**4. Discussion**

Numerous feeding trials have demonstrated that the feedstock rations rich in carotenoids (tomato powder, alfalfa, marigold extract) and/or unsaturated fatty acids are transferred to the eggs [10,17]. Studies have also demonstrated improved bioavailability of lutein from enriched eggs in comparison to lutein found in spinach or dietary supplements [18] with enhanced intestinal absorption of lutein when consumed with dietary lipids, suggesting that eggs may be a superior delivery system for some carotenoids. However, the inclusion of specialty feed ingredients (alfalfa meal, marigold, fish meal, linseed meal) is not cost-effective or commercially viable for animal food production. On the contrary, few studies have examined the enrichment of consumable food products (eggs or meat) using agricultural waste by-products rich in polyphenolic compounds such as peanut skins as poultry feedstock ration. Value-addition of agricultural waste by-products, such as peanut skins to poultry feedstock rations, could promote agricultural sustainability and provide creative solutions for agricultural waste by-products with considerable residual nutritional value.

Overall, this study demonstrates that peanut skins can be effectively used in the diets of egg-producing hens at inclusion levels of 3% of the conventional diet, without adversely affecting hen performance (feed intake, FCR, dozens of eggs produced), egg quality (HU, shell strength, albumen height, vitelline membrane strength, yolk color) or the fatty acid profile of the eggs produced. Additionally, this study parallels previous poultry feeding trials demonstrating that unblanched high-oleic peanuts enrich the eggs and meat produced with unsaturated fatty acids with reduced saturated and trans fats, with reduced egg mass compared to the controls [10] and broiler chickens [19].

While hens fed the HOPN diet had reduced feed intake, 8-week average body weights, and total dozens of eggs produced relative to the other treatments, there were no significant differences in the FCR between the treatment groups. In previous experiments, we demonstrated that hens fed the HOPN dietary treatment had reduced feed intake due to increased ileal fat digestibility and apparent metabolizable energy compared to the other treatment groups [20]. Hence, HOPN fed birds consumed less of a more energetically dense diet to meet the metabolic needs in comparison to the other dietary treatment groups.

In general, egg weights were increased in the PN Skin treatment group relative to the other treatments in the last 4 weeks of the study, while egg weights from the HOPN and OA treatment groups were smaller than the other treatment groups. Similarly, other studies have demonstrated that feeding hens diets rich in unsaturated fatty acids, such as conjugated linoleic acid (CLA), reduce egg weights and body weights [21,22], suggesting that dietary supplementation with CLA causes a reduction in hen body weights, similar to weight loss in humans consuming dietary CLA, which correlates with reduced egg weights and/or size. Egg size has been shown to be greatly influenced by body weight [23]. With every 45 g of body weight increase, there is approximately a 0.5 g increase in egg size from 18 weeks of age in laying hens [24].

In contrast, our previous studies demonstrated that yolk color in eggs produced from hens fed a diet containing unblanched high-oleic peanuts had an approximately 2-fold increase in yolk color in comparison to conventional eggs [10], while in this study, egg yolk color was significantly less in eggs produced from hens fed the HOPN diet relative to the other treatment groups. Eggs produced from hens fed the PN Skin and control diets had similar levels of palmitic and elaidic fatty acid for most of the study, while eggs produced from the HOPN and OA treatment groups had reduced saturated and trans fatty acid levels comparatively.

Chemical analysis of the four experimental diets revealed increased levels of omega 3 fatty acid levels in the PN Skin diet relative to the other dietary treatments. Nonetheless, omega 3 fatty acid level in eggs produced from hens fed the PN Skin experimental diet was similar between all treatment groups. The soybean oil, whole peanuts and/or peanut skins, and yellow corn (very low levels) are the predominate feed ingredients containing omega 3 fatty acids [25–27], which may have correlated to elevated omega 3 fatty acid content found in the PN Skin experimental diets that contained modest amounts of each of these feed ingredients relative to the other dietary treatments.

