Fortification of silage and hay crops with trace elements

Abstract

Feeding out conserved hay or silage to animals over winter or in early spring is an integral part of New Zealand pastoral farming. However, the mineral content of conserved feed is usually below that of the original pasture, and is fed to stock at a time when their mineral requirements are high. During these periods, iodine and copper concentrations in pasture are marginal or deficient, exacerbating the problem. Three trials were laid down, two in Southland and one in the Waikato, looking at the uptake of copper (Cu), cobalt (Co), selenium (Se), and iodine (I) when applied in liquid form at various times between the shutting‐up stage and harvesting of conserved silage and hay paddocks. Application times for the Southland trials were 4 weeks prior to cutting, 2 weeks prior to cutting, the same day as cutting and onto the windrow after cutting. Minerals applied and rates of application were Cu: 0, 0.5, 1 and 3 kg copper sulphate ha^–1, Se: 10 g Se ha^–1 as sodium selenate, I:200 g potassium iodate ha^–1, and Co: 60 g cobalt sulphate ha^–1. For the Waikato trials two rates of copper sulphate (1 and 2 kg ha^–1) along with one rate of Co, Se and I were spray applied to silage and hay crops 4 and 7 weeks before harvesting respectively. The application of 3 kg CuSO4ha^–1 as a spray to pastures 4 weeks prior to them being harvested increased the Cu status of the silage from 9 to 18 mg kg^–1 and from 8 to 15 mg kg^–1, and of the hay from 12 to 49 mg kg^–1 and from 7 to 13 mg kg^–1 at the two Southland trials respectively. However, only the increase from 12 to 49 mg kg^–1 was statistically significant (P < 0.001). In the Waikato the application of 2 kg CuSO4 ha^–1 lifted the Cu concentration from 7 to 11 ppm, and from 6 to 9 ppm for the silage and hay respectively (P < 0.01). In Southland the application of 0.5 kg CuSO4 ha^–1 directly onto the windrow following cutting increased Cu concentrations from 8 to 31 ppm for the silage and from 12 to 63 ppm and 7 to 24 ppm for the hay (P < 0.001). It is recommended that to increase the Cu status of silage and hay sufficient to supply the animal requirements that 3 kg CuSO4 ha^–1 be applied as a spray to pastures 4 weeks prior to harvest for silage or hay, or alternatively that Cu be applied to the windrow once cut at a rate no greater than 0.5 kg CuSO4 ha^–1. The addition of the other trace elements, I and Co to the Cu spray further enhanced the conserved feeds’ mineral concentrations, and this is likely to be reflected in enhanced animal mineral status.

Key words:

• silage
• hay
• copper
• cobalt
• selenium
• iodine
• animal nutrition