Simplified strong ion difference approach to acid–base balance in healthy foals

Objective To determine the strong ion difference (SID a ) and total nonvolatile weak buffers (A TOT ) in healthy foals during the first year of life and to compare reference biochemistry laboratory with analyzers available during emergency hours. Design Prospective study performed over 2 years. Setting University teaching hospital. Animals Two hundred thirty‐six healthy foals distributed in 6 groups: A (21 days–2 months), B (2–3 months), C (3–6 months), D (6–9 months), E (9–12 months), and 33 neonatal foals (< 21 days old). Interventions Blood samples were obtained to determine L‐lactate, sodium, potassium, chloride, and total plasma protein concentrations. In neonatal foals, samples were analyzed using 4 different devices. Reference intervals of SID a and A TOT for each of the analyzers under comparison were established using mean ± 2 standard deviations. Age effect was evaluated using one‐way ANOVA analysis. Linear regression in neonatal foals was employed to obtain a new equation to estimate A TOT from total plasma protein concentration. Measurements and Main Results A significant age effect was observed for A TOT and SID a . In all foals younger than 6 months, A TOT values were lower than in older foals ( P < 0.003). A clinically and statistically significant difference in SID a was detected only in the neonatal period ( P < 0.001). The equation to estimate A TOT from total plasma protein adjusted for neonatal foals is A TOT = 2.5 × total plasma protein concentration. Conclusions Reference intervals of A TOT should be considered different from adults during the first 6 months of life in horses. Regarding SID a , values should be considered different only during first 21 days of life.