Effect of source and frequency of rumen-protected protein supplementation on mammary gland amino acid metabolism and nitrogen balance of dairy cattle

• Published in: Journal of dairy science 2024-09, Vol.107 (9), p.6797-6816
• Main Authors: Nichols, K., Wever, N., Rolland, M., Dijkstra, J.
• Format: Article
• Language: English
• Subjects: amino acid profile; Amino Acids - metabolism; Animal Feed; Animals; Cattle; Diet - veterinary; Dietary Proteins - administration & dosage; Dietary Proteins - metabolism; Dietary Supplements; Digestion - drug effects; Female; Lactation; Mammary Glands, Animal - metabolism; Milk - chemistry; Milk - metabolism; milk nitrogen efficiency; Nitrogen - metabolism; oscillation; Rumen - metabolism; rumen-protected amino acid; Silage
• ISSN: 0022-0302; 1525-3198; 1525-3198
• DOI: 10.3168/jds.2023-24370

The list of standard abbreviations for JDS is available at adsa.org/jds-abbreviations-24. Nonstandard abbreviations are available in the Notes. The AA profile of MP affects mammary gland metabolism and milk N efficiency of dairy cattle. Further, the frequency of dietary protein supplementation may influence N partitioning leading to reduced N excretion. This study investigated the effect of source and frequency of rumen-protected (RP) protein supplementation on apparent total-tract digestibility, milk production, mammary gland AA metabolism, and N balance of dairy cattle. Twenty-eight Holstein-Friesian cows (2.3 ± 0.9 lactations; 93 ± 27 DIM; mean ± SD) were used in a randomized complete block design and fed a basal TMR consisting of 41% corn silage, 32% grass silage, and 27% concentrate (DM basis) and formulated to meet 100% and 95% of net energy and MP requirements, respectively. Cows were adapted to the basal TMR in a freestall barn for 7 d, moved to individual tiestalls for 13 d of adaptation to dietary treatments, and then moved into climate respiration chambers for a 4-d measurement period. Treatments consisted of the basal TMR (CON; 159 g CP/kg DM) or the basal TMR including 1 of 3 iso-MP supplements: (1) 315-g mixture of RP soybean meal and RP rapeseed meal fed daily (ST-RPSR), (2) 384-g mixture of RP His, RP Lys, and RP Met fed daily (ST-RPAA), and (3) 768-g mixture of RP His, RP Lys, and RP Met fed every other day (OS-RPAA). The basal TMR with the addition of treatment supplements was designed to deliver 100% of required MP over a 48-h period. The mixture of His, Lys, and Met was formulated to deliver digestible AA in amounts relative to their concentration in casein. Compared with ST-RPSR, ST-RPAA increased milk protein and fat concentration, increased the arterial concentration of total His, Lys, and Met (HLM), decreased mammary clearance of HLM, and increased clearance of Phe, Leu, and Tyr (tendency for Leu and Tyr). Rumen-protected protein source did not affect N balance, but the marginal use efficiency (efficiency of transfer of RP protein supplement into milk protein) of ST-RPAA (67%) was higher than that of ST-RPSR (17%). Milk protein concentration decreased with OS-RPAA compared with ST-RPAA. Arterial concentration of HLM increased on the nonsupplemented day compared with the supplemented day with OS-RPAA, and there was no difference in arterial HLM concentration across days with ST-RPAA. Mammary uptake of HLM tended to increase on the no