**1. Introduction**

Feed ingredients used to make dietary rations for food production animals account for approximately 60–70% of the total production cost annually [1]. Peanut skins, which are an abundant low-value waste by-product of the peanut industry, contain residual nutrients that may serve as an energy-rich, antioxidant-rich, affordable feed additive or ingredient for production animals. Peanut skins contain 19% fat, 12% fiber, and 14% to 15% polyphenolic compounds [2]. Nevertheless, approximately 70 million pounds of peanut skins are discarded annually with no identified uses and little to no economic value [3].

Dairy and beef cattle feeding trials have shown that peanut skin dietary inclusion rates greater than 8–16% inhibits protein digestion and absorption due to the high content of tannin and procyanidin [4,5]. Interestingly, reduction in the tannin and procyanidin content in peanut skins by ammoniation did not improve protein digestibility, nitrogen retention, or production performance in steers [6]. In contrast, a small goa<sup>t</sup> feeding trial using whole peanuts and/or peanut skins in the diets of goats demonstrated that whole peanuts and/or peanut skins had similar rates of rumen digestibility as conventional forages such as alfalfa hay cubes, while peanut skins providing a high level of dietary antioxidants [7]. While there are several published reports on the use of peanut skins as a feed additive in ruminant diets, there are no published peanut skin feeding trials to date in monogastric production animals. Hence, in this study, we aimed to determine the effect of peanut skins as a feed ingredient on the production performance of layers.

**Citation:** Toomer, O.; Vu, T.; Wysocky, R.; Moraes, V.; Malheiros, R.; Anderson, K. The Effect of Feeding Hens a Peanut Skin-Containing Diet on Hen Performance, and Shell Egg Quality and Lipid Chemistry. *Agriculture* **2021**, *11*, 894. https:// doi.org/10.3390/agriculture11090894

Academic Editors: Lubomira Gresakova and Emilio Sabia

Received: 12 August 2021 Accepted: 13 September 2021 Published: 17 September 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Secondly, we aimed to determine the effect of peanut skins on the chemical composition and quality of the eggs produced from layers fed a peanut skin-containing diet. Poultry feeding trials using carotenoid-rich feed ingredients such as tomato powder, alfalfa concentrate, and marigold extract demonstrate significant enrichment of egg yolk color intensity and carotenoid content in eggs produced from quail [8] and layers [9] versus conventionally fed hens. However, commercial use of these feeding programs is costly and often not viable due to the high cost of inclusion in the diets. Interestingly, studies have shown that hens fed a diet containing peanuts with the skin intact produced eggs enriched in yolk color (2-fold) and in β-carotene content conventional eggs [10]. For this reason, we aimed to determine the effect of feeding peanut skins or oleic acid on egg yolk color and/or chemistry in the eggs produced from hens fed a peanut skin or oleic acid-supplemented diet.

#### **2. Materials and Methods**

All animal research procedures used in these feeding trials were approved by the North Carolina State University Institutional Animal Care and Use Committee (IACUC #17-001-A).

#### *2.1. Experimental Design, Animal Husbandry, Dietary Treatments, and Hen Performance*

Two hundred 40-week-of-lay Hy-Line W36 hens were randomly assigned to one of 4 isonitrogenous (18% crude protein) and isocaloric (3080 kcal/kg) treatments, with 5 replicates per treatment, to meet and/or exceed the NRC requirements for layers. Hens were individually housed and fed *ad libitum* for 8 weeks one of the following dietary treatments: control conventional soybean meal + corn, 24% unblanched high-oleic peanut (HOPN), 3% peanut skin (PN Skin), or 2.5% food-grade oleic acid (OA)-supplemented diet. High-oleic peanuts were crushed using a roller mill into crumbles prior to inclusion in the finished HOPN diet. The OA diet was prepared by supplementing the control diet with 2.5% food-grade OA (Millipore Sigma, Burlington, MA, USA). Peanut skins were collected after the blanching process and were ground finely using a blender into a powder prior to inclusion in the diet. There were five replicates per treatment with hens individually housed in battery cages (each cage 12 inches wide × 18 inches deep × 18 inches height) in one room at the Chicken Education Unit, NC State University (Raleigh, NC, USA). Hens were provided feed and water *ad libitum* and 14 L:D 8 weeks. Finished feed samples were analyzed for aflatoxin and microbiological contaminants by the NC Department of Agriculture and Consumer Services, Food and Drug Protection Division Laboratory (Raleigh, NC, USA).

Body weights were recorded for each individual hen at week 1 and week 8, with feed weights recorded weekly. Shell eggs were collected, enumerated, and weighed daily. The total number of eggs produced per treatment was calculated for each experimental week and for the total 8-week feeding trial. The average feed conversion ratio (FCR) was calculated as total feed consumed over the 8-week feeding (kg)/dozens of eggs produced for each treatment group over the 8-week feeding trial.

#### *2.2. Egg Quality and Grading*

Bi-weekly DSM egg yolk color, Haugh unit (HU), albumen height, vitelline membrane strength, and USDA grade were determined bi-weekly with 15 eggs per treatment by randomly selecting 3 eggs from each replicate. Fresh shell eggs were collected on the day of quality assessment and USDA grading. Haugh unit values were determined using methods described by Haugh [11] and were recorded with the Technical Services and Supplies (TSS) QCD system (Dunnington, York, UK). The QCD system was calibrated to the DSM Color Fan consisting of a series of 15 colored plastic tabs with a range of yolk colors from light yellow to orange-red (color index 1 to 15) defined by Vuillemier [12]. In general, a texture analyzer (TA.XTplus, Stable Micro Systems Ltd., Surrey, UK) was used to measure the shell strength and vitelline membrane strength by the breaking strength using

a 5 kg load cell per the manufacturer's instructions (Stable Micro Systems Ltd., Surrey, UK) with measurements in grams of force. Vitelline membrane strength was determined using methods described by Jones et al. 2005 with a 2 mm/s test speed and 0.0001 kg trigger force [13]. Modified methods of Jones et al. 2002 were used to measure shell strength with a 2 mm/second test speed and a 0.001 kg trigger force [14].

#### *2.3. β-Carotene, Lipid Content, and Fatty Acid Analysis*

All experimental diets and eggs were analyzed for total cholesterol, crude fat, fatty acid, and β-carotene content in triplicate by an AOAC-certified lab, ATC Scientific (Little Rock, AK, USA), using AOAC-approved standard chemistry methods. Each egg sample was mixed for homogeneity in a whirl-pak® (Millipore Sigma, St. Louis, MO, USA) bag for 3 min using a Smasher™ Lab Blender (Weber Scientific, Hamilton, NJ, USA). Subsequently, all egg samples were frozen at −20 ◦C and stored frozen until chemical analysis within two weeks of collection. Frozen homogenous egg samples were shipped on dry ice overnight to the vendor for analysis within 2 weeks of collection. Lipid (total cholesterol, crude fat) and fatty acid analysis of homogenous egg samples and feed samples were analyzed using direct methylation methods as described by Toomer et al. [10]. Total cholesterol was measured as mg cholesterol/100 g sample weight (feed or egg), while crude fat was measured as percentage of gram crude fat/gram sample weight (feed or egg). Fatty acid content was measured as percentage of gram of fatty acid/gram total lipid content of the sample (feed or egg). Methods used to determine β-carotene content in eggs are detailed in the AOAC 958.05 [15] color of egg yolk method. Egg fat hydrolysis methods were determined using the AOAC method 954.02 [16]. Gross energy analysis of feed samples was performed by ATC Scientific using an adiabatic oxygen bomb calorimeter with standard methods.
