Dietary cation-anion difference (DCAD) is being used as a basis for diet formulation in the dairy industry. While extensive research has been conducted on the effects of DCAD concentration on animal performance and rumen characteristics, the effects of the individual strong ions that contribute to DCAD have yet to be determined. In addition to DCAD, there is evidence that cation source (Na vs. K) affects animal performance (Iwaniuk et al., 2015). We hypothesized that dietary strong ion concentrations (Na, K, and Cl) would affect the rumen ion concentrations. Our objective was to determine if rumen Na, K, and Cl concentrations were affected by dietary mineral content. Literature data were collected from 2 dairy cattle studies (Bailey, 1961; Bennink et al., 1978) that included 11 different diets with (mean ± SE) concentrations of 47 ± 35, 358 ± 312, and 108 ± 188 mEq/kg dietary Na, K, and Cl, respectively. Rumen samples, collected by rumen cannula, were taken between 0 to 9 h (Bennink et al., 1978) and 1 to 14 h post-feeding (Bailey, 1961). Principal components analysis (PCA) suggested that rumen Na and K were PCA negative, while rumen Cl and diet K clustered together. Subsequent multiple regression analysis (PROC GLMSELECT) showed that dietary K and Cl were significant factors (P < 0.01) associated with changes in rumen Na, K, and Cl, and diet Na was associated (P ≤ 0.06) with changes in rumen Na and K. As rumen K increased, rumen Na decreased (P < 0.001). We concluded that manipulation of diet strong ion concentrations could be used to alter rumen Na, K, and Cl concentrations and, thus, alter the rumen environment. Table 1.

Item	Rumen ion
Na	K	Cl
Regression statistics
Mean, mEq/L	122.0	46.9	18.7
Root MSE	17.4	11.8	4.04
Adj. R2	0.61	0.60	0.63
Regression coefficients
Intercept, mEq/L	151.9	63.4	9.35
Diet Na, mEq/kg	0.254	−0.83	NS
Diet K, mEq/kg	−0.07	0.042	0.251
Diet Cl, mEq/kg	0.064	−0.08	−0.193
Rumen Na, mEq/L	—	−0.21	NS
Rumen K, mEq/L	−0.47	—	NS
Rumen Cl, mEq/L	NS	0.22	—
Time post-feeding, h	NS	NS	−0.38