The occurrence of plastic impaction in ruminants is a growing concern. As indiscriminate feeders, cattle may consume plastic foreign materials incorporated into their diets and it is currently estimated that 20% of cattle contain plastic foreign materials in their rumen. These materials are indigestible and accumulate for the lifetime of the animal. As these materials accumulate, they may reduce feed efficiency and production by erosion and ulceration of rumen epithelium, stunting of papillae, blockage of the reticulo-omasal orifice, and leaching of toxic heavy metals. It is necessary to reduce the incidences of plastic impaction in domestic ruminants. Using polyhydroxyalkanoate (PHA) and poly(butylene succinate-co-adipate) (PBSA) biodegradable materials for feed storage products such as bale netting could reduce the incidences and effects of polyethylene-based plastic impaction in ruminants. The objectives of these studies were to evaluate the degradability of PHA and PBSA materials in the reticulorumen via in vitro, in situ, and in vivo methods. Our hypothesis was that these materials would degrade in the rumen and that a melt-blend of PHA and PBSA may degrade faster than its individual components.
An in vitro study incubated a proprietary PHA-based polymer, PBSA, and PBSA:PHA melt blend nurdles, and forage controls in rumen fluid for up to 240h in DaisyII Incubators. Mass loss was measured, and digestion kinetic parameters were estimated. Thermogravimetric and differential scanning calorimetry analyses were conducted on incubated samples. Results indicated that the first stage of degradation occurs within 24h and PHA degrades slowly. Degradation kinetics demonstrated that polymer treatments were still in the exponential degradation phase at 240h with a maximum disappearance rate of 0.0031%/h, and mass loss was less than 2% for all polymers. Melting temperature increased and onset thermal degradation temperature decreased with incubation time, indicating structural changes to the polymers starting at 24h.
Further in situ degradation, however, indicated these biodegradable materials degrade at more accelerated rates in the rumen. Polyhydroxyalkanote, PBSA, PBSA:PHA blend, and low-density polyethylene (LDPE) films were incubated in the rumens of three cannulated, non-lactating Holsteins for 0, 1, 14, 30, 60, 90, 120, and 150d. In situ disappearance (ISD) and residue length were assessed after every incubation time. Polyhydroxyalkanoate achieved 100% degradation by 30d, with initiation occurring at 14d indicated by ISD and a reduction in residue length. The fractional rate of disappearance of PHA was 7.84%/d. Poly(butylene succinate-co¬-adipate) and Blend did not achieve any significant ISD, yet fragmentation of PBSA occurred at 60d and the blend at just 1d likely due to abiotic hydrolysis. Low-density polyethylene achieved no ISD and residue length did not change over incubation time. From these results, we proposed a PBSA:PHA blend is a valid alternative to polyethylene single-use agricultural plastic products based on its fragmentation within 1d of incubation.
Administration of PBSA:PHA film boluses compared to LDPE films and a control further supported this dissemination. Holstein bull calves (n = 12, 62 ± 9d, 74.9 ± 8.0kg) were randomly allocated to one of three daily bolus treatments: 13.6g of PBSA:PHA in 4 gelatin capsules (Blend), 13.6g of LDPE in 4 gelatin capsules (LDPE), or 4 empty gelatin capsules (Control) for 30d. Hemograms were conducted on blood samples collected on d0 and d30. On d31, animals were sacrificed to evaluate gross rumen measurements and pathology, determine papillae length, and characterize polymer residues present in rumen contents. Feed intake, body weight, body temperature, and general health were determined throughout the study. No animals presented any symptoms related to plastic impaction and animal health was not particularly affected by treatment. Daily grain and hay intake, body weight, rectal temperature, hematological parameters, gross rumen measurements and pathology, and rumen pH and temperature were not affected by treatment. There was evidence that degradation of PBSA:PHA may release byproducts that support rumen functionality. Methylene blue reduction time of Blend calves tended to be decreased by 30% compared to LDPE calves, and caudal ventral papillae length of Blend calves were 50% longer than those of Control animals. Though studies are needed to specifically elucidate the production of byproducts due to degradation of PBSA:PHA and their correlations. Polymer accumulation and residue length differed among treatments. Calves dosed with LDPE retained 6.7% of the dosed polymer, undegraded, while Blend calves retained 0.4% of the dosed polymer. The polymer residues in Blend calves were 10% of their original size.
