|Abstract:||The pet food market follows human nutrition trends such as being gluten-free, non-genetically modified, and wheat-free. Additionally, alternative sources of grains and carbohydrates are needed to feed production animals, companion animals, and the growing human population. Sorghum bicolor is an ancient cereal grain that is highly adaptable and non-genetically modified making it a prime candidate as a replacement carbohydrate source for corn. Furthermore, the use of feed technologies such as extrusion, which can potentially increase nutrient digestibility and animal performance, is increasing in the nutrition sector. However, the current scientific literature on the use of sorghum in companion animal diets and the effects of extrusion on sorghum nutritive value is limited.
The overall objective of this research was to evaluate two varieties of sorghum, red (RSH) and white (WSH), and the impact of extrusion on nutrient profile and in vivo nutrient digestibility and hindgut fermentation using multiple animal species. Thus, the research aims were to 1) compare RSH and WSH as the primary carbohydrate source in comparison with corn in extruded diets for adult dogs and cats, evaluating apparent total tract macronutrient digestibility, fecal characteristics, and fecal fermentative metabolites and microbiota, 2) compare the nitrogen-corrected true metabolizable energy (TMEn) and amino acid digestibility of the raw and extruded RSH and WSH grains using the precision-fed rooster assay, 3) compare the raw and extruded RSH and WSH grains in broiler chick diets by evaluating weight gain, feed intake, and feed efficiency, and 4) compare the raw and extruded RSH and WSH grains on total tract nutrient and energy digestibility by pigs.
In our first aim, we determined that inclusion of 30% of either sorghum variety did not lead to any negative health effects. For the canine study, all diets were well digested by the dogs and apparent total tract digestibility (ATTD) for dry matter (DM), organic matter (OM), crude protein (CP), and acid hydrolyzed fat (AHF) were not different from corn (P > 0.05). Digestibility values for all those criteria were >80% and metabolizable energy was consistent for all dietary treatments. However, ATTD of total dietary fiber (TDF) differed (P < 0.05) with WSH having the highest ATTD (62.7%), corn having the lowest (52.1%), and RSH being intermediate (57.8%; P > 0.05). Most fecal metabolites (i.e., ammonia, isobutyrate, isovalerate, valerate, butyrate, and propionate) were not different (P > 0.05) among the three dietary treatments. However, acetate and total short-chain fatty acids (SCFA) were greater (P < 0.05) for RSH compared with WSH, with CORN being intermediate. Bacteroidetes, Firmicutes, Fusobacteria, and Proteobacteria were the major phyla observed in the fecal microbiota of dogs fed the three experimental diets, with no differences seen amongst all treatments. For the feline study, ATTD of DM, CP, and AHF were not different amongst all three dietary treatments, while OM was greatest (P < 0.05) for both sorghum diets (86.4% for both) and lowest for corn (84.2%). Apparent total tract digestibility of TDF was greatest (P < 0.05) for WSH and RSH (56.0% and 53.2%, respectively) and lowest for corn (44.7%). Digestible energy concentrations were highest (P < 0.05) for WSH (4.66 kcal/g) and lowest for corn (4.54 kcal/g), RSH was intermediate (4.64 kcal/g; P > 0.05). Most fecal metabolites were not different among the three dietary treatments, but total phenol/indole concentrations were lower (P < 0.05) for the RSH diet compared with the corn diet. Similar to the canine study, Bacteroidetes, Firmicutes, Fusobacteria, and Proteobacteria were the major phyla observed in the fecal microbiota of cats fed the three experimental diets, with no differences seen amongst all treatments.
In our second aim, we determined that TMEn did not differ among raw corn, RSH, and WSH, but extrusion increased (P < 0.05) the TMEn of RSH in conventional roosters and WSH in cecectomized roosters. The standardized amino acid digestibility of all grains was greater than 75% except lysine for raw WSH and extruded RSH. Extrusion increased the digestibility of arginine, histidine, lysine, methionine, threonine, and tryptophan in WSH and increased tryptophan in corn. However, extrusion decreased leucine, alanine, and glutamate in extruded RSH. The third aim consisted of incorporating 62% of raw and extruded grains into experimental diets for growing broiler chicks for 14 days. The results of our third aim showed little to no improvement in broiler performance when the grains were extruded. Extrusion decreased feed efficiency for chicks fed corn and RSH. Additionally, the raw variety of WSH was inferior to raw corn, with raw RSH being inferior to raw corn in body weight gain and not different from raw corn in feed efficiency.
In our fourth aim we conducted an experiment to determine ATTD of macronutrients and energy in swine. The ATTD of AHF for extruded RSH was greater (P < 0.05) compared with its raw counterpart, with no differences in ATTD of macronutrients for corn or WSH. Extrusion increased (P < 0.05) the digestible and metabolizable energy concentrations of the WSH ingredient and also a diet containing 97% WSH, with no effect of extrusion for corn or RSH.
This research provided justification for incorporating the varieties of sorghum used in the current study into companion animal nutrition. The beneficial effects of using sorghum and utilizing the extrusion process on grains for poultry nutrition appears to be limited based on the results of the rooster and broiler chick assay. Finally, extrusion of this variety of WSH holds potential for swine nutrition and further research is needed to determine the feasibility of using extruded cereal grains in swine diets.