Evaluation of Extreme Thermal Processing Methods to Improve Nutrient Utilization of Low-Energy Diets for Finishing Pigs

A total of 270 pigs (PIC 337 × 1050; initially 115.7 lb) were used in a 79-d experiment to determine the effects of long-term conditioning or extrusion on finishing pig nutrient digestibility, growth performance, and carcass characteristics. There were 7 or 8 pigs per pen and 9 pens per treatment. Treatments included the same basal diet processed as: 1) nonprocessed mash; 2) pelleted with 45-s conditioner retention time; 3) pelleted with 90-s conditioner retention time; or 4) extruded. Diets were fed in three phases with the same low-energy diet formulation fed across treatments, containing 30% corn dried distillers grains with solubles and 19% wheat middlings. Pigs fed thermally processed feed, regardless of method, had improved ADG, F/G, ether extract, and crude fiber apparent total tract digestibility (P < 0.05) compared to those fed the mash diet, but thermal processing did not affect ADFI . Extruded diets tended to improve F/G compared to pelleted diets (P = 0.09). Pigs fed any thermally processed treatment had greater HCW compared to those fed mash (P < 0.05). Improvements in fat and crude fiber digestibility (P < 0.05) led to improved caloric efficiency in pigs fed thermally processed diets. Thermal processing did not influence percentage yield, backfat, or loin depth when HCW was used as a covariate. However, pigs fed thermally processed diets had greater jowl fat iodine value compared to those fed mash diets (P < 0.05). Electrical energy usage during thermal processing was recorded. Pigs fed mash diets had greater (P < 0.05) cost per lb of gain, as well as reduced gain value and income over feed costs, compared to those fed thermally processed diets. This experiment confirms the benefits of thermally processing feeds to improve ADG and F/G, but compromises carcass fat iodine value. Additionally, this research suggests that more extreme thermal processing conditions may be used without hindering nutrient utilization.


Swine Day 2015
Introduction High-fiber byproduct ingredients often price into least-cost formulas.However, their inclusion may have negative consequences, including increased nutrient variability, and decreased growth performance, carcass yield, and fat quality. 2,3In addition, the physical characteristics of these ingredients often create handling challenges because they have decreased bulk density compared to the original grain or oilseed.It is often difficult to produce a high quality pellet due to the increased fracture points and poor starch gelatinization potential because of their high fiber content.
Still, if thermal processing parameters are manipulated so a high-quality pellet is produced, advantages in diet quality may be captured.Increasing conditioning time during the pelleting process improves pellet quality and increases the diet's propensity for starch gelatinization and susceptibility to enzymatic hydrolysis. 4While extended processing is beneficial for some nutrients, others may be negatively affected.Furthermore, pelleting is already an energetically expensive process that reduces feed mill throughput, and harsher processing conditions exacerbate these disadvantages. 5It is important to evaluate the effects of pelleting diets that include low-energy byproducts to calculate the cost:benefit ratio of these harsh thermal processing methods in pork production.The objective of this experiment was to assess how long-term conditioning or extrusion of low-energy diets impacts nutrient digestibility, growth performance, and carcass characteristics in finishing pigs.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used for this experiment.The experiment was conducted at the Kansas State University Swine Teaching and Research Center in Manhattan.

Diet Manufacturing
Four treatments were manufactured for this experiment by varying the same diet with different thermal processing methods: 1) nonprocessed mash, 2) pelleted with 45-s conditioner retention time, 3) pelleted with 90-s conditioner retention time, and 4) extruded.The 45-s conditioner retention time would be typical of what is used in commercial pellet diet production.Diets were fed in 3 phases with the same low-energy diet formulation fed across treatments with 30% corn dried distillers grains with solubles and 19% wheat middlings (Table 1).

