Ruminal degradability of alfalfa and corn after processing or maceration

The effects of mechanical treatment on ruminal degradability of alfalfa and corn were determined in three experiments using nylon bags incubated in th e rumen of two fistulated dry cows. The first experiment was a 2 x 2 x 2 fa ctorial design applied to chopped alfalfa at two levels of mechanical treat ment (processing with two corrugated rolls in a forage harvester or no proc essing), two throughput rates (medium or high) and two moisture contents (a fter a 4-h or a 24-h field wilting period prior to processing). The second experiment was a 2 x 2 factorial design applied to chopped corn at two leve ls of mechanical treatment (processed or not) and two throughput rates (med ium or high). In these two experiments, forages were immediately frozen (no t fermented) for later degradability measurements. In the third experiment, alfalfa was mowed either with a conventional mower-windrower or an experim ental mower-macerater with three corrugated rolls. After 40 h of field wilt ing, alfalfa was dehydrated and processed into pellets. In the first experi ment (chopped and frozen alfalfa), throughput, processing and wilting perio d had no effect (P > 0.05) on the effective degradability of DM, CP, NDF an d ADF. In the second experiment, DM degradability of chopped corn decreased with an increased throughput (46.4% vs. 43.7%) but increased with processi ng (43.9% vs. 46.2%). Processing also increased CP degradability of corn. I n the third experiment, maceration with subsequent field wilting during 40 h and dehydration produced alfalfa pellets with a higher degradability of D M (56.0% vs. 50.4%) and of NDF (27.1% vs. 17.3%) than pellets from non-mace rated alfalfa. These results suggest that the increase in ruminal degradabi lity is greater with alfalfa macerated and wilted in the field (erp. 3) tha n with alfalfa frozen immediately after harvesting and processing(exp. 1). Maceration probably reduced the loss of nutrients by decreasing field respi ration. Processing of corn may have increased the ruminal degradability bec ause of increased kernel breakage that facilitated starch digestion.