Effect of maize silage maturity on site of starch and NDF digestion in lactating dairy cows

The effect of feeding whole crop maize silage ensiled at three stages of maturity on forestomach and intestinal digestion of starch and neutral detergent fibre (NDF) was studied in an extended 3 × 3 Latin square experiment. Three multiparous lactating Danish Holstein-Friesian cows fitted with ruminal, duodenal and ileal cannulae were offered maize silage based diets supplemented with soybean meal and a grass clover hay. The three treatments differed in the dry matter (DM) content of the maize silage, being 257, 350 or 403 g/kg. Ruminal degradation characteristics of starch and NDF were also determined in situ using a nylon bag method. Average DM intake was 15.9 kg/day of which starch comprised 2.10-3.72 kg/day and NDF 5.29-5.80 kg/day. The increasing maturity stage of the maize silage increased (P = 0.003) the duodenal flow of starch by 0.20 kg/day, due to increased starch intake. However, an increased (P = 0.02) amount of starch was excreted in faeces with increasing silage maturity and a negligible increase in post ruminal digestion of starch, of only 0.12 kg, was obtained. In vivo ruminal starch digestibility decreased (P = 0.04) from 0.93 to 0.91 and total tract digestibility of starch decreased (P = 0.01) from 1.00 to 0.98 with increased maturity. Increased maturity resulted in a large decrease (P = 0.02) in total tract digestibility of NDF from 0.56 to 0.43. In situ degradation of starch and NDF showed the same tendencies as in vivo; but the effect of maturity on in situ starch degradation was altered by fermentation during ensiling. With fresh chopped maize, starch degradation decreased (P = 0.0003) as maturity increased while after the maize crop had been fermented, in situ starch degradation was not altered by stage of maturity. The NDF degradation of ensiled maize decreased (P = 0.02) with increasing maturity, due to an extended lag time, consistent with earlier in situ experiments on effects of maturity of maize for silage on starch and NDF digestibility.