Semester

Summer

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Joseph Moritz

Committee Co-Chair

Janet Tou

Committee Member

Janet Tou

Committee Member

Jacek Jackzynski

Committee Member

Eugenia Pena-Yewtukhiw

Committee Member

Angela Lamp

Abstract

This doctorate dissertation consists of four individual studies with the overarching theme of the effect of feed manufacture on exogenous enzymes and antinutrients found in soybeans.

Study 1. Including exogenous enzymes in poultry diets can liberate nutrients that are typically inaccessible to monogastric animals. Phytase feeding research has traditionally been conducted by rearing broilers in raised wire cages, whereas commercially grown broilers are reared on built-up litter. Therefore, cage-based studies may not accurately represent commercial bird performance response to phytase. Birds with access to litter consume it, possibly increasing phosphorus intake leading to suggestions that lower phytase concentrations are required. The authors hypothesized that the broilers reared in cages express a greater response to phytase relative to birds reared in floor pens because they are not consuming soluble phosphorus via litter. The objective was to determine the effect of different concentrations of Optiphos Plus on day 0-21 live performance and tibia mineralization of male Hubbard × Ross 708 chicks reared in raised wire cages and floor pens. Broilers in floor pens remained on study until day 49 and performance and tibia mineralization were reassessed. A nutritionally adequate positive control (PC) diet and a negative control (NC) diet deficient in calcium and non-phytate phosphorus were conditioned for 30 sec at 82℃ and pelleted. Optiphos Plus was added to the NC diet at 250, 500, 1,000, 1,500, 2,000, and 2,500 FTU/kg. All 8 treatments were fed and analyzed using a multiple comparison within housing system. A two-way ANOVA was also employed to analyze the 6 (Phytase level) × 2 (Housing system) factorial arrangement of treatments on day 21. Diets were fed to 8 replicate floor pens of 22 chicks and 8 replicate raised wire cages of 7 chicks. On day 21, live performance and tibia ash content were measured. Grower and finisher diets were manufactured for birds in floor pens. In both housing systems, 1,500 FTU/kg or greater increased weight and live weight gain (LWG) relative to the NC diet and all lower levels (P < 0.05). The observed response curves were comparable between the two systems. Tibia ash percent was also restored to PC levels with the addition of 1,500 FTU/kg or greater in both systems (P < 0.0001). Bird weight and LWG decreased and feed conversion ratio increased for birds reared in pens relative to cages (P < 0.0001). There was a housing system by phytase level interaction where tibia ash mg/chick did not differ between systems at 250 FTU/kg, but above this the cages expressed improved bone mineralization (P < 0.05). Live performance did not differ between levels of phytase on day 49; however, 250 FTU/kg statistically yielded the lowest tibia ash percent with the exception of 1,000 FTU/kg and yielded the lowest mg per chick (P < 0.05). The phytase response between the housing systems was similar, indicating that consumption of litter likely does not have a significant impact on broiler performance. This particular phytase source demonstrated optimal efficacy at an inclusion of 1,500 FTU/kg on day 21.

Study 2. Starch gelatinization, or swelling of starch granules and leaching of amylose, occurs in the presence of heat and moisture. Gelatinized starch acts as a pellet binder, thereby increasing pellet quality. Increasing pellet quality has been shown to improve bird performance. The use of antimicrobial feed additives has been increasing due to the risk of salmonellosis to consumers. A previous experiment included an antimicrobial primarily composed of formaldehyde and propionic acid added at the mixer to poultry feed. When the authors steam conditioned the feed for a shorter duration compared to a longer duration, it resulted in a decrease in pellet quality. We hypothesize that the product inhibited starch gelatinization and that the degree of inhibition is based on heating time. Therefore, the study objective was to determine the effect of formaldehyde and propionic acid on starch gelatinization via glucose release and spectrophotometry across two heating times. Corn starch suspensions were heated at 82℃ for 2 min 30 sec or 15 min and added to base reagents. Formaldehyde and/or propionic acid were added to the appropriate corn starch suspensions prior to heating, while the control lacked either chemical. The absorbance of the 4 formulations at each heating time were measured using spectrophotometry. Three replications were performed per treatment. All 4 formulations were analyzed using a multiple comparison. A two-way ANOVA was also employed to explore the 4 (formulation) × 2 (heating time) factorial arrangement of treatments. There was a heating time × formulation interaction where all formulations heated for 15 mins had a significant increase in gelatinization relative to the 2.5 min formulations, with the control formulation showing the least amount of change (P < 0.05). Formaldehyde and propionic acid did not reduce starch gelatinization regardless of heating time. The increase in starch gelatinization with increased heating time may translate to increasing pellet quality.

