Poultry is the number one agricultural commodity in West Virginia. Decreasing diet cost and environmental impact, and improving the overall sustainability of production are a few of the most important issues currently surrounding the poultry industry in the state as well as the poultry intensive Eastern United States (US). Recent legislation surrounding agricultural run-off and the increase of phosphorus deposition in the Chesapeake Bay has promoted West Virginia broiler producers to find alternative management strategies for poultry manure. Gasification of poultry litter and feeding the resultant ash may represent a viable solution to manure application problems and provide a cost effective essential nutrient for poultry diets. This accomplishes two goals: 1) provides a source of heat for poultry houses and 2) the ash can replace part, or all, of the expensive inorganic feed phosphorus sources currently used in poultry feeds.
Our goal is to perform applied research pertaining to feed manufacture manipulations that can directly benefit the poultry industry. The long-term goal of this project is to provide the industry with a simple, viable alternative to applying litter to the land. The objective of this project is to assess the effectiveness of poultry litter biochar (PLB) as a replacement for expensive ingredients in poultry diets. This research project has been fully completed and demonstrated that PLB can improve pellet quality. Differences in broiler performance, bone mineralization, and amino acid digestibility were observed, demonstrating that birds fed PLB resulted in similar or greater values compared to birds fed a positive control diet. No differences in digesta viscosity were observed.
The majority of U.S. raised broilers consume a corn-soybean based diet with approximately 2/3 of the phosphorus being present as unavailable phytate bound phosphorus. Rock phosphorus is typically added to broiler diet formulations to increase dietary nPP. However, high amounts of dietary rock phosphorus can be costly and does not address the environmental impact of litter phosphorus. Phytases can be added to diets to improve plant phosphorus digestibility and reduce environmental impact, but rock phosphorus sources, particularly tricalcium phosphorus, are still incorporated to increase pellet mill production rate, electrical energy use of the pellet mill, and pellet quality; all of which are important economic factors associated with feed manufacture.
One alternative to rock phosphorus sources is poultry litter biochar, or PLB. This product is created through gasification of poultry litter. During gasification, poultry litter is subjected to pyrolysis, where temperatures reach 400°C and higher in an oxygen controlled environment. In this process, pathogens are destroyed and organic matter is consumed, leaving behind an ash containing minerals that may be available nutritionally, specifically phosphorus that can be liberated from a phytate molecule under these high temperatures. O’Dell reported approximately 88% of phytate in soybean meal could be degraded at 115°C. In addition to the possible nutritional benefits, PLB may have the potential to enhance feed manufacture similar to that of rock phosphorus. In a previous study, PLB addition to diets demonstrated improved pellet quality; however, broiler performance upon feeding was not maximized, though some contribution to bone mineralization was observed. The authors speculated that performance detriments may have been a result of arsenic contamination of the PLB or detrimental effects of PLB on digesta viscosity. The objective of the current study was to obtain a PLB product with a lower arsenic content and assess its effects on descriptive feed manufacture, broiler performance, digesta viscosity, bone mineralization, and amino acid digestibility.
The overall purpose for this project is to determine if the PLB is successful at partially replacing the rock phosphorus in the diet and the birds fed this diet will perform similar to birds receiving a diet sufficient in phosphorus. Five specific objectives have been identified.
1. Decrease heavy metal content in PLB
2. Determine pellet quality of diets with/without PLB
3. Determine digesta viscosity
4. Determine tibia ash content
5. Determine ileal amino acid digestibility
Prior to diet formulation, PLB samples were obtained and sent to a commercial laboratory to determine proximate analysis and mineral content (Table 2). This study was conducted at West Virginia University’s pilot feed mill using a 4 Diet Formulation X 2 Phytase factorial design. The four levels of Diet Formulation were: PC formulated with 0.45% nPP, NC formulated with 0.23% nPP, 2% PLB formulated with 0.45% nPP, and 4% PLB formulated with 0.45% nPP (Table 1). Phytase was either withheld or included. Batching was accomplished by creating 544.5 kg allotments of each diet formulation (without phytase) that were mixed for ten minutes dry, and an additional ten minutes post fat addition using a single screw vertical mixer. Each batch of feed was split into two equal aliquots (272.25 kg) with one aliquot receiving the addition of a commercially available phytase. Prior to pelleting, 4.5 kg of mash from each aliquot receiving phytase were mixed for 10 minutes using a small paddle mixer. The 4.5 kg allotment was then placed back into the designated batch and mixed an additional ten minutes prior to pelleting. This batching technique created a total of eight dietary treatments.
