Amino acid efficiencies of utilization vary by different mechanisms in response to energy and protein supplies in dairy cows: Study at mammary-gland and whole-body levels

Abstract

Variations of mammary gland (MG) metabolism were studied in dairy cows in response to diets containing 2 levels of net energy of lactation [NE L ; 25.0 and 32.5 Mcal/d for low (LE) and high energy (HE), respectively], combined with 2 levels of metabolizable protein [MP, 1,266 and 2,254 g/d of protein digestible in the intestine for low (LP) and high protein (HP), respectively] in a 2 × 2 factorial arrangement. Four cows received 4 diets (LELP, HELP, LEHP, and HEHP) in a 4 × 4 Latin square design with 2-wk experimental periods. Milk production and feed intake were measured on the last 5 d of each period, whereas MG net uptake of AA was determined on d 13. Efficiencies were estimated as the sum of measured milk true protein yield (MPY) and of estimations of metabolic fecal and scurf proteins multiplied by their respective AA profile and divided by the estimated AA supply minus the AA endogenous urinary loss. The increased MPY in the HE compared with the LE diets (higher by 123 g/d) was accompanied by increased mammary plasma flow and MG uptake of the nonessential AA (NEAA) and the essential AA (EAA), except for branched-chain AA. In contrast, the increase in MPY (higher by 104 g/d) observed in the HP compared with the LP diets was linked to increased MG uptake of EAA without a change in mammary plasma flow and a decreased NEAA uptake. Because MG uptake of total AA-N was almost equal to cows' milk output on a nitrogen basis, these different mechanisms involve a large MG flexibility, with variable synthesis of NEAA. In addition, MP efficiency did not increase only through increased MPY in the HE compared with the LE diets but also through metabolic fecal protein, estimated to increase (by 65 g/d) with dry matter intake. The MPY increased in the HP compared with the LP diets, but the increase was smaller than the calculated increase (greater by 993 g/d) in MP supply. The highest MG clearance rates of individual EAA could suggest that Met, His, and Lys were limiting in LP, and Met was the most limiting AA in HP. Interestingly, a similar hypothesis could be stated by analyzing estimated AA efficiencies. The highest efficiencies among EAA, observed for His in HELP and for Met with the other diets, could indicate that they were the most limiting AA in these respective diets, whereas other EAA (including Lys) efficiencies varied with MP efficiency. The MG metabolic flexibility with regard to individual AA utilization partially contributes to the anabolic fate of AA through MPY; however, other export proteins also contribute to variations in MP and AA efficiencies.

Nitrogen metabolism and mammary gland amino acid utilization in lactating dairy cows with different residual feed intake

“…However, few studies have reported the relationship between efficiency of mammary AA utilization and RFI. Many studies have been conducted to improve AA utilization efficiency through nutritional manipulation, such as infusing AA or hormones [ 20 , 21 ] and altering dietary levels of energy or protein [ 22 ]. In comparison with nutritional manipulation, genetic selection may provide cumulative, longer-term enhancements of traits [ 23 ].…”

Milk production and efficiency of utilization of nitrogen, metabolizable protein, and amino acids are affected by protein and energy supplies in dairy cows fed alfalfa-based diets

“…Effects of energy and MP supplies on MPY have been reported to be additive and independent (Broderick, 2003;Raggio et al, 2006;Omphalius et al, 2019a), except in one study (Brun-Lafleur et al, 2010). Increased energy intake or postruminal glucose infusion led to an increased efficiency use of MP, whereas an increased MP supply decreased it (Omphalius et al, 2019a(Omphalius et al, , 2020. Maintaining an adequate supply of EAA with a reduced supply of MP combined with an increased energy supply might further increase MP efficiency use and MPY.…”

Amino acid transportation, sensing and signal transduction in the mammary gland: key molecular signalling pathways in the regulation of milk synthesis

“…The functions of amino acids have been extensively studied in the gut, liver, muscle and adipose tissue, especially in the field of protein (4) and fat metabolism (5) . In the mammary gland, amino acid uptake from blood is almost equal to milk output based on a nitrogen basis in dairy cows (6)(7)(8) , goats (9) , sows (10) and ewes (11) . However, the destinies of different amino acids in mammary cells are different (6)(7)(8)(10)(11)(12) .…”

“…In the mammary gland, amino acid uptake from blood is almost equal to milk output based on a nitrogen basis in dairy cows (6)(7)(8) , goats (9) , sows (10) and ewes (11) . However, the destinies of different amino acids in mammary cells are different (6)(7)(8)(10)(11)(12) . The mammary amino acid uptake:output ratios could be larger (for example, valine, isoleucine, leucine and arginine), equal (for example, methionine and histidine) or less than 1 (for example, asparagine and proline) (mammary amino acid uptake:output ratios in cows, goats, sows and ewes are shown in Table 1) (6)(7)(8)(10)(11)(12) .…”

“…However, the destinies of different amino acids in mammary cells are different (6)(7)(8)(10)(11)(12) . The mammary amino acid uptake:output ratios could be larger (for example, valine, isoleucine, leucine and arginine), equal (for example, methionine and histidine) or less than 1 (for example, asparagine and proline) (mammary amino acid uptake:output ratios in cows, goats, sows and ewes are shown in Table 1) (6)(7)(8)(10)(11)(12) . Those amino acids with uptake:output ratios greater than 1 can be metabolised to CO 2 , urea, polyamine or simply other non-essential amino acids (13) .…”