Moderated milk replacer restriction of ewe lambs alters gut immunity parameters during the pre-weaning period and impairs liver function and animal performance during the replacement phase

Undernutrition during the first stages of life may impair maturation of the immune system, harming the health status permanently. Thus, the aim of the present study was to define the impact of moderated milk replacer (MR) restriction during the artificial rearing period on the gut-associated lymphoid tissues of pre-weaned ewe lambs and long-term effects on biochemical profile and animal performance during the replacement period. Forty female Assaf lambs [average live body weight (LBW) 4.73 ± 0.116 kg] were penned individually. The first group of lambs (n = 20) was fed MR ad libitum (ADL) whereas the second one (restricted, RES; n = 20) only received approximately 62.5% of the MR intake measured in the ADL group. All the lambs were weighed twice a week until they were 35-days-old. Then, 8 lambs from each group (pre-weaned) were harvested and ileal samples collected. The rest of the lambs (12 ADL vs. 12 RES) were weaned progressively, and then offered a total mixed ration (TMR) ad libitum until the end of the experiment (7.5-months-old). The lower nutrient intake of RES pre-weaned lambs caused greater percentages for T lymphocytes (CD4+, CD8+, WC1+) and an increased secretory immunoglobulin A (sIgA) production in the ileum compared to the ADL group (P < 0.05). These results, together with the significant differences in the expression of toll-like receptors and cytokines at this level (e.g., interferon gamma was increased in the RES group; P<0.05) suggest the existence of pro-inflammatory conditions in the ileum of pre-weaned lambs promoted by early feed restriction. Moreover, the biochemical profile revealed that liver function (e.g., albumin, gamma glutamyl transpeptidase) was impaired during several months once the feed restriction period was finished, whereas the average daily gain during the replacement phase was reduced for the early feed restricted lambs (182 vs. 202 g/day for RES and ADL groups, respectively; P < 0.05). Therefore it can be concluded that moderated MR restriction promoted both, pro-inflammatory conditions at ileal level in the pre-weaned lambs and an altered liver function which lasted several months after the end of feed restriction. Both circumstances might have impaired animal performance during the replacement phase of the ewe lambs.