All batches of feed were passed through a 1.3 m long conditioner with a diameter of 0.31 m and 10 sec retention time. Treatments were steam conditioned at 82°C and pellets formed using a 40-horsepower California Pellet Mill equipped with a 38.1 mm x 4.8 mm pellet die. Pellets were cooled with ambient air utilizing a horizontal belt cooler. Once conditioning temperature reached a steady state during pelleting, mash samples were taken from the feed screw auger that conveys feed into the conditioner and corresponding pellet samples were taken from the cooler discharge. These samples were then analyzed for crude protein, calcium, total P, phytic acid, and phytase activity at a commercial laboratory. In vitro phytase activity and retention were determined using the Association of Official Agricultural Chemists (AOAC) 2000.12 method. The nPP values were calculated for all diets using the following equation: total P of feed – (0.282 X phytic acid of feed). A pelleted sample was collected directly from the pellet die and placed into an insulated container to determine hot pellet temperature; temperature measurements were obtained using a thermocouple thermometer and an 80PK-24 temperature probe. Pellet durability index (PDI) and modified pellet durability index (MPDI) were performed using a Pfost tumbling box on all treatments one day after pelleting. In addition, pellet durability was determined using a New Holmen Pellet Tester. All batches of feed were ground with a roller-mill prior to feeding; particle size after grinding was performed to ensure feed form differences were eliminated.
Live Bird Performance
A total of 1,472 1-d old straight-run Hubbard X Cobb 500 broiler chicks were obtained from a commercial hatchery. Twenty three chicks were randomly allocated to one of 64 pens to create the experimental unit. Each of the dietary treatments were randomly assigned to pens blocked by location, creating a randomized complete block design. Feed and water were provided for ad libitum consumption. Measured variables for the 21d experimental period included: starting pen weight, feed intake (FI), ending bird weight (EBW), live weight gain (LWG), and mortality corrected feed conversion ratio (FCR). On day 21, all birds were killed via cervical dislocation, weighed by pen, and ten birds were chosen whose weights were 100 grams ± the pen mean weight. The left tibia was excised from all ten birds; the birds were then randomly allocated for lower ileum (five birds) and total GI tract collection (five birds). Contents of the lower ileum were used to determine AIAAD using similar methodologies described by Evans and cohorts. The AIAAD data are presented as the percentage of digestible amino acid within the total diet and was calculated using the following equation:
AIAAD (%) = [((AAdiet / Tidiet) – (AAdigesta / Tidigesta)) / (AAdiet / Tidiet)] X AAdiet
Contents of the entire GI tract were removed by hand and viscosity measurements were determined using similar methodologies described by Lee and coauthors. Tibiae were dried, ether extracted to remove residual fat, and ashed using a muffle furnace to determine bone mineralization. All animals were reared according to protocols established by the West Virginia University Animal Care and Use Committee.
The proximate analysis and mineral content of the PLB used in this study are presented in Table 2. The authors were successful in obtaining a PLB product with a lower arsenic level (22 ppm) than the product used in previous research (99 ppm). Descriptive feed manufacture results are presented in Table 3. Production rate and hot pellet temperature were similar among treatments. The addition of PLB to diets without phytase at either 2 or 4% numerically increased pellet durability compared to PC (63.3 and 68.0 vs 58.0% PDI, respectively). When phytase was included in diet formulation, PDI was also increased for diets containing 2 or 4% PLB compared to PC (60.7 and 69.1 vs 55.4% PDI, respectively). Similar results were observed for New Holmen Pellet Tester and MPDI. Particle size of ground pellets revealed no more than 130 micron difference between treatments.
Live Bird Performance
Live bird performance results are presented in Table 4. Diet Formulation x Phytase interactions were observed for EBW, LWG, FI, and mortality percentage (P < 0.0001). These interactions revealed that birds fed the NC diet without phytase demonstrated a decrease in performance and supplementing this diet formulation with phytase balanced the phosphorus deficiency and performance was improved. It should be noted that the phytase dose utilized was considered a super-dose and therefore could have enhanced performance by decreasing gut irritation of phytate phosphorus in addition to meeting phosphorus requirement.
