The effect of mineral-vitamin free choice blocks on transition cows’ rumen health.

The transition period is an extremely difficult phase of the lactation cycle. The cows face the challenge of NEB, massive mineral utilization, and perturbed immune function. Furthermore, in high-forage diets, minerals may be insufficient. The study tested the effect of different molasses- based mineral-vitamin free choice blocks (FC-BLOCK) as alternatives to conventional TMR mineral-vitamin additives on rumen health in transition dairy cows. Multiparous Holstein cows (n = 42), blocked by BCS, parity, and previous lactation, were fed a TMR at 75% of the mineral requirements during the dry period, followed, postpartum, by a lactating TMR at 75% of the mineral requirements plus concentrates fed via robotic milking system. The treatments were: control (CTL; n = 16) receiving a top-dressed mineral supplementation to reach 100%of the requirement; mineral-vitamin (MINVIT; n = 14) receiving, in the dry period, an FC-BLOCK followed by an FC-BLOCK containing propylene glycol (FC-BLOCKg) postpartum; linseed (LIN; n = 12) receiving, in the dry period, an FC-BLOCK with linseed oil and yeast, followed by an FC-BLOCKg postpartum. Intake, eating, rumination time, and milk yield were recorded daily; rumen fluid was collected as farm monitoring practice via stomach tube at 20 and 60 DIM to evaluate rumen pH, protozoa count, and enzymes activity. Data were analyzed with GLM procedures. The FC-BLOCK intake was signifi- cantly higher in LIN compared with MINVIT (P < 0.01). However, none of the treatments affected TMR intake in the dry period, but CTL and LIN had a significantly higher intake compared with MINVIT (P < 0.05) in summer. Postpartum TMR intake in spring and summer was the highest in MINVIT (P < 0.05). In the first 60 DIM, CTL had the highest milk yield, thus receiving more concentrate (P < 0.05) compared with the other groups. No differences in protozoa count and enzymatic activity were observed. In conclusion, the FC-BLOCK may be a valid approach to ensure satisfaction of mineral requirements while keeping ruminal health, showing possible applications under free-range condi- tions. Furthermore, the MINVIT proved to sustain intake in potential heath stress season.