Effects of increasing dietary arginine supply during the three first weeks after weaning on pig growth performance, plasma amino acid concentrations, and health status.

A total of 425 weaned pigs (Exp. 1: 225 pigs [5.8 ±â€…0.9 kg]; Exp. 2: 200 pigs [6.1 ±â€…1.2 kg]) were used to determine the optimal dietary standardized ileal digestible (SID) arginine (Arg) level in early nursery diets based on growth and health responses. The basal diet in Exp.1 was formulated to meet SID Arg recommendation (0.66%; NRC, 2012) and in Exp. 2, SID Arg was set to simulate current industry practices for feeding nursery pigs (1.15 %). Basal diets were supplemented with 0.3%, 0.6%, 0.9%, and 1.2% of l-arginine to provide five levels of dietary SID Arg. Experimental diets were fed during phases I (days 0 to 7) and II (days 8 to 21) with common diets until market. Feed disappearance and body weight (BW) were measured on days 7, 14, 21, and 43. Final BW was recorded at first removal of pigs for market. Pen fecal score was assigned daily from days 0 to 21. Plasma immunoglobulin A (IgA) was determined on days 0, 7, and 14 and amino acids (AAs) concentration and plasma urea nitrogen (PUN) on days 0 and 14. Orthogonal polynomial contrasts were used to determine the linear and quadratic effects of dietary Arg. Optimal SID Arg was determined by fitting the data with piecewise regression, using growth performance as the primary response variable. In Exp. 1, dietary Arg linearly increased (P < 0.1) BW, average daily gain (ADG), and gain to feed ratio (G:F) ratio on day 21, as well as reduced (χ2 = 0.004) the percentage of pigs that lost weight (PLW) in week 1 by 29%. Dietary Arg resulted in linear improvement (P = 0.082) of ADG for the overall nursery period and quadratic improvement (P < 0.1) of final BW at marketing. In Exp. 2, dietary Arg linearly increased (P < 0.05) ADG and average daily feed intake (ADFI) in week 1, BW and ADFI (P < 0.1) on day 14, as well as reduced (χ2 ≤ 0.001) PLW in week 1. From days 0 to 21, G:F was improved quadratically (P < 0.1). Dietary Arg linearly increased (P < 0.1) ADG and BW on day 43. Dietary Arg supplementation decreased the incidence (χ2 < 0.05) of soft and watery feces during the first weeks after weaning and lower concentration of plasma IgA on days 7 and 14. Dietary Arg linearly and/or quadratically influenced plasma AA concentrations (P < 0.05), including an increase in Arg, Leu, Phe, Val, citrulline, ornithine, and PUN concentrations. Overall, weaned pigs exhibit optimal nursery growth performance and health when provided with dietary SID Arg ranging from 1.5% to 1.9%. This dietary range contributes to a reduction in the occurrence of fall-back pigs and improvements in final BW at marketing.

Pathways regulating equine skeletal muscle protein synthesis respond in a dose-dependent manner to graded levels of protein intake.

Activation of the mechanistic target of rapamycin (mTOR)-controlled anabolic signaling pathways in skeletal muscle of rodents and humans is responsive to the level of dietary protein supply, with maximal activation and rates of protein synthesis achieved with 0.2 to 0.4 g protein/kg body weight (BW). In horses, few data are available on the required level of dietary protein to maximize protein synthesis for maintenance and growth of skeletal muscle. To evaluate the effect of dietary protein level on muscle mTOR pathway activation, five mares received different amounts of a protein supplement that provided 0, 0.06, 0.125, 0.25, or 0.5 g of crude protein (CP)/kg BW per meal in a 5 × 5 Latin square design. On each sample day, horses were fasted overnight and were fed only their protein meal the following morning. A preprandial (0 min) and postprandial (90 min) blood sample was collected and a gluteus medius muscle sample was obtained 90 min after feeding the protein meal. Blood samples were analyzed for glucose, insulin, and amino acid concentrations. Activation of mTOR pathway components (mTOR and ribosomal protein S6 [rpS6]) in the muscle samples was measured by Western immunoblot analysis. Postprandial plasma glucose (P = 0.007) and insulin (P = 0.09) showed a quadratic increase, while total essential amino acid (P < 0.0001) concentrations increased linearly with the graded intake of the protein supplement. Activation of mTOR (P = 0.02) and its downstream target, rpS6 (P = 0.0008), increased quadratically and linearly in relation to the level of protein intake, respectively. Comparisons of individual doses showed no differences (P > 0.05) between the 0.25 and 0.5 g of protein intake for either mTOR or rpS6 activation, indicating that protein synthesis may have reached near maximal capacity around 0.25 g CP/kg BW. This is the first study to show that the activation of muscle protein synthetic pathways in horses is dose-dependent on the level of protein intake. Consumption of a moderate dose of high-quality protein resulted in near maximal muscle mTOR pathway activation in mature, sedentary horses.

