OPTIMISATION OF THE GC METHOD FOR ASSESSING VOLATILE FATTY ACIDS IN RUMEN LIQUID

Mariana Ropotă, Ana Cişmileanu, Smaranda Toma, Iulia Vărzaru

Abstract
   Accurate determination of the volatile fatty acids (VFA) content of the rumen liquid is indispensable for assessing feedstuffs utilization and effects at ruminal level. Moreover, nowadays feeding strategies require more detailed information such as post-prandial dynamics of VFAs, content of minor VFAs, etc. which leads to the need for precise, rapid and economic determination. In this context, the purpose of this study was to optimize the current GC method by modifying chromatographic conditions and sample preparation in order to reduce the analysis time and the reagents amounts. The optimized method was practically applied by testing VFA from rumen liquid of fistulated wethers challenged with sudden change of the concentrates: forage ratio of the diet from 20:80 to 50:50 (diet 1), 100:0 (diet 2) and 0:100 (diet 3). Rumen content was sampled 4 hours after the morning feeding, prepared and analyzed using the optimized method. Acetic acid content was reduced by diet 1 (72.51 % to 67.46 %) and diet 2 (68.11 % to 64.15 %) whereas diet 3 induced an increase (from 69.95 % to 72.16 %), results that are consistent with the known effects of concentrates: forages ratio. Propionic acid tended to express inverse effects, also consistent with the previous literature reports. These preliminary results showed that the modified GC method enables rapid and sensitive VFA determinations.

Key words: volatile fatty acids, rumen liquid, GC method

OPTIMIZAREA METODEI GC DE DETERMINARE A ACIZILOR GRAŞI VOLATILI DIN LICHIDUL RUMINAL

Mariana Ropotă, Ana Cişmileanu, Smaranda Toma, Iulia Vărzaru

Rezumat
   Determinarea cu acuratete a acizilor grasi volatili (AGV) din lichidul ruminal este indispensabila pentru estimarea utilizarii furajelor si a efectelor lor la nivel ruminal. Mai mult, strategiile de furajare din prezent necesita o informare mai detaliata asupra fenomenelor cum ar fi dinamica post-prandiala a VFA, continutul in acizi VFA minori, etc. In acest context scopul acestui studiu a fost de a optimiza metoda gaz-cromatografica GC curenta prin modificarea conditiilor cromatografice si de preparare a probei in ideea de a reduce timpul de analiza si cantitatile de reactivi. Metoda optimizata a fost aplicata practic in determinarea AGV din probe de continut ruminal de la batali fistulizati. Acestia au fost supusi unei schimbari bruste a ratiei de baza avind raport concentrat:furaj de volum de 20:80 cu ratiile urmatoare: ratia 1 (raport 50:50), ratia 2 (raport 100:0) si ratia 3 (raport 0:100). Probele de continut ruminal pentru testarea cu metoda GC optimizata au fost prelevate la 4 ore dupa furajarea de dimineata. Continutul de acid acetic a fost redus dupa ratia 1(de la 72.51 % la 67.46 %) si ratia 2 (de la 68.11 % la 64.15 %) in timp ce ratia 3 a determinat o crestere (de la 69.95 % la 72.16%), rezultate care sint in concordanta cu efectele cunoscute induse de raportul modificat din ratie. Acidul propionic a prezentat o tendinta inversa. Aceste rezultate preliminare arata ca metoda GC modificata permite determinarea rapida si precisa a acizilor VFA.

Cuvinte cheie: acizi grasi volatili, lichid ruminal, metoda gaz-cromatografica