Milk and dairy products contribute to about 20% of the average daily intake of trans-fatty acids (TFA) in UK adults⁽Reference Henderson, Gregory and Irving¹⁾. The evidence of their effects on human subjects health are equivocal, but at current intakes and food compositional levels TFA from ruminant products are thought not to be a significant risk factor for CVD. However, there is concern that current strategies to reduce milk SFA will lead to substantial increases in TFA concentrations. Feeding rumen-protected sources of cis-MUFA to dairy cows would minimise the appearance of TFA in milk fat, but research to date has been inconsistent⁽Reference Chouinard, Girard and Brisson²⁾. The aim of the present study was to measure the effect of feeding incremental amounts of a novel calcium salt (CS) of cis-MUFA on TFA isomer composition of milk fat.

Four multiparous, late-lactation Holstein–Friesian cows were randomly allocated to one of four dietary treatments in a 4×4 Latin Square design with 21 d experimental periods. Treatments were a control diet (control) containing no supplemental fat, or the same basal diet with CS of cis-MUFA (Volac International Ltd.) fed at 20, 40 and 60 g/kg DM (CS2, CS4 and CS6, respectively). Milk composition was analysed during the last 3 d of each experimental period⁽Reference Givens, Kliem and Humphries³⁾.

P (LIN) represents linear effect. CS2, CS4 and CS6 – treatment diets containing 20, 40 or 60 g/kg DM calcium salts.

Incremental inclusion of CS linearly (P<0.001) decreased milk fat SFA and increased cis-MUFA concentrations. However, there were also significant increases (P<0.001) in all trans-18:1 isomers measured, some trans-PUFA, and total conjugated linoleic acid (CLA), leading to an overall increase in total TFA (16 g/100 g fatty acids for CS6). This indicates CS of cis-MUFA were at least partially metabolised in the rumen and that alternative rumen-protection methods for MUFA are needed to minimise increases in TFA concentrations that accompanied decreased SFA in milk fat.