Precision Feeding: how rumen protected aminoacids can reduce the protein content of diets for Parmigiano reggiano?

Introduction. Dietary protein content (CP) reduction is important to restrain nitrogen excretion and improve the nutrition efficiency also for cows producing milk for Parmigiano Reggiano (PR) cheese. In this production chain rations are based on local dry forages and cereals while silages, many protein sources, added fat and fermented by products are not allowed. The use of rumen-protected amino acids (RPA) helps in rations balance, reducing CP without compromising productions [1]. More knowledge about the optimal combination of carbohydrates sources (CHO), CP and RPA use is still needed for diet without silages. Aim of this study was to evaluate the effect of diets with high or low CP (HP vs LP) and a high or low starch (ST) content (HS vs LS). The main dietary CP were alfalfa hay and soybean meal. All diets were balanced using RPA (Smartamine® and AjiPro-L®) to have the same theoretical quantity of intestinal available methionine (M=71g/d) and lysine (L=191g/d.), as predicted by the NDS software (CNCPS 6.55). Animals, materials and methods. 8 Italian Friesian cows were assigned to a Latin square design (14d adaptation, 4d sampling) with different diet profiles (%DM): HPHS:14.8 CP, 26.8 ST; HPLS 14.8 CP, 19.7 ST; LPHS: 12.5 CP, 25.9 ST and LPLS: 12.5 CP, 19.8 ST. Dry matter intake (DMI), daily water intake (DWI), body weight (BW), body condition score (BCS), rumination time (RT), reticular pH (r-pH) and milk yield (MY) were recorded. Ammonia in rumen fluid (ARF), milk and feces composition were determined. Energy corrected milk (ECM) was calculated [2]. Mixed model procedure was used for data analysis; period, CP and ST levels (HP vs LP and HS vs LS diets) and interactions were used as fixed effects, while animals as random effect. Multiple comparisons were then performed by Student's t-test. Results and discussion. No differences in DMI (26.5kg/d, P=.22) and BW (636kg, P=.92) were observed, however higher BCS resulted in LP diets (+0.16pts, P<.05), suggesting a different energy utilization. DWI was higher in HP diets (+22 L/d; P=.05). RT was affected by CHO (-30min/d in HS, P=.01) but all diets induced good RT (505min/d) and r-pH resulted always safe excluding any risk of SARA. MY and ECM were higher with HP diets (+1.3, +1.5kg/d respectively, P<.01). Highest milk protein % resulted in HPHS diet (P<,05). ARF and urea content were influenced by HP diets (+1.3 ARF; +9.2 urea, mg/dl; P<.01). LP diets resulted in higher fecal starch concentration (+0.4, %DM, P<.01), showing a possible influence of diet CP on starch utilization in rumen and gut. Conclusion. The results showed that diets with lower CP seemed inadequate to support MY and milk components even if balanced with RPA use. Moreover, the CP level of the ration to support the highest performances in the PR diet need to be higher than 12.5 (%DM) when only M and L are considered as potential limiting amino acids.