Grower-finisher gilts with high and low feed conversion fed diets with varied crude protein content differ in pancreatic enzyme activity and gut morphology

• Few pancreatic enzymes differ in activity between grower-finisher with low and high FCR. • Few differences in small and large intestinal morphology between grower-finisher with low and high FCR. • No differences between grower-finisher with low and high FCR in terms of pancreatic oxidative stress markers. • Minor impact of dietary crude protein level on pancreatic enzyme activity and small and large intestinal morphology. Reducing the feed conversion ratio (FCR) in pigs during the grower-finisher phase is crucial for improving the herd's economy, while also reducing nutrient excretion and carbon footprint. Therefore, understanding the biological factors contributing to FCR is important. In this study, sixty grower-finisher gilts were divided between three dietary treatments and fed a low (LCP; 148 g CP/kg), standard (SCP; 152 g CP/kg), or high (HCP; 158 g CP/kg) crude protein (CP) diet from 30 to 115 kg of body weight, for a period of 10 weeks. Feed intake and weight were measured individually. Within each diet, pigs were categorized based on their FCR during the final four growing weeks as the 30 % highest (high FCR), medium 40 %, and 30 % lowest (low FCR). The pigs categorized as low and high FCR were euthanized at 20 weeks of age where pancreatic as well as small (SI) and large intestinal samples were collected, and subsequently subjected to an analysis of enzyme activity and morphological characteristics. Differences with respect to enzyme activity in low compared with high FCR pigs included lower ( P = 0.05) trypsin activity, and greater ( P = 0.02) alanine aminotransferase activity. There was a tendency for a diet and FCR interaction with respect to aspartate aminotransferase ( P = 0.06) and lactate dehydrogenase ( P = 0.08) activity. In addition, differences in gut morphology between low and high FCR pigs were found, where a thinner ( P = 0.04) caecal muscular layer and a tendency ( P = 0.07) for shorter distal SI villous height were observed in the low FCR pigs. In conclusion, the results indicate a possible link between the level of feed efficiency of grower-finisher gilts and their pancreatic enzyme activity.