Effects of Ruminal Short-chain Fatty Acids and pH on Gastrointestinal Development of Dairy Calves
Creators: Paez Martins Narciso, Matheus Henrique
Publisher: name: University of Alberta Library
Year: 2024

<p>While the importance of pH and short-chain fatty acids (SCFA) on rumen development in calves is well-known, their impact on the small and large intestines are unclear. This study investigated the effects of ruminal SCFA concentrations ([SCFA]) and pH on performance and hindgut fermentation and development of dairy calves. Holstein bull calves (n = 32) were individually housed and fed 900 g/day of milk replacer twice daily and ad libitum calf starter and water. At day 10 ± 3 of life, the rumens were fistulated and cannulated. At day 14 of life, calves were grouped by body weight and assigned in a 2 × 2 factorial arrangement of treatments into high or low <a href="285%20vs.%2010%20mM" rel="noopener noreferrer" target="_blank">SCFA</a> and high or low pH (6.2 vs. 5.2), creating four <br>
 treatment groups: high [SCFA], high pH (HS-HP); high [SCFA], low pH (HS-LP); low [SCFA], high pH (LS-HP); and low [SCFA], low pH (LS-LP). Body weight was measured weekly. On days 21, 35, and 49, feces were sampled to calculate apparent total tract digestibility, determinate short-chain fatty acid concentrations and pH. Then, the rumen was evacuated and washed for 4 h with one of four treatment buffers. Buffer samples were taken hourly to calculate ruminal SCFA disappearance rates. On day 49, following the rumen wash, calves were harvested, and the tissue weight and length, and digesta of the rumen, cecum, colon, and rectum were collected to measure organic acid concentrations and pH, followed tissue sampling for histomorphometric and gene expression<br>
analysis. The digesta pH of the duodenum, jejunum, and ileum were also recorded. Data were analyzed with main factors (SCFA, pH, and SCFA × pH) as fixed effects and repeated measures for weekly measurements (e.g., body weight, digestibility, and SCFA disappearance rates, as well as fecal and ruminal organic acid concentration and pH). Treatment and day did not affect performance parameters such as apparent total tract digestibility and gut measurements. In the duodenum (P = 0.05), jejunum (P = 0.04), and ileum (P &lt; 0.01), HS-HP had a greater digesta pH than LS-HP, while the hindgut digesta pH was only affected by the <a href="P%20%3C%200.01" rel="noopener noreferrer" target="_blank">SCFA</a>. High<br>
[SCFA] increased the concentration of colonic isovaleric acid (P = 0.05) and fecal branched-chain fatty acids (P &lt; 0.01), while only colonic acetic acid (P = 0.05) and fecal lactic acid concentrations (P &lt; 0.01) were lower in the HS-LP group. Cecum mucosal thickness tended to be greater in calves in the low pH groups (P = 0.07) while decreasing the colonic crypt depth (P = 0.02) and tending to decrease relative cyclin A2 expression (P = 0.09). The high [SCFA] groups had a better  cecal crypt development score (P = 0.03), an increase in colonic cyclin A2 (P &lt; 0.01) and NBC1 expressions (P &lt; 0.01), and a tendency to increase ruminal IGF-1R expression (P = 0.08), and the total ruminal SCFA disappearance rate (P = 0.08). The HS-LP group had increased propionate (P = 0.05) and butyrate disappearance rates (P = 0.05). Therefore, 4 h of buffer infusion in the rumen does not change calf performance but does affect hindgut fermentation and epithelium development, in which calves ruminal infused with physiological buffer containing a high short-chain fatty acid concentration and low pH may represent a decreased risk of hindgut acids.<br>
However, further investigations are required to understand if calves can experience hindgut acidosis in nutritional trials.</p>