Maternal Nutrition and Stage of Early Pregnancy in Beef Heifers: Impacts on Hexose and AA Concentrations in Maternal and Fetal Fluids1

We examined the hypothesis that maternal nutrition and day of gestation would affect the concentrations of AAs and hexoses in bovine utero-placental fluids and maternal serum from days 16 to 50 of gestation. Forty-nine cross-bred Angus heifers were bred via artificial insemination and fed a control diet (CON = 100% of requirements for growth) or a restricted diet (RES = 60% of CON) and ovariohysterectomized on days 16, 34, or 50 of gestation; nonpregnant controls were not bred and ovariohysterectomized on day 16 of the synchronized estrous cycle. The resulting design was a completely randomized design with a 2 × 3 factorial + 1 arrangement of treatments. Maternal serum, histotroph, allantoic fluid, and amniotic fluid were collected at time of ovariohysterectomy. Samples were then analyzed for concentrations of AAs and intermediary metabolites: alanine (Ala), arginine, asparagine (Asn), aspartate (Asp), citrulline, cysteine, glutamine, glutamate (Glu), glycine (Gly), histidine, isoleucine, leucine (Leu), lysine, methionine (Met), ornithine, phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), tryptophan, tyrosine (Tyr), and valine (Val). The concentrations of Gly, Ser, and Thr in maternal serum were greater (P ≤ 0.05) in CON compared with RES. Furthermore, day of gestation affected (P ≤ 0.05) concentrations of Asn, Glu, Phe, Thr, and Tyr in maternal serum. Status of maternal nutrition affected the Asp concentration of histotroph where RES was greater (P = 0.02) than CON. In histotroph, Ala, Leu, Met, and Val concentrations were greater (P ≤ 0.05) on day 50 compared with day 16. Additionally, Glu and Pro concentrations in histotroph were greater (P < 0.01) on days 34 and 50 compared with day 16. A day × treatment interaction was observed for the concentration of Val in allantoic fluid where day 34 CON was greater (P = 0.05) than all other days and nutritional treatments. In addition, the concentration of Gln in amniotic fluid experienced a day × treatment interaction where day 34 RES was greater (P ≤ 0.05) than day 34 CON, which was greater (P ≤ 0.05) than day 50 CON and RES. These data support our hypothesis that day of gestation and maternal nutrition affect the concentrations of various neutral and acidic AA in beef heifer utero-placental fluids and maternal serum from days 16 to 50 of gestation.