Preliminary Study: High‐Concentrate Feeding During the Growing Period Induces Region‐Specific Growth and Alters Growth Hormone Dynamics in Japanese Black Heifers

This study investigated the effects of high-concentrate (HC) feeding during the growing stage on growth allocation and endocrine dynamics in Japanese Black heifers. Six heifers were assigned to a HC (3.0% body weight [BW]/day) or control (CON: 1.5% BW/day) group from 5 to 10 months of age. Feed intake, BW, muscle, bone, fat depot and visceral organ weights, histological traits of longissimus thoracis (LT), serum metabolites, and growth hormone (GH) dynamics were evaluated. At 10 months, the HC group showed greater BW and total muscle weight, with 18 muscles being heavier. The radius and ulna weights increased, but BW-adjusted ratios of several load-bearing bones tended to decrease. Subcutaneous fat deposition increased. LT adipocyte diameter and fat contents were greater, while muscle fiber type composition was unchanged. Liver weight and γ-glutamyl transferase activity increased. GH pulsatile secretion was reduced, whereas pituitary GH-positive cells, circulating IGF-1, and insulin concentrations remained unchanged. These findings indicate that HC feeding promotes overall growth but induces nonuniform development across tissues, reflecting a shift in growth allocation and endocrine regulation. Nutritional conditions during the growing stage may therefore play a critical role in shaping tissue development and subsequent productivity.