Persistency of milk trans-18:1 isomers and rumenic acid in Holstein cows over a full lactation

Mohammed, R., Khorasani, R. G., Goonewardene, L. A., Kramer, J. K. G. and Kennelly, J. J. 2011. Persistency of milk trans-18:1 isomers and rumenic acid in Holstein cows over a full lactation. Can. J. Anim. Sci. 91: 147-167. A long-term lactation study was undertaken to determine whether the previously reported short-term persistency in vaccenic acid [VA; trans(t)11-18:1] and rumenic acid (RA) could be maintained. To test this hypothesis, 24 Holstein cows were allotted to two experimental diets (control and test) from 2 wk before calving until they were 270 d in milk (DIM). The test diet was similar to the control diet, but supplemented with sunflower seed (11.2% diet DM), fish oil (0.5%) and monensin (22 mg/kg DM) by replacing an equivalent amount of barley grain. The forage: concentrate ratio was 50:50 (DM basis) with 35% barley silage and 15% alfalfa hay. Milk was sampled every fortnight from the start of lactation until cows were 270 DIM. Data obtained were averaged into three equal periods of 90 d eac...