Study 3. Poultry are primarily fed corn and soybean-based diets in the Unites States. Soybean meal (SBM) has a high crude protein content and well-balanced amino acid profile; however, it contains several antinutritional factors that have been shown to hinder bird performance. Soybean crush plants utilize a toasting step to degrade these heat labile antinutrients in meal, but many factors vary across crush plants that can make it difficult to determine processing adequacy. Furthermore, current analytics may not properly indicate optimal processing. Therefore, two experiments were conducted. The objectives of these two studies were to characterize under processed, optimal processed, and over processed solvent extracted SBM obtained from a commercial soybean crush plant with trypsin inhibitor activity (TIA) using the new USDA-ARS method, TIA with the AOCS method, urease, solubility in potassium hydroxide (KOH) and protein dispersibility index (PDI) in addition to evaluating assay variation within and across commercial laboratories. The objective of the second experiment was to determine the effect of the three aforementioned SBM types on broiler performance when included in mash diets and fed for 21 days. Three diets were formulated at 85% crude protein and digestible amino acid requirements, differing only in the type of SBM (under, peak, over processed). A nutritionally adequate positive control (PC) diet was also formulated. Diets were fed in mash form. Analysis of the SBM samples indicated an increase in TI from under to peak processed, then a decrease from peak to over processed. Urease, KOH, and PDI analysis revealed variation within and among laboratories, with the most consistent measure of processing adequacy being urease. Urease decreased with increasing processing according to 2 of the 3 laboratories. Live weight gain (LWG) increased by 52 g for birds fed the peak processed diet relative to the under processed diet (P < 0.05). Feed conversion ratio increased when birds were fed the under processed diet relative to all other diets (P < 0.05). Broiler chick live performance demonstrated nutritional differences in SBM samples that were not consistently described through various ingredient assays. Bird performance results aligned best with the urease assay.

Study 4. Soybean meal (SBM) is referred to as the “gold” standard of protein, as other oilseeds are compared to it due to its superior quality; however, SBM also contains antinutritional factors that have been shown to hinder bird performance. Soybeans are toasted during manufacture, but the optimal temperature and holding time to ensure adequate processing is not well defined. An initial companion experiment (paper 1) determined that including under processed SBM in mash diets hinders bird performance. Therefore, a follow up study was performed with the objective of examining assay variation within and across laboratories of diets containing under and peak processed SBM conditioned at 70, 80, or 90℃ in addition to an over processed SBM mash diet and determining the optimal conditioning temperature via live bird performance and amino acid digestibility. The 3 SBM types (under, peak, over processed) were obtained from a commercial soybean crush plant. Three diets were formulated to 85% crude protein and digestible amino acid requirements, differing only in the type of SBM. The under and peak diets were steam conditioned at 70, 80, or 90℃ prior to pelleting. The over processed diet remained in mash form. Diets were fed for 18 days and contrasts were performed to explore differences between treatments. A 2 (SBM type) × 3 (Conditioning temperature) factorial was also analyzed. The 7 diets were each fed to 12 replicate cages of 9 chicks. On day 18, live performance metrics were measured, and ileal contents were collected. Day 0-18 feed intake (FI) per bird increased with increasing conditioning temperature (P < 0.05). SBM type and conditioning temperature interacted. Birds fed the under processed SBM diet gained more with increasing conditioning temperature while LWG decreased for the peak diet (P < 0.05). Increasing the conditioning temperature of the under processed SBM diet to 80℃ restored weights to that of the Peak 70℃ diet. Feed conversion ratio of birds fed the peak diet increased with increasing conditioning temperature while the FCR for the under diets was reduced (P < 0.05). Birds fed the over processed SBM diet gained the least and had the lowest FI (P < 0.05). The digestibility of all amino acids increased when the conditioning temperature of the under diet increased from 70℃ to 80℃ (P < 0.05) and did not change for the peak diets. Diets containing under processed soybean meal conditioned above 70°C and pelleted mitigated antinutritional performance effects.

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