Effect of crude protein level in lamb feed on circulating malondialdehyde and cytokine expression in rumen and ileum

Abstract

Diets for intensive light lambs in Spain have crude protein (CP) levels above their nutritional requirements. To optimize feed costs, it is necessary to understand how CP reduction affects the balance between immune mechanisms of defence or tolerance in gastrointestinal tract. Low protein diets have been linked to oxidative stress (OS) status, which is associated that the formation of free radicals and pro-inflammatory cytokines, causing damage in the intestinal mucosa. In addition, as a product of the lipid peroxidation, an animal with OS develops high levels of malondialdehyde (MDA), that can be evaluated in blood plasma as an indicator of oxidative status. The aim of this study was to assess the effect of dietary CP on circulating MDA concentration and gene expression of pro-inflammatory (TNF-alfa) and anti-inflammatory (IL-10 y TGF-beta) cytokines as indicators of ruminal and intestinal health. Ripollesa male lambs aged 45-60 days were used (n = 120). The animals were fed in two phases: growth from 14 to 19 kg and fattening from 19 to 25 kg of body weight. Half of the lambs received a control CP in feed (20.4 % and 19.1 % on a dry matter basis (DM), respectively) and the rest received a low CP content (18.3 % and 17.4 % on DM). Plasma MDA concentrations was determined in blood samples taken from 48 lambs (n = 24 for each treatment) in the last week of each phase by liquid chromatography with diode detector (HPLC-DAD). At the time of slaughter, rumen and ileum samples were taken from 8 lambs (n = 4 for each treatment) which were kept in RNA later until the time of extraction. RNA was extracted according to Trizol protocol (Invitrogen), was treated with DNAsas and DNA copy was obtained by reverse transcription in the presence of the random primers. Gene expression of TNF-alfa, IL-10, TGF-beta and reference gene GAPDH was determined by real-time PCR in ruminal and ileum. The results showed that MDA concentrations were not different between control and low CP treatments, neither in the growth phase (7.30 vs 7.41 ± 0.21 μM respectively, P>0.05) nor in the fattening phase (7.06 vs 7.43 ± 0.32 μM respectively, P>0.05). There were not significant differences in cytokine gene expression in rumen and ileum at slaughter between control animals and those fed low CP (P>0.05). In conclusion, the reduction of CP in lambs’ diet did not negatively affect their oxidative blood status nor did it alter the immune response in the gastrointestinal tract.