Effects of 00-rapeseed meal inclusion in Parmigiano Reggiano hay-based ration on dairy cows' production, reticular pH and fibre digestibility

Hay-based diets are typically used in Parmigiano Reggiano cheese production. Parmigiano Reggiano feeding regulation prohibits 00-rapeseed dietary inclusion. The objectives of this study were to investigate the effects of substituting soybean-meal with different levels of 00-rapeseed-meal in dairy cows' diets, to evaluate the possibility to include it in Parmigiano Reggiano regulation. The study had a Latin square design with 8 tie stall dairy cows. The isoenergetic and isoproteic dietary treatments differed in protein source (% of DM): S (0.0% 00-rapeseed-meal, 9.3% of soybean-meal), LR (3.8% 00-rapeseed-meal, 6.8% of soybean-meal), MR (8.5% 00-rapeseed-meal, 3.4% of soybean-meal), and HR (13.2% 00-rapeseed-meal, 0.0% of soybean-meal). DMI, milk production and composition, rumination and reticular-pH were recorded daily. Dietary fibre digestibility was evaluated by in vitro fermentation and milk gointrin content was quantified by liquid chromatography-tandem mass spectrometry. Statistical analysis was performed by mixed model. Milk yield, protein and casein content increased for incremental 00-rapeseed-meal dietary levels. MR treatment compared to the others resulted in higher daily reticular-pH (5.92), and fewer minutes with pH below 5.8 (467) and 5.5 (72). Goitrin was detectable in milk when 00-rapeseed-meal was included in the diet. Overall, the inclusion of 00-rapeseed-meal in the Parmigiano Reggiano type ratio did not compromise the performances of cows pointing to it as a reliable substitute for soybean-meal. Our results suggest that 00-rapeseed-meal should be tested in feeding studies to determine its effects on milk organoleptic characteristics and cheese production and quality to see if it can be included in the Italian PDO cheese regulation.