The present study investigated the effects of low-protein (LP) diets on growth performance, intestinal morphology, apparent ileal digestibility (AID), and jejunal amino acid (AA) transporter mRNA expression in heat-stressed Pekin ducks. A total of 108 fourteen-day-old male ducks were randomly allotted to three treatments, each with six replicates of six birds: a thermoneutral (TN) group fed a control (CON) diet, a heat stress (HS) group fed the CON diet, and an HS-LP group fed the LP diet. Ducks were maintained at 22 °C (TN) or 30 °C (HS and HS-LP) for 3 wk. The CON and LP diets contained 17.5% and 16.0% CP, respectively, with similar AA profiles. Compared with the TN group, the HS group showed reduced BW, ADFI, and ADG and increased F:G (p < 0.05). Compared with the HS group, the HS-LP group showed higher BW and ADG and lower F:G (p < 0.05), although BW and ADG remained lower than in the TN group. HS decreased villus height (VH), jejunal villus height-to-crypt depth (VH:CD) ratios, and goblet cell counts (p < 0.05). Compared with the HS group, the HS-LP group showed higher jejunal and ileal VH:CD ratios and lower ileal CD (p < 0.05), whereas VH and goblet cell counts were not restored to TN values. Although AID of CP and AAs did not differ between the TN and HS groups, the HS-LP group showed higher AID of CP and AAs than the HS group (p < 0.05). In addition, the HS-LP group showed lower PEPT1 and higher LAT1 mRNA expression (p < 0.05). In conclusion, a reduction in dietary CP from 17.5% to 16.0% partially alleviated HS-induced growth depression and intestinal morphological impairment and was accompanied by increased AID of AAs and altered mRNA expression of jejunal AA transporters.
Shen et al. (Sat,) studied this question.