PS8-24. Forage Inclusion Modifies Ruminal Fermentation and Methane Production in Dairy Calves Fed High-starch Total Mixed Rations.

Abstract Early-life feeding strategies play an important role in the development and long-term performance of dairy calves. Early rumen development facilitates the transition from a preruminant to a functional ruminant during weaning. Feeding methods, diet composition, and microbial colonization influence this process. The aim was to evaluate the inclusion of different forage sources in TMRs on ruminal fermentation parameters and methane production in post-weaned dairy calves. Twenty dairy calves were blocked by body weight at 28 d and randomly assigned to one of four treatments: a starter concentrate without forage, coarsely ground (CON; n = 5); a TMR containing 7.5% (DM basis) medium-quality Tifton hay (MQH; n = 5); a TMR containing 7.5% low-quality Tifton hay (LQH; n = 5); or a TMR containing 10% corn silage (CS; n = 5). The experiment lasted 70 days. During the first 27 days, calves received 6 L/day of whole milk, a commercial pelleted starter concentrate, and ad libitum access to water. At 28 days of age, calves were assigned to experimental diets and weaned at 56 days. Calves were slaughtered at 70 days of age. At slaughter, rumen samples were collected to evaluate short-chain fatty acids (SCFA) and methane (CH4) production through ex situ analysis. Ruminal contents were incubated in penicillin-type flasks at 39 °C for 0 or 30 min. After incubation, fermentation was stopped using ice-cold water, and gas and liquid samples were collected for CH4 and SCFA analysis. Relative energy loss (REL, %) was estimated from CH4 and SCFA data. Data were analyzed using contrasts in the MIXED procedure of SAS. Orthogonal contrasts were used to determine the effects between the groups: control × all forage containing TMR (CON × F); corn silage × hay, regardless of the quality (CS × H); medium hay quality × low hay quality (MQH × LQH). Forage inclusion did not affect the acetate (2.04±0.36 mol/kg), butirate (0.47 ± 0.15 mol/kg), and total SCFA production (3.76 ± 0.62 mol/kg), however, the contrast CON × F indicated that the inclusion of any type of forage decreased propionate production (CON: 1.69; F: 1.10 mol/kg; P = 0.05). There was no effect between forage types on propionate production. Additionally, the inclusion of forage (CON × F) increased methane production (CON: 0.50; F: 0.68 mol/kg; P = 0.02), however, there was no effect between the forage sources evaluated. Consequently, the inclusion of forage increased the REL (CON: 8.25%; F: 13.9%; P = 0.05). No effects were observed for the CS × F or MQH × LQH contrasts (P ≥ 0.24) for any of the evaluated variables. In conclusion, the inclusion of forage sources altered ruminal fermentation and increased ruminal methane synthesis, however, no differences were observed among forage source.