Fatty acid metabolism in lambs fed citrus pulp

In the present study, we have hypothesizedthat replacing barley with high proportions ofdried citrus pulp in a concentrate-based diet for lambscould increase the intake of unsaturated fatty acids andcould reduce the rate of the ruminal biohydrogenationof PUFA, with a consequent improvement of the intramuscularfatty acid composition. To test this hypothesis,26 Comisana lambs were divided into 3 groups and for56 d were fed a barley-based concentrate diet (CON; 8lambs) or 2 diets in which barley was replaced with 24%(CIT24; 9 lambs) or 35% (CIT35; 9 lambs) dried citruspulp. An overall improvement of the fatty acid compositionof LM from lambs fed citrus pulp–containing dietswas found. The PUFA/SFA ratio was lower (P < 0.05)in the LM from lambs in the CON group compared withboth the CIT24 and CIT35 groups. The thrombogenicindex was lower (P < 0.05) in meat from lambs fed theCIT35 diet compared with those fed the CON diet. TheCIT35 diet increased the proportion of C20:5 n-3 in theLM (P < 0.05), whereas the CIT24 diet enhanced thatof C22:6 n-3 (P < 0.05) compared with the CON diet.Some of these results might be explained consideringthat feeding the CIT24 and CIT35 diets increased theintake of total fatty acids (P < 0.05) and of C18:3 n-3(P < 0.01) compared with feeding the CON treatment.On the other hand, phenolic compounds present in citruspulp could have inhibited the ruminal biohydrogenationof PUFA. This is supported by the fact that regardless ofthe level of inclusion in the diet, citrus pulp increasedthe proportion of rumenic acid (P < 0.001) in LM comparedwith the CON diet. The plasma from lambs fedboth CIT24 and CIT35 diets had a greater percentage ofvaccenic acid (VA; P < 0.001) compared with that fromlambs fed the CON diet, and the CIT35 diet increasedthe proportion of rumenic acid in plasma compared withthe CON treatment (P < 0.05). In the ruminal fluid, stearicacid (SA) tended to decrease, and the sum of CLAtended to increase (P = 0.09) with increasing level ofcitrus pulp in the diets. Furthermore, the SA/(SA + VA)ratio tended to be lower (P = 0.10) in the ruminal fluidfrom lambs fed the CIT35 diet compared with that ofthe CON group. In conclusion, our results support thehypothesis that replacing barley with citrus pulp in thediet of growing lambs improves intramuscular fatty acidcomposition and underline the need for specific studiesto clarify the mechanisms by which feeding citrus pulpaffects the fatty acid metabolism in ruminants.