In contrast to our previously published reports [10], β-carotene content in this study was not significantly different between eggs produced from hens fed the four different dietary treatment groups at any of the experimental time points measured in this study. Studies conducted by Pattee and Purcell (1967) revealed that peanut oil extracted from young peanuts contained 60 μg of β-carotene and 138 μg of lutein per liter, while peanut oil extracted from more mature peanuts had lower concentrations of these carotenoids [28]. However, the determination of peanut maturity has been correlated with the increasing color of the mesocarp from white to yellow, orange, brown, and black [29]. Peanuts have an indeterminate growth pattern, in which at harvest, the combine collects peanut pods ranging in different maturity levels present on the plant [30]. Therefore, a given peanut harvest may contain a higher percentage of young/immature pods that contain elevated levels of carotenoids in the seed and oil [28], suggesting that a potentially higher percentage of young/immature peanuts may have been harvested for use in our earlier layer hen feeding trials with unblanched high-oleic peanuts in which enriched the eggs produced with unsaturated fatty acids and β-carotene [10].

β-carotene is a lipid-soluble carotenoid found abundantly in plants and responsible for the rich yellow and deep orange colors in plants [31]. Conventional commercial eggs are rich in lutein and zeaxanthin [32], which are carotenoids that are most likely transferred from yellow corn in the diet to the egg yolks. Layer feeding trials have demonstrated the transfer of carotenoids and their pigments from the diet to the yolks of eggs produced [9]. While our previous layer feeding trials demonstrated that eggs produced from hens fed a HOPN diet had significantly increased β-carotene levels and yolk color relative to conventional eggs, in which the rich yellow/deep orange pigment of β-carotene was transferred to the eggs. However, in this study, β-carotene content was not elevated, and hence the yellow/orange pigments were not available to transfer from the diet to the yolks of eggs produced by hens fed the HOPN or PN Skin diets. Moreover, eggs produced from hens fed the HOPN diet had less available dietary carotenoids from yellow corn (lutein and zeaxanthin) in the diet relative to the other treatment groups (Table 1 content of yellow corn: control 47.5%, 36.9%, PN Skin 56.9%, OA 57.0%), which may have also correlated to reduced yolk color scores.

Most importantly, this study reports similar body weights, feed intake, FCR, and egg chemistry between the PN Skin and control treatment groups, implying the effective use of PN skins as an alternative layer feed ingredient. These results support the valueadded use of peanut skins as a poultry feed ingredient, an abundant agricultural waste by-product of the peanut industry. While this study has positive implications for the use of peanut skins as an alternative poultry feed ingredient, this study fails to parallel commercial egg production commonly using floor pens or alternative housing systems. Moreover, we aim to repeat this study with larger sample sizes to more closely parallel industry. In addition, we aim to conduct additional feeding trials with hens housed in floor pens and fed a peanut and/or peanut skin-containing diet for comparative analysis of the production performance to hens housed in battery cages and fed a peanut and/or peanut skin-containing diet.

**Author Contributions:** All authors actively contributed to the care and husbandry of all research animals, while co-authors O.T., R.M. and K.A. were active participants in the data analysis, data interpretation, and preparation of the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the Food Science & Market Quality and Handling Research Unit, Agricultural Research Service (CRIS Project 6070-43440-012-00D), and the North Carolina Peanut Growers Association (Award (1119) 2021-0561).

**Institutional Review Board Statement:** The procedures used in these studies were approved by the North Carolina State University Institutional Animal Care and Use Committee (IACUC #17-001-A).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. The sensory protocol was reviewed and deemed exempt by the NC State University Institutional Review Board (IRB) for human subjects.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors would like to acknowledge the students and staff of the Prestage Department of Poultry Science, Hampton Farms-Jimbo's Jumbos and to Birdsong Peanuts for a donation of high-oleic peanuts for this feeding trial.

**Conflicts of Interest:** The authors declare no conflict of interest.
