Effects of ensiled wheat straw with brewer’s spent yeast on milk production and nutrient utilisation in dairy cows

Brewer’s spent yeast (BSY) is one of the most abundant byproducts of the brewing industry that creates environmental disposal challenges. However, its high nutritional value offers an opportunity to upgrade low-quality roughages in dairy cows’ nutrition. This study evaluated the effects of ensiled wheat straw with BSY and molasses on feed intake, digestibility, milk yield, and methane production in dairy cows compared to untreated wheat straw (UWS). Wheat straw was ensiled with BSY (0.6 l/kg) and molasses (10%) for five weeks. Three mid-lactation dairy cows (¾ Friesian × Boran) were assigned to three diets: UWS + 0.5 kg concentrate/l of milk (UWS+0.5C), ensiled wheat straw (EWS) + 0.5 kg concentrate/l of milk (EWS+0.5C), and EWS + 0.3 kg concentrate/l of milk (EWS+0.3C). EWS with BSY doubled crude protein content and reduced in vitro methane production by 28.3% (P < 0.01). EWS diets increased nutrient intake and digestibility (P < 0.01), except for neutral detergent fibre digestibility (P > 0.05). Milk yield increased by 1.13 kg/day in EWS+0.3C (P < 0.001), along with an improvement in milk total solids. Predicted methane emissions decreased by 15.7% in EWS+0.5C (P < 0.01), and net profit increased by 1.21 USD/day/cow in EWS+0.5C. These results demonstrate that ensiling wheat straw with BSY and molasses is an effective strategy to improve feed quality, milk production, sustainability emissions, and economic returns in dairy farming.