Melamine, from fertilizer to pasture to cow's milk

[摘要] ENGLISH ABSTRACT: The aim of this study was to determine the rate of transfer of melamine as fertilizer ingredient tokikuyu pastures and if melamine would be transferred from the fertilized pasture to cow's milk.Three trials were conducted in the study, viz. a pilot pot plant trial, an applied pasture trial and amilk production trial.Melamine is a commercially available industrial chemical with a high nitrogen content. Largequantities of melamine waste can sometimes be incorporated into crop and pasture fertilizers dueto the high N content. An initial pot plant trial with kikuyu was conducted to determine whethermelamine would be absorbed as such from the soil to the plant material. The pots were fertilized inthe form of melamine adulterated Chinese maize Gluten 60, at a rate equivalent to 8.8 kg ofmelamine/ha. Results indicated that melamine was indeed absorbed and 7 days after fertilization,the concentration of melamine in the grass was 228 mg/kg.An applied pasture trial was then conducted were three pastures of 0.3 ha each were used. Onepasture served as a control and received N fertilization in the form of LAN at a rate of 40 kg N/ha.The other two pastures also received LAN, but with 10% (Treatment 1) and 20% (Treatment 2) ofthe LAN-N substituted with melamine-N. All three pastures also received P-fertilization in the formof Single Superphosphate at a rate of 20 kg P/ha and KCl fertilizer at a rate of 50 kg K/ha. Pasturesamples were taken once a week for 10 weeks, each time at the exact same spot in each camp.Samples were dried and finely milled before analysis via LC-MS/MS for melamine content. Theinitial concentration of melamine in the grass of Treatment 2 was higher than that in the grass ofTreatment 1. The rate at which melamine decayed in the plant material was found to be quitesimilar for the two melamine treatments. In this trial, melamine took around 10 weeks to reachundetectable levels in the grass. It was concluded that melamine was absorbed as such from thesoil by pasture grass when included in a fertilizer.For the milk production study, eighteen lactating Holstein cows, 60 ± 5.1 (SE) DIM, with a daily milkproduction of 36.5 ± 2.0 (SE) kg/d and weighing 609 ± 12.8 (SE) kg, were stratified according to milk production and then randomly allocated to three groups of six cows. The groups were thenrandomly allocated to the three pastures used in the applied pasture trial. Cows were kept on themelamine fertilized pasture for 9 days, in which they were allowed to graze the pasture forapproximately 10 hours each day. After the 9 day period, melamine was withdrawn by placing thecows on the control pasture that did not receive melamine contaminated fertilization for another 7days. During these 16 days, milk was collected twice a day, viz. during the morning and afternoonmilkings. Milk samples of each cow were sub-divided into two samples, one was preserved withpotassium dichromate and analysed for milk composition and the other was frozen until analysedfor melamine by LC-MS/MS. For the duration of the trial, melamine containing milk was destroyedin order to prevent it from contaminating milk collected from the rest of the herd. Results from theanalysis for melamine confirmed that melamine was transferred from melamine fertilized pasture tomilk. In this study, it took 6 days from melamine withdrawal for melamine to reach undetectablelevels in the milk. It was also found that the melamine fertilized pasture did not have any significanteffect on the average milk production and milk composition of the cows. The aim of the study wasmet and it was confirmed that melamine can be transferred from fertilizer to the soil, to the pasture and to the milk of cows grazing these pastures.

[发布机构] Stellenbosch University