PS3-25. Visceral Organ Mass and Gastrointestinal Development of Cattle from Different Production Systems.

Abstract The objective of this study was to evaluate visceral organ mass and gastrointestinal tract (GIT) development of cattle from different production systems under feedlot conditions. Ninety-six cattle (195 ± 17.45 kg initial BW) were assigned to four 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. During the growing phase, pens were composed of three animals each, and pen was considered the experimental unit. Animals were fed sequential diets throughout the experiment, transitioning from forage-based diets during the growing phases to a high-concentrate diet during finishing. At the end of the second growing phase, one animal per pen was slaughtered for organ evaluation, and the remaining animals were redistributed (two animals per pen) for the finishing phase. Organ measurements were obtained from one animal per pen. Total GIT mass differed among production systems, with HOL steers presenting greater GIT full weight compared with the other groups (84.4 vs. 58.9, 59.1, and 68.8 kg for DC, NEL, and ANG, respectively; P < 0.001). Similarly, GIT empty weight was greater for HOL steers (52.1 vs. 35.6 to 39.0 kg; P < 0.001), as well as GIT relative to body weight (16.0 vs. 11.6 to 12.8% of BW; P < 0.001). Reticulorumen (8.68 vs. 6.71 to 7.54 kg; P = 0.0012), omasum (4.17 vs. 2.16 to 3.22 kg; P < 0.001), and abomasum weights (1.39 vs. 0.99 to 1.04 kg; P = 0.040) were also greater for HOL steers. Small intestine mass was greater for HOL and ANG compared with NEL (5.04 and 4.68 vs. 3.58 kg; P = 0.0037), whereas large intestine weight did not differ (P = 0.65). Mesenteric fat was greater for HOL steers compared with the other production systems (29.5 vs. 17.6 to 19.5 kg; P < 0.001). Spleen weight tended to differ (P = 0.071), whereas small intestine length was not affected (P = 0.45). These results demonstrate that production systems influence visceral organ mass and gastrointestinal development, with Holstein steers presenting greater GIT mass and visceral tissue deposition, which may be associated with increased metabolic activity and maintenance energy requirements.