Unveiling the energy metabolism of primiparous F1 Holstein × Gyr cows throughout lactation

Crossbreeding is central to dairy production in the tropics, where combining adaptability and productivity is essential. The Brazilian Girolando, a synthetic breed originating from Bos indicus Gyr and Bos taurus Holstein genes, successfully exemplifies this strategy. While F1 Holstein × Gyr cows seem to thrive under tropical conditions, their growth dynamics and energy use throughout lactation remain largely unknown. This study aims to fill this gap by describing the performance, milk composition, and energy intake and utilization of primiparous F1 Holstein × Gyr cows over 294 days in milk. We collected data from 29 primiparous F1 Holstein × Gyr cows with an initial body weight (BW) of 563 ± 40.1 kg and an age of 2.5 ± 0.09 years at the trial’s onset. The cows were housed in a free-stall barn, provided with a total mixed ration (TMR) and water ad libitum , and milked twice daily. The TMR consisted, on average, of 717.2 g/kg dry matter of roughage and 282.8 g/kg dry matter of concentrate. Performance, milk composition, and energy metabolism were evaluated over 294 days in milk and reported by lactation stage (1–3). Our results show progressive and moderate body weight gains and high body condition scores throughout lactation, with a mean milk yield of 16.1 ± 4.5 kg/d and fat-corrected milk yield of 18.4 ± 5.6 kg/d. Dry matter intake, digestible energy intake, and metabolizable energy intake ranged from 15.7 ± 2.1 kg/d, 182.2 ± 26.9 MJ/d, and 151.1 ± 26.0 MJ/d in lactation stage 1 to 14.7 ± 2.0 kg/d, 176.2 ± 33.1 MJ/d, and 149.2 ± 31.5 MJ/d in lactation stage 3. Heat production was the largest energy expenditure, accounting for 34.1% of total energy intake, followed by energy lost in feces (33.2%) and energy diverted to milk production (20.0%). Methane production, consistent with typical emissions from cattle, represented 7.6% of total gross energy intake. Our findings demonstrate that F1 Holstein × Gyr cows are a viable option for confined tropical milk production systems.