It is commonly believed that rumen acidosis, resulting from feeding high concentrate diets, is the main cause of claw horn lesions (sole hemorrhage, sole ulcers and white line lesions). It is thought that acidosis results in the release of chemicals from the rumen that circulate in the bloodstream and cause laminitis – inflammation and degradation of tissues (laminae – see diagram below) that support the internal structures within the claw capsule. Sinking of the pedal bone puts added pressure on the sole corium, creating the typical lesions.
Since these lesions often come to light in early lactation, an association with high concentrate, early lactation diets may seem logical. However, studies designed to prove this connection have failed to establish a clear cause-and-effect relationship. A number of studies where very highly fermentable diets have been fed in order to provoke laminitis have not had the desired effect.
Could there be other explanations to account for increased pressure of the pedal bone on the sole corium? British researchers have demonstrated that relaxation of the supporting structures of the claw (laminae, tendons) around calving time, perhaps due to hormonal changes, may have a role.
The other nutrition-related explanation, for which research evidence is accumulating, relates to the digital cushion. A previous post described a study showing that thin digital cushions, related to low body condition score, may be a factor in the development of claw horn lesions. The authors of that study suggested that thin cows had mobilised fat from the digital cushion during weight loss, resulting in reduced cushioning and the development of claw horn lesions. However, an alternative explanation might be that lame cows with claw horn lesions could have lost body condition, resulting in thin digital cushions. The question is: ‘Do lame cows become thin, or do thin cows become lame?’
Undoubtedly lame cows become thin – a number of studies have shown that lameness reduces feed intake leading to loss of body condition. However if is true that thin cows become lame, body condition score management could be an important lameness prevention strategy. In support of this idea, 3 recent studies in the UK clearly demonstrated that loss of body condition preceded animals either being identified lame by mobility scoring or being treated for lameness. Details of these studies are available here.