Maternal nutrition and stage of early pregnancy in beef heifers: Impacts on hexose and AA concentrations in maternal and fetal fluids.

We examined the hypothesis that maternal nutrition and day of gestation would affect the concentrations of amino acids (AA) and hexoses in bovine utero-placental fluids and maternal serum from d 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 d 16, 34, or 50 of gestation; non-pregnant (NP) controls were not bred and ovariohysterectomized on d 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 amino acids and intermediary metabolites: alanine (Ala), arginine (Arg), asparagine (Asn), aspartate (Asp) citrulline (Cit), cysteine (Cys), glutamine (Gln), glutamate (Glu) glycine (Gly), histidine (His), isoleucine (Ile), leucine (Leu), lysine (Lys), methionine (Met), ornithine (Orn), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), tryptophan (Trp), 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 d 50 compared with d 16. Additionally, Glu and Pro concentrations in histotroph were greater (P < 0.01) on d 34 and 50 compared with d 16. A day × treatment interaction was observed for the concentration of Val in allantoic fluid where d 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 d 34 RES was greater (P ≤ 0.05) than d 34 CON, which was greater (P ≤ 0.05) than d 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 d 16 to 50 of gestation.