NOVEMBER 2018 Feature fever. Grass silage supplies what is required. Importance of trace minerals during the dry period Trace minerals, or micro minerals, play a huge role in the overall immunity, fertility and production of dairy cows. Throughout the dairy cows’ cycle, calving is the most stressful period for the immune system. As such, it is important that, throughout the dry period, the cow is allowed to build up the necessary amount of trace minerals to allow the cow to draw from its reserves when it calves down. Irish grass silages have been shown to be 63 per cent low in copper, 69 per cent low in selenium and 29 per cent low in zinc (Rogers and Murphy, 2000). Thus, supplementation is essential. Research has shown, time and time again, the critical role of trace elements in dry cow nutrition. These elements include copper, zinc, selenium and manganese. Offering these minerals in their standard inorganic form, such as copper sulphate or zinc oxide, will have little effect, due to their low absorption levels by the cow. However, research has shown that feeding these trace minerals in their organic form — Bioplex® copper and zinc and Sel-Plex®, an organic form of selenium — leads to better absorption, storage and utilisation by the cow. This builds up the cow’s immune system and lowers the risk factors associated with a difficult calving and retained placenta. Using proven technologies as part of a dry cow nutrition programme generates greater return on investment, benefitting both cow performance and farm profitability. Many farmers across Ireland are now seeing a positive response in their herds thanks to using Bioplex and Sel- Plex in their dry cow mineral programmes. 30 25 l Inorganic Se l Organic Se 25.7 Incidence (%) 20 15 10 10.8 5 0 2.9 Retained placenta Metritis 17.4 Potassium in Irish silages is typically between 1.8-2.4 per cent; however, the dry cow requirement is only 0.52 per cent. Potassium interacts closely with magnesium by tying up magnesium in the rumen, which can slow down the absorption and mobilisation of calcium, leading to milk fever. With sufficient magnesium supplementation, the typical levels of potassium can be managed. If potassium levels are greater than 2.7 per cent in silage, alternative measures should be taken, such as introducing Cal-Mag or sweetened Cal-Mag to the diet. Grass silage supplies the necessary calcium requirements during the dry period. Unless following a DCAD diet program, calcium is not required during the dry period. This ensures that the cow mobilises calcium reserves within her bones and bloodstream, reducing the risk of milk 21