Effects of calf early nutrition on muscle fiber characteristics and gene expression

The aim of this study was to evaluate the effect of herbage allowance treatment of native pastures from calf conception to weaning on muscle fiber density and diameter and gene expression (insulin-like growth factor (IGF) system and adipogenesis) during the first year of age of purebred (Hereford and Angus) and crossbred (F1) dams offspring. Forty crossbred calves, offspring of purebred or crossbred dams, were used in a randomized block design with a factorial arrangement of herbage allowance (HA) of native pastures (high and low; 4 vs. 2.5kg dry matter/kg body weight (BW)) and dam genotype resulting in 4 calf groups (high-purebred, high-crossbred, low-purebred, low-crossbred offspring). Calf BW were registered while blood and Semitendinosus muscle samples were collected at birth, weaning (142 days) and at 380 days old to measure plasma IGF-I concentrations and muscle expression of genes related with the IGF system and adipogenesis by quantitative real time PCR. Calf BW at birth did not differ between calf groups but during the postnatal period, low purebred offspring were lighter (P<0.05) than the other three calf groups. Lean to fat tissue ratio tended to be greater (P=0.08) in high than in low HA offspring. Muscle fiber density did not differ among calf groups, but fiber diameter was greater in low than high and in crossbred than purebred offspring. Plasma IGF-I concentrations were lower (P<0.05) in low purebred offspring than in the other three calf groups. The IGFBP5 mRNA expression was greater in low crossbred offspring when compared to the other three groups and PPARG mRNA expression was greater in high than in low and in purebred than crossbred offspring at birth whereas SREBF1 mRNA expression was greater in high crossbred compared to the other three groups at birth and at weaning. At 380 days, after winter restriction, IGF receptor type 1 (IGF1R) and IGFBP5 mRNA expression were greater in high purebred than in high crossbred offspring. The environment provided by the dams during gestation and lactation is probably influenced by the nutritional plane and genotype of the cow. As a consequence, changes appeared between calf groups in calf BW, body composition, Semitendinosus muscle fiber diameter and expression of genes related with the IGF-I system and adipogenesis.