Mineral balances including TMR, drinking water and assay minerals in the milk

Abstract Text:

Drinking water for dairy animals or manure for soil applications can be both a source of mineral nutrients or toxic substances. Commercial dairy production systems (grazing or indoors) are evolving to a larger scale, with more cows per farm and milk production per cow. Including assayed concentrations of minerals in the diet, drinking water and milk could improve the accuracy of calculations of herd or pen mineral balances. The aim of this presentation is to discuss mineral contents in TMR, water and milk on mineral balances and excretion in lactating dairy cows. A mineral balance study in California on 40 dairies with low total salts (TS) drinking water for lactating dairy animals (0.2 to 1.5 g TS/L) was carried out to compare TMR mineral content with the NRC requirement, with and without including minerals in drinking water, and the average NRC values for milk mineral concentrations to assayed minerals in the bulk tank milk. Most TMR minerals were in excess of NRC requirements. When including minerals in drinking water, Mg, Na, Cl, S, and Cu increased TMR median mineral contents by about 5% (ranged from 3.6% for S to 7% for Na). The assayed values of minerals in milk were lower than NRC averages (i.e.  Mg - 49%, Na -58%, Cu - 295%, and Fe - 525%).  Estimated excretions of minerals via manure varied substantially across farms. Farms in the 10th percentile had estimated mineral excretions via manure 2 to 3 times less than those in the 90th. For example, daily K median excretion was 321 g/cow, from 240 (10th) to 425 g/cow (90th percentile), daily Na excretion varied from 69 (10th) to 168 g/cow (90th percentile) with a median of almost 100 g. Median Cu and Zn excretions were 417 and 1700 mg/cow per day, but Cu excretion increased more than 3 times and Zn more than 2.5 times from 10th to 90th percentiles.  Estimates of dairy farm mineral balances should be based on assayed mineral concentrations in dietary ingredients, drinking water and milk.  Accurate estimates of mineral balance can then be used to manage excess of minerals (diet and manure) and improve animal mineral nutrition, nutrient management plans and soil mineral nutrition. 

Keywords: dairy sustainability, dairy cows, drinking water, mineral balances