49 Award Talk: The effect of bermudagrass cultivar on the comprehensive comparison of digestive and metabolic profiles in beef heifers.

Abstract Over the past 80 years of bermudagrass (Cynodon dactylon [L.] Pers.) cultivar development, research comparing cultivars under in vivo (IV) and in situ (IS) conditions in grazing animals is limited. Therefore, the objectives of the IV study were to evaluate four bermudagrass cultivars for fermentation profiles, cell wall digestibility, energetics, and nitrogen balance in beef heifers. The objective of the IS study was to evaluate the impact of bermudagrass cultivar on the digestive kinetics. In a Latin square design, ruminally fistulated heifers (n = 4) were assigned to one of four bermudagrass cultivars (Coastal [COS], Russell [RUS], Tifton 44 [T44], Tifton 85 [T85]) for four 30-d IV periods (21-d adaptation, 9-d collection). Hay, ort, and fecal samples were collected from d 14 to 30 (fecal on d 21to 25). On d 31 of periods 3 and 5, an IS experiment was conducted as a randomized complete block design with three treatment factors: (i) IV diet fed (as above), (ii) bermudagrass cultivar (as above), and (iii) incubation timepoints (0, 0.25, 0.50, 0.75, 1, 2, 3, 4, 8, 12, 16, 20, 24, 48, 72, 96, 120, 144, 168 h). Samples were composited based on a 48-h passage rate. Data were analyzed using SAS v. 9.4. There was no effect of treatment (0.13) for IV digestibility of DM (52.4%), NDF (55.9%), ADF (50.9%), ADL (9.6%), hemicellulose (59.3%), or acid detergent cellulose (59.6%). Total IV VFA production of COS, RUS, T44, and T85 averaged 36.3, 54.7, 62.0, and 62.4 mM, respectively. Improved cultivars RUS, T44, and T85 retained more N (34.6, 33.6, and 22.7%, respectively) compared with COS (15.5%). No differences were observed for digestion of SolP, ISolP, NPN, or NDIN. However, COS and T44 had a greatest disappearance of ADIN (50.6 and 48.6%) and RUS the least (28.7%) with T85 intermediate (38.1%). There was no effect of treatment (P 0.13) was seen for GE of intake (4.2 Mcal/kg), GE output (4.3 Mcal/kg), DE (2.2 Mcal/kg), ME (1.8 Mcal/kg), or NEma (0.9 Mcal/kg). A visual appraisal of the IS degradation curve for DM, NDF, and ADF degradability, regression curve would suggest that full digestion capacity was not realized at 168 h. The results of this study suggest that the passage of different bermudagrass cultivars may not affect the reaction time of ruminal microorganisms to nutrients, and, as a result, may not significantly influence nutrient degradation. Overall, bermudagrass cultivar appears to have little impact on IV and IS digestibility parameters. However, management practices should be carefully considered to ensure that all nutritional requirements are met for optimal growth and development.