The objective of this study was to estimate the dietary apparent digestible fraction of nonfiber carbohydrates (NFC) using the Lucas test concept. The dataset contained a total of 167 observations with 57 originated from two trials conducted with lactating cows and 110 from three experiments with growing and finishing cattle. The dataset was randomly divided in two subsets. The first subset was used to estimate the model parameters while the second for model validation. Tests for checking equality of models were conducted using a Dummy variable for comparing animal categories. The true digestibility coefficient did not differ between animal categories, and the estimated value was 0.9705. It was observed greater metabolic fecal NFC for lactating cows than for growing and finishing cattle. The metabolic fecal NFC expressed as a percentile of dietary NFC levels (NFC%) did not change in this study. Thus, the dietary apparent digestible NFC (NFCad%) can be estimated by the following equations: NFCad% = 0.9507NFC% - 5.72 for lactating cows and NFCad% = 0.9507NFC% - 5.11 for growing and finishing cattle. The model validation procedure indicated that observed and estimated values of NFCad% were not different. It can be concluded that the Lucas test yields reliable estimates of NFCad%.
apparent digestibility; NRC system; summative equations; total digestible nutrients
