Abstract
Rations with low to negative dietary cation-anion difference (DCAD) given to dairy cows before calving reduce the risk of hypocalcaemia (milk fever). Different strategies for increasing forage DCAD were investigated in field trials in Central and Western Norway. Fertilisation with 70, 140 or 210 kg Cl per hectare as calcium chloride and low supply rates of K reduced DCAD in forage harvested at late developmental stages in spring growth of timothy and meadow fescue. The ideal negative DCAD was only attained on soils very low in plant available K. Timing (spring versus late spring) and source of Cl (CaCl2 versus MgCl2) were of no importance for the result. When pure stands of seven grasses were fertilised in spring either without chloride or with 140 kg chloride per hectare, the lowest values of DCAD after chloride fertilisation were found in perennial ryegrass and reed canary grass. By comparison, cocksfoot had equally high or higher Cl concentrations in its tissues, but accumulated more K, and seemed to be poorly suited for low DCAD forage production. It was concluded that Cl fertilisation is a more efficient means of controlling DCAD than sward species composition.
Highlights
Hypocalcaemia is a common metabolic disease in dairy herds in the Nordic countries
In the present study, which was conducted in Central and Western Norway, close to the coast of the North Sea, we have further explored whether dietary cation-anion difference (DCAD) in forages could be controlled by Cl fertilisation
The difference in DCAD between applications of 70 and 140 kg Cl ha-1 was not statistically significant, but a further increase to 210 kg Cl ha-1 resulted in a lower DCAD
Summary
Hypocalcaemia (milk fever) is a common metabolic disease in dairy herds in the Nordic countries. Forages for dry cows should preferably be of low digestibility and energy concentration, which is presently obtained by harvesting the grass crop at late phenological stages. To further produce this feed with a low DCAD, by Cl fertilisation, would be a cost-effective method to reduce the risk of hypocalcaemia. If feasible, this strategy would have the potential to reduce the challenges related to low palatability and intake of anionic salts
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