Effects of dietary processing conditions on nutrient digestibility and fecal characteristics, metabolite concentrations, and microbiota populations of healthy adult dogs

Geary, Elizabeth Louise

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https://hdl.handle.net/2142/129558 Copy

Description

Title

Effects of dietary processing conditions on nutrient digestibility and fecal characteristics, metabolite concentrations, and microbiota populations of healthy adult dogs

Author(s)

Geary, Elizabeth Louise

Issue Date

2025-04-23

Director of Research (if dissertation) or Advisor (if thesis)

Swanson, Kelly S

Doctoral Committee Chair(s)

Swanson, Kelly S

Committee Member(s)

• Cattai de Godoy, Maria R
• Parsons, Carl M
• Fahey, George C
• Dilger, Ryan N

Department of Study

Animal Sciences

Discipline

Animal Sciences

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• canine
• nutrition

Abstract

Processing conditions, particularly temperature and duration of heating, impact the extent and mechanism of protein denaturation. Mild thermal processes can increase the digestibility of proteins, while more intensive heat treatments can decrease digestibility. Novel pet food formats that differ in processing methods are gaining popularity, but few have been tested thoroughly. Additionally, “premium” extruded diets are often formulated with meat slurries. Meat slurries are believed to be of higher quality than rendered meals, but inadequate research has been performed. Questions remain about how the processing of diets and pet food ingredients influence these pet food formats’ digestibility and impact on gastrointestinal health measures. Therefore, the purpose of this dissertation was to determine the nitrogen-corrected true metabolizable (TMEn) energy, standardized amino acid (AA) digestibility, and apparent total tract nutrient digestibility of dog food of various processing formats and different processing conditions of incorporated dog food ingredients, as well as their effects on fecal characteristics, metabolites, and microbiota in healthy adult dogs. The first aim was to determine the AA digestibilities and TMEn values of frozen raw, freeze-dried raw, fresh (mildly cooked), and extruded dog foods using the precision-fed cecectomized and conventional rooster assays. The diets tested were: Chicken and Barley Recipe [Hill’s Science Diet, extruded diet (EXT)], Chicken and White Rice Recipe [Just Food for Dogs, fresh diet (FRSH)], Chicken Formula [Primal Pet Foods, frozen raw diet (FRZN)], Chicken and Sorghum Hybrid Freeze-dried Formula [Primal Pet Foods, hybrid freeze-dried raw diet (HFD)], and Chicken Dinner Patties [Stella & Chewy’s, freeze-dried raw diet (FD)]. Two precision-fed rooster assays utilizing Single Comb White Leghorn roosters were conducted. Cecectomized roosters (n=4/treatment) and conventional roosters (n=4/treatment) were used to determine standardized AA digestibilities and TMEn, respectively. In general, FD had the highest, while EXT had the lowest AA digestibilities; however, all diets performed relatively well, and few differences in AA digestibility were detected among the diets. Lysine digestibility was higher (P<0.05) in FD and FRZN than EXT, with other diets being intermediate. Threonine digestibility was higher (P<0.05) in FD than EXT, with other diets being intermediate. Digestibilities of the other indispensable AA were not different among diets. The reactive lysine:total lysine ratios were 0.94, 0.96, 0.93, 0.93, and 0.95 for EXT, FRSH, FRZN, HFD, and FD, respectively. TMEn was higher (P<0.05) in FRZN than FD, FRSH, and EXT, higher (P<0.05) in HFD than FRSH and EXT, and higher (P<0.05) in FD than EXT. The second aim was to determine the apparent total tract macronutrient digestibility (ATTD) of frozen raw, freeze-dried raw, fresh, and extruded dog foods and assess their effects on serum metabolites, hematology, and fecal characteristics, metabolites, and microbiota of healthy adult dogs. Ten beagle dogs (4.10 ± 0.74 yr) were used in a replicated 5x5 Latin square study to test the following diets: EXT, FRSH, FRZN, HFD, and FD. The experiment was composed of five 35-d periods, with each ending with fecal and blood collections. Protein ATTD was higher (P<0.05) for FRZN and FD than other diets and higher (P<0.05) for HFD than FRSH and EXT. Fat ATTD was higher (P<0.05) for HFD than FRZN and EXT and lower (P<0.05) for EXT than other diets. Fecal output was higher (P<0.05) for dogs fed EXT than those fed other diets and higher (P<0.05) for dogs fed FRSH than those fed FRZN, HFD, or FD. Fecal pH was lower (P<0.05) in dogs fed EXT and FRSH than those fed other diets. Fecal scores were higher (P<0.05) (looser) in dogs fed EXT and FRSH than those fed FRZN and FD. Fecal dry matter (DM) was higher (P<0.05) in dogs fed FD than those fed other diets and higher (P<0.05) in those fed FRZN and HFD than those fed EXT and FRSH. In general, fecal short-chain fatty acids were highest in dogs fed EXT, intermediate in dogs fed FRSH and HFD, and lowest in dogs fed FRZN and FD. Fecal isobutyrate and isovalerate were highest (P<0.05) in dogs fed HFD, lowest (P<0.05) in dogs fed FRSH, and intermediate in dogs fed other diets. Fecal primary bile acids were higher (P<0.05), while secondary bile acids were lower (P<0.05) in dogs fed FRSH than in dogs fed other diets. Fecal microbiota were greatly impacted by diet, with alpha diversity, beta diversity, and relative abundances of over 40 bacterial genera being different among treatments. The third aim was to determine how chicken slurry inclusion affected the palatability and ATTD of dog foods and to assess their