The effect of cumin (Cuminum cyminum) seed extract on the inhibition of PUFA biohydrogenation in the rumen of lactating goats via changes in the activity of rumen bacteria and linoleate isomerase enzyme

- Dietary cumin addition, affected PUFA biohydrogenation and rumen microbial activity.
- Dietary inclusion of cumin increased PUFA concentration in the rumen.
- More species are engaged in the biohydrogenation process other than Butyrivibrio sp.
- There is a potential to affect bacterial enzyme activity in the rumen through diet.

In this study, two experiments were conducted to evaluate the effect of cumin (Cuminum cyminum) seed extract (CSE) on PUFA biohydrogenation. The first experiment was arranged in a completely randomized design in which eighteen crossbred goats were assigned to three dietary treatments: one group received basal diet (control; C0) consisting of forage and concentrate at equal ratio while the other two groups received the same diet with supplemented CSE (at 1.27% and 2.53% of dry matter intake as C1 and C2, respectively). The rumen content was sampled on day 27 and 29 of the experiment and then subjected to volatile fatty acids (VFA) and long chain fatty acids analyses. The CSE had no effect on molar proportion of VFA (P > 0.05). However, the addition of the CSE to the diet of goats increased the ruminal concentration of rumenic acid (RA; C18:2(c9,t11)) by 34.8% (P = 0.041) and vaccenic acid (VA; C18:1(11)) by 11.4% (P = 0.01) in lower supplemented group in comparison to the CSE-free diet. In the CSE-fed goats, the concentration of linoleic acid (LA; C18:2(9,12)) and linolenic acid (LNA; 18:3(9,12,15)) was higher (P < 0.05) and stearic acid (SA; C18:0) was lower (P = 0.036) than that of the control group, suggesting the inhibition of biohydrogenation. There was no dose dependent effect of the CSE on PUFA content. In the second experiment, linoleate isomerase activity and the growth of five strains of Butyrivibrio sp. and ten predominant species of rumen bacteria was tested at presence of the CSE. The results revealed that CSE did not inhibit the growth of Butyrivibrio sp. but it decreased the growth of some main species of the rumen bacteria such as Prevotella brevis, Streptococcus bovis, Peptostreptococcus anaerobius and Lachnospira multiparus (P < 0.05), which are involved in ruminal biohydrogenation. Moreover, the linoleate isomerase activity of the only stearate forming bacterium, Butyrivibrio proteoclasticus, decreased by 53% in the presence of the CSE (4.25 μg CSE/ml; P = 0.002). Initially, the inhibition of LA metabolism by this species decreases the rate of RA and VA formation, but it gradually results in the accumulation of RA and VA. It was found that CSE altered the bacterial biohydrogenation activity, thus increasing RA and VA concentration in the rumen.