Lameness is a very important animal welfare issue on dairy farms. Unfortunately there‘s still a lot to learn regarding the cause(s) of lameness from claw horn disorders, such as sole ulcers, sole hemorrhages, and white line disease.
Research knowledge from equine lameness (laminitis) has been generalized to dairy cows without taking into account the anatomical and physiological differences between horses and cows. Interestingly, the link between subclinical laminitis and claw horn disorders in the cow has been challenged in recent years. The current idea is that claw horn disorders are a result of a bruise within the claw horn capsule.
Poor housing conditions may increase the risk of bruising. The suspensory apparatus in cows is less developed than in horses so the digital cushion supports a greater proportion of the body weight in cows. The digital cushion is made up of mostly fat, is located underneath the distal phalanx, and is important in dampening compression of the corium tissue beneath the digital cushion.
It’s kind of like a running shoe for cows that absorbs the impact shock of every step a cow takes. The thickness of the digital cushion as measured by an ultrasound machine was strongly related to lameness in a Cornell study. Of the 501 cows evaluated, cows in the bottom 25% of digital cushion thickness had a prevalence of lameness that was 15 percentage points higher than cows in the top 25%. In addition, the digital cushion thickness was associated positively with body condition score; thinner cows had lower digital cushion thickness. Also, digital cushion thickness and body condition score decreased steadily until the 4th month of lactation when both reached their lowest value.
Knowing that cows mobilize fat from multiple locations in the body in early lactation, it is likely that cows mobilize fat from the digital cushion. Until recently it was believed that low body condition score was just a consequence of lameness due to decreased feeding time. However, European and American researchers suggested recently that low body condition may be a cause for, rather than a result of, lameness.
Lame cows don’t always reduce feeding time and only the most severely lame cows decrease feed intake. Some lame cows even increase their rate of feed intake. In a UK study with 1137 cows, it was found that low body condition (≤2 on a 1 to 5 scale) contributed to the development of horn related claw lameness in the following 2 or 2 to 4 months but not infectious claw diseases. In another UK study that followed 724 cows in one herd for 8 years, it was confi rmed that maintaining a body condition score ≥2.5 is ideal to minimize the risk of lameness. The challenge is balancing body condition loss in early lactation to support lactational performance and metabolic health vs. minimizing the risk of lameness. However, it’s clear that managing body condition during the transition period and early lactation is critical for animal welfare.