Praseodymium and copper cation‐exchange capacities of neutral‐detergent fibres relative to composition and fermentation kinetics

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Abstract
The cation‐exchange capacity (CEC) of 12 neutral‐detergent fibres (NDF) was measured using the elements praseodymium (Pr III) and copper (Cu II) at pH 3.5. CEC was positively correlated with lignin and nitrogen content as well as the lignin: acid‐detergent fibre ratio of the NDF. CEC was also measured using Pr at pH 7.0. Increasing the pH of exchange from 3.5 to 7.0 significantly increased the CEC. Lignin had a higher correlation with CEC at pH 7.0. The relationship between CEC and the fermentation rates of NDF was non‐significant. However, lag, i.e. the period of time before the initiation of fermentation, tended to decrease with increasing CEC. NDF influences the rumen ecosystem by buffering rumen pH, exchanging cations to influence osmotic pressure, and providing substrate and microenvironments for anaerobic microorganisms. Consequently, CEC needs to be measured at conditions which simulate the rumen. It is recommended that the Pr method should be used to measure CEC as it is a simple, yet robust technique that can be buffered to simulate conditions of the entire gastrointestinal tract ranging in pH from 2.0 to 7.0.