After a review of nearly 200 publications, researchers from Fonterra, AgResearch, and Massey University concluded that studies investigating the differences between organic and conventionally-produced milk "have so far been largely equivocal."
In their review, Organic and conventionally produced milk - An evaluation of factors influencing milk composition, the New Zealand-based investigators attributed this to "the complexity of the research question and the number of factors that can influence milk composition."
"When comparing organic and conventional milk composition (especially milk fatty acids), previous studies have generally compared organic dairying with milk produced from grass-fed cows to conventional dairying with milk produced from concentrate-fed cows," said lead investigator, Don Otter, senior scientist, AgResearch Grasslands Research Centre.
"The differences in milk composition observed are actually due to the different diets of the cows (i.e. pasture versus concentrate feeding) rather than organic versus conventional farming systems," Otter added.
One "complication" is that organic dairy farming regulations "vary in detail" from country-to-country.
In New Zealand, for example, cows producing organic milk must graze throughout the 150 day grazing season, according to the study.
Meanwhile, in the US, the same cows have to graze for just 120 days, it said.
This, the study concluded, does "not allow for a distinct separation from conventionally produced milk."
"In other words, no 'organic effect' exists that can be credited to a holistic combination of factors affected by the organic system."
"If animal genetics, health, breed, diet, management, or environment differs, then so will the composition of the milk produced," it added.
Source: The Journal of Dairy Science doi:10.3168/jds.2014-8389
Title: Organic and conventionally produced milk - An evaluation of factors influencing milk composition
Authors: B Schwendel, T Wester, P Morel, M Tavendale, C Deadman, N Shadbolt, D Otter