Dietary Cation–Anion Difference of Timothy as Affected by Development Stage and Nitrogen and Phosphorus Fertilization

Abstract

Dry dairy cows (Bos taurus) fed forages with a high dietary cation–anion difference (DCAD) are more likely to develop hypocalcaemia. We determined how development stage at harvest and N and P fertilization can be used to reduce the DCAD to <250 mmolc kg−1 dry matter (DM) for timothy (Phleum pratense L.) grown on a soil high in K content. Stages of development (stem elongation, early heading, late heading, and early flowering) in spring growth, and treatments of P (0, 15, 30, and 45 kg ha−1) and N (0, 60, 120, and 180 kg ha−1) fertilization were evaluated. Concentrations of K, Na, Ca, Mg, Cl, S, and P of timothy were determined and the DCAD was calculated with a short (DCADS) and a long (DCADL) equation. From stem elongation to early flowering, DCADS decreased from 326 to 196 mmolc kg−1 DM and DCADL from 297 to 181 mmolc kg−1 DM; this reduction was attributed to a decrease in K concentration and a slight increase in Cl concentration with development stage. Nitrogen fertilization increased DCADS and DCADL only at stem elongation; the lack of a response at later stages of development is explained by the concomitant increase in both K and Cl concentrations with increasing N fertilization. Phosphorus fertilization did not affect DCADS and DCADL even though it increased timothy P concentration. Harvesting timothy at late heading, with an appropriate N fertilization to ensure adequate yield, is an option to produce a forage with a DCAD of <250 mmolc kg−1. DM on a soil high in K.