Rendered products from the meat industry can provide economical quality sources of proteins to the animal and feed industry. Similar to lipids, rendered proteins are susceptible to oxidation, yet the stability of these proteins is unclear. In addition, interest in understanding how oxidative stress can impact efficiency in production animals is increasing. Recent studies show that consumption of oxidized lipids can lead to a change in the oxidative status of the animal as well as decreases in production efficiency. To date, little is known about how consumption of oxidized proteins impacts oxidative status and growth performance. The objectives of this study were to determine if feeding diets high in oxidized protein to growing pigs would: 1) impact growth performance and 2) induce oxidative stress. Thirty pigs (42 d old; initial body weight [BW] 12.49 ± 1.45 kg) were randomly assigned to one of three dietary treatments with increasing levels of oxidized protein. Spray-dried bovine plasma was used as the protein source and was either unheated upon arrival, heated at 45 °C for 4 d, or heated at 100 °C for 3 d. Diets were fed for 19 d and growth performance was measured. Blood plasma (days 0 and 18), jejunum, colon, and liver tissues (day 19) were collected to analyze for markers of oxidative stress (e.g., protein oxidation, lipid oxidation, DNA damage, and glutathione peroxidase activity). Average daily gain (ADG;P < 0.01) and average daily feed intake (ADFI;P < 0.01) had a positive linear relationship to increased protein oxidation, but there was no effect on gain to feed ratio. Furthermore, protein (P = 0.03) and fat (P < 0.01) digestibility were reduced with increased protein oxidation in the diet. Crypt depth showed a positive linear relationship with dietary protein oxidation levels (P = 0.02). A trend was observed in liver samples where pigs fed the plasma heated to 45 °C had increased lipid oxidation compared with pigs fed the plasma either unheated or heated to 100 °C (P = 0.09). DNA damage in the jejunum tended to have a linear relationship with the dietary protein oxidation level (P = 0.07). Even though results suggest dietary oxidized protein did not induce oxidative stress during short-term feeding, differences in performance, gut morphology, and digestibility are likely a result of reduced protein availability.

Rendered products used in animal feed and pet food undergo extreme temperatures during manufacturing and may be stored up to two years. No information is available on protein oxidation in these products. The objective of this study was to determine the extent to which typical antioxidant inclusion at different storage conditions may limit protein oxidation in typical rendered protein meals. Two experiments were conducted on 14 rendered products stored at either 45°C for 7 or 14 days, or at 20°C for 3 or 6 months to determine the extent to which time, temperature, and antioxidants affect protein oxidation. Results from this study show that fish meal and chicken blood meal are susceptible to protein oxidation during storage at 45°C (P = 0.05; 0.03) as well as during storage at 20°C (P = 0.01; 0.04). Natural antioxidants were effective at limiting carbonyl formation in fish meal during short term storage at 45°C whereas ethoxyquin was effective at limiting the extent of protein oxidation in fish meal stored long term at 20°C.

Rendered products from the meat industry provide quality proteins in diets for companion animals. These proteins are exposed to extreme temperatures during processing leading to the potential for decreased diet digestibility and subsequent growth performance. While this would impact production efficiency in livestock species, oxidized ingredients in companion animal diets may impact health and longevity. The objective of this study was to determine the extent to which a feedstuff containing oxidized protein and lipid affect diet digestibility, growth performance, and oxidative stress in nursery pigs. Fifty-six male pigs (21 d of age, initial body weight 5.51 ± 0.65) were randomly assigned to 1 of 4 dietary treatments in a 2 × 2 factorial arrangement with two levels of heat and two levels of antioxidant (AOX). Diets were fed for 35 d and growth performance was measured, while total tract digestibility and nitrogen (N) balance was determined during the trial on d 18 to 20. Blood plasma was collected on d 34 and jejunum, colon, and liver tissues were collected on d 35 to analyze for markers of oxidative stress. Average daily feed intake (ADFI) was reduced in pigs fed diets without antioxidants (P = 0.02). Additionally, pigs consuming diets containing heated chicken by-product meal (CBP) had decreased gain:feed (GF; P = 0.02). There was an interaction between heat and AOX (P = 0.02) where heating CBP reduced N digestibility in the presence of an AOX but did not have an impact when AOX was not present. The removal of AOX resulted in reduced GE digestibility (P < 0.01). Dry matter (P < 0.01), ash (P < 0.01), and protein (P < 0.01) digestibility were reduced (P < 0.01) as a result of heating. Furthermore, heating (P =0.01) as well as absence of antioxidant (P =0.01) resulted in reduced digestible energy. No difference was detected in N retention suggesting that oxidation reduces digestibility but has no impact on N utilization. This is supported by the fact that systemic oxidative stress was not consistently affected by heating or AOX inclusion. These results suggest that feeding pigs CBP containing oxidized proteins and lipids did not induce oxidative stress. However, feeding young pigs CBP containing oxidized proteins and lipids did result in reduced energy and nutrient digestibility as well as negatively affected feed efficiency. Because CBP is commonly used in companion animal diets, it is reasonable to revisit their impacts on those species.

The student author, whose presentation of the scholarship herein was approved by the program of study committee, is solely responsible for the content of this dissertation. The Graduate College will ensure this dissertation is globally accessible and will not permit alterations after a degree is conferred.

Endogenous protein oxidation as a result of oxidative stress is known to reduce the efficiency of livestock species (Boler et al., 2012; DeRouchey et al., 2004; Dibner, Atwell, Kitchell, Shermer, & Ivey, 1996). Additionally, rendered by-products are common feedstuffs in livestock diets. During processing, these sources have the potential to become oxidized. While most research on oxidative stress has focused on consumption of dietary oxidized lipids, little research has been done in the area of dietary oxidized proteins and the potential to induce oxidative stress. The objective of this study was to determine the effects of dietary oxidized protein on oxidative stress in pigs. For this study, 30 pigs 6 weeks old were divided into three dietary treatments of control, medium, and high dietary oxidized protein. Each treatment was fed the same diet, with the exception of the degree of oxidation in bovine plasma which was included in the diet at 10 percent. Pigs were fed for 19 days and then euthanized for tissues collected. Jejunum, liver, and colon were collected along with urine and plasma samples on day 0 and 18. Jejunum samples were also collected for histology. Markers of oxidative stress included protein carbonyls, thiobarbituric acid reactive substance (TBARS), 8-hydroxyguanine, and glutathione peroxidase activity. Pigs in the high oxidation treatment had an increase in crypt depth of 16 percent (p-value less than 0.05) when compared to control further resulting in an 11 percent decrease in villi height to crypt depth ratio (p-value less than 0.05). Additionally, lipid oxidation products, measured by TBARS, was 28 percent greater in the liver of pigs in the medium oxidation treatment (p-value less than 0.05) when compared to control. Even with the short duration of this study, dietary oxidized protein did impact the oxidative status of the animal. Using pigs as a model for companion animals, it could be hypothesized then that long-term exposure could have implications on longevity.