Due to the decreased performance of birds fed NC, preplanned contrasts were employed to compare the performance of PC (with or without phytase supplementation) and 2 or 4% PLB (with or without phytase supplementation). Based on these contrasts, birds fed 2% PLB demonstrated similar EBW, LWG, and FI compared to PC and was found to be superior for tibia ash percentage and tibia ash mg/g of gain (P < 0.05). In addition, birds fed 4% PLB also resulted in superior tibia ash mg/g of gain compared to PC (P = 0.0225), while birds fed 2% PLB with phytase demonstrated similar EBW, LWG, FI, FCR, and greater tibia ash mg/bird compared to PC with phytase (P < 0.05). Birds fed 4% PLB with phytase was similar to PC with phytase for all performance metrics (P > 0.05).
Displayed in Table 5 are digesta viscosity data. No differences were observed for digesta viscosity measurements (P > 0.05). Increased digesta viscosity was speculated to be in part responsible for reduced broiler performance in a previous PLB experiment. In the current experiment, dietary PLB inclusion did not impair performance; therefore, significant differences in digesta viscosity were not expected. In addition, digesta viscosity measurements in the current study are lower than results from previous research where performance was affected by these much higher viscosity levels.
The AIAAD data are presented in Table 6. The preplanned contrasts revealed that birds fed 2% PLB resulted in higher lysine, cysteine, threonine, valine, alanine, proline, glutamic acid, and aspartic acid digestibility compared to PC (P < 0.05). Preplanned contrasts also showed that birds fed 4% PLB demonstrated greater methionine and cysteine values compared to PC (P < 0.05). Birds fed 2% PLB with phytase demonstrated a higher digestible methionine value compared to PC with phytase (P < 0.0001). The authors speculate this effect was observed due to the 14.4% crude protein value of the PLB used (Table 2). Also, PLB digestible amino acid values were not accounted for during diet formulation, likely resulting in protein and amino acid values above the diet’s calculated nutrients.
Additional research had been conducted to assess PLB as a replacement for phosphorus in turkey and broiler diets. While PLB production, nutrient content, and dietary inclusion differ among these studies and the current study, all agree that PLB can be used as a replacement for rock phosphorus without compromising bird performance. In the current study, performance, digesta viscosity, and AIAAD data suggests that diet formulations containing modest inclusions of PLB, either 2 or 4%, can be used by Hubbard x Cobb broilers without causing a detriment to performance.
- PLB numerically improved pellet quality compared to diets that did not contain PLB, regardless of phytase supplementation.
- Diet formulations containing PLB demonstrated greater tibia ash values and imporved AIAAD compared to the PC diet.
- No significant differences were observed for digesta viscosity.
- Diet formulations containing modest incorporations of PLB (2 and 4%) can be used without detriment to broiler growth or performance.
As the poultry industry becomes aware of results from this research, PLB will become used more and more by the industry.
Education & Outreach Activities and Participation Summary
A manuscript is currently being created for publication in the Journal of Applied Poultry Research. Additionally, results from this project were presented at the 2014 Mid-Atlantic Nutrition Conference and 2014 Mountaire Feed Mill Manager Conference. Also, an abstract for 2015 Poultry Science Association Annual Meeting has been accepted and an oral presentation of results will be given to poultry professionals from around the world in July 2015. The results of this project will also be utilized in various Extension workshops and meetings during Summer and Fall 2015.
To date no economic analysis has been conducted. However, this is an important factor to consider and will be completed prior to final publication of these data.
Farmers in West Virginia and surrounding states are being to create and use PLB. This trend is expected to increase, lending to the use of PLB by the poultry industry as a viable alternative to expensive feed ingredients, as well as a way to reduce potential environmental impact.
Areas needing additional study
The production of PLB can be influenced by the temperture used to burn the litter as well as the composition of the litter itself. This becomes a major concern as to the consistency of the PLB. Future research should focus on different production methods and how this can impact the nutrient analysis of PLB.