1695
Ruminal Starch Degradation of Maize Silage affected by Ensiling Time and Dry Matter Content
Quantitative evaluation of rumen degradation of maize silage is relevant for accurate determination of its nutritional value. Our objective was to quantify combined effects of ensiling time and dry matter (DM) at harvesting on effective rumen degradation (ED) of starch, crude protein (CP) and NDF in maize silage.
Maize silage (hybrid Nutreka) was harvested at 30, 35 or 40% DM with 2-week intervals, allowing different maturity to develop in the same crop. Fresh samples were stored at -18°C. 25 liter plastic vessels were filled with thin layers of material and compressed manually to remove air. Full vessels were sealed then stored for 4, 8 or 12 months at ambient temperature. After opening, samples were stored at -18°C.Three fistulated mid-lactation Holstein cows fed a basal ration consisting of maize silage, grass silage, hay and compound feed, were used to incubate nylon bags. Bags (pore size 37 um) were inserted at 08.00am and removed after 3, 8, 16, 32, 56, 96 and 336 hours. All bags were machine washed, freeze dried and weighed. Outliers were removed using Dixon Q-test. Residues were analyzed by NIRS for DM, starch, CP and NDF using calibration lines specifically developed for maize silage residues. Washable and undegradable fractions were based on residues after 0 and 336 hour incubation respectively. Rate of degradation (kd) was calculated in SAS using PROC NLIN. ED was calculated as Washable + Degradable x (kd/(kd+ passage rate)) and analyzed in SAS using PROC MIXED for significant differences between treatments using ensiling time and DM as fixed factors and cow as random factor.
Starch and CP ED increased with increasing time ensiled (P<0.0001) from 63.3% to 85.4% and from 42.2% to 71.4% respectively. Starch and CP ED decreased with increasing DM (P<0.0001) from 82.3% to 71.7% and from 63.9% to 58.5% respectively. Higher DM at ensiling led to a more pronounced effect of ensiling time on starch and CP ED (P<0.0001 for interaction time x DM). NDF ED was not significantly affected by ensiling time or DM (P>0.10). It can be concluded that ED of starch and CP in maize silage is affected by combined effects of ensiling time and DM at harvesting. These results can be applied in ration formulation systems for dairy cows to further optimize nutrient utilization and rumen conditions.
Keywords: maize silage, ensiling time, rumen starch degradability