Abstract:

The aim of this study was to investigate the effects of milk replacer with different protein levels on the diarrhea rate, serum immunity indices, intestinal organ indices and morphology, and small intestinal microbiota in lambs. Forty-eight healthy second-generation 3-day-old male lambs of East Friensian Sheep×Hu sheep crossbreeds with same genetic background and birth weight (4.34±0.15 kg) were selected and randomly divided into four groups by a one-way experimental design, namely, low protein level milk replacer group (L-Group, 22% protein group), the medium-low protein level milk replacer group (ML-Group, 24% protein group), the medium-high protein level milk replacer group (MH-Group, 26% protein group), and the high-protein level milk replacer group (H-Group, 28% protein group). The formal test was carried out after 5 d of pre-test feeding period, and slaughter performance measurement and test sample collection were conducted after 54 d of feeding. The results showed that: 1) The rate of diarrhea in the MH and H groups were extremely significantly higher than that in the ML and L group (P < 0.01). 2) The concentration of IL-2 in MH and H groups were significant higher than that in L group (P < 0.05), the concentration of IgA, IgG, IgM, TNF-α, IL-6, IL-1β didn't present significant differences (P>0.05). 3) There was no significant difference in intestinal organ index (P>0.05). 4) The depth of duodenal crypt in MH group was significantly deeper than that in L and ML groups (P < 0.01).The ratio of villi height to crypt depth in L and ML groups was dramatically higher than that in MH and H groups (P < 0.01). 5) Sequencing of jejunal 16S rRNA showed that there was no significant difference in alpha diversity among groups (P>0.05). At the phylum level, the Actinobacteriota relative abundance of H group was significantly lower than that of L and ML groups (P < 0.05). At the genus level, the Lachnospiraceae_NK3A20_group relative abundance of H group was significantly higher than that of L and ML groups (P < 0.05). In summary: milk replacer protein levels exceeding 24% increased the rate of diarrhea and serum IL-2 levels in lambs, and decreased the ratio of duodenal villi height to crypts depth, and the relative abundance of the beneficial intestinal bacterium Actinobacteria phylum was reduced when the protein level reached 28%. Therefore, under the experimental conditions of this study, it was concluded that milk replacer protein levels not exceeding 24% were more favorable to the intestinal health of lambs.

Key words: lamb, milk replacer, protein, intestinal health