The Effect of Starch Digestibility of Two Corn Silage Varieties on Lactation Performance in Dairy Cows
The objective of this study was to investigate the effect of storage on two corn silage varieties with varying amounts of floury and vitreous endosperm. Floury endosperm is expected to have faster rates of ruminal starch digestion at harvest, resulting in increased overall starch digestibility. However it is unclear if these differences persist during storage. Two multiparous, ruminally cannulated dry cows were used to assess ruminal degradability of starch in ensiled corn silage derived from a floury and vitreous varieties of corn. Cows were fed lactating high cow TMR twice daily ad libitum. Ruminal degradability characteristics were determined as described by NRC (2001). Approximately 10 g of dried and ground corn silage stored for 54 and 80 days sealed in duplicate polyester bags and suspended in the rumen in a large nylon mesh bag for 2, 4, 8, 12, 24, and 36 h. Samples were placed in the rumen in reverse order at varying times and removed simultaneously at the end of the experiment. A 0-h sample was immersed in 39°C water for 20 min. Residues were submitted to Agri Analysis for fiber and starch content determination. Starch disappearance was calculated as the difference between the original starch mass and the mass remaining after ruminal fermentation and expressed as a percentage of the original starch mass. The two varieties of corn silage did not differ for soluble starch (24.10 vs. 26.41% P=0.99), degradation rate (0.35 vs. 0.24%/hr P =0.79), slowly digestible starch (67.65 vs. 68.22% P =1.00), and resistant starch (8.24 vs. 5.36% P =0.70) after 54 days storage. There were also no difference after 80 days of storage for rapidly digestible starch (19.06 vs. 36.71% P =0.28), degradation rate (0.23 vs. 0.24 P =1.00%/hr), slowly digestible starch (78.49 vs. 59.11% P =0.11), and resistant starch (2.45 vs. 4.18% P=0.90). Thus any differences amount corn varieties did not persist by 54 days of storage.
National Research Council. 2001. Nutrient Requirements of Dairy Cattle. Natl. Acad. Sci., Washington, DC.
Keywords: starch digestibility, corn silage