Long-term effect of early-life diet on rumen structure and function and selected blood parameters in sheep

Early-life nutrition can program gastrointestinal tract development in ruminants; however, the extent to which these effects persist into later life is not fully understood. We hypothesised that early-life diet would have a lasting impact on rumen structure and function in sheep. Fifty-four male lambs were divided into two groups and fed milk replacer (MR) and either a mixture of meadow and alfalfa hay (high-fibre; HF) or concentrate (high-starch; HS) in the first weeks of life. The MR was fed for 7 weeks, and experimental solid feeding was continued for 2 weeks after weaning. Animals were then transitioned to a hay-based diet over 3 weeks (stage 1), which was continued until 7.8 ± 0.53 months of age (stage 2). Subsequently, animals were challenged with a high-starch diet for 7 days (stage 3). In stage 1, absolute and relative DM intake and digestibility were higher for HS (P ≤ 0.03), as was BW (tendency, P = 0.09). Moreover, DM, organic matter and CP digestibility, reticulorumen (RR) tissue mass (g/kg BW), papillae dimensions, rumen epithelium and stratum corneum thickness, number of balloon cells, expression of monocarboxylate transporter 1, putative anion transporter 1 (PAT1) and acetyl-CoA acetyltransferase 2 in rumen epithelium were or tended to be greater, whereas RR pH, RR digesta mass, expression of ten-eleven translocation 1 and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) in the rumen epithelium was or tended to be less for HS (P ≤ 0.09). In stage 2, BW was higher (P ≤ 0.01) and absolute DM intake tended to be higher for HS (P = 0.06), but relative DM intake was higher for HF (P = 0.01). Only minor differences in investigated parameters of RR development and function were observed. In stage 3, the stratum corneum was thicker for HS, whereas the expression of PAT1 and histone deacetylase 3 was higher (P ≤ 0.03) and HMGCS1 tended (P = 0.08) to be higher for HF. Moreover, in stages 2 and 3, plasma urea was higher for HF (P ≤ 0.01). Diet fed early in life had a long-term impact on BW, feed intake and plasma urea, but no long-term impact on nutrient digestibility, digesta passage or global DNA methylation in rumen epithelium. Most of the effects on rumen epithelium function were revealed only after a dietary challenge later in life. These results indicate that early diet affects the response of the rumen epithelium to nutritional changes later in life.