Effects of reduced metabolizable protein diets supplemented with rumen-protected His under adequate Met and Lys supply on production, nutrient digestibility, N utilization, and manure ammonia emissions in lactating cows
Year: 2025
Type: article
Abstract: Balancing for limiting AA may prevent reduced production when deficient MP is provided.The objective of the study was to determine the effects of rumen-protected (RP) His supplementation at different levels of MP when Lys and Met supplies meet the requirements.Sixty lactating cows (mean ± SD; parity, 2.47 ± 1.346; DIM, 112 ± 27; milk yield, 50 ± 8 kg/d) were used in a randomized complete block design and allocated to one of the following diets: an MP-adequate diet that meets the MP, Met, Lys, and His requirements (CP, 17.0%) has been reported; an MP-moderately deficient diet (92.6% of the requirement) meeting the requirement of Met and Lys (MDMP; CP, 15.4%); the MDMP diet supplemented with RP-His to meet the His requirement; an MP-deficient diet (86.7% of requirement) meeting the requirement of Met and Lys (DMP; CP, 14.5%); the DMP diet supplemented with RP-His to meet the requirement of His.The experiment lasted for 6 weeks of data collection after 2 wk of covariate.During the last week, feces and urine collected from 8 blocks were used to reconstitute manure based on the individual daily excretion of feces and urine.Manures were incubated for 12 d using a steady-state airflux chamber system.Milk yield, milk fat and protein, DMI, and BW were not affected by treatments.Lowering MP supply linearly decreased total-tract N digestibility and urinary N excretion but increased N use efficiency for milk protein (MNE; 31.4% to 38.3% of N intake).Lowering MP supply also linearly decreased plasma urea-N (11.2 to 8.12 mg/dL) and tended to decrease plasma His (57.6 to 48.0 μmol/L).Supplementation of RP-His decreased MNE because it did not increase milk N excretion.Blood hemoglobin (8.21 to 8.40 g/dL) and plasma His (50.4 to 52.2 μmol/L) and carnosine (14.4 to 14.9 μmol/L) numerically increased by RP-His, but the differences were not significant.Lowering MP supply tended to linearly increase the ratio of feces to urine and linearly decreased daily and cumulative NH 3 emissions from manure.However, RP-His supplementation did not affect daily and cumulative NH 3 emissions.In conclusion, the diets supplying deficient MP but adequate Met and Lys did not negatively affect milk yield and protein yield.Supplementing the MP-deficient diets with RP-His did not increase milk and milk protein yields.It is likely that additional His was provided from the endogenous His pool during the 6-wk feeding period, resulting in lack of His deficiency.Further studies on the sources of endogenous His and their contribution to milk protein synthesis under varying degrees of His deficiency.
Source: Journal of Dairy Science
Authors: K. Park, J. Kim, H. Hu, M. Kambara, K. Nakagawa, C. Lee
Institutions: The Ohio State University, Ajinomoto (Japan)
Language: English
Subfield: Agronomy and Crop Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: gold
Estimated APC paid: $3,500
Funders: Ajinomoto, Ohio State University
OpenAlex ID: W7117684974