Digestibility, methane production and chewing activity of steers fed whole-crop round bale corn silage preserved at three maturities

The effects of the lengths of growth of round bale whole-crop corn silage on its nutritive value, the methane production, chewing time, and ruminal fermentation were evaluated in three Holstein steers (599.3 ± 31.5 kg). Corn forages were harvested, baled and wrapped on the same day at 129 (D129), 118 (D118) and 107 (D107) days from planting. All steers were fed the three corn silages along with urea at maintenance energy requirements during three 14-day periods in a 3 × 3 Latin square design. A balance trial was conducted to investigate whole tract digestibility by the collection of total feces and urine over a 7-day test period. For 2 days of the test period, a head hood-type respiration chamber was used to measure methane production. Ruminal fluid was collected immediately before and 3 h after, the morning feeding on the last day of the test period. There was no spoilage in any of the silages (n = 9). The average fresh weight of the bales was 326.4 ± 10.7 kg. The DM content of the corn silage was highest in D118 and lowest in D129 (P<0.01). The pH of all silages was lower than 4.0. The aNDFom content of the corn silage was higher in D129 than in other forages (P<0.05). There were no differences in the metabolizable energy content of the corn silage. The ruminating and chewing times, chewing per unit of DM intake and chewing per unit aNDFom intake were higher (P<0.05) in steers fed D129 than those fed other forages. Before the morning feeding, the acetate proportion of total volatile fatty acid in the steers fed D129 was higher (P<0.01) than that in other steers. The nutrients and energy value of each corn silage in this study ranged from 232 to 305 g/kg of DM, from 87 to 90 g/kg of crude protein, from 426 to 492 g/kg of aNDFom, from 667 to 707 g/kg of TDN and from 11.39 to 11.84 MJ/kg of metabolizable energy on a DM basis. These results show that the DM and aNDFom contents of corn silage and total chewing time of the steers, and the acetate proportion of the total VFA in the rumen before the morning feeding were affected by the lengths of growth of corn forage.