Mammary Uptake, Portal-Drained Visceral Flux, and Hepatic Metabolism of Free and Peptide-Bound Amino Acids in Cows Fed Steam-Flaked or Dry-Rolled Sorghum Grain Diets

Abstract

Our objectives were to measure net fluxes of free AA (FAA) and peptide-bound AA (PBAA) across portal-drained viscera, liver, splanchnic tissues, and mammary tissues, and milk AA output of lactating Holstein cows (n = 8, 86 +/- 8 d in milk). Cows were fed an alfalfa-based total mixed ration containing 40% steam-flaked (SFS) or dry-rolled (DRS) sorghum grain. The total mixed rations were offered at 12-h intervals in a crossover design. Blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and from mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter was 17.9 and 18.6 kg/d of the SFS and DRS diets, respectively, but dropped to 16.3 kg/d for cows fed the SFS diet in the last 3 experimental days, sampling day included. Milk and milk crude protein yields (kg/12-h sampling) were 13.85 vs. 13.25 and 0.425 vs. 0.396 for cows fed SFS or DRS, respectively, and were not affected by the considerable drop in dry matter intake of cows fed the SFS diet during the last 3 experimental days. The portal-drained visceral flux of total essential FAA was 417 and 442 g/12 h (SEM 63) in cows fed SFS and DRS, respectively. However, the portal-drained visceral flux of 7 essential PBAA out of the 9 determined was numerically greater in cows fed the SFS diet, and total essential PBAA in that treatment was 77.4 +/- 22.2 compared with 35.4 +/- 50.2 g/12 h for cows fed the DRS diet. This phenomenon was again observed in a greater total splanchnic flux (FAA + PBAA) of 462 and 371 g/12 h in SFS- and DRS-fed cows, respectively. Mammary uptake of essential AA from both pools (free and peptide bound), and recovery of essential AA in milk, was again numerically higher in SFS-fed cows. In addition to FAA, quantifying the contribution of PBAA may improve our understanding of tissue use of AA substrates, and this may ultimately lead to improved diet formulations with respect to intestinal absorption and mammary uptake of AA.

Dipeptide (Methionyl-Methionine) Transport and Its Effect on β-Casein Synthesis in Bovine Mammary Epithelial Cells

“…Taken together, our data support the possibility that PepT2 plays an important role in Met-Met uptake in BMECs. PBAA has been reported to promote protein synthesis and secretion in different studies [15,26]. In the study, 80 μg/ml Met-Met significantly increased β-CN expression in BMECs.…”

Characterization of chiral amino acids from different milk origins using ultra-performance liquid chromatography coupled to ion-mobility mass spectrometry

“…Although the somatic cell count (SCC) in milk is the routine index of mastitis in dairy stock, the measure of D-AAs in milk can facilitate a deeper understanding of mastitis pathogenesis and its effects on lactation. As different feedstuff exert influences on AA compositions in milk50, specific analysis of L-AAs and D-AAs may provide deep insight into metabolic mechanism of dairy animals and humans. The significant discrepancy of the concentrations of some D-AAs in cow milk between the present research and a published study18 may be a reflection of differences of microorganism numbers between both samples51.…”

Responses of mammary amino acid metabolism and aminopeptidase N gene expression to duodenal soyabean small peptides and infusion of free amino acids in lactating goats

“…In the control group of the present study, the mammary gland uptake of AA (TEAA+TNEAA) was 18 g/d (0.75×24), and was lower than the 24 g/d AA in milk protein output. The supply of AA for milk protein synthesis was therefore deficient by 24% in the control treatment, and lack of AA might be compensated for by uptake of circulating peptide-bound AA (Tagari et al, 2004(Tagari et al, , 2008, suggesting that peptide-bound AA could be used by the mammary gland. In the SSP and FAA groups, the uptake of AA (32 vs 55 g/d) was higher than the milk protein output (29 vs 36 g/d).…”

“…Numerous studies report that free amino acids (FAA) and peptide-bound amino acids (PBAA) are the sources for milk protein synthesized by the mammary gland (Tagari et al, 2004(Tagari et al, , 2008Mabjeesh et al, 2005). Some of the amino acids (AA) circulating in blood plasma are in the form of peptides (Seal and Parker, 1991;Koeln et al, 1993), and variable contributions of PBAA to the total concentration of AA have been reported (Remond et al, 2000, Tagari et al, 2004.…”