There is a wide array of factors, of which feed formulation is one, that can drastically affect both the quality of the feed produced as well as the parameters associated with the production of the feed in the mill. It has long been the practice in commercial broiler production to pellet the feed. It has been accepted at this point that feeding a diet with high quality pellets leads to better performance compared to the same diet with low quality pellets or in mash form. On the other hand, producing a high quality pellet is not the typical result in a large feed mill. In large mills, great quantities of feed must be produced in a short time frame and this is usually accomplished by running the mill at a high production rate and pelleting the diet through a relatively thin die. This usually results in decreased conditioning time and contact with the die for the diet, and consequently a lower quality pellet results, mainly because these are the two primary locations for the physiochemical reactions such as starch gelatinisation and protein denaturation that cause pellet binding. In this review we will discuss research pertaining to the use of different grains, by-products, minerals, pellet binders and most notably feedstuff constituents and their effects on both physical pellet quality as well as feed manufacturing variables such as energy usage and production rate when the data is available. The main focus will be given to research performed within the last decade. However, we have placed no restrictions on the research referenced based on publication date as there is always quality research with pertinent findings that have stood the test of time.

This review highlights the limited amount of research conducted regarding the optimum particle size of different feeds for efficient poultry production. The current industry practice of using highly processed, pelleted diets masks the influence of particle size, but some reports suggest that the effects of feed particle size on performance may be maintained even after pelleting. There appears to be a general consensus that particle sizes of broiler diets based on maize or sorghum, optimum particle size should be between 600 and 900 μm. Available data clearly show that grain particle size is more critical in mash diets than in pelleted or crumble diets. Although it has been postulated that finer grinding increases substrate availability for enzymatic digestion, there is evidence that coarser grinding to a more uniform particle size improves the performance of birds maintained on mash diets. This counter-intuitive effect may result from the positive effect of feed particle size on gizzard development. A more developed gizzard is associated with increased grinding activity, resulting in increased gut motility and greater digestion of nutrients. Although grinding to fine particle size is thought to improve pellet quality, it will markedly increase energy consumption during milling. Systematic investigations on the relationships of feed particle size and diet uniformity with bird performance, gut health and pellet quality are warranted if efficiency is to be optimised in respect of the energy expenditure of grinding.