Abstract #M322

# M322
Relationship between mineral composition of milk and lactation performance.
A. R. Alfonso-Avila*1, E. Charbonneau1, P. Y. Chouinard1, G.F. Tremblay2, D. E. Rico1, R. Gervais1, 1Université Laval, Quebec, QC, Canada, 2Agriculture and Agri-Food Canada, Quebec, QC, Canada.

Minerals could be implicated in cellular transport of milk constituents or their precursors in the mammary epithelial cell. Our objective was to examine associations between mineral composition of milk and lactation performance in dairy cows. A total of 120 observations from 2 separate randomized complete block design experiments comprising 60 early-lactation Holstein cows (38 ± 11 DIM; Mean ± SD) were used. In both experiments, treatment periods lasted 28 d and were preceded by a 1-wk pretreatment collection period. In both trials, diets had a forage-to-concentrate ratio of 40:60 (DM basis) and were supplemented, on a DM basis, with (1) 1.5% K2CO3, (2) 1.8% K2CO3, (3) 2.6% KHCO3, (4) 2% KCl, (5) 1.4% Na2CO3, (6) 1.5% K2CO3 + 2% soybean oil, (7) 2% soybean oil, or (8) unsupplemented. Milk yield was recorded and samples collected on the last 3 or 5 d of each period, pooled by cow and period, and analyzed for fat, protein, lactose, and mineral concentrations (Na, K, Cl, S, Mg, P, Ca). Associations between minerals and milk yield and component concentrations were assessed using mixed model regressions, considering cow and experiment as random effects, and parity and individual mineral concentrations as fixed effects. Parity was removed from the model when not significant (P > 0.10). Milk concentrations of Ca, Mg, P, and S were positively associated with both fat (P < 0.01; R2 > 0.28) and protein (P < 0.01; R2 > 0.30) contents. Negative relationships were observed between Cl and fat (P = 0.02; R2 = 0.48), protein (P < 0.01; R2 = 0.40) as well as lactose (P < 0.01; R2 = 0.71) contents, whereas K was negatively associated with lactose concentration (P < 0.01; R2 = 0.62). Finally, Ca, Mg, and P were negatively related with milk yield (P < 0.01; R2 > 0.86), whereas a positive association was observed with Cl (P < 0.01; R2 = 0.79). The strong relationship of milk Cl concentration with milk yield suggests that this mineral is involved in milk synthesis. Mineral concentrations in milk are recognized to reflect their cellular levels, it is then possible to explore the biological role of minerals in the secretory mechanisms of milk constituents.

Key Words: chlorine, milk constituent, milk synthesis