Effect of a supplement containing trans-10,cis-12 conjugated linoleic acid on the performance of dairy ewes fed 2 levels of metabolizable protein and at a restricted energy intake

Trans-10,cis-12 conjugated linoleic acid (CLA) inhibits milk fat synthesis in dairy ewes, but the effects under varying dietary metabolizable protein (MP) levels when energy-limited diets are fed have not been examined. The objectives of the study were to evaluate the response of lactating dairy ewes to CLA supplementation when fed diets limited in metabolizable energy (ME) and with either a low or high MP content. Twelve multiparous ewes in early lactation were randomly allocated to 1 of 4 dietary treatments: a high MP (110% of daily MP requirement) or low MP (93% of daily MP requirement) diet unsupplemented or supplemented with a lipid-encapsulated CLA to provide 2.4 g/d of trans-10,cis-12 CLA, in each of 4 periods of 25 d each in a 4 × 4 Latin square design. All diets were restricted to supply each ewe with 4.6 Mcal of ME/d (equivalent to 75% of ME requirement). Supplementation with CLA decreased milk fat percentage and yield by 33% and 24%, respectively, and increased milk, milk protein, and lactose yields by 16, 13, and 17%, respectively. Feeding the high MP diet increased the yields of milk, fat, protein, and lactose by 18, 15, 19, and 16%, respectively. Milk fat content of trans-10,cis-12 CLA (g/100 g) was 0.09 and <0.01 for the CLA-supplemented and unsupplemented ewes, respectively. Ewes supplemented with CLA had a reduced yield (mmol/d) of fatty acids of C16, although the effect was greatest for C16. Plasma urea concentrations were lowest in ewes supplemented with CLA compared with those unsupplemented (6.5 vs. 7.4 mmol/L, respectively) and receiving low compared with high MP diets (5.6 vs. 8.3 mmol/L, respectively). In conclusion, dairy ewes fed energy-limited diets and supplemented with CLA repartitioned nutrients to increase yields of milk, protein, and lactose, with the response to CLA supplementation and additional MP intake being additive.