Statistical Analysis
Data were analyzed as a completely randomized design using the GLIMMIX procedure in SAS (SAS Institute Inc., Cary, NC) with pen as the experimental unit.Hot carcass weight was used as a covariate for backfat and loin depth.Results were considered significant if P < 0.05, and a trend if 0.05 < P < 0.10.Orthogonal contrasts were used to evaluate differences between pelleted vs. extruded diets, pelleted vs. control diets, 45-s pellet vs. 90-s pellet, and thermally processed vs. control diets.

Diet Manufacturing
Post-mixing production rate varied widely among treatments due to differences in equipment (Table 2).Both pelleted diets were manufactured using the same model pellet mill with a variable frequency drive to control conditioner speed.The extruded diet was manufactured at a lower production rate, but was more stable throughout the phases and was held at a constant 2,650 lb/h.The electrical energy consumption of the thermal processing equipment was as predicted, with the pelleted diets having lower energy usage than extruded diets, and 45-s conditioning time having less energy usage than the 90-s conditioning time for pelleted diets.The differences in equipment also influenced pellet durability index (PDI).The longer conditioning time in the pelleted diets improved standard and modified PDI, by 1.6 and 5.2%, respectively.The extruded treatment had substantially higher PDI than either pelleted treatment.This is likely due to greater starch gelatinization in the extruded diet due to the higher moisture and heat.
While many nutrients are consistent with formulated values, differences existed between treatments (Table 3).Notably, the pelleted diets conditioned for 90-s had the greatest DM.It is likely that the reduction in production rate for the 90-s pellets resulted in longer time spent in the cooler, where more water was pulled off the pellets.In addition, mash diets had greater ADF concentrations and much greater NDF concentrations than the thermally processed diets.Potentially, more of the fibrous particles from wheat middlings or distillers dried grains with solubles were part of the fines separated from the complete pelleted diet because they have a low propensity for starch gelatinization and pelleting and were not used in the pelleted diets analysis.The extruded diet had the lowest crude fiber concentration in phases 1 and 2, but was intermediate in phase 3.Both cellulose and beta-glucan concentrations were greatest in the extruded diet in phase 3, but were intermediate in phases 1 and 2. Future research should include evaluating the nutritional composition of fines compared to pelleted diets, which may explain some of the differences in nutrient concentration between the mash and thermally processed feeds.
In addition to crude nutrients, the role of feed processing on both fatty acid and amino acid composition was evaluated (Table 4).The majority of fatty acids in the diet were linoleic, oleic, palmitic, and linolenic acids.Based on our findings, feed processing method did not appear to alter fatty acid concentrations within the diet.Amino acids also did not seem altered by dietary treatment, but lysine availability, as measured by chemical analysis, was slightly decreased with increasingly harsh thermal processing conditions compared to mash.Thermal processing is known to alter protein availability, and particularly Lys reactivity.Reactive lysine values were greatest in mash diets and lowest in extruded diets in all but the last phase.It is logical that extruded diets would have the least reactive Lys due to the formation of Maillard reactions.Maillard reactions brought on during conditioning or preconditioning irreversibly bind the free ε-NH 2 group of Lys and other amino acids to a reducing sugar.Only Lys that retains its reactivity, and thus has not undergone this binding chemical process, is bioavailable to the animal but is still present in nutrient analyses for total Lys.

Growth Performance
Feed processing method had a large impact on finishing pig growth performance overall, but particularly during the early stages of the study (Table 5).There were no differences between pelleted diets, but diet form affected ADG and F/G from d 0 to 25, 25 to 46, and overall, where thermally processed diets improved growth performance compared to mash diets (P < 0.05).Interestingly, ADFI was impaired when pigs were fed extruded diets from d 0 to 25 (P < 0.05), but was not affected after the initial phase.

