NUTRITION
Making magnesium easy Close attention to the management of the ‘close up dry cow’ (CUDC) and the ‘fresh cow’, is the key to helping ensure on farm profitability. This is the most important period of a cow’s production cycle, and when managed correctly it will help set the cow up for the entire lactation. WORDS AND IMAGE SUPPLIED BY SEALES WINSLOW The CUDC period is the 21 days prior to calving, when the cow is preparing to start the next lactation. The newly calved cow, the ‘fresh cow’, is the 21-day period post calving. This whole time frame may be referred to as the ‘transition period’, given we are making the transition from a dry cow to a lactating cow.
Calcium and magnesium connection
production which has twice as much calcium as milk. Ten litres of colostrum have the same amount of calcium as a cows entire blood stream. Post calving the ‘fresh’ cow’s demand for calcium rapidly increases as milk volume increases. For these reasons, ensuring continued magnesium support as well as calcium supplementation as soon after calving as possible can also help prevent milk fever.
One of the things the CUDC needs to do in the 21 days prior to calving is begin the process of mobilising calcium from her bones. Cows have substantial stored calcium reserves in bone and can increase the amount of calcium they absorb from the diet, but these mechanisms need to be ‘turned on’, which requires supplementation of magnesium. When cows have enough magnesium, the switch gets turned on reducing the risk of hypocalcaemia (milk fever). Milk fever is a gateway disease. Cows that have clinical milk fever (the tip of the iceberg)1 and subclinical milk fever have a heightened risk of experiencing a whole range of other animal health problems including ketosis, metritis, reduced conception rates and mastitis to mention a few. This compounded by the reduced immune function through the calving phase may contribute to detrimental effects on health and production.2 The increased requirement for calcium after calving is due to the initiation of colostrum
Magnesium (Mg) is an important macro mineral that has many functions within the body including nerve and muscle function, immune system function and bone health. Ruminants have no readily available pool of magnesium stored in their body, so require daily supplementation. It is important to provide the CUDC with adequate magnesium. It is also a good idea to take a multiple pronged approach to magnesium supplementation, especially during the risky spring period. Given that not all magnesium is created equally, it is important to understand the quality and amount of available magnesium to the animal. Accuracy of dosage and regularity of delivery to the cow is hugely important. Circumstances can dictate how magnesium is supplemented. For example, with cows wintered at the runoff molasses blocks may be the only viable option, and the accuracy of
Magnesium bioavailability
conventional dusting is at best questionable in adverse weather conditions.
Solutions The SealesWinslow Calver Max block is an effective way to overcome nutritional shortfalls in pastoral diets and top up trace mineral and vitamin levels during the dry period, leading into the stressful calving time. This dehydrated molasses block helps maintain blood magnesium levels as it has two highly available forms of magnesium, helping reduce the risk of milk fever. A crossbred CUDC requires 16g per cow per day of supplementary magnesium, and Calver Max at the standard feed rate of 200g delivers 16g of magnesium. SealesWinslow recommends that Calver Max be added to the diet two months prior to calving. SealesWinslow also recommends feeding lime flour to ‘fresh cows immediately post calving. Balanced mineral nutrition is crucial, none more so than that between calcium and magnesium. This is one of the most important aspects to get right in the pre-calving period. For information on including SealesWinslow products in your Pre-calving plan, and/or for SealesWinslow Nutritional advice contact your local technical sales representative. http://www.veterinaryirelandjournal.com/images/pdf/large/ la_dec_2016.pdf 2 http://onlime.co.nz/media/17176/mcd8910_calcium_dairy_cow.pdf 1
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