Growth performance and nutrient intake of Gir x Holstein dairy calves reared in a tropical outdoor system and inoculated with rumen-derived fungi.

The effects of oral inoculation with a probiotic containing Rhodotorula mucilaginosa and Trichoderma longibrachiatum were evaluated during the first 60 d of life in Gir x Holstein dairy calves across two seasons. Twenty calves were assessed in northern Minas Gerais, Brazil (n = 10 in period 1, late winter-spring; n = 10 in period 2, late summer-autumn). The study used a 2 × 2 factorial arrangement with probiotic supplementation (with or without fungal inoculation) and experimental periods as factors. Growth performance, structural development, and nutrient intake were evaluated. Fungal supplementation increased total hip width gain (4.5 vs. 3.6 cm) and tended to increase hay dry matter intake during the preweaning phase in both periods. However, supplementation did not influencied other performance parameters (p > 0.05). Calves evaluated during Period 2 showed greater average daily gain (0.674 vs. 0.537 kg/d) and improved feed efficiency (1.44 vs. 1.69) compared with Period 1. In conclusion, fungal inoculation enhanced structural growth, specifically hip width gain, whereas overall performance was more strongly influenced by season. Dairy calves reared under a tropical outdoor system in a semi-arid region exhibited improved growth performance during late summer and autumn.