Response to Increased Rumen Undegradable Protein Intake by Lactating Dairy Cows1

A dataset was constructed from literature published between 1988 and 2000 to determine whether increased intake of rumen undegradable protein (RUP) was related to increased milk and milk component production. The dataset represented 436 treatment means from 77 published reports. Nutrient intakes were calculated using tabular values for nutrient contents of individual feeds. There was no relationship between RUP content of diets and milk production, unless RUP content of feeds was adjusted to reflect differences in DMI. Increased intake of RUP was associated with increased yield of milk, 4% fat-corrected milk (FCM), and energy-corrected milk (ECM). Using new systems to adjust intake of rumen undegradable intake protein for diet and DMI effects resulted in marginal improvement to the relationships when compared with the use of tabular values for the RUP content of feeds. Within the dataset, a 526-g increase in RUP intake at constant DMI was required to produce a 1-kg increase in milk. Further improvement in predicting milk production response to undegradable protein intake will require investigation of other factors such as amino acid flow, specific attributes of feeds, and/or stage of lactation.