Persistency of the effect of long-term administration of a whey protein gel composite of soybean and linseed oils on performance and milk fatty acid composition of dairy cows

To study the persistency of the effect of supplementing a whey protein emulsion gel (WPEG) of a mixture of linseed and soybean oil on milk fatty acids, a 10-wk experiment was carried out with 32 lactating Holstein Friesian dairy cows. During the first 5 wk, all cows were managed on a restricted grazing regime with pasturing during the daytime and receiving a mixed ration of maize silage, grass hay, soybean expeller and a mineral mix during night-time. During the last 5 wk, all cows were indoors throughout the day and received a mixed ration containing grass silage, maize silage, grass hay, and concentrates. Cows were randomly allotted to one of two treatments: a control treatment with no supplementation and a “Gel” treatment supplementing WPEG at a rate of approximately 1.5 kg/d per cow. Feed intake and milk production were monitored and samples of a.m. milking were analyzed for fat, protein, lactose and fatty acids. Supplementing WPEG had no significant effect on monitored dry matter intake (14 kg DM/d during restricted grazing — grass intake not determined; 21 kg DM/d during the last 5-wk period). Supplementing WPEG had no effect on milk yield (average 35 kg/d) and on concentrations and yields of milk fat and milk protein. Supplementing WPEG increased lactose concentration. Supplementing WPEG decreased the proportions in milk of medium-chain fatty acids and increased the proportions of most C18 fatty acids, except cis9 C18:1 and trans10, cis12 C18:2. Supplementing WPEG led to doubling of cis9, cis12 C18:2 (from 1.8 to 4.0 g/100 g of fatty acid) and a fourfold increase above control in cis9, cis12, cis15 C18:3 (from 0.5 to 2.2 g/100 g of fatty acids). From these results it is concluded that feeding vegetable oils as WPEG to dairy cattle has a persistent effect on the proportions of poly-unsaturated fatty acids in milk.