Effects of nucleotide supplementation in milk replacer on small intestinal absorptive capacity in dairy calves.

Milk replacer was supplemented with nucleotides and fed to dairy calves from birth through weaning to examine the potential for enhancing recovery of small intestinal function after enteric infection. Three treatments of 23 calves each were fed milk replacer (10% body weight/d) supplemented with no nucleotides (C), purified nucleotides (N), or nucleotides from an extract of Saccharomyces cerevisiae (S). Average daily gain, health scores, fecal dry matter, and fecal bacteria were monitored, and blood was analyzed for packed cell volume, glucose, blood urea nitrogen (BUN), and creatinine. Calves were monitored twice daily for fecal score, and 48 h after increased fecal fluidity was recorded, intestinal function was evaluated by measuring absorption of orally administered xylose (0.5 g/kg of body weight). Packed cell volume of blood was greater for treatment N for wk 2 and 5 compared with other treatment groups. Four calves per treatment were killed, and intestinal tissue was evaluated for morphology, enzyme activities, and nucleoside transporter mRNA expression. Treatment S calves had increased abundance of nucleoside transporter mRNA, numerically longer villi, and lower alkaline phosphatase than other groups. Growth measurements and plasma concentrations of glucose, BUN, creatinine, and IgG were not different between treatments; however, BUN-to-creatinine ratio was higher for treatment N, possibly indicating decreased kidney function. There were also no treatment effects on fecal dry matter and fecal bacteria population. However, N-treated calves had the highest detrimental and lowest beneficial bacteria overall, indicating an unfavorable intestinal environment. Supplementation of purified nucleotides did not improve intestinal morphology or function and resulted in higher fecal water loss and calf dehydration. Supplementation of nucleotides derived from yeast tended to increase calf intestinal function, provide a more beneficial intestinal environment, and improve intestinal morphology.