It has been established that enhanced early life nutrition progresses sexual development in the bull calf through neuroendocrine signalling via the hypothalamic-pituitary-testicular axis. However, the underlying molecular mechanisms regulating this process have not been fully elucidated. This study measured the impact of contrasting feeding regimes in the first 12 wk of life, known to impact age at puberty, on the proteomic landscape of the testes of bull calves. Holstein bull calves with a mean (±SD) bodyweight and age of 48.8 (± 5.3) kg and 17.5 (± 2.8) days, were designated to high (HI; n=10) or moderate (MOD; n=10) dietary groups, with diets designed to provoke growth rates of 1.0 and 0.5 kg/day, respectively. At 12 wk of age, all calves were euthanized, and testes parenchyma harvested. HI calves were heavier at slaughter (112.4 v 88.7 (2.98) kg, P<0.001), and had a greater average daily gain (ADG) of (0.88 v 0.58 kg, P<0.001). The turquoise network from the protein analyses contained the protein CDH13 which is involved in testes development. Gene ontology analysis of the turquoise network revealed enrichment of genes with functions related to cholesterol biosynthesis, IGF-1 signalling, insulin receptor/secretion signalling, androgen signalling and Sertoli cell junction signalling.