Swine Day 2015
As described above, the PDI of the extruded diets was substantially greater than that of the pelleted diets in all phases.This feed hardness may have contributed to the poor ADFI of pigs during the first phase, but then they became acclimated to the physical characteristics of the diet and intake was no longer affected.
Overall, thermal processing improved pig ADG by 3.1 to 5.9% and F/G by 5.6 to 8.1% without affecting overall ADFI.Ultimately, these growth performance improvements resulted in pigs that were 6.8 to 11.5 lb heavier at market compared to those fed mash diets, with the greatest weight increase coming from those fed pelleted diets that had been conditioned for 90-s.Thermal processing had a substantial impact on pig growth performance, but there was little differentiation among the thermal processing methods themselves.

Nutrient Digestibility and Carcass Quality
While some of the differences in growth performance may be attributed to changing physical diet form, broad differences in nutrient digestibility due to differences in feed manufacturing method suggest the bulk of differences are due to digestibility (Table 6).Pigs fed pelleted diets conditioned for 90-s had the greatest CP, and NDF digestibility (P < 0.05) compared to all other treatments, and the extruded diet had the lowest (P < 0.05) ash digestibility.Additionally, pigs fed thermally processed diets had improved ether extract, crude fiber, and cellulose digestibility compared to those fed mash diets (P < 0.05).Alterations in nutrient digestibility led to improved caloric efficiency in pigs fed thermally processed diets compared to those fed mash diets.
Feed processing method did not affect percentage carcass yield or backfat depth but tended (P = 0.08) to increase loin depth compared to pigs fed the mash diets.While the quantity of pork fat did not change significantly, the composition of fat was altered.Jowl fat iodine value was increased (P < 0.05) when pigs were fed diets that were thermally processed.While the 2 points in iodine value shift is important, it is not necessarily dramatic.Still the mode of action driving this shift is unknown.Potentially, thermal processing increases the digestibility of dietary lipids, which are predominantly from grain and therefore relatively unsaturated in nature.Therefore, we can link the effects of thermal processing on carcass iodine value with dietary fatty acid concentrations.Since more dietary lipids are available for deposition, pigs potentially have reduced de novo fatty acid synthesis.The fatty acids created during de novo fatty acid synthesis are highly saturated to maximize energetic efficiency.Thus, thermally processing diets likely shifts fat deposition from saturated de novo products to more unsaturated dietary lipids.This makes the interaction with thermal processing and ingredient inclusion an important factor in carcass fat quality.The diets used in this study were high in fiber compared to diets with low byproduct inclusion levels.Still, the relationship between thermal processing, fatty acid digestibility, and the degree of unsaturation in carcass fat deposition is important to continue to evaluate.
In summary, thermal processing, regardless of type, improved overall ADG and F/G, but not ADFI in finishing pigs.Pigs fed any thermally processed treatment had greater jowl fat iodine value compared to those fed the mash diet.This experiment again confirms the benefits of thermally processing feeds to improve ADG and F/G, but neither extended conditioning nor extrusion extracted additional nutrients from low-energy feedstuffs compared to traditional pelleting.
Meanwhile, the basal diet was transported to Wenger Manufacturing, Inc. in Sabetha, KS, where treatment 4 was manufactured using a Universal Pellet Cooker (Model UP/C, Wenger Manufacturing, Sabetha, KS) with 338°F preconditioning temperature.Pellet durability was determined according to the standard and modified ASAE Standard S269.4 where five ½-in.hexnutswere added to the each tumbling compartment (Table2).
The basal diets, as well as treatments 1, 2, and 3, were manufactured at the Kansas State University O. H. Kruse Feed Technology Innovation Center in Manhattan.Treatments 2 and 3 were conditioned at 180°F and pelleted using a pellet mill (California Pellet Mill Model #3016-4, Crawfordsville, IN) fit with a 0.17 × 1.13-in.die.The conditioner motor speed was decreased to manufacture treatment 3 with a longer conditioning time to mimic the time of a double-pass conditioner.Digestibility coefficients were calculated according toStein et al. (2006). 6

Table 4 .
Analyzed fatty acid and amino acid composition of the diet (as-fed basis) 1

Table 6 .
Effects of feed processing method on finishing pig nutrient digestibility, caloric efficiency, and carcass characteristics 1