Table 1: Checklist to mitigate milk fever 9 Ensure cows are at target BCS two to three weeks before calving 9 Identify at-risk cows prior to calving and feed according to their BCS • if less than 5.0 BCS, give 100% of daily requirement; if greater than 5.0 BCS, give 90% of daily requirement 9 Supplement all cows with magnesium pre- and post-calving (0.4% and 0.3% of DM requirement, respectively) 9 Keep dietary calcium levels low pre-calving (less than 0.5% of DM requirement) 9 Supplement all colostrum cows with calcium 9 Maintain dietary phosphorus between 0.25% and 0.45% of DM pre-calving • avoid feeds high in phosphorus, e.g., PKE • supplement with phosphorus if diets are low in phosphorus, e.g., fodder beet 9 Avoid grazing effluent or recently fertilised paddocks with high potassium levels pre-calving (more than 4.5% of DM) Strategies to prevent milk fever In New Zealand pasture-based systems, supplementing cows with magnesium from two to three weeks pre-calving until mid- lactation is a common strategy to prevent milk fever. That’s because magnesium plays a crucial role in maintaining blood calcium concentrations. Other mitigation strategies ( Table 1 ) include ensuring body condition score (BCS) targets at calving are met, and supplementing cows with limeflour, a calcium source, during the colostrum period. Despite these strategies, subclinical milk fever remains highly prevalent, and clinical milk fever is still a major issue on many farms. How can synthetic zeolite help? Synthetic zeolite is a sodium aluminosilicate supplement. It is commonly fed pre-calving in European indoor systems to reduce the risk of cows developing clinical and subclinical milk fever after calving. This strategy is well supported by peer-reviewed research in these systems 3 and, more recently, has been validated to reduce hypocalcaemia in high-yielding cows managed in a North American housed system 4 . By feeding synthetic zeolite for two to three weeks before calving, dietary calcium and other minerals are bound in the cow’s rumen and pass through into the faeces. This stimulates her to increase calcium absorption from the intestines and prepares her to cope with increased calcium demands after calving. As a result, her blood calcium concentrations are maintained. Small-scale studies yield promising results As research data in grazing systems was lacking, DairyNZ conducted a series of experiments investigating synthetic zeolite under New Zealand conditions. We confirmed that zeolite reduces the risk of subclinical and clinical milk fever in grazing cows supplemented with maize silage pre-calving. In trials conducted at DairyNZ’s Lye Farm, Waikato, we determined that feeding cows 500g/day of synthetic zeolite for two to three weeks before their expected calving date increased blood calcium concentrations at calving 5 ( Figure 1a ). Zeolite also resulted in a large pre-calving reduction in blood phosphate concentrations that persisted until about three days post-calving 5 ( Figure 1b ). This effect was expected, based on results from overseas trials, and is part of zeolite’s mechanism of action to prevent milk fever. However, the effects and safety of synthetic zeolite in diets already deficient in phosphorus are presently unknown. Therefore, synthetic zeolite is not currently recommended when diets include high amounts of fodder beet. Cows fed synthetic zeolite had lower blood magnesium concentrations but were not at risk of becoming hypomagnesaemic 5 ( Figure 1c ). Both control cows and zeolite-treated cows were supplemented with magnesium as per best farm practice. Careful management of magnesium supplementation pre- and post-calving is still required when using zeolite, especially in herds with a borderline magnesium status, to minimise the risk of grass staggers. Inside Dairy | April / May 2022 23
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