Following a request from the European Commission, the European Food Safety Authority (EFSA) was asked to deliver a scientific opinion on the safety and efficacy of Yea-Sacc1026® (Saccharomyces cerevisiae) as a feed additive for horses. Yea-Sacc1026® is the trade name for an additive based on a live preparation of a strain of brewers yeast (Saccharomyces cerevisiae CBS 493.94). The product is permanently authorised for use with calves, cattle for fattening and dairy cows. It was also provisionally authorised for use in feed for horses but this authorisation was limited to horses from two months post-weaning onwards at a minimum dose of 4 x 109 CFU kg-1 complete feed. The applicant is now seeking an extension of use to the whole life of the animal and a reduction of the minimum dose to 4 x 108 CFU kg-1 complete feed. In addition, the applicant has requested the re-evaluation of the current authorisation, i.e. for horses from two months postweaning onwards. In an opinion issued in 2003, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) considered the safety of the product when used in feed for leisure horses and concluded that the product was safe for adult horses but, in the absence of relevant data, could not conclude on its safety for foals. Subsequently, EFSA introduced QPS as an assessment tool. As the species Saccharomyces cerevisiae is considered by EFSA to have QPS status, no further assessment of safety is required for the active agent. Consequently, and in the absence of any concerns about the other components, the additive can be presumed as safe for horses of all ages, for consumers of products derived from animals fed the additive, and for the wider environment. The safety for the user was also subject to previous assessments and the FEEDAP Panel is not aware of any additional data which would require its reconsideration. In its earlier opinion on the use of Yea-Sacc with horses, EFSA considered only the safety of the product and not its potential efficacy. The efficacy of the product and the practical issues pertaining to its use in equine feed are the subject of the present opinion. The nine trials described provide consistent evidence that YeaSacc1026® can have a significant effect on nutrients digestion in horses of all ages. In all the studies, there was a numerical increase in one or more measures of cell wall degradation, reaching significance in seven trials made with mature horses, yearlings and mares. When given to lactating mares, the resulting improvement in fibre digestion is reflected in changes to milk quality, to the benefit of suckling foals which show improved growth compared to foals suckling mares given feed without supplementation. Significant effects on phosphorus metabolism were also seen. Efficacy was demonstrated in the seven trials over the range 3.0–6.4 x 1010 CFU head-1 day-1, with a mean value of 4.7 x 1010 CFU head-1 day-1. Calculations made using these data and the information supplied on intake where this was controlled (six studies on mares and mature horses) gave an approximate range of 1.6–8.2 x 109 CFU per kg complete feed, with a mean of 4.7 x 109 CFU per kg complete feed. This is close to the present minimum recommended dose. The data provided do not support the reduction to a minimum dose of 4.0 x 108 CFU kg-1 complete feed as proposed by the applicant. Because of the difficulties of defining the doses in terms of complete feeds in grazing animals, the FEEDAP Panel recommends the additional provision of doses in terms of CFU head-1 day-1.