Effect of micronization on the performance of growing/finishing pigs fed diets based on hulled and hulless barley

Sixty-four crossbred pigs (19.1 ± 0.35 kg) were assigned on the basis of sex, weight and litter to one of four dietary treatments in a factorial (2 barley types × 2 heat treatments × 2 sexes) design experiment. All diets were based on barley and soybean meal with the treatments consisting of either non-processed hulled or hulless barley or similar diets in which the barley was subjected to micronization. Six castrates and ten gilts were fed each diet. Micronization increased the percentage of gelatinized starch in the hulled barley diets from 10.9% to 32.9% for the grower diets and from 16.3% to 52.2% for the finisher diets. For the hulless barley diets, micronization increased the percentage of gelatinized starch from 11.9% to 23.1% for the grower diets and from 13.3% to 30.3% for the finisher diets. Diet viscosity also increased with micronization. Micronization increased the digestibility of crude protein by 8.0% (P = 0.005) and gross energy by 4.4% (P = 0.02). Barley type had no effect on digestibility coefficients for dry matter and energy. However, the digestibility coefficient for crude protein was 9.2% lower (P = 0.002) for the hulless barley diets than for the hulled barley diets. There was a significant interaction between barley type and micronization for dry matter (P = 0.038) and protein (P = 0.004) digestibility. Over the entire experiment (19–80 kg), pigs fed micronized diets gained 10.3% (P = 0.006) slower than pigs fed untreated barley. The slower growth appeared to be due, at least partially, to a 14.3% (P = 0.001) reduction in feed intake. There were no performance differences between pigs fed hulled or hulless barley-based diets or between castrates and gilts when performance over the entire experimental period was considered. The overall results of this experiment indicate that the performance of pigs fed hulless barley-based diets is similar to that of pigs fed diets based on hulled barley. Micronization increased the percentage of gelatinized starch in the barley-based diets and this increase in starch gelatinization was associated with improvements in the digestibility of crude protein and gross energy. However, likely as a result of increased diet viscosity, feed intake was significantly reduced, leading to a reduction in growth rate for pigs fed the micronized barley-based diets. Micronization would, therefore, appear to be an ineffective means of improving the nutritional value of barley for growing-finishing pigs.