Interactions of starter starch and sodium butyrate for preweaned dairy calves: Growth performance, rumen development, and microbiota

The objective of the present study was to evaluate the effects of sodium butyrate (SB) supplementation in calf starters with varying starch content on the growth performance, rumen fermentation, morphological and functional development of the rumen, and rumen microbiota in preweaned dairy calves. In experiment 1, 120 Holstein calves (41.7 +/- 2.81 kg BW; 16.0 +/- 1.75 d age) were grouped and organized in a complete randomized design with a 2 x 2 factorial arrangement of treatments: (1) low starch (270 g/kg DM) starter without SB supplementation (LS), (2) low starch starter with SB supplementation (5 g/kg of dietary DM; LSB), (3) high starch (370 g/kg) starter without SB supplementation (HS), and (4) high starch starter with SB supplementation (HSB), and data on calf growth performance and intake were collected. In experiment 2, 32 individually fed Holstein calves (39.4 +/- 1.05 kg BW; 2 d age) followed the same experimental design as experiment 1, and data on growth performance, intake, blood parameters, and ruminal development were collected. Calves were fed milk until fully weaned on d 65, and water and starter were provided daily ad libitum. Interactions between starter starch and SB supplementation significantly affected (P < 0.05) or showed tendencies (P < 0.10) in final BW, frame size measurements, average daily gain, dry matter intake, and selected serum indexes. For the rumen fermentation indexes, the starter starch x SB supplementation interaction tended to affect (P < 0.10) the propionate concentration and acetate/propionate ratio. For ruminal morphology and function, a starter starch x SB supplementation interaction was observed on muscularis thickness (P < 0.05); similar interaction effects were observed in the physical structure (keratinization score), proliferation and apoptosis of rumen papilla, and the expression of monocarboxylate transporter 4 and peptide transporter 1 of the ruminal epithelium (P < 0.05). For the rumen microbiota, starch x SB supplementation interaction effects were observed on the community diversity and evenness and on the abundances of the microbial genera Erysipelotrichaceae_UCG-002, NK4A214_group, and Family_XIII_UCG-001 (P < 0.05). These findings underscore the importance of considering the starch content of calf starters when incorporating SB supplementation in preweaned dairy calves.