Effects of High Concentrate-Induced Subacute Ruminal Acidosis Severity on Claw Health in First-Lactation Holstein Cows

SIMPLE SUMMARY: In this study, 24 first-lactation Holstein cows were evaluated to investigate how different levels of diet-induced subacute rumen acidosis (SARA) during early lactation (up to 70 days in milk; DIM) affect claw health. Claw health was monitored by recording claw lesions at three hoof trimming visits (before calving, at 70 DIM, and three months thereafter), and by assessing locomotion scores (LCS) 1 to 5 at two-week intervals. An intraruminal sensor monitored pH continuously, enabling the determination of the number of days the cows experienced SARA (pH below 5.8 for more than 330 min in 24-h), which allowed us to derive a severity index for SARA. In this manner the cows were assigned to three groups retrospectively: light, moderate, and severe SARA. A statistically significant increase in lameness incidence was observed when comparing light and severe SARA groups, but no effect was observed on LCS and claw lesion prevalence. ABSTRACT: This study aimed to evaluate the effects of diet-induced subacute rumen acidosis (SARA) severity during transition and the early lactation period on claw health in 24 first-lactation Holstein heifers. All heifers were fed a 30% concentrate (in dry matter) close-up ration three weeks before calving, then switched to a high-concentrate ration (60% dry matter), which was fed until the 70th day in milk (DIM) to induce SARA. Thereafter, all cows were fed the same post-SARA ration with around 36% concentrate in dry matter. Hoof trimming was performed before calving (visit 1), at 70 (visit 2) and at 160 DIM (visit 3). All claw lesions were recorded, and a Cow Claw Score (CCS) was calculated for each cow. Locomotion scores (LCS 1–5) were assessed at two-week intervals. Intraruminal sensors for continuous pH measurements were used to determine SARA (pH below 5.8 for more than 330 min in 24 h). The cluster analysis grouped the cows retrospectively into light (≤11%; n = 9), moderate (>11–<30%; n = 7), and severe (>30%; n = 8) SARA groups, based on the percentage of days individual cows experienced SARA. Statistically significant differences were found between SARA groups light and severe in terms of lameness incidence (p = 0.023), but not for LCS and claw lesion prevalence. Further, the analysis of maximum likelihood estimates revealed that for each day experiencing SARA, the likelihood of becoming lame increased by 2.52% (p = 0.0257). A significant increase in white line lesion prevalence was observed between visits 2 and 3 in the severe SARA group. The mean CCS in severe SARA group cows were higher at each visit compared to cows in the other two groups, but without statistical significance. Overall, this is the first study indicating that first-lactation cows fed a similar high-concentrate diet but with a higher severity of SARA tended to have poorer claw health, albeit with only partial statistical evidence.