The objectives of the present study were (1) to assess the adequacy of the in vitro and chemical methods to predict post-ruminal crude protein supply (PRCP) from fresh tropical forage, and (2) to identify PRCP supply predictors. Twenty-three fresh forage grasses and 15 forage legumes commonly used in domestic cattle feeding in the tropics and subtropics were incubated in the rumen of cows to determine ruminal crude protein (CP) degradation. The PRCP supply was calculated from in situ rumen-undegraded CP and in vitro organic matter digestibility (i.e., reference method), from ammonia-nitrogen release during in vitro incubation (i.e., in vitro method), and from the concentrations of chemical CP fractions (i.e., chemical method). The adequacy was evaluated using error-index and dimensionless parameters, and stepwise regression was used to select PRCP predictors. Adequacy ranged from poor to moderate (0.53 to 0.74) for the in vitro method being lower for forage legumes at a slow rumen passage rate (0.20), and even poorer (0.02 to 0.13) for the chemical method. Hence, the in vitro method can estimate PRCP supply in tropical forages with moderate to high but not with slow passage rates. Equations developed in the present study appear to predict PRCP supply with reasonable adequacy.

Rising platemeters are commonly used in Ireland and New Zealand for managing intensive pastures. To assess the applicability of a commercial rising platemeter operating with a microsonic sensor to estimate herbage mass with its own equation, the objectives were (i) to validate the original equation; (ii) to identify possible factors hampering its accuracy and precision; and (iii) to develop a new equation for heterogeneous swards. A comprehensive dataset (n = 1511) was compiled on the pastures of dairy farms. Compressed sward heights were measured by the rising platemeter. Herbage mass was harvested to determine reference herbage availability. The adequacy of estimating herbage mass was assessed using root mean squared error (RMSE) and mean bias. As the adequacy of the original equation was low, a new equation was developed using multiple regression models. The mean bias and the RMSE for the new equation were overall low with 201 kg dry matter/ha and 34.6%, but it tended to overestimate herbage availability at herbage mass < 500 kg dry matter/ha and underestimate it at >2500 kg dry matter/ha. Still, the newly developed equation for the microsonic sensor-based rising platemeter allows for accurate and precise estimation of available herbage mass on pastures.

The present study evaluated the influence of three dietary levels of undegraded crude protein in the fermentative compartment (UDCP) on intake, fecal and urinary excretion, nitrogen partitioning, and apparent organic matter digestibility in alpacas. Eight male alpacas were assigned to low (14% crude protein), medium (24% crude protein), and high (34% crude protein) UDCP treatments in an incomplete and unbalanced 3‐period crossover design using isoproteic and isoenergetic diets. No differences were observed among treatments in dry matter intake, organic matter intake, fecal excretion of dry matter, organic matter, and nitrogen; nitrogen retention; or apparent organic matter digestibility. In contrast, water intake, nitrogen intake, urinary nitrogen excretion, nitrogen absorbed, and nitrogen efficiency ratios were influenced by UDCP treatment. The high UDCP treatment was characterized by lower urinary nitrogen losses and a higher proportion of retained nitrogen relative to absorbed nitrogen compared with the low UDCP treatment, despite similar nitrogen intake. Conversely, the low UDCP treatment promoted higher nitrogen absorption but was associated with greater urinary nitrogen excretion and a lower retention‐to‐absorption ratio. Overall, these results indicate that increasing the dietary contribution of UDCP reduces post‐absorptive nitrogen losses in alpacas, thereby improving nitrogen utilization efficiency relative to low UDCP diets.