effects on the fecal characteristics, metabolites, and microbiota of dogs. A replicated 3x3 Latin square design digestibility study was conducted using 9 healthy adult dogs (age = 5.44 ± 0.53 yr) to test diets containing 0% (control; CON), 8% (low inclusion; LOW), and 16% (high inclusion; HIGH) chicken slurry. The experiment comprised three 21-day experimental periods (14 days of adaptation, 5 days of total fecal collection (used for ATTD calculations), and 2 days of blood collection). A 2-day palatability study (n=20 dogs) was also conducted to compare CON vs. HIGH. In the palatability study, dogs were shown to prefer (P<0.05) the HIGH diet by a ratio of 2:1. In the digestibility study, fecal output, scores, pH, and DM percentage were not different among diets. The ATTD of protein was higher (P<0.05) for the HIGH diet (84.61%) than for the LOW (82.73%) or CON (82.56%) diets. The ATTD of other nutrients and energy were not different among diets (all over 80%). Fecal propionate, butyrate, and total short chain fatty acid concentrations were higher (P<0.05) in dogs fed the LOW diet (122.03, 67.40, 408.17 umol/g, respectively) than those fed the HIGH diet (89.02, 46.93, 338.20 umol/g, respectively). The other fecal metabolites (acetate, branched-chain fatty acids, ammonia, phenol, and indole) were not different among treatments. Few changes to the fecal microbiota were noted. However, the relative abundance of fecal Fusobacterium was higher (P<0.05) in dogs fed the CON diet than those fed the HIGH diet by approximately 6 percentage units. The fourth aim was to determine AA digestibilities and TMEn of diets having the same ingredient formulations and nutrient concentrations, but manufactured using different processing methods. Five diets were manufactured using the following processing methods: retort (RT), mildly cooked [sous vide (SV) and steamed (ST)], and raw [high-pressure processing (HPP) and freeze-drying (FD)]. Those diets were compared against the raw ingredient batch (RAW) that served as a control. Prior to feeding, wet diets (RT, SV, ST, HPP, and RAW) were freeze-dried, and all diets were ground. Two precision-fed rooster assays utilizing Single Comb White Leghorn (1.5 to 2.5 y old, 2.5 to 3 kg body weight) were conducted to determine the standardized AA digestibility (30 cecectomized roosters; n=5) and TMEn content (30 conventional roosters; n=5) of the six pet foods. The digestibilities of 6 essential AA were affected by processing. The SV and ST diets had higher (P<0.05) histidine digestibilities than all other diets. For valine, methionine, leucine, phenylalanine, and isoleucine, the RAW diet tended to have higher (P<0.10) digestibilities than the RT diet. There was also a trend for the ST diet to have a higher (P<0.10) isoleucine digestibility than the RT diet. The RT diet had lower (P<0.05) aspartic acid digestibility than ST, HPP, FD, and RAW diets. Dietary TMEn tended to be higher (P<0.10) for the SV and ST diets than the RT and HPP diets. The final aim was to determine how diets of different formats formulated to similar nutrient targets using similar ingredients may affect the ATTD and the gastrointestinal transit time (GTT) and fecal characteristics, metabolites, and microbiota of healthy dogs. Ten spayed female adult beagles (age = 6.10±1.20 yr) were used in a replicated 5x5 Latin square design to test the following diets: RT, SV, ST, HPP, and FD. The study comprised five 26-d periods, including a 7-d diet transition phase, 14-d treatment phase, and 5-d fecal collection. Fecal scores, pH, DM%, and GTT were not different among treatment groups. Dogs consuming the RT and FD diets had a higher (P<0.05) as-is fecal output to DM intake ratio than dogs consuming the ST and HPP diets. The HPP and ST diets had higher (P<0.05) DM and OM ATTD than the RT, FD, and SV (ST not different) diets. All diets had greater (P<0.05) crude protein ATTD than the RT diet and higher (P<0.05) fat ATTD than the FD diet. Energy ATTD was higher (P<0.05) in the ST, HPP, and SV diets than in the FD and RT (SV not different) diets. Fecal acetate and butyrate concentrations were higher (P<0.05) in dogs consuming the RT diet than the ST and SV (butyrate only) diets. Fecal isobutyrate, isovalerate, total BCFA, indole, and ammonia concentrations were higher (P<0.05) in dogs consuming the RT diet than all other diets (ST not different for indole and ammonia). Alpha and beta diversity measures were not impacted, but diet altered the relative abundances of 3 bacterial phyla and 18 bacterial genera (P<0.05). Our findings indicate that not only does the final processing format impact the qualities of the diet and health implications in dogs, but the processing of the raw ingredients has influences as well. Chicken slurry inclusion improved palatability but had minimal effects on nutrient digestibility and fecal characteristics, metabolites, and microbiota. Differences in commercial diets of different formats led to great differences in AA digestibility, TMEn, nutrient digestibility and fecal characteristics, metabolites, and microbiota. Likely due to the high heat used for processing, AA digestibilities were lower in the retorted diet. Mildly cooked diets had higher metabolizable energy content, suggesting that those cooking methods are less damaging and allow for higher nutrient digestibility. Processing method influenced differences in digestibility, which drove changes in fecal output, metabolites, and microbiota.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129558

Copyright and License Information

Copyright 2025 Elizabeth Geary

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