PSIV-2 Changes in free glutamine and glutamate in mare milk during early lactation

Glutamine plays an important role in neonatal health. This amino acid serves as a nitrogen and amine carrier between tissues, as a major energy source and as a precursor for nucleic acids and proteins in rapidly proliferating intestinal cells. This study aimed to evaluate changes over time in free Gln and Glu concentrations in mare milk in early lactation and their relationship with foal gut health. Thirteen Thoroughbred mare and foal pairs were studied. Milk samples were collected at 12 h, 3, 5, 7, 10, 14, and 21 d after parturition and daily milk yield was estimated at 7 and 14 d postpartum. Milk samples were centrifuged (10 min, 3500 x g, 4 °C) to remove fat, then centrifuged twice (5 min, 10,000 x g, 22 °C) to remove protein. Free Glu and Gln were analyzed in triplicate using a membrane-based glutaminase and glutamate oxidase method (YSI 2700 Analyzer, YSI Life Sciences, OH). Daily fecal scores were recorded to monitor foal diarrhea and body weights were recorded weekly. Mixed model ANOVA with repeated measures (SAS 9.4) were used to evaluate changes over time in free Gln and Glu. Relationships between variables were assessed using regression analyses and Pearson’s correlation coefficient. Free Gln and Glu changed over time (P < 0.0001). Glutamine increased from 12 h to 5 d, (0.24±0.11 mmol/L and 1.09±.11 mmol/L, respectively; P < 0.05) then decreased to 0.90±0.11 mmol/L by 21 d postpartum. In contrast, free Gln was the lowest at 12 h (0.36±0.04 mmol/L) and continued increasing through 21 d postpartum (0.80±0.04 mmol/L; P < 0.05). Bouts of diarrhea were negatively related to milk Gln (P < 0.05) and foal ADG was positively related to milk Glu (P < 0.05). These results suggest that Gln may have a role in foal gut health while Glu may influence foal growth.