Dietary substitution of palm oil with sunflower oil in dairy beef bulls: effects on animal performance, enteric methane emissions, and environmental footprint.

Palm oil is a commonly used dietary fat source in European dairy beef production, but concerns about deforestation associated with its cultivation have stimulated interest in alternative fat sources with the potential to mitigate enteric methane emissions and reduce the carbon footprint of beef production. Oils richer in polyunsaturated fatty acids have been suggested as promising alternatives due to their potential to modify rumen fermentation. The present study aimed to evaluate the dietary substitution of palm oil with sunflower oil, which is rich in polyunsaturated fatty acids, on animal performance, enteric methane emissions, and environmental footprint. Ninety-four crossbred bulls (399 ± 9.3 kg BW and 271 ± 4.0 days of age) were allocated into six pens and fed concentrate and straw separately, both ad libitum. Treatments were based on the fat source of the concentrates: (1) CTR (n = 46), with 3.50% palm oil on a weight basis as control; and (2) SUN (n = 48), with 3.50% sunflower oil. The study lasted 42 days. Individual feed intake was recorded daily. Bulls were weighed every two weeks. Enteric emissions (CH4, CO2, and O2) were recorded daily with a "sniffer" measurement system installed in each concentrate feeder per pen. Daily CH4 production (L/day) was estimated based on Madsen et al. (2010). Data were analysed using a mixed-effects model. The environmental impact of the two diets was evaluated with the life cycle assessment methodology. No differences in average daily weight gain were observed between dietary oil sources (1.83 vs 1.85 ± 0.141 kg/day, P = 0.87; CTR vs SUN, respectively) and concentrate intake (7.48 vs 7.48 ± 0.420 kg DM/day, P = 1.00; CTR vs SUN). A treatment × period interaction (P < 0.05) with no clear pattern was observed in most of the enteric CH4 emissions data. Nevertheless, in the first 14 days of the study, enteric CH4 emission expressed relative to concentrate intake was lower (P < 0.01) in SUN bulls than in CTR bulls. Carbon footprint was lower in SUN concentrate (0.75 kg CO2 eq/kg concentrate feed) compared with the CTR concentrate (0.89 kg CO2 eq/kg concentrate feed). Thus, the substitution of palm oil with sunflower oil reduces enteric methane emissions expressed relative to concentrate intake during the first days after dietary substitution without detrimental effects on animal performance and reduces the carbon footprint of the dietary concentrate, which is the main contributor to meat's carbon footprint.