Abstract:
Globally the demand for food, especially for food of animal origin, will double by the year 2025 and almost tripled by the year 2050. This means that animal nutritionists need to explore ways of ensuring that there will be adequate amounts of animal protein available for consumption by using natural resources more efficiently. Improving the efficiency of utilisation of modern day broiler feeds may be key to achieve high levels of animal protein production at affordable cost. The manipulation of the particle size of the two main ingredients of broiler feed namely, maize and soybean meal, may improve efficiency of overall broiler performance.
This trial assessed the effect of maize and soybean particle size on broiler performance, gizzard and proventriculus development and pellet hardness. Additionally, different combinations of maize and soybean meal particle sizes were compared with the aim of finding the optimal combination where commercial value can be maximised. This trial had 12 treatments with 10 replications for each treatment. The twelve treatments contained different combinations of maize and soybean meal particle sizes. Seven thousand two hundred day-old chicks were placed in a broiler facility at 23 birds/m2 and raised up to slaughter at 35 days-of-age on a three-phase feeding program. Bodyweight (BW), feed intake (FI), feed conversion ratio (FCR), production efficiency factor (PEF) and mortality were recorded on a weekly basis. Gizzard and proventriculus measurements were taken on 7, 14 and 35 days-of-age and pellet hardness were measured for the grower and finisher phase diets.
The production efficiency factor (PEF) values increased as the particle size of the soybean meal in the diet was reduced, with treatment 4 (15% coarse maize; 2 mm soybean meal) giving the highest value. When the diet contained soybean meal milled on a roller mill with a screen size of 4 mm (treatment 3 and 5), broilers that received treatment 5 containing 30% coarse maize outperformed treatment 3 containing only 15% coarse maize in terms of BW and FCR. Maize and soybean meal particle size in a pelleted diet did not have a significant effect on gizzard development during the first two weeks, but it had a significant effect on the gizzard development during the latter stage of production. Furthermore, no effect was seen on the proventriculus development. Pellet hardness and pellet durability were influenced by the maize and soybean meal particle size with treatment 4 that contained 2 mm soybean meal and 15% coarse maize resulted in the hardest pellets.
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Up to now, soybean meal was mostly used by feed mills as received from the suppliers without any further processing. The recommendation from this study is that the soybean meal destined for broiler diets should rather be milled through a sieve of 2 mm screen size. The smaller soybean particle size promotes higher bodyweights and better FCR and PEF values. The improved feed efficiency obtained with the smaller particle sizes means that less resources can be used to produce food for humans. For optimum broiler performance a pelleted diet with a 15% coarse maize and 2 mm soybean meal combination must be used.
