Effects of prepartum dietary cation-anion difference intake on production and health of dairy cows: A meta-analysis.

Prepartum diets influence cow performance for weeks to months postpartum. This observation leads to questions about milk yield and physiological and health responses to diets with negative dietary cation-anion difference (DCAD). Further, responses to increased intake of a diet with lower DCAD (Eq/d) have not been explored using meta-analysis. Our objectives were to explore the effects of prepartum DCAD intake on metabolism and production and health as well as the potential for differences in intake of other macrominerals to influence responses to differences in DCAD intake using classical meta-analytical methods. Not all treated groups were fed a diet with negative DCAD, and the effect studied is that of reducing the DCAD. We hypothesized that reducing DCAD intake would improve Ca metabolism and postpartum performance. We used a maximum of 58 comparisons from 31 experiments and a total of 1,571 cows. Intakes of DCAD were 2.28 Eq/d and -0.64 Eq/d for the control, higher DCAD and treated, lower DCAD groups, respectively. Diets with lower DCAD reduced urine pH [standardized mean difference (SMD) = 1.90 and weighted mean difference (WMD) -1.23 pH]. Intake of lower DCAD decreased prepartum DMI (SMD = 0.23; WMD = 0.29 kg/d), increased postpartum DMI (SMD = 0.40; WMD = 0.63 kg/d), and increased milk yield (SMD = 0.172). However, we found an interaction with parity; diets with lower DCAD increased milk yield in parous cows (SMD = 0.29; WMD = 1.1 kg/d) but resulted in numerically lower milk yield in nulliparous cows (SMD = -0.20; WMD = 1.28 kg/d) compared with controls. The FCM yield increased with treatment (SMD = 0.12; WMD = 0.56 kg/d); however, yield of treated cows tended to be greater in parous cows but smaller for nulliparous cows compared with controls. Milk fat percentage, milk fat yield, and milk protein percentages were not affected by treatment, although milk protein yield tended to increase in cows fed the lower DCAD diet (SMD = 0.21; WMD = 0.02 kg/d). Treatment increased blood Ca (SMD = 0.53; WMD = 0.13 mM) and P (SMD = 0.40; WMD = 0.13 mM) on the day of calving and Ca postpartum (SMD = 0.36; WMD = 0.06 mM). Treated cows had smaller concentration of blood BHB before calving than controls (SMD = -0.39; WMD = -0.04 mM). Reducing DCAD in cows resulted in decreased risks of clinical hypocalcemia (risk ratio = 0.60) and retained placenta (risk ratio = 0.59), and reduced the odds of metritis (odds ratio = 0.46) and overall disease (OR = 0.61). We observed no effect on risk of abomasal displacement or mastitis and no effect of differences between treated and control cows in Ca intake (g/d) on the outcomes evaluated. A positive role for increased Mg intake between groups for increased milk fat yield and in reducing the risk of retained placenta was identified. Diets with lower DCAD improved performance of parous dairy cows, and our findings suggest a need for more studies on the effects of a lower DCAD on nulliparous transition cows.