Effect of mineral supplementation on lactational performance in early-lactating dairy cows fed a high-concentrate diet
Previous studies reported an increase in milk fat synthesis when lactating dairy cows were fed diets with higher dietary cation-anion difference (DCAD) or K, supplied as K2CO3. This study investigated the effects of DCAD, cation source, and buffering capacity of the mineral supplement on lactational performance of early-lactating dairy cows fed a high concentrate diet. Ten primiparous and 25 multiparous Holstein cows averaging 38 ± 13 DIM were distributed according to a randomized block design (7 blocks) for 5 wk, including a 1-wk pretreatment collection period, used as a covariate. Treatments consisted of C) a basal diet formulated to contain 40% forage (60% corn silage) and 60% concentrate (16% CP, 47% non-fibrous carbohydrates, 29% NDF, DCAD +65 mEq/kg) as control; K1) C + 1.8% K2CO3 (DCAD: +326); K2) C + 2.6% KHCO3 (DCAD: +324); K3) C + 1.9% KCl (DCAD +64); and Na) C + 1.4% Na2CO3 (+322). Orthogonal contrasts were used to assess the effects of K2CO3 (C vs. K1), buffering capacity (K1 vs. K2), DCAD (K1 vs. K3), and cation type (K1 vs. Na). Treatment period was 28 d with the last 5 d used for data and sample collection. The selected comparisons detected no effect of treatments on DMI (24.1 ± 1.2 kg/d; P>0.14) and milk yield (36.8 ± 1.8 kg/d; P>0.12). Blood K+ concentration was higher in cows fed K1 (3.99 mmol/L) as compared with C (3.75; P<0.01), K2 (3.79; P=0.02), and Na (3.68; P<0.01), whereas no difference was observed with cows fed K3 (3.89; P=0.20). Blood Cl- concentration was lower in cows fed K1 (106.1 mmol/L) as compared with Na (108.3; P=0.01). However, no difference was observed in blood Na+ concentration of cows fed K1 and Na (139.9 ± 0.4 mmol/L; P=0.18). As compared with Na, cows fed K1 had a higher milk protein content (3.12 vs 2.93%; P=0.04) but a similar milk protein yield (1087 ± 67 g/d; P=0.56). Milk fat percentage was higher in cows fed K1 compared with C (4.03 vs 3.26%; P=0.02), whereas milk fat yield (1305 ± 134 g/d; P=0.21) or 4% fat corrected milk (34.0 ± 2.6 kg/d; P=0.61) were not affected. As opposed to previously published results, under conditions of the current experiment, increasing DCAD or K+ concentration in a high concentrate diet did not improve milk fat yield in early lactating cows.
Keywords: DCAD, Potassium carbonate, Milk fat synthesis