Sheep fed only silage or silage supplemented with concentrates: 2. Effects on lamb performance and fatty acid profile of ewe milk and lamb meat

Production performance of ewes fed only silage, or silage supplemented with a maximum of 50% concentrates (barley, peas, rapeseed cake), from mid-gestation until weaning was evaluated during two years. Lambs had access to the same diets as their dams while nursing. Ewe milk samples were collected at weeks 2 and 4 after lambing to evaluate the dietary influence on the fatty acid (FA) profile. After weaning, lambs from each ewe feeding programme either continued on the same diet or were switched to the other and the study continued for an additional five weeks year 1 (Y1) and seven weeks year 2 (Y2). Feed intake, weight gain and body condition of the lambs were recorded. At slaughter, muscle samples were taken to study the FA profile. The silage fed during Y2 was lower in crude protein content and contained more indigestible neutral detergent fibre and a higher amount of acids than the silage fed in Y1. The intake level of the lambs, particularly those fed only silage, was generally lower in Y2. In both years, weight gain was highest in the lamb groups fed concentrates after weaning and lowest in the group fed only silage. The FA profiles of milk and lamb muscle were influenced by the diet and nutritional status of the ewes. Milk from silage-fed ewes was higher in C18:3n-3 and conjugated linoleic acid, whereas milk from concentrate-fed ewes was higher in C18:0 and C18:2n-6. In Y1 the muscle of lambs fed concentrates pre-weaning had lower C16:0 and higher C18:1c-9 levels. The influence of diet on lamb muscle FA profile was less pronounced in Y2. In both years the C18:3n-3 levels were lower in muscle from lambs fed concentrates. In conclusion, the FA profile of lamb muscle was strongly influenced by the ewe diet and milk FA profile. Lambs on the same pre-weaning diet had a more similar profile than lambs with the same post-weaning diet. Feeding intensity and duration were the factors influencing the lamb muscle FA profile. A diet with only silage produced meat with a higher proportion of n-3 FA beneficial for human health; however, the lamb nutritional requirements for optimal growth were difficult to meet even with high-nutrient-quality silage.