The DMD (dry matter digestibility) value of silage is the best indicator of its feeding value.
Silage yields can increase by up to two tonnes per acre per week, but DMD declines by more than two units per week after heading out, and at double this rate if crops are lodged. Poor fermentation can decrease DMD by up to seven units. Ryegrass is two to four units higher for DMD, and is easier to ensile than poorer grasses.
Each drop of five DMD units reduces milk yield by almost half a gallon of milk per day, and raises the cost of finishing cattle by over €70.
High yielding cows need good quality silage during the dry period so that they calve down in proper condition. Replacements also need high quality silage. Trials show that finishing cattle on no concentrates can gain 0.51kg of carcase weight on 75 DMD silage, while only gaining only 0.33kg on 67 DMD silage.
The ideal time for harvesting is when the crop is heading out (DMD 75+) but this is difficult to judge in a crop with mixed species of grass. While a silage DMD of 75 should be the target for feeding to most animals, a well-preserved lower DMD (68-70) silage would be sufficient for dry cows in good condition.
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