An investigation of the safety of oral calcium formate in dairy cows using clinical, biochemical and histopathological parameters

Calcium transport in bovine rumen epithelium as affected by luminal Ca concentrations and Ca sources

The quantitative role of different segments of the gastrointestinal tract for Ca absorption, the respective mechanisms, and their regulation are not fully identified for ruminants, that is, cattle. In different in vitro experiments the forestomach wall has been demonstrated to be a major site for active Ca absorption in sheep and goats. In order to further clarify the role of the bovine rumen for Ca transport with special attention to luminal Ca concentrations, its ionic form, and pH, electrophysiological and unidirectional flux rate measurements were performed with isolated bovine rumen epithelial tissues. For Ca flux studies (Jms, Jsm) in vitro Ussing chamber technique was applied. Standard RT-PCR method was used to characterize TRPV6 and PMCA1 as potential contributors to transepithelial active Ca transport. At Ca concentrations of 1.2 mmol L(-1) on both sides of the tissues, Jms were higher than Jsm resulting under some conditions in significant Ca net flux rates (Jnet), indicating the presence of active Ca transport. In the absence of an electrical gradient, Jnet could significantly be stimulated in the presence of luminal short-chain fatty acids (SCFAs). Increasing the luminal Ca concentrations up to 11.2 mmol L(-1) resulted in significant increases in Jms without influencing Jsm. Providing Ca in its form as respective chloride, formate, or propionate salts there was no significant effect on Jms. No transcripts specific for Ca channel TRPV6 could be demonstrated. Our results indicate different mechanisms for Ca absorption in bovine rumen as compared with those usually described for the small intestines.

Re: The safety of oral calcium formate

A Short Communication was published in the October 2002 issue of the New Zealand Veterinary Journal entitled An investigation of the safety of oral calcium formate in dairy cows using clinical, biochemical and histopathological parameters (McIntyre and Weston 2002). It appeared to be comparing results directly with those of a prior communication (Scott and Van Wijk 2000). The following should be considered when comparing the two papers. Haptoglobins were propounded by McIntyre and Weston as definitive indicators of acute inflammation, yet current literature does not give consistent viewpoints as to their value. The authors cited instances where the haptoglobin concentration was measured in cases of infective disease. However, Skinner et al (1991) believed that haptoglobin concentrations increase as a result of the infection rather than the trauma. To further complicate matters Alsemgeest et al (1994) found that haptoglobin concentrations were elevated in cattle with chronic rather than acute conditions whereas Horadagoda et al (1999) believed the concentrations of acute-phase proteins were higher in acute inflammation. However, they found serum amyloid A was more reliable as an indicator of acute, rather than chronic, inflammation than was haptoglobin. Therefore, histopathology would appear to give much more conclusive evidence of mucosal inflammation than the determination of haptoglobin...