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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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Interestingly, the DairyNZ experiments also indicated that synthetic zeolite may improve uterine health and herd reproductive performance, as zeolite-treated cows tended to conceive earlier in the breeding season. This later result was consistent with a recent trial in housed cows fed a total mixed ration at Cornell University, USA 4 . However, both DairyNZ and overseas experiments were conducted with a small number of animals under highly controlled conditions and required validation with larger numbers of cows across commercial herd environments. Large-scale studies in commercial herds validate milk fever reduction Therefore, a two-year study was conducted to: 1. test the practicality of feeding synthetic zeolite pre- calving under grazing conditions 2. confirm its effectiveness in reducing the risk of milk fever 3. verify its potential to improve herd reproduction. During the 2019/20 season, approximately 1000 cows across three herds in the Waikato were enrolled in the Zeolite Scale-Up Trial, with another 1500 cows across three herds participating the next season. During each season, half of the cows in each herd received 500g/day of synthetic zeolite for three weeks pre-calving. Results clearly demonstrated that feeding synthetic zeolite pre-calving consistently reduced the incidence of clinical milk fever cases: from an average of 4.4% in untreated control cows to 1.2% in zeolite-treated cows. This meant zeolite- treated cows were nearly four times less likely to succumb to clinical milk fever. It also reduced the incidence of subclinical milk fever, as cows fed zeolite had higher blood calcium concentrations within one day of calving ( Figure 2 ). As expected, blood magnesium and phosphate concentrations at this time were lower in zeolite-treated cows. There were some differences between herds in their blood mineral responses to zeolite ( Figure 2 ), indicating that herds with a history of milk fever issues are likely to benefit the most from this strategy. Results also indicated that synthetic zeolite is most effective in reducing milk fever when delivered to springer cows using maize silage or meal in troughs/bins or using pelletised feed via in-shed systems. Poorer responses will be obtained if synthetic zeolite is top- dressed onto pasture silage in the paddock, as large amounts are wasted and not ingested by cows. We did not detect any improvements in submission, conception or in-calf rates in zeolite-treated cows. This suggests the strategy will not lead to better herd reproductive performance. 24 Inside Dairy | April / May 2022 Figure 1. The effect of feeding synthetic zeolite for two to three weeks pre- calving on blood concentrations of (A) calcium, (B) phosphate and (C) magnesium, relative to untreated controls. Pink shaded area shows threshold for hypocalcaemia. A 2.60 Blood calcium (mmol/L) 2.40 2.20 2.00 1.80 Control 1.60 Zeolite 1.40 -21 -14 -7 0 7 14 21 28 B Days (relative to calving) 2.50 Blood phosphate (mmol/L) 2.00 1.50 1.00 0.50 0.00 -21 -14 -7 0 7 14 21 28 Days (relative to calving) C 1.20 Blood magnesium (mmol/L) 1.00 0.80 0.60 0.40 -21 -14 -7 0 7 14 21 28 Days (relative to calving) Figure 2. Feeding synthetic zeolite for three weeks pre-calving improved blood calcium concentrations within one day of calving, especially in herds with hypocalcaemia issues in untreated controls. Blood calcium (mmol/L) 2.20 Control Zeolite 2.10 2.00 1.90 1.80 1.70 1.60 1 2 3 4 5 6 Herd