Single-use agricultural plastics developed from PBSA:PHA may be a suitable alternative to LDPE-based products in the case of ingestion in ruminants due to no acute health inflictions, fragmentation of polymers with 1d, and improved clearance from the reticulorumen. As such, utilization of these materials may reduce the incidences of plastic impaction in ruminants in commercial operations. Further long-term feeding studies are needed to evaluate specific byproduct production of PBSA:PHA and their potential influences on rumen function and animal health and production in normal commercial conditions. / Master of Science in Life Sciences / Plastic feed-storage materials may unintentionally be incorporated into animal feeds. Net wraps and bale twines may be stuck or left on forages when they are ground and incorporated into mixed rations. As cattle are largely non-selective, they may inadvertently consume these plastic materials. Approximately 20% of cattle contain plastic foreign materials in their rumen. These materials are indigestible and accumulate for the animal's lifetime. As plastics build up in the rumen, they may reduce feed efficiency, body weight, and milk production by damaging the rumen lining, blocking the digestive tract, and leaching toxic heavy metals. Therefore, it is necessary to reduce the incidences of plastic impaction in domestic ruminants to improve their health and productivity. Using biodegradable materials that degrade by bacteria, such as polyhydroxyalkanoate (PHA) and poly(butylene succinate-co-adipate) (PBSA), for feed storage products could reduce the occurrence and effects of plastic impaction in ruminants due to the materials' potential degradation in and passage from the rumen. The objectives of these studies were to evaluate the breakdown of PHA and PBSA materials in the rumen. Our hypothesis was that these biodegradable materials would degrade in the rumen and that a blend of PHA and PBSA may degrade faster than its individual components.
In our first study, PHA, PBSA, a PBSA:PHA blend, and forage controls were incubated in rumen fluid for up to 240h. Mass loss, degradation rate, and the structure of polymers were determined over incubation time. Results indicated that biodegradable polymers may begin to break down within 24h. Polymer treatments were still in the early stages of degradation at 240h with a maximum degradation rate of 0.0031%/h, and mass loss of polymers was less than 2%. However, within 24h, the structures of polymers may have altered to promote future degradation at longer incubation times.
Accelerated degradation was observed when PHA, PBSA, PBSA:PHA (Blend), and polyethylene (LDPE) films were incubated in the rumens of three Holstein cows up to 150d. Mass loss and the length of the remaining polymers were assessed monthly. Polyhydroxyalkanoate began to degrade by 14d and completely degraded by 30d with a disappearance rate of 7.84%/d. The remaining polymer did not achieve any mass loss. However, PBSA and Blend residue size began to decrease by 60d and 1d, respectively. Based on Blend's structural degradation within 1d of incubation that may promote its clearance from the rumen if ingested, we proposed that the material may be an alternative to polyethylene single-use agricultural plastic products.
When Blend films were fed to calves, breakdown of the material further supported our dissemination that PBSA:PHA may be a suitable alternative to LDPE in the case of animal ingestion. Holstein bull calves (n = 12, 62 ± 9d, 74.9 ± 8.0kg) were randomly allotted to one of three daily bolus treatments: 13.6g of PBSA:PHA (Blend), 13.6g of polyethylene (LDPE), or no polymer (Control) distributed over 4 gelatin capsules for 30d. Feed intake, body weight, body temperature, and general health were determined throughout the study. Blood analyses were conducted on blood samples collected before and after the experimental period. On d31, animals were sacrificed to evaluate rumen growth and health, measure rumen papillae length, and describe polymers that may reside in the rumen. No animals presented any signs related to plastic impaction and animal health was not particularly affected by treatment. Daily grain and hay intake, body weight, rectal temperature, blood parameters, and rumen growth and health were not affected by treatment. There was evidence that degradation of Blend may support rumen function. Methylene blue reduction time of Blend calves tended to be decreased by 30% compared to LDPE calves, which indicates the rumen microbiome of Blend calves may better ferment feeds. Papillae length of Blend calves were also 50% longer than those of Control animals, which would improve the absorption of nutrients. Byproduct formation from Blend degradation could explain this; however, studies are needed to specifically elucidate the production of byproducts and their relationship to rumen function. Polymer accumulation and residue length differed among treatments. Calves dosed with LDPE retained 6.7% of the dosed polymer, undegraded, while Blend calves retained 0.4% of the dosed polymer. The polymer residues in Blend calves were 10% of their original size.
Single-use agricultural plastics developed from PBSA:PHA may be a suitable alternative to polyethylene-based products in the case of ingestion in ruminants due to no short-term health inflictions, the reduced polymer size within 1d, and improved clearance from the rumen. As such, utilization of these materials may reduce the incidences of plastic impaction in ruminants in commercial operations. Further long-term feeding studies are needed to evaluate specific byproduct production of PBSA:PHA and their potential influences on rumen function and animal health and production in normal commercial conditions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110856 |
| Date | 21 June 2022 |
| Creators | Galyon, Hailey Roselea |
| Contributors | Dairy Science, Cockrum, Rebecca, Ferreira, Gonzalo, Whittington, Abby Rebecca |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/vnd.openxmlformats-officedocument.wordprocessingml.document |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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