Abstract:
Currently, recommendations of fibre requirements for lactating cows grazing highly digestible pastures are based on dietary neutral detergent fibre (NDF) concentrations. Data from experiments investigating milk production responses of grazing cows to concentrate and forage supplements were examined to determine if dietary NDF concentrations reliably predicted milk fat concentrations. Within 2 pasture types, predominantly clover or ryegrass, dietary NDF concentration was related (p<0.05) to milk fat concentration. However, the large variation within these relationships and the differences between sward types highlighted issues with using dietary NDF concentration as a sole predictor of milk fat concentration. The effective NDF (eNDF) system has improved the precision of estimating fibre requirements of cows fed total mixed rations. However, when applied to our data, there was no relationship between dietary eNDF concentration and milk fat concentration for cows grazing either pasture type. More precise estimates of the effectiveness factors for grazed herbage may assist in defining the minimum level of NDF required to maintain milk fat concentration.