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Abstract
AIMS: To determine the variability of concentrations of Zn in feed, when used as a supplement to prevent facial eczema, and to determine the variability in concentrations of Zn in serum between cows and herds that are being supplemented with ZnO in feed, using in-shed feeders or on a feed pad.
METHODS: Sixteen commercial dairy farms in the Waikato region of New Zealand were enrolled, that were supplementing cows with ZnO in the feed using either an automatic in-shed feeder (ASF) or a feed pad (FP) using a feed-out or mixer wagon. On each farm 10 cows were selected by the farmer, that were assumed to be representative of the age and liveweight of the herd. Four hours after supplement feeding, each cow was weighed and a blood sample collected for measurement of concentrations of Zn in serum. Three samples of feed were collected from each farm for Zn analysis, from the beginning, middle and end of the feed being distributed. Levene’s test for homoscedasticity was used to analyse whether there were differences in variation of individual concentrations of Zn in serum, and in the feed, between the two feeding systems. Multivariable linear regression was used to examine associations between age, feeding method or liveweight and concentrations of Zn in serum, after accounting for the variability between farms.
RESULTS: Of the 163 cows sampled, concentrations of Zn in serum were between 20–35 µmol/L in 75/163 (46 (95% CI=38–54)%) cows; were <20 µmol/L in 71/163 (44 (95% CI=36–52)%) cows, and >35 µmol/L in 17/163 (10 (95% CI=6–16)%) cows. The variation in concentrations of Zn in serum in individual cows differed between farms (p<0.001), and the variability was greater for cows fed using a FP than ASF (p<0.001). There was no difference in the variation of concentrations of Zn in feed between the two feeding methods (p=0.54), but concentrations of Zn in serum were associated with the amount of Zn offered in feed (p=0.008).
CONCLUSIONS AND CLINICIAL RELEVENCE: There was significant variability between farms in the concentrations of Zn in the serum of cows being supplemented with ZnO in feed. Only 46% of cows sampled had concentrations of Zn between 20–35 µmol/L. Effective management of facial eczema should include monitoring Zn in the feed and in serum to ensure cows are receiving the correct dose they require.
| ASF | = | Automatic in-shed feeder |
| FP | = | Feed pad |
Acknowledgements
The authors would like to thank VetEnt for funding the study and publication to ensure their internally funded trials reach the industry. Thank you to Chris Mulvaney from StockCare for helping design the study, Richard Laven from the Institute of Veterinary, Animal and Biomedical Sciences, Massey University, for advice on editing the manuscript and to the farmers for their involvement in the study.