Reducing Protein Content with and without Yeast Probiotic Actisaf Sc 47 Supplementation in the Diet of Dairy Cow: Effects on Milk Performance, Milk Fatty Acid Composition, Digestibility, Feed, and Economic Efficiency

Abstract

The objective of the present study was to evaluate the effect of reducing CP levels in the diet of dairy cows alone or in combination with a yeast probiotic on milk quantity and quality, milk fatty acid profile, feed and economic efficiency. In total, six cows were included in a 3 × 3 Latin square design with 3 experimental periods of 28 days long (23 days for adaptation and 5 days for data collection). Cows were randomly assigned to one of the three diets according to protein level and supplementation: control diet with 16.5 CP%DM (CTR), a diet with 14.5 CP%DM without Actisaf Sc 47 supplementation (LCP), and a diet with 14.5 CP%DM with Actisaf Sc 47 supplementation at 5 g/cow/day (LCPActisaf). Regarding total milk yield (TMY), a tendency for lower TMY was observed in LCP group compared with the CTR group ( P = 0.1). No difference was observed between CTR and LCPActisaf groups ( P = 0.90). The use of Actisaf Sc 47 mitigated the TMY reduction observed in LCP group. Milk fat (MF) and energy-corrected milk (ECM) were unaffected by treatments. Milk protein (MP, kg/d) resulted higher and tended to be higher in LCPActisaf compared to CTR ( P = 0.03) and LCP ( P = 0.06) but similar between CTR and LCP ( P = 0.4). Compared with the CTR group, milk urea nitrogen (MUN) was reduced by both LCP and LCPActisaf (−31.8% and −23.8%, respectively, P = 0.04). No difference was observed between LCP and LCPActisaf ( P = 0.49). Reducing protein alone or in combination with Actisaf Sc 47 did not impact feed efficiency (FE) when compared to CTR ( P = 0.15 and P = 0.39, respectively) but reducing protein in combination with Actisaf Sc 47 increased FE compared to reducing protein alone ( P = 0.02). No differences in milk fatty acid (FA) profile were observed with the exception of a tendency for a greater concentration of linoleic acid in LCPActisaf group compared with the CTR group ( P = 0.09) and LCP group ( P = 0.08). Linoleic acid concentration was similar between CTR and LCP groups ( P = 0.93). De novo fatty acid concentration resulted higher ( P = 0.13) in LCPActisaf (28.90%) compared to CTR (27.75%) and LCP (27.9%). Health indexes explained by Atherogenic index, Thrombogenic index and omega 6/omega 3 were similar between the three treatments. From economic perspective, compared with the CTR and LCP, net revenue/kg of milk was increased and tended to increase with LCPActisaf ( P = 0.05 and P = 0.1, respectively). No difference was observed between CTR and LCP groups ( P = 0.77). The use of Actisaf Sc 47 increased economic efficiency (EE) by 10% and 8.24% compared with the CTR and LCP groups, respectively. Supplementing reduced-protein diets with Actisaf Sc 47 maintained milk yield, enhanced milk protein output, improved feed efficiency, and increased economic returns, supporting its use as a strategy to optimize dairy production under lower dietary protein conditions.