Feeding natural-source minerals or calcium carbonate to horses: Is there a relationship with TCO2?

The illegal practice of “milk-shaking” in horse-racing is characterized by administering large quantities of alkalizing agents to buffer hydrogen ions and provide a potential ergogenic effect to exercising horses. The TCO2 blood test allows states to detect this practice, as indicated by concentrations of CO2, CO3, H2CO3, and HCO3 above 37 mmol/L plasma. Suggestions have been made that feeding smaller amounts of buffers or minerals to horses can increase TCO2 and result in positive tests. The objective of this studywas to test the hypothesis that feeding a mineral complex (Purina Outlast, OL) or calcium carbonate (CC) would not increase TCO2 due to relatively low feeding rates. In trial 1, 9mature, unfit QHswere fed the active ingredient of OLinacrossoverdesign,atarateof0, 50and200ginaone-timemeal mixed with molasses and beet pulp. Blood samples were taken prefeeding and 4, 6 and 8 h post-feeding. In a second trial, 48 unfit, mature QHs and TBs were fed either 50g/head/day OL or CC in 2 meals, or 150g/head/day OL or CC in 4meals for 85 d. Blood samples were taken before and after 34 and 83 d on diets, with all samples obtained 4e5 h after 0700 feeding. All blood was taken via jugular venipuncture into 10 mL heparinized tubes, immediately cooled and shipped to theNYDrug Testing andResearch Program(Ithaca,NY) for analysis via Nova 4 Electrolyte Analyzer (Nova Biomedical,Waltham, MA). Analysis of variance was done with mixed models using GLIMMIX procedure in SAS (SAS 9.4, Cary, NC) and least squares means were compared using Fisher's LSD (P < 0.05). All horses remainedwell belowthelegal limit of37mmol/L.Horses onthe200g feeding rate of OL in the first trial did have a small increase in TCO2 (P = 0.0347, 0 HR= 31.89 ± 0.63mmol/L, 8 HR = 33.47 ± 0.63mmol/L). Horses on OL and CC in the second trial also had small increases (P < 0.0001) in TCO2 over time, but therewere no treatment (P = 0.4468) or treatment≤ time differences (P= 0.8276).Mean baseline samples were reportedas 28.48±0.19mmol/L,34dsampleswere 29.90±0.19 mmol/L, and 83 d samples were 30.14 ± 0.19 mmol/L. These results indicate that feeding OL or CC as directed does not result in positive TCO2 results. However, horse owners are cautioned to feed supplements and feeds according to manufacturers' directions and not to combine them with other buffering agents.