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Effect of Pre-calving Dietary Cation Anion Difference on Milk Production: A Meta-analysis
The effects of dietary cation anion difference (DCAD) of pre-calving diets on milk production. A total of 15 studies and 34 comparisons were identified and analyzed (Stata 13.0 Statacorp, Tx, USA) using a random effects model. A weighted mean difference between treated and control was also calculated. Meta-regression analysis evaluated whether parity of the cattle, difference in DCAD between treatment and the control diet and estimated energy density, crude protein, crude fat, neutral detergent fiber, non fiber carbohydrates, DCAD, calcium, magnesium, phosphorus, potassium, and content of the control diet influenced responses.
The average ± SE days of exposure to transition diets was 29±3 and the DCAD of controls and treated cows was 232±37 and -27±33 meq/Kg, respectively. Only the parity of the cow (P = 0.003) and NDF of the control diet (P = 0.02) influenced responses with milk production increased in cows (P = 0.0001) and lowered in heifers (P = 0.027). The effect size (ES) for milk production of studies in cows was positive (0.629 95% CI 0.292 to 0.965). Estimated responses in milk or fat corrected milk over 65±14 days of lactation were 1.153 (95% CI 0.335 to 1.971) L per day. In heifers, milk production responses were ES of -1.211 (95% CI -2.288 to -0.135) and the weighted mean difference was -1.482 (95% confidence interval -1.872 to -1.093) L per day. The I2 was 77.1 for cows and 87.2 for heifers indicating very considerable variability in responses. The effect size response was lower with higher NDF diets. The lower response to DCAD in high NDF studies may indicate a role for ruminal outputs to influence acid-base status. Critically, other sources of variation, as indicated by the high I2, were not identified, despite the large number of covariates tested.
Lean IJ, DeGaris PJ, McNeil DM, Block E (2006) Hypocalcemia in dairy cows: Meta-analysis and dietary cation anion difference theory revisited. Journal of Dairy Science. 89: 669-684.
Keywords: dietary cation anion difference, pre-calving diet, meta-analysis