Susceptibility to milk fat depression in dairy sheep and goats: Individual variation in ruminal fermentation and biohydrogenation

Small ruminants are susceptible to milk fat depres-sion (MFD) induced by marine lipid supplementation. However, as observed in dairy cows, there is wide in-dividual variation in the response to MFD-inducing diets, which may be due to individual differences in ruminal processes. Therefore, we compared the rumi-nal responses of goats and sheep with varying degrees of MFD extent to improve our understanding of this complex syndrome. Our specific aims were to attempt to elucidate whether pre-existing variations in ruminal fermentation and biohydrogenation determine a higher tolerance or susceptibility to MFD, and whether the severity of MFD depends exclusively on the response to the diet. The trial was conducted with 25 does and 23 ewes fed a basal diet without lipid supplementation for 3 wk (control period). Then, 2% fish oil (FO) was added to the same diet for 5 additional weeks (MFD period). Based on the extent of the elicited MFD (i.e., the percentage variation between milk fat concentra-tions recorded at the end of the control and MFD periods), the 5 most responsive (RESPON+) and the 5 least responsive (RESPON-) animals were selected within each species. On the last day of each period, ruminal fluid samples were collected to examine fer-mentation parameters and fatty acid profiles. In gen-eral, the individual degree of MFD in sheep and goats did not seem to be predetermined by traits related to ruminal fermentation and biohydrogenation, including fatty acids that may serve as biomarkers of microorgan-isms. Regarding differences in the response to FO, the results suggest no link between MFD susceptibility and concentration of biohydrogenation intermediates such as trans-10-containing C18, C20, and C22 metabolites. The explanation for individual responses based on a shortage of ruminal acetate and 18:0 for mammary uptake also seems to be dismissed, based on the lack of variation in these compounds between RESPON+ and RESPON-. However, the concentration of unsaturated fatty acids provided by FO (e.g., cis-9 16:1, cis-11 18:1, and 20:5n-3) was higher in the rumen of RESPON+ than RESPON- ewes and does. Thus, although further research is needed, the extent of biohydrogenation of these fatty acids might be associated with tolerance or susceptibility to MFD.

Automated summary

By comparing the ruminal responses of goats and sheep, we found that the degree of milk fat depression is not predetermined by ruminal fermentation and biohydrogenation traits, but is associated with the concentration of unsaturated fatty acids.