Grass silage composition and nutritive value on Northern Ireland farms between 1998 and 2017

Grass silage is the predominant conserved forage offered to ruminant livestock within Northern Ireland (NI) when housed. This study involved the analysis of a dataset (n = 76,452 samples) comprising silage samples from commercial farms, analysed by the Agri-Food and Biosciences Institute (AFBI) between 1998 and 2017. The effects of harvest number (1, 2 or 3) and year were examined. Most of the differences between harvests 1-3 were significant although these differences were of little biological significance. Silage crude protein (CP) increased from harvests 1 to 3, while ammonia N concentration was higher in 3rd harvests. Acid detergent fibre (ADF) and neutral detergent fibre (NDF) concentrations decreased from harvest 1 to 3, while dry-matter (DM) digestibility and D-value (% DM) were higher in 1st compared to 2nd harvest. Across the twenty year period, silage DM and water soluble carbohydrate concentrations increased, while ADF and NDF concentrations decreased. Crude protein concentration did not change over time. There was no significant improvement in silage digestibility. While silage intake potential for dairy cows increased by approximately 8% (from 88.8 to 96.1 g kg W-0.75, meant across all harvests), silage intake potential for beef cattle increased only within harvest 1. Despite overall increases in silage DM concentration, silage digestibility parameters did not show any significant improvement over the 20-year period, highlighting the need for a renewed focus on improving silage nutritive value.