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Impact of early weaning on small intestine, metabolic, immune and endocrine system development, growth and body composition in artificially reared lambs1.

Journal of Animal Science 2019 November 27
This study evaluated the effect of early weaning (EW) of artificially-reared lambs using a restricted milk replacer (MR) feeding and step-down weaning system on the short- and long-term effects on growth, feed intake, selected blood metabolites and hormones, body composition and small intestine development. Mixed-sex twin-born 2-5 d old lambs were randomly allocated to individual pens and fed MR at 20% of initial individual BW in wk 1 and 15% in wk 2 followed by weaning off MR by the end of wk 4 (EW; n=16) or wk 6 (Control; Ctrl, n=16) using a step-down procedure. Concentrate starter and fiber diets were offered ad libitum to wk 9, then gradually removed over a 10 d period. All lambs were managed as a single group on pasture from wk 6 to 16 of the trial. Feed intake was recorded daily in the first 6 wks, and BWs recorded weekly. At wk 2, 4, 6 and 8, and pre- and post-clostridial vaccination at wk 8, blood samples were collected for analysis of selected blood metabolites, IGF-1 and immune function. Body composition was evaluated in 8 animals per group at wk 4 and 16 after euthanasia, and duodenal samples collected for histomorphometric evaluation. Early weaned lambs had lower DM, ME, CP and NDF intake than Ctrl lambs at 21, 15, 21 and 36 d of rearing respectively (P < 0.001) driven by lower intakes of MR from d 15 (P < 0.001) as per the experimental design, and lower total DMI of fiber (P = 0.001) from 21 to 42 d of rearing. Lamb BW tended (P = 0.097) to be lower in EW than Ctrl lambs from five to 10 wks of rearing, with lower ADG in EW lambs from wk 3 to 6 (P = 0.041). Early weaning had negligible effects on duodenal morphology, organ and carcass weights at wk 4 and 16. Plasma metabolites (urea nitrogen, triglycerides, NEFA, glucose and total protein) were similar between groups, while beta-hydroxybutyrate was greater in EW than Ctrl lambs at wk 4 and 6 (P = 0.018) but not wk 8 indicative of early rumen development. Serum IGF-1 tended to be lower in EW than Ctrl lambs from wk 2 to 6 only (P = 0.065). All lambs developed antibody responses post-vaccination but there was no effect of treatment (P = 0.528) indicating similar immune function. The results of this study illustrate that artificially-reared lambs can be weaned off MR by 4 or 6 wks of rearing without compromising growth, small intestine morphology, major organ development and body composition, nor immune function at either 4 (pre-weaning) or 16 (post-weaning) wks of age.

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