Effects of dietary amino acid supplementation on measures of whole-body and muscle protein metabolism in aged horses.

The objective of this study was to examine markers of whole-body and muscle protein metabolism in aged horses fed a diet typical for North American aged horses, supplemented with amino acids. In a replicated Latin square design, six aged horses (20 ± 1.1 years) were studied while receiving each of three isocaloric, isonitrogenous diets, a control treatment concentrate (CON; 100 mg/kg-1 BW day-1 lysine, 84 mg kg-1  day-1 threonine, 51 mg kg-1  day-1 methionine), LYS/THR (134 mg kg-1 BW day-1 lysine, 110 mg kg-1 BW day-1 threonine, 52 mg kg-1 BW day-1 methionine) and LYS/THR/MET (132 mg kg-1 BW day-1 lysine, 112 mg kg-1 BW day-1 threonine, 62 mg kg-1 BW day-1 methionine). In each 15-days period, urine and faeces were collected for assessment of nitrogen balance. Blood samples were collected before and after feeding for analysis of plasma urea nitrogen (PUN), glucose, insulin and plasma amino acid concentrations. Skeletal muscle samples were collected for measurement of proteins associated with muscle protein synthesis and degradation, and horses underwent stable isotope infusion procedures for comparison of differences in whole-body rates of protein synthesis and degradation. There was no effect of treatment on relative abundance of proteins involved in protein synthesis, nitrogen retention or phenylalanine kinetics. PUN concentrations tended to be higher for LYS/THR (p = 0.054) and were higher for LYS/THR/MET (p = 0.0056) than for CON. Atrogin-1 abundance tended to be higher in the post-absorptive state for the CON treatment (p = 0.07), indicating that amino acid supplementation resulted in less muscle protein degradation when horses were in the post-absorptive state. However, lack of differences in nitrogen retention and phenylalanine kinetics indicated that whole-body protein metabolism was not improved, and higher PUN concentrations in the supplemented diets suggest that the supplemented amino acids may have been catabolized. Amino acid availability was not limiting protein synthesis in the sedentary aged horses in this study when fed the CON diet.

Effects of a docosahexaenoic acid-rich microalgae nutritional product on insulin sensitivity after prolonged dexamethasone treatment in healthy mature horses.

OBJECTIVE: To determine effects of a microalgae nutritional product on insulin sensitivity in horses. ANIMALS: 8 healthy mature horses. PROCEDURES :Horses (n = 4/group) received a basal diet without (control diet) or with docosahexaenoic acid-rich microalgae meal (150 g/d) for 49 days (day 0 = first day of diet). On day 28, an isoglycemic hyperinsulinemic clamp procedure was performed. Horses then received dexamethasone (0.04 mg/kg/d) for 21 days. On day 49, the clamp procedure was repeated. After a 60-day washout, horses received the alternate diet, and procedures were repeated. Plasma fatty acid, glucose, and insulin concentrations and glucose and insulin dynamics during the clamp procedure were measured on days 28 and 49. Two estimates of insulin sensitivity (reciprocal of the square root of the insulin concentration and the modified insulin-to-glucose ratio for ponies) were calculated. RESULTS: Baseline glucose and insulin concentrations or measures of insulin sensitivity on day 28 did not differ between horses when fed the control diet or the basal diet plus microalgae meal. On day 49 (ie, after dexamethasone administration), the microalgae meal was associated with lower baseline insulin and glucose concentrations and an improved modified insulin-to-glucose ratio for ponies, compared with results for the control diet. CONCLUSIONS AND CLINICAL RELEVANCE: Although the microalgae meal had no effect on clamp variables following dexamethasone treatment, it was associated with improved plasma glucose and insulin concentrations and insulin sensitivity estimates. A role for microalgae in the nutritional management of insulin-resistant horses warrants investigation.

Amino acid supplementation does not alter whole-body phenylalanine kinetics in Arabian geldings.

