Intake, milk production, ruminal, and feed efficiency responses to DCAD in lactating dairy cows

Abstract Text: Previous meta-analyses (Hu and Murphy, 2004, J. Dairy Sci. 87:2222) of the effects of dietary cation anion difference (DCAD) in lactating dairy cow diets utilized studies conducted after the development of the DCAD concept. Dietary buffers such as NaHCO₃ and K₂CO₃ increase DCAD and have been used in lactating dairy cow diets for several decades. However, most published studies on buffer feeding were conducted prior to the development of the DCAD concept. Our objective was to determine the intake, milk production, ruminal, and feed efficiency responses to DCAD using previous studies with dietary buffer addition and more recent studies that focused on DCAD as dietary treatments.  The database consisted of 44 articles that were published between 1965 and 2011.  The studies included 196 dietary treatments, and 89 treatment comparisons that varied in DCAD. For studies that lacked analyses of one or more of the dietary cations (Na, K, or Cl), ion percentages were estimated from ingredient composition using the 2001 Dairy NRC Software.  Two basic models were used to evaluate DCAD responses using the NLMIXED procedure in SAS 9.2: 1) A simple linear model: Y = A + B*(DCAD) where A = intercept and B = the increment (slope) in performance per unit DCAD (meq/kg diet DM); and 2) a nonlinear model: Y = A + M(1-e^{(K x DCAD)}) where M = maximal increment in performance from DCAD and K = the rate constant. In both models, study was designated as the random effect. DCAD effects best described by the linear model included milk fat percent, fat yield, rumen pH,  NDF digestibility, and FCM/DMI where a 100 meq/kg increase in DCAD resulted in respective increases of  0.10% (P < 0.001; RMPSE = 0.01), 35 g/d  (P < 0.001; RMPSE = 5), 0.033 pH units (P < 0.001; RMPSE = 0.001), 1.5% NDF digestibility (P < 0.001; RMPSE =  0.4), and 0.0013 FCM/DMI units (P < 0.001; RMPSE = 0.005).  DMI, milk yield, and 3.5% FCM were best described by the nonlinear model where the maximal responses were 3.05, 2.88, and 6.57 kg/d, respectively (P < 0.001). The DCAD concentration at which 80% of the maximal response occurred was 456, 207, and 617 for DM intake, milk yield, and 3.5% FCM, respectively.  These results suggest that DCAD has significant effects on intake, milk production and composition, digestion, and feed efficiency in lactating dairy cows.

Keywords: DCAD, Meta-analysis, Dairy Cows