Comparison of ruminal lipid metabolism in dairy cows and goats fed diets supplemented with starch, plant oil or fish oil

Abstract

Direct comparison of cow and goat performanceand milk fatty acid responses to diets known to inducemilk fat depression (MFD) in the bovine revealsrelevant species-by-diet interactions in ruminal lipidmetabolism. Thus, this study was conducted to inferpotential mechanisms responsible for differences in therumen microbial biohydrogenation (BH) due to dietand ruminant species. To meet this objective, 12 cowsand 15 goats were fed a basal diet (control), a similardiet supplemented with 2.2% fish oil (FO), or a dietcontaining 5.3% sunflower oil and additional starch(+38%; SOS) according to a 3 × 3 Latin square designwith 25-d experimental periods. On the last day of eachperiod, fatty acid composition (by gas chromatography)and bacterial community (by terminal-RFLP),as well as fermentation characteristics, were measuredin rumen fluid samples. Results showed significant differencesin the response of cows and goats to dietarytreatments, although variations in some fermentationparameters (e.g., decreases in the acetate-to-propionateratio due to FO or SOS) were similar in both species.Main alterations in ruminal BH pathways potentiallyresponsible for MFD on the SOS diet (i.e., the shiftfrom trans-11 to trans-10 18:1 and related increases intrans-10,cis-12 18:2) tended to be more pronounced incows, which is consistent with an associated MFD onlyin this species. However, changes linked to FO-inducedMFD (e.g., decreases in 18:0 and increases in totaltrans-18:1) were stronger in caprine rumen fluid, whichmay explain their unexpected susceptibility (althoughless marked than in bovine) to the negative effect ofFO on milk fat content. Altogether, these results suggestthat distinct ruminal mechanisms lead to eachtype of diet-induced MFD and confirm a pronouncedinteraction with species. With regard to microbiota,differences between cows and goats in the compositionof the rumen bacterial community might be behindthe disparity in the microorganisms affected by theexperimental diets (e.g., Ruminococcaceae, Lachnospiraceae,and Succinivibrionaceae in the bovine, andPseudobutryrivibrio, Clostridium cluster IV, Prevotella,and Veillonellaceae in the caprine), which hinderedthe assignation of bacterial populations to particularBH steps or pathways. Furthermore, most relevantvariations in microbial groups corresponded to as yetuncultured bacteria and suggest that these microorganismsmay play a predominant role in the ruminal lipidmetabolism in both cows and goats.