GROWTH AND DEVELOPMENT OF BOVINE FETUSES AND NEONATES REPRESENTING 3 GENOTYPES

Growth was examined in bovine fetuses and neonates that typically diff er in mature size and postnatal developmental pattern. Pregnancies wer e established from matings expected to produce early (E), late (L), an d intermediate (I) maturing postnatal growth patterns. Tissues were co llected at 100. and 200 d of gestation and 30 d postnatal. Muscle:body weight ratios were lower at 100 and 200 d for the E maturity type tha n for the L maturity type (P < .05). This differs from observations of muscle:body weight ratios made at 30 d postnatal, at which time ratio s for E were either greater than (triceps brachii, P < .05) or similar to those for L. Few differences due to maturity type were observed at 100 d for bone weight:body weight ratios; however, at 200 d of gestat ion E. bone weight:body weight ratios were generally lower (P < .05) t han those for L. The genotypic relationship for bone weight:body weigh t ratio at 30 d postnatal was similar to that observed at 200 d of ges tation. Observations of organ weight:body weight ratios revealed no cl ear patterns hue to maturity type. The genotypic relationship for tota l muscle DNA content was similar to that observed for muscle weight. T hese results indicate that fetal muscle development differs in cattle that have different postnatal growth patterns by as early as 100 d of gestation and that differences in fetal muscle growth are related to d ifferences in muscle hyperplasia.