Recipes determine the quality of livestock feed and the hydraulic adders are one of the elements determining if the given recipe will be carried out. Generally, construction of existing adders does not allow accomplishment of that aim i.e. they do not meet recipe requirements. Consequently, researches which determined deviations in ingredient adding present with existing adders and with the experimental hydraulic adder were conducted. The research was conducted for two years (2005 and 2006) in two livestock feed factories in the Republic of Croatia on samples of feed mixtures for pigs weighing up to 15 and 25 kilos. Relative error was the means for comparison of weighing deviations between the hydraulic adder and the adders powered by means of an electric motor. Research results indicate that none of the two observed livestock feed production plants in 30 repetitions for two kinds of feed mixture showed a feed mixture weighing that would correspond to the specifications in the recipe. Additionally, hydraulic adders showed a greater precision in adding fish meal, extruded soybean and soybean meal when compared with the adders powered by means of an electric motor. However, the adders powered by means of an electric motor showed greater precision in adding corn. Based on the research results it can be concluded that using hydraulic adders instead of the adders powered by means of an electric motor will result in more accuracy in dosing ingredients with fine and middle granularity, whereas this can not be applied to dosing coarse grained ingredients.