Evaluation of National Academies of Sciences, Engineering, and Medicine (NASEM, 2021) feed evaluation model on predictions of milk protein yield on Québec commercial dairy farms.

A recent study assessed the ability of 4 feed evaluation models to predict milk protein yield (MPY) in a commercial context, with data of 541 cows from 23 dairy herds in the province of Québec, Canada. However, the recently published Nutrient Requirements of Dairy Cattle from the National Academies of Sciences, Engineering, and Medicine (NASEM, 2021) was not released at that time. Thus, the current study evaluated NASEM using the same dataset.

Effects of protein and forage source on performance and splanchnic and mammary net fluxes of nutrients in lactating dairy cows.

This study was conducted to determine if the decreased MP supply predicted by the NRC (2001) when canola meal (CM) substitutes soybean meal (SBM) was supported by direct measurement of net portal absorption of AA or energy-yielding nutrients, plus the effect of the type of forage in CM-based rations. Nine Holstein cows with indwelling catheters in splanchnic blood vessels, 8 also with a ruminal cannula, were used to examine the effects of protein source in corn silage-based diets, comparing SBM versus CM, and forage source in CM-based diets, comparing corn versus grass silage. The cows were allocated to a triple 3 × 3 Latin square design with 21-d periods.

A meta-analysis of the relationship between milk protein production and absorbed amino acids and digested energy in dairy cattle.

Milk protein production is the largest draw on AA supplies for lactating dairy cattle. Prior NRC predictions of milk protein production have been absorbed protein (MP)-based and used a first-limiting nutrient concept to integrate the effects of energy and protein, which yielded poor accuracy and precision (root mean squared error [RMSE] >21%). Using a meta-data set gathered, various alternative equation forms considering MP, absorbed total EAA, absorbed individual EAA, and digested energy (DE) supplies as additive drivers of production were evaluated, and all were found to be superior in statistical performance to the first limitation approach (RMSE = 14%-15%).

Ability of three dairy feed evaluation systems to predict postruminal outflows of amino acids in dairy cows: A meta-analysis.

Adequate prediction of postruminal outflows of essential AA (EAA) is the starting point of balancing rations for EAA in dairy cows. The objective of this meta-analysis was to compare the performance of 3 dairy feed evaluation systems (National Research Council [NRC], Cornell Net Protein and Carbohydrate System version 6.5.

Synthesis of milk components involves different mammary metabolism adaptations in response to net energy and protein supplies in dairy cows.

Net energy for lactation (NE) and metabolizable protein (MP) are the 2 main nutritional forces that drive synthesis of milk components. This study investigated mammary-gland metabolism in dairy cows in response to variations in the supply of NE and MP. Four Holstein dairy cows were randomly assigned to a 4 × 4 Latin square design, in which each experimental period consisted of 14 d of dietary treatment.