Dietary L-carnitine supplied to early feed-restricted lambs during the fattening period

Early feed restriction of lambs (suckling period) reduces feed efficiency during the fattening phase due to mitochondrial dysfunction and increased fat accumulation. The administration of L-carnitine in the diet might help to alleviate these effects through different mechanisms (e.g. activation of the transport of fatty acids to the mitochondria and modification of ruminal fermentation and microbiome). Twenty-two newborn Merino lambs early feed restricted during the suckling period were weaned and divided into two groups of 11 lambs each. The control group (CTRL) received a complete pelleted diet (CPD) ad libitum, and the carnitine group (CARN) received the same ration formulated with 6 g of Carniking® (50% L-carnitine, 35% silica and 15% water, Lonza) per kg. After 75 days in fattening conditions, the lambs were slaughtered. No differences were observed in residual feed intake (RFI=-25.9 vs 25.9 g/day for CTRL and CARN, respectively; P=0.293). However, the ruminal pH was lower in CARN (5.70 vs. 5.18; P=0.023), whereas the concentration of total VFA (113 vs. 154 mmol/l; P=0.036) and the proportion of propionate (18.5 vs. 22.6 mmol/100 mmol VFA; P=0.079) were increased. On the other hand the proportions of isovalerate (1.50 vs. 0.65 mmol/100 mmol VFA; P=0.045) and isobutyrate (1.20 vs 0.67 mmol/100 mmol VFA; P=0.040) were lower in the CARN group. These differences could be caused by variations in the microbiota promoted by the degradation of L-carnitine, which produced a decrease in the relative abundances of Fibrobacteraceae, Lachnospiraceae, Rikenellaceae and Spirochaetaceae, whereas Succinivibrionaceae (involved in propionic acid production) was increased. Therefore, the administration of 6 g Carniking®/kg CPD modifies ruminal fermentation and microbiota but does not improve the feed efficiency during the fattening period of early feed restricted lambs.