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The relationship between high intake of rapidly fermentable carbohydrates and the subsequent response on plasma glucose, insulin sensitivity and clinical signs of laminitis in dairy heifers was studied. Ten dairy heifers with a mean body weight of 275 kg (SD 13.8 kg), were parallelly subjected (n=5/treatment group) to either a total mixed ration (TMR) low (LC, 130 g DM/kg) or high (HC, 480 g DM/kg) in cassava (starch). Results showed that mean DM intake, rectal temperature, heart rate, respiration rate and rumen contractions were not affected by the dietary treatments. All heifers fed the HC-TMR had diarrhea while all the heifers fed the LC-TMR had a pasty, soft consistency of feces. Three of the 5 heifers fed the HC-TMR displayed clinical signs of acute laminitis compared to none in the LC-TMR group. Mean postprandial rumen pH values of heifers fed the HC-TMR, but not the LC-TMR, were lower than 6.0 at all the time points measured. The reduction in rumen pH was associated with 49% greater concentration of total VFA and a concomitant shift from acetic to propionic acid and increased rumen lactic acid concentrations. Moreover, the HC-TMR caused greater plasma insulin levels and insulin resistance. The three laminitis animals had 1.9 greater basal plasma insulin values and a 46% lower insulin sensitivity values, respectively compared to their non-laminitis counterparts fed the HC-TMR. Insulin sensitivity was shown to be associated with clinical signs of laminitis in heifers only when plasma insulin concentrations were greater than ~ 700 pmol/L.

Laminitis is considered an important health problem facing the Thai dairy industry. Although the etiology of laminitis is multifactorial, nutrition is considered an important risk factor. Rumen acidosis, lipopolysaccharides (LPS) and histamine may play a role in the development of laminitis in dairy cattle. However, the relevancy of these risk factors in relation to the occurrence of laminitis under practical feeding conditions in Thailand is not clear. In Thailand, dairy rations are generally low in physically effective NDF because roughage is not always provided ad libitum. Furthermore, cassava which is rich in rapid fermentable carbohydrates, is an important concentrate in practice and the crude protein (CP) content of Thai dairy rations is usually low. When these practical feeding conditions are taken into account, it may be suggested that dairy cattle are prone to the condition of rumen acidosis. Therefore, rumen acidosis appears to be relevant in the light of the observed high incidence of laminitis in Thailand. This reasoning is in line with the outcome of the observational study showing that the prevalence of (sub) clinical laminitis and the dietary NDF content were negatively related. In the condition of rumen acidosis, both histamine and LPS can be produced and both factors are implicated to play a role in the etiology of laminitis. However, under Thai feeding conditions, histamine is most likely not important to explain the occurrence of laminitis because it was shown that the prevalence of (sub) clinical laminitis was not related with the dietary CP content. This observation is corroborated by the outcome of controlled feeding trial; rumen histamine levels remained too low to induce laminitis. Rumen LPS also was monitored after the feeding of high concentrate rations. In two studies rumen acidosis was successfully induced but only in one study observed cases of laminitis were related to high rumen LPS values.Clearly, the issue on LPS is not yet settled and the differential responses in rumen LPS between the two studies prevents to draw a clear conclusion with respect to the relevancy of LPS under Thai feeding conditions. Due to their chemical and conformational structure, phyllosillicates have the potential to trap LPS. The idea that a specific phyllosillicate, in the form of hydrate sodium calcium aluminosilicate (HSCAS), can adsorb LPS, was tested in cows suffering from experimentally induced rumen acidosis. However, it appeared that HSCAS had no effect on the concentration of free LPS in rumen fluid. Therefore, the use of supplemental HSCAS does not appear to be an effective strategy to prevent laminitis. In conclusion, there appear to be no agents available that can effectively adsorb LPS under practical feeding conditions. This implicates, that the prevention of rumen acidosis appears to be the most effective strategy to prevent the occurrence of nutrition related laminitis. Consequently, Thai dairy farmers should raise the content of physically effective NDF of the dairy ration. From a practical viewpoint, it is recommended that Thai dairy farmers should supply roughage ad libitum and/or mix appropriate amounts of roughage with concentrates.