Feature NOVEMBER 2018 www.irishfarmersmonthly.com Pre-calving mineral requirements Eddie Phelan, Southwest Regional Manager, Alltech Ireland, discusses mineral nutrition for dry cows Dry cows should be fed a dry cow mineral for the duration of the dry period — ideally, between six to eight weeks — to ensure there is a good reserve of minerals built up that will allow the cow to calve down and continue into lactation without any issues. However, most Irish silages don’t supply the required amount of minerals to get the cow through the dry period. As such, these minerals should be supplemented. If you haven’t already done so, test your silage for minerals. This will give you a good indication of the mineral status and ensure that you are feeding a balanced mineral supplement. Managing milk fever When it comes to major mineral nutrition, the most important issue is establishing a good basis for the control of milk fever and subclinical milk fever. Milk fever is known as the “gateway disease” because it leads to many other complications, such as retained cleanings and displaced abomasum. Research has shown that, where milk fever is relatively well-controlled, approximately 33 per cent of cows may still experience sub-clinical milk fever. The risk of milk fever is reduced if cow body condition score is monitored and controlled in late lactation and throughout the dry period. Cows should be dried off between BCS 3-3.25 and should maintain this BCS throughout the dry period. Cows with BCS that are either too high or too have both been shown to have an increased risk of experiencing milk fever. Clinical milk fever is usually easy to detect; sub-clinical milk fever, however, is often difficult to detect and can go unnoticed. Since sub-clinical milk fever affects more cows, it can increase costs, and it can also lead to varying metabolic disorders, such as retained cleanings, metritis, mastitis and ketosis. Major mineral requirements Magnesium is a key major mineral in relation to the control of milk fever. Magnesium is needed for the metabolism and absorption of calcium within the cow around calving. Throughout the dry period, a cow needs between 25-30 g of magnesium per day. If a silage mineral analysis is 0.15 per cent magnesium, a cow with 11 kg of dry matter intake during the dry period will take in 1.65 g/mg from silage. As a result, the mineral supplement will need to supply at least 24 g of magnesium. If the feed rate of the mineral is 120 g/head/day, there must be a minimum of 20 per cent mg supplied to make up the deficit. 20