Effect of bermudagrass cultivar on the comprehensive profile of digestion and metabolism in beef cattle

Abstract

Since the release of ‘Coastal’ bermudagrass in 1943, much effort has been made toward the genetic advancement to improve yield and nutritive value. There is a gap in research comparing the in vivo digestibility among cultivars under grazing conditions. Therefore, the objectives of the in vivo study were to evaluate the fermentation profiles, cell wall digestibility, energetics, nitrogen, and mineral balance of beef heifers consuming four bermudagrass cultivars. The objective of the in situ study were to determine effect of bermudagrass cultivar on in situ digestive kinetics of beef heifers. Finally, the objective of the in vitro study were to determine the effect of incubation technique on in vitro digestibility of bermudagrass cultivars. In a Latin square design, ruminally-fistulated heifers (n = 4) were randomly allocated one of four bermudagrass cultivars (Coastal [COS], Russell [RUS], Tifton 44 [T44], or Tifton 85 [T85]) for four 30-d in vivo periods (21-d adaptation and 9-d collection). There was no effect of treatment (P  0.13 ) for digestibility of DM (52.4%), NDF (55.9%), ADF (50.9%), ADL (9.6%), hemicellulose (59.3%), Acid detergent cellulose (59.6%), or KL (18.3%). However, there was an effect of treatment for PL cellulose (P = 0.02) and PL (P = 0.02). The digestibility of PL cellulose was greater for COS, RUS, and T85 diets (27.3% average), then T44 diets (-8.9%). However, COS and T85 were not different from T85. Digestion of PL was greater for improved cultivars (64.5%) over COS (51.5% PL). Total 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 dissapearance of ADIN (50.6 and 48.6%) and RUS the least (28.7%) with T85 intermediate (38.1%). There was no effect of treatment on apparent absorption of macrominerals (P  0.08) or microminerals (P  0.10). 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 in situ degradation curve for DM, NDF, and ADF degradability, regression curve would suggest that the asymptote of digestion was not reached at the measured 168 h. Results from this study suggest passage of cultivars may not impact the reaction time of ruminal microorganisms on the nutrients, and consequently, its potential degradation. Overall, bermudagrass cultivar may not influence in vivo digestibility parameters when evaluated within grazing systems. However, management decisions should be made to ensure all requirements are being met for optimum growth and development.