313. Ruminal Papillae Morphology and Feeding Behavior of Beef Cattle from Different Production Systems During Growing and Finishing Phases.

Abstract The objective of this study was to evaluate ruminal papillae morphology, papillae shape descriptors, and feeding behavior of beef cattle from different genetic backgrounds during growing and finishing phases under feedlot conditions. Ninety-six cattle (195 ± 17.45 kg initial BW) were assigned to four genetic groups representing Brazilian beef production systems: Nellore bulls (NEL), dairy-origin crossbred bulls (DC), Holstein steers (HOL), and Nellore × Angus steers (ANG). Animals were distributed in a randomized block design with eight pens per production system and three animals per pen, with pens considered the experimental unit during both the growing and finishing phases. Feeding management followed a progressive dietary scheme, transitioning from forage-based diets during the growing phases to a high-concentrate diet during finishing. At the end of the growing phase, one animal per pen was removed for comparative slaughter, and the remaining animals were regrouped into pens with two animals each for the finishing phase. Feeding behavior was recorded at 5-min intervals for each animal within each pen during two evaluation periods, one in the growing phase and another in the finishing phase, each lasting 12 h (from 0600 to 1800 h). At slaughter, ruminal tissue samples were collected from the ventral cranial sac, where standardized 1-cm² sections were excised for subsequent morphological and morphometric evaluation of papillae. Data were analyzed using a mixed model including treatment as a fixed effect and block as a random effect, with pen considered the experimental unit. During the growing phase, the production system affected feeding behavior.Angus steers showed a greater number of meals compared with DC and NEL bulls (6.9 vs. 5.3 and 5.7 meals/d; P ≤ 0.01). Angus steers also presented greater feeding time (199 vs. 127 and 137 min/d; P ≤ 0.01) and longer first meal duration compared with DC bulls (43 vs. 29 min; P ≤ 0.01). Idle time was greater for DC and NEL bulls compared with Angus steers (412 and 395 vs. 343 min/d; P ≤ 0.01), whereas ruminating time did not differ among production systems (P = 0.47). During the finishing phase, feeding behavior variables were not affected by the production system (P ≥ 0.17). Ruminal papillae morphology, including average papillae area (0.11–0.14 cm²), papillae density (57.9–67.5 papillae/cm²), absorptive surface area (8.23–9.47 cm²/cm²), and ruminal absorptive surface area (88.1–90.3%), did not differ among production systems (P ≥ 0.05). Likewise, papillae morphometric descriptors (perimeter, width, length, circularity, aspect ratio, and solidity) were not affected (P ≥ 0.05). These results indicate that differences in feeding behavior during the growing phase were not associated with changes in ruminal papillae morphology.