Glutamine and Glutamate Supplementation Increases the Levels of These Amino Acids in the Milk of Pasture-fed Mares

Background: L-Glutamine (Gln), the most abundant free alpha amino acid in the body, plays a major role in the transport of nitrogen and carbon between tissues, and is an important source of respiratory energy for intestinal and immune system cells. Mares lose lean body mass during lactation, when plasma and milk Gln levels change significantly. However, supplementation with Gln combined with other amino acids may not alter equine plasma Gln levels. The work reported here was designed to test the hypothesis that supplementation with a mixture of glutamine and glutamate (AminoGut) alters blood and milk free glutamine and glutamate levels in pasture-fed lactating mares. Materials, Methods & Results: This study involved 31 multiparous Quarter Horse mares, which were divided into three groups immediately postpartum, as follows: G-CON (n = 19); G-50 g supplemented with 50 g of Gln + Glu plus 200 g of concentrate (n = 6); and G-100 g, supplemented with 100 g of Gln + Glu plus 200 g of concentrate (n = 6). Blood and milk samples were collected on the day of parturition prior to supplementation, and monthly until weaning. The milk samples were used to analyze the Gln, Glu composition and levels, while the blood samples were used for further analysis of blood biomarkers. The results were analyzed by ANOVA and by Tukey's test and the P value was set at 5%. The G-CON group showed a significant reduction of 11-35% in the mean blood glutamine levels from the first month postpartum and throughout lactation. In contrast, blood glutamine levels in groups G-50 g and G-100 g did not change significantly from parturition through 5 months of lactation. The supplemented groups showed no significant differences in blood variables such as protein, albumin, urea, creatinine, cholesterol, triglycerides and minerals. Free glutamine levels in milk did not change from parturition through the end of lactation in the G-CON group, but groups G-50 g and the G-100 g showed a marked rise in milk glutamine levels throughout the first three months of lactation (similar to 3x), which remained high (similar to 2x) until the foals were weaned (P > 0.05). Discussion: The results of this study indicate that Gln + Glu supplementation successfully increased Gln levels in mare milk in the first three months of lactation, and Glu levels in G-100 g in the first four months, without affecting the levels of these amino acids in the animals' blood, which remained similar to data obtained at parturition. In fact, the Gln levels in both supplemented groups exceeded 1,000 mmol/mL throughout lactation, unlike those of the control group and of the samples obtained at parturition. Moreover, supplementation did not produce significant changes in blood biomarkers, including those pertaining to protein metabolism (urea, creatinine, uric acid, albumin and total proteins), indicating that the product used for supplementation did not interfere in these biomarkers, which remained within the normal physiological variations for the species. It was concluded that daily dietary supplementation with 50 g of a mixture of glutamine and glutamate produced an effect similar to supplementation with 100 g/day. Both supplementation protocols succeeded in raising glutamine levels in mare milk in the first three months of lactation, without interfering in blood biomarkers or milk composition. In view of the cost of the product, we recommend that the daily diet of mares during lactation be supplemented with 50 g of a mixture of Gln + Glu in order to produce the desired nutritional effects.