Effect of mineral supplementation on lactational performance in early-lactating dairy cows fed a high-concentrate diet

Abstract Text:

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