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
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