage on the diet digestibility and the performance of growing lambs

The effect of dietary substitution of different levels (0, 100, 200 or 300 g/kg dry matter [DM]) of mixed potato-wheat straw silage (PWSS) for alfalfa and concentrate on nutrient digestibility, feed intake, growth performance, microbial nitrogen supply (MNS) and blood parameters of fattening lambs (24 lambs, 25 ± 1.2 kg initial body weight) was assessed. The potato-wheat straw (57:43 ratio on a DM basis) mixture was ensiled for 90 days before use. Four isonitrogenous and isocaloric diets were randomly assigned to 4 groups of lambs (n = 6/group) in a completely randomized design for a 75-day period (15 days for adaptation and 60 days for data collection). The animals were fed diets as a total mixed ration to ensure 10% orts. Diet digestibility, DM and nutrient intake, growth rate, MNS and blood metabolites were determined. There was a linear response (P < 0.001) to increasing dietary level of PWSS for crude protein (CP) digestibility, with no effect (P > 0.05) on the digestibility coefficients of DM, OM, ash-free neutral detergent fiber and EE. The daily intakes of DM, organic matter (OM) and CP were not affected (P > 0.05) by the dietary inclusion of PWSS. The average daily weight gain was not influenced (Linear, P = 0.22) with increasing levels of PWSS offered. Consequently, feed efficiency increased linearly (P = 0.048) with increasing levels of PWSS in the diet as did urinary excretions of purine derivatives and MNS (Linear, P = 0.01). PWSS inclusion had no effect (P > 0.05) on blood metabolites in the experimental animals. It is concluded that PWSS can be fed to fattening Mehraban lambs as a replacement (300 g/kg diet DM) for an alfalfa and concentrate diet without adverse effects on animal performance. This silage is a safe feedstuff to use in the diet of sheep.