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Milling method, thermal treatment, and particle size are important variables determining feed production costs, feed intake and digestibility and potentially egg quality in laying hens. Besides the raw material, the energy needed during production has a major impact on the total feed costs and energy saving milling methods such as the roller mill are becoming more used in the feed industry. Diminution of feed is the largest energy cost in layer feed production (DEATON et al., 1989) and the second largest after pelleting in broiler feed production (REECE et al., 1985). Hammer mills and roller mills are commonly used to reduce particle size of grains (AMERAH et al., 2007; KOCH, 2002). The hammer mill is easier to handle and to maintain, but requires more energy than the roller mill (AMERAH et al., 2007). The hammer mill produces more spherical and uniform shaped particles (REECE et al., 1985), whereas the roller mill generates a more uniform particle size (AMERAH et al., 2007) with irregular cubic or rectangular shape (KOCH, 2002). In addition, hammer mills produce a greater amount of fine particles (REECE et al., 1985). Due to the fact that chickens have a preference for larger feed particles (SCHIFFMAN, 1968), the particle size distribution may affect egg quality, as nutrients may not be equally ingested or effectively utilized (TANG et al., 2006). In contrast, the comparison between corn based diets milled with hammer or roller mills showed no effects on bird performance and egg shell breaking strength (DEATON et al., 1989). Interestingly, layers fed with a barley based diet ground by roller mill had higher egg weight compared to the same diet produced by a hammer mill (HAMILTON, 1994). Layers fed a barley based diet ground by roller mill reduced feed intake and egg production as compared to maize and wheat diets, while no differences were observed when a hammer mill was used. Egg quality was not affected by milling methods (PEREZ-BONILLA et al., 2014). |
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