Synthesis of milk components involves different mammary metabolism adaptations in response to net energy and protein supplies in dairy cows.

Net energy for lactation (NEL) and metabolizable protein (MP) are the 2 main nutritional forces that drive synthesis of milk components. This study investigated mammary-gland metabolism in dairy cows in response to variations in the supply of NEL and MP. Four Holstein dairy cows were randomly assigned to a 4 × 4 Latin square design, in which each experimental period consisted of 14 d of dietary treatment. The diets provided 2 levels of NEL (low energy, 25.0 Mcal/d vs. high energy, 32.5 Mcal/d) and 2 levels of MP (low protein, 1,266 g/d vs. high protein, 2,254 g/d of protein digestible in the intestine) in a 2 × 2 factorial arrangement. Performance and dry matter intake (DMI) were measured during the last 5 d of each period, and the mammary net balance was measured on d 13 by collecting 6 sets of blood samples from the left carotid artery and left mammary vein. Mammary plasma flow was measured according to the Fick principle for Phe and Tyr. The mammary net balance of carbon equaled the uptake of nutrients expressed as carbon minus the output of lactose, fatty acids (FA) synthesized in the mammary gland, AA of milk protein, and glycerol-3P from triglyceride on d 13. Milk, lactose, fat, and protein yields increased when NEL and MP supplies increased. However, increasing the NEL supply increased FA synthesis more than increasing the protein supply did. In addition, FA secretion increased more than lactose secretion when the NEL supply increased. Increasing the NEL supply increased the left half-udder uptake of all major energy-yielding nutrients by increasing mammary plasma flow. However, nutrient uptake increased more than milk output did, which in turn increased carbon dioxide output. This increase in nutrient oxidation by the mammary gland decreased the mammary efficiency of nutrients utilization when the NEL supply increased. Increasing MP supply tended to increase glucose uptake through mammary clearance and increased mammary AA uptake with no change in mammary plasma flow. In addition, the protein supply did not change the mammary uptake of acetate or ß-hydroxybutyrate. The increase in milk-component secretions in response to either NEL or MP supplies occurred through different metabolic adaptations (increase in mammary plasma flow vs. clearances, respectively). These results suggest that the nutrient use by the mammary gland is highly flexible, which helps in maintaining milk and milk-component yields even with limiting nutrient supplies.

Postruminal infusions of amino acids or glucose affect metabolisms of splanchnic, mammary, and other peripheral tissues and drive amino acid use in dairy cows.

Effects of AA and glucose infusions on efficiency of use of essential AA (EAA) were studied according to a 2 × 2 factorial using 5 multicatheterized cows in a 4 × 4 Latin square plus one cow, with 2-wk periods. The diet provided 87% of energy and 70% of metabolizable protein requirements, and the 4 treatments were abomasal infusions of (1) water, (2) an AA mixture with a casein profile (695 g/d), (3) glucose (1,454 g/d), or (4) a combination of AA and glucose infusions. Milk samples were collected on the last 6 milkings. On d 14, 6 blood samples were collected from arterial, and portal, hepatic, and mammary venous vessels. Splanchnic plasma flow was calculated by dilution of p-aminohippurate and mammary flow by the Fick principle using Phe + Tyr. The net flux of AA across tissues [splanchnic, i.e., portal-drained viscera (PDV) + liver, and mammary gland] was calculated as the efflux minus the influx across that tissue. The efficiency of EAA was calculated as the sum of exported true proteins [milk protein yield (MPY), scurf, and metabolic fecal protein] multiplied by their respective AA profile and divided by the predicted AA supply minus AA endogenous urinary loss. In addition, catabolism was estimated for each tissue: AA supply - (portal net flux + metabolic fecal protein) for the PDV; -hepatic net flux for the liver; splanchnic net flux - (-mammary net flux + scurf) for the other peripheral tissues; and -mammary net flux - milk for the mammary gland. The MIXED procedure (SAS Institute Inc., Cary, NC) was used with cow as a random effect. No AA × glucose interaction existed for most of the measured parameters. With infusions of AA and glucose, MPY increased by 17 and 14%, respectively. The decreased efficiency of EAA-N with AA infusion resulted from increased EAA-N in MPY smaller than the increased EAA-N supply and was accompanied by increased liver catabolism of His + Met + Phe (representing group 1 AA) and increased mammary and PDV catabolisms of group 2 AA-N (Ile, Leu, Lys, and Val). In contrast, the increased efficiency of EAA-N with glucose infusion, resulting from increased EAA-N in MPY with no change in EAA-N supply, was accompanied by decreased mammary catabolism of group 2 AA-N and hepatic catabolism of His + Met + Phe. No mammary catabolism of His, Met, and Phe existed in all treatments, as indicated by the mammary uptake to milk output ratio close to one for these EAA. Therefore, the mammary gland contributes significantly to variations of efficiency of group 2 AA-N through variations of AA catabolism, in response to both AA and glucose supplies, whereas additional PDV catabolism was observed with increased AA supply. Partition of AA use between tissues allows to delineate their anabolic or catabolic fate across tissues and better understand changes of efficiency of EAA in response to protein and energy supplies.

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.

Variations of mammary gland (MG) metabolism were studied in dairy cows in response to diets containing 2 levels of net energy of lactation [NEL; 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.

Association between nutritional values of hays fed to horses and sensory properties as perceived by human sight, touch and smell.

Although hay is the foundation of most equine diets, horse owners rarely ask for biochemical analysis and the routine practice is to choose hay based on its 'perceived' nutritional value. The present study aimed at exploring the relationship between sensory properties as perceived by sight, touch and smell, and the nutritional value of hay measured by biochemical analysis using a 'free sorting task' method. Fifty-four non-expert participants were asked individually to: (1) observe 21 hays samples, (2) group together hays that they perceived as similar for each of the three modalities (hay appearance, odour or texture) and (3) characterize each formed group with a maximum of five descriptive terms. For each modality, results were recorded in a contingency matrix (hays × terms) where only terms cited at the minimum five times for at least one sample, were kept for data analysis. A correspondence analysis (CA) was performed on the contingency matrix to plot both samples and descriptive terms on a χ2 metric map. Then, a Hierarchical Ascending Classification (HAC) was performed on the coordinates of samples in the CA space. Clusters were identified by truncating the HAC tree-diagrams. The attributes that defined the best resulting clusters were identified by computing their probability of characterizing a cluster. Correlations were computed between each biochemical parameter on one hand, and the first two dimensions of the CA map on the other. Finally, correlations between the values of each hay on the first dimension of the three CA maps (appearance, odour and texture) were computed. Hedonic descriptive terms were primarily used for describing odour and texture modalities. For describing hay appearance, participants spontaneously used visual cues referring to colour or aspect. Based on the tree-diagrams resulting from the HAC, 3, 5 and 2 groups were clustered, respectively for appearance, odour and texture description. Digestible energy was correlated to the first dimension on the three CA maps, whereas CP was correlated to the first dimension of the CA appearance map only. While NDF value was correlated to the first and second dimensions on the CA odour map only, ADF content was correlated to the first dimension on the three CA maps. Non-fibre carbohydrates were correlated to the first dimension of the CA appearance map only. The similarity-based approach which is part of the standard toolbox of food sensory evaluation by untrained consumers was well adapted to animal feeds evaluation by non-experts.