Growth and development of bovine fetuses and neonates representing three genotypes.

Growth was examined in bovine fetuses and neonates that typically differ in mature size and postnatal developmental pattern. Pregnancies were established from matings expected to produce early (E), late (L), and intermediate (I) maturing postnatal growth patterns. Tissues were collected 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 than for the L maturity type (P < .05). This differs from observations of muscle:body weight ratios made at 30 d postnatal, at which time ratios 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 gestation E bone weight:body weight ratios were generally lower (P < .05) than those for L. The genotypic relationship for bone weight:body weight ratio at 30 d postnatal was similar to that observed at 200 d of gestation. Observations of organ weight:body weight ratios revealed no clear patterns due to maturity type. The genotypic relationship for total muscle DNA content was similar to that observed for muscle weight. These 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 differences in muscle hyperplasia.