Stable isotope infusion methods have not been extensively used in horses to study protein metabolism. The objectives were to develop infusion and sampling methodologies for [1-(13)C] phenylalanine and apply these methods to determine whether the addition of supplemental amino acids to a control diet affected whole-body phenylalanine kinetics in mature horses. Arabian geldings were studied using a 6-h primed (9 µmol/kg), constant (6 µmol · kg(-1) · h(-1)) i.v. infusion of L-[1-(13)C] phenylalanine, with blood and breath sampled every 30 min, to measure whole-body phenylalanine kinetics in response to receiving the control diet (n = 12) or the control diet supplemented with equimolar amounts of glutamate (+Glu; 55 mg · kg(-1) · d(-1); n = 5), leucine (+Leu; 49 mg · kg(-1) · d(-1); n = 5), lysine (+Lys; 55 mg · kg(-1) · d(-1); n = 5), or phenylalanine (+Phe; 62 mg · kg(-1) · d(-1); n = 6). The plasma concentrations of the supplemented amino acid in horses receiving the +Leu, +Lys, and +Phe diets were 58, 53, and 36% greater, respectively, than for the control treatment (P < 0.05). Isotopic plateau was attained in blood [1-(13)C] phenylalanine and breath (13)CO(2) enrichments by 60 and 270 min, respectively. Phenylalanine flux (+20%) and oxidation (+110%) were greater (P < 0.05) in horses receiving the +Phe treatment than in those fed the control diet. There was no effect of treatment diet on nonoxidative phenylalanine disposal or phenylalanine release from protein breakdown. The developed methods are a valuable way to study protein metabolism and assess dietary amino acid adequacy in horses and will provide a useful tool for studying amino acid requirements in the future.

Coadministration of ornithine and alpha-ketoglutarate is no more effective than ornithine alone as an arginine precursor in piglets enterally fed an arginine-deficient diet.

Simultaneous administration of alpha-ketoglutarate and ornithine, in a 1:2 molar ratio, may improve the effectiveness of ornithine as an arginine precursor in neonatal piglets by shifting ornithine metabolism away from oxidation and toward the synthesis of arginine and other metabolically important compounds. To study this proposed mechanism, enterally fed piglets were allocated to receive 1 of 4 diets for 5 d: an arginine-deficient [1.2 mmol/(kg . d) arginine] diet (basal), or the basal diet supplemented with either alpha-ketoglutarate [4.6 mmol/(kg x d)] (+alpha-KG), ornithine [9.2 mmol/(kg x d)] (+Orn), or both ornithine and alpha-ketoglutarate (+alpha-KG/+Orn, molar ratio 1:2). Primed, constant infusions of [1-(14)C]ornithine given both intragastrically and intraportally were used to measure ornithine kinetics and determine the role of first-pass intestinal metabolism in ornithine metabolism. Whole body arginine and glutamate kinetics were measured using a primed, constant intragastric infusion of [guanido-(14)C]arginine and [3,4-(3)H]glutamate. The diets did not affect plasma arginine or ammonia concentrations, arginine flux, or arginine synthesis from ornithine. Therefore, arginine synthesis was not increased by the simultaneous infusion of ornithine and alpha-ketoglutarate. Piglets that received dietary ornithine had a 2-fold greater rate of proline synthesis from ornithine (P < 0.05) and oxidized a greater (P < 0.05) portion of the infused ornithine than piglets in the basal and +alpha-KG groups. Overall, ornithine addition to an arginine deficient diet had a greater effect on ornithine and arginine metabolism than the addition of alpha-ketoglutarate. First-pass intestinal metabolism was critical for ornithine synthesis and conversion to other metabolites but not for ornithine oxidation.

Citrulline is an effective arginine precursor in enterally fed neonatal piglets.

Although neonatal piglets can synthesize some arginine from proline, there is a limit to this synthesis, and piglets fed an arginine-deficient diet have diminished whole-body arginine status. To help elucidate where the limitation in arginine synthesis may occur, our objective was to determine the most effective arginine precursor in 1-wk-old enterally fed piglets. Piglets were administered either an arginine-deficient (basal) diet [1.15 mmol arginine/(kg.d)] or the basal diet supplemented with equimolar [9.18 mmol/(kg.d)] amounts of proline (+Pro), ornithine (+Orn), citrulline (+Cit) or arginine (+Arg) for 5 d (n = 5/diet). Daily blood samples were taken and indicators of whole-body arginine status including plasma amino acid, ammonia, and urea concentrations were measured. A primed, constant intragastric (i.g.) infusion of l-[U-(14)C]proline was given to measure the proline to arginine conversion, and intravenous (i.v.) and i.g. infusions of l-[guanido-(14)C]arginine were given to determine arginine flux and to quantify the splanchnic extraction of dietary arginine. Piglets fed the +Cit and +Arg diets had lower plasma ammonia and urea concentrations (P < 0.05) and higher plasma arginine concentrations (P < 0.0001) and arginine fluxes (P < 0.05) than piglets fed the other 3 diets. Piglets fed +Cit and +Arg had a lower proline to arginine conversion (P < 0.05). During first-pass splanchnic metabolism, 52% of the dietary arginine was extracted, and this extraction was not affected by whole-body arginine status (P > 0.05). These data indicate that citrulline, but not ornithine or proline, is an effective arginine precursor, and that either citrulline formation or availability appears to limit arginine synthesis in neonatal piglets.