Abstract
Certain fatty acids (FAs), such as omega-3 and conjugated linoleic acid (CLA) are considered essential FAs with beneficial health effects for humans. Milk is considered a relatively inexpensive and readily available source of these FAs and is part of a recommended healthy daily diet. The aim of the study was to determine the effect of diet changes on the FA composition of Jersey (J) and Fleckvieh x Jersey (FxJ) milk. Cows were alternately put on kikuyu-ryegrass pasture, followed by a feedlot system, then returned to kikuyu-ryegrass pasture for four weeks each. The same concentrate mixture was fed to cows regardless of feeding system. The feedlot system consisted of a partial total mixed ration (pTMR). Milk samples were collected two and four weeks after diet changes and stored at −20 °C until laboratory analysis by gas chromatography. The FA concentration of milk was not affected by breed, although it was affected significantly by diet changes. Most notably, the total omega-3 and -6 FAs decreased when cows were fed pTMR while increasing when the diet was changed back to pasture feeding. The CLA content of milk was similarly affected. That is, concentrations decreased significantly when the cows were on the pTMR diet and increased when cows were put back on the pasture-based diet. The results suggested that the health benefits of milk fat are affected negatively when cows are fed pTMR compared with being fed in a pasture-based system. The health benefits of milk are reduced owing to decreased levels of the CLA content of milk fat. Therefore, feeding additional hay in a pasture-based production system should be reconsidered when aiming to produce milk that provides health beneficial qualities. Keywords: breed, diet, n-3 fatty acid, n-6 fatty acid, pasture, Fleckvieh
Highlights
Until recently, fat in milk, saturated fatty acids (SFAs), was regarded as an unhealthy food source as it was linked to obesity, heart disease and some forms of cancer (Salter, 2005)
In contrast with an earlier study which showed that breed and lactation stage affected the content in milk fat and some FAs (Sasanti et al, 2015), the present study showed that the FA content of the milk of cows was not affected by breed (P >0.05) except for C8:0 (P
There was no significant difference between the breeds for days in milk (DIM), with overall means for the DIM of both breeds at the three time points being 44 ± 18, 107 ± 20, and 166 ± 33, respectively, for Pasture 1, partial total mixed ration (pTMR) and Pasture 2
Summary
Fat in milk, saturated fatty acids (SFAs), was regarded as an unhealthy food source as it was linked to obesity, heart disease and some forms of cancer (Salter, 2005). This resulted in fat-free and low-fat milk (0% or 2% fat, respectively) becoming popular choices among consumers. More recent results indicate the beneficial effects of milk fat for humans as it is not composed solely of SFAs. Milk contains a number of types of FAs, of which several appear to have beneficial effects on the health of human beings (Muller & Delahoy, 2016). Reducing the fat content in milk to produce skimmed and low-fat milk decreases or removes beneficial FAs from milk, thereby in effect reducing the health status of low-fat milk compared with full-cream milk
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