SERUM CONCENTRATIONS OF INSULIN-LIKE GROWTH-FACTORS AND PLACENTAL-LACTOGEN DURING GESTATION IN CATTLE .1. FETAL PROFILES

Sixty crossbred beef heifers pregnant with fetuses of either high (H; n = 30) or low (L; n = 30) genetic potential for growth were used to e stablish fetal serum profiles of insulin-like growth factor (IGF)-I, I GF-II, and placental lactogen (PL), and to examine relationships betwe en serum hormone concentrations and fetal growth parameters. Three H a nd three L fetuses were collected by caesarean section at 21-d interva ls from Day 85 through Day 274 of gestation. Arterial, venous, and mix ed umbilical blood samples were collected during surgery. Fetal body w eight, crown-rump length, hip height, and heart girth were measured. S erum concentrations of IGF-I and IGF-II increased (P < 0.0001) with ad vancing gestational age, whereas serum PL declined (P < 0.0001) linear ly (P < 0.01) throughout gestation. Serum concentrations were greater in the umbilical vein compared with the umbilical artery for IGF-II (P < 0.0001) and PL (P < 0.05), but not IGF-I. Fetal IGF-I, IGF-II, and PL serum concentrations were not correlated with serum concentrations of the respective mate:mal hormones. Fetal serum IGF-I concentrations were correlated to fetal body weight (r = 0.66), growth rate (r = 0.72 ), crown-rump length (r = 0.20), hip height (r = 0.17), and heart girt h (r = 0.20). Correlations between fetal serum IGF-II concentrations a nd the same parameters were 0.60, 0.62, 0.39, 0.34, and 0.37, respecti vely. Fetal serum PL concentrations were negatively correlated to body weight (r = -0.40) and growth rate (r = -0.40) and not correlated wit h any fetal linear measure. Fetal genotype (L vs. Fl) differences were detected for ICF-I (P < 0.05) and PL (P = 0.09) concentrations. Fetal sex effects were not observed for any hormone. Maternal sire breed, h ip height, and body condition score did not influence fetal serum horm one concentrations. (C) Elsevier Science Inc. 1997.