Dry cow pasture silage mineral concentrations and dry cow mineral requirements and supplementation practices on Irish dairy farms

In the Republic of Ireland, pregnant dry dairy cows are typically housed and fed pasture silage. However, its mineral concentrations vary greatly, and dietary mineral recommendations are based on other main feedstuffs and cow types. This study, which is part of a larger project, aims to describe pasture silage mineral composition, comparing it to estimated Irish dry cow requirements, and describe mineral feeding practices. Macrominerals and trace minerals were determined for pasture silage samples from 27 commercial farms. Farmers completed a feeding management questionnaire, and mineral requirements for each farm were calculated for pregnant dry cows at 270 d of gestation, with mean estimated live weight of 557 kg and dry matter (DM) intake of 9.2 kg/d. Mineral concentrations in pasture silage exceeded the estimated dietary requirements for all macrominerals and some trace minerals (samples exceeding; Ca, Cl, K, Mg, Na, P, S, and Fe: 100.0%, Mn: 88.9%, and Co: 55.6%), while it didn’t meet them for some trace minerals (samples not meeting; Cu, I and Se: 100.0%, and Zn: 51.9%). Calculated pasture silage dietary cation-anion difference ranged from 18 to 49 mEq/100 g DM. All farms supplemented minerals; 91.6% provided a multi-mineral product (types/brands varied), which was mostly top-dressed over pasture silage (77.8% of farms) once a day (51.9% of farms). Only 26.0% of farms tested pasture silage for mineral composition, the importance of which should be promoted. Our estimated requirements and findings should be considered along with recommendations for disease prevention for dry cow mineral feeding optimization.