Changes in milk fatty acid profile and animal performance in response to fish oil supplementation, alone or in combination with sunflower oil, in dairy ewes

12 páginas, 4 figuras, 4 tablas.Ruminant diet supplementation with sunflower oil (SO) and fish oil (FO) has been reported as a good strategy for enhancing some milk fat compounds, such as conjugated linoleic acid (CLA) and omega-3 polyunsaturated fatty acids (PUFA) in dairy cows, but no information is available regarding dairy sheep. In this work, ewe diet was supplemented with FO, alone or in combination with SO, with the aim of improving milk nutritional value and evaluating its effect on animal performance. Sixty-four Assaf ewes in mid-lactation, fed a high-concentrate diet, were distributed in 8 lots of 8 animals each and assigned to 4 treatments (2 lots per treatment): no-lipid supplementation (Control), or supplementation with 20 g SO/kg (SO), 10 g FO/kg (FO), or 20 g SO plus 10 g FO/kg (SOFO). Milk production and composition, including a complete fatty acid profile, were analysed on days 0, 3, 7, 14, 21, and 28 on treatments. FO supplementation tended to reduce DM intake in comparison with the Control treatment (-15%), and its use in combination with SO (SOFO) resulted in a significant decrease in milk yield as well (-13%). All lipid supplements reduced milk protein content, and FO also reduced milk fat content, by up to 21% alone (FO) and 27% in combination with SO (SOFO). Although the mechanisms involved in FO-induced milk fat depression are not wellestablished yet, the observed increase in some milk trans-FA that are putative inhibitors of milk fat synthesis, such as trans-9 cis-11 CLA, and the almost 3-fold decrease in C18:0 (consistent with the theory of reduced milk fat fluidity) may be involved. When compared with the Control, lipid supplementation remarkably improved the milk content of rumenic acid (cis-9 trans-11 CLA; up to 4-fold increases with SO and SOFO diets), whereas FO-containing diets also increased milk omega-3 PUFA, mainly docosahexanoic acid (DHA, with mean contents of 0.29 and 0.38% of total fatty acids for SOFO and FO, respectively), and reduced the omega-6/omega-3 FA ratio to approximately half the control value. All lipid supplements resulted in high levels of some trans-FA, mainly trans-11 C18:1 (vaccenic acid) but also trans-10 C18:1.This work was supported by the Spanish Ministry of Science and Innovation (MICINN; AGL2008-04805). The authors from the Instituto de Ganadería de Montaña would like to thank the Council of Castile and Leon for complementary financial support (GR158) and the farm staff for their help in the field work. P.G. Toral gratefully acknowledges receipt of a predoctoral grant from the CSIC (I3P Programme). The authors from the Instituto del Frío (CSIC) wish to thank the Comunidad Autónoma de Madrid (S- 505/AGR-0153) and the Ministerio de Ciencia e Innovación (Consolider Ingenio 2010 Programme; FUN-C-FOOD CSD2007-063) for their financial support. They also wish to thank M.V. Rodríguez-Pino for her technical assistance in the chromatographic analysis.Peer reviewe