Plante, P. A., Laforest, J.-P. and Farmer, C. 2011. Effect of supplementing the diet of lactating sows with NuPro® on sow lactation performance and piglet growth. Can. J. Anim. Sci. 91: 295-300. The impact of supplementing the diet of lactating sows with NuPro® (a source of yeast-derived proteins) on their performance and that of their piglets was studied. Treatments were: control (CTL, n=22), 30 g of NuPro per day (NuPro30, n=22), and 60 g of NuPro per day (NuPro60, n=21). The NuPro was mixed daily with 500 g of feed and provided over a 21-d lactation. Jugular blood samples were obtained from sows on days 2, 7 and 20 of lactation to measure urea concentrations. Milk samples were obtained on days 7 and 20 of lactation for compositional analyses and quantification of 5' monophosphate nucleotides. Litter size was standardized to 10±1 at 48 h postpartum. Sow body weight loss and backfat loss during lactation were recorded, as well as the weights of piglets until day 56. Feed intakes of sows during lactation and of piglets for 5 wk post-weaning were noted. Statistical analyses were performed with PROC MIXED using an analysis of variance with one factor (three levels) according to a completely randomized design. None of the animal performance data differed among treatments (P>0.1). Standard milk composition was also similar across treatments (P>0.1). Concentrations of nucleotides in milk were greater on day 7 than on day 20 of lactation (P<0.001) but were not affected by treatments (P>0.1). In conclusion, supplementing the diet of lactating sows with NuPro did not increase nucleotide concentrations in milk and had no beneficial effects on sow or piglet performances.