Investigating the effect of different levels of peanut waste feed on performance, nutrient digestibility, rumen antioxidant activities, and feeding behavior of Lori-Bakhtiari fattening lambs

Introduction: In recent years, the increasing demand for feed to increase livestock production and the climate problems have led to a significant increase in the price of feed, especially protein-based feed. The proper processing and use of alternative and cheap by-products therefore increases livestock production and contributes to the country's livestock feed shortage. Peanut waste is one of such by-products. Peanut, with the scientific name of Arachis hypogaea, belongs to the Legume family, which is also called groundnut or pistachio. Peanuts are classified as an oil seed because of their high oil content and are grown in much of the world and are rich in protein and fiber. The crude protein (CP) digestibility of peanuts is reported to be about 70%, but its fat digestibility varies based on the fatty acid structure. Peanuts contain anti-nutritional factors such as phenolic compounds (procyanidins) and phytic acid, which reduce the bioavailability of other nutrients, but this amount is lower in peanuts than in legumes such as soybeans. After oil extraction, peanut meal is produced, which is used as a source of protein in animal feed. By-products of peanut cultivation include almond husk, almond outer shell, thin skin on almond kernel, and peanut waste feed (PWF). Peanut shells are produced in large quantities annually and are discarded without any specific use or economic value. About 34 -35 grams of shells are produced per kg of peanut kernel. The annual production of peanut shells in the world is about 740 thousand tons as waste from the peanut processing industry. In a study, the CP, neutral detergent insoluble fiber (NDF), crude fat, total digestible nutrients, and condensed tannins of peanut shells were reported to be 22.7, 32.6, 19, 87.8, and 15.6% dry matter (DM), respectively. Phenolic compounds in peanut shells, such as tannins, may have positive effects on animal performance. In another study, the CP, crude fat, and total carbohydrate contents of peanut kernel shells were determined to be 12, 16, and 72% (DM basis), respectively, and the total phenolic content was determined to be 140-150 mg/g DM. In a study, supplementing goat diets with 25 and 50% peanut shells on a DM basis increased DM intake and daily weight gain, while also reducing fecal microbial load. In Iran's northern provinces, a significant area of land is devoted to peanut production. Peanuts are mostly consumed as nuts in Iran, so unfortunately, accurate amounts of peanut waste production are not available. The PWF is a new food waste produced in Iran and consists of the almond shell (hard shell), kernel waste, and the thin brown shell around the kernel. So far, few studies have been conducted to investigate the effects of feeding diets containing PWF on ruminant nutrition. Therefore, the purpose of this research was to investigate the effects of different levels of PWF on performance, apparent nutrient digestibility, rumen antioxidant activity, and nutritional behavior of Lori-Bakhtiari fattening lambs.
Materials and methods: In this research, 28 fattening lambs with an average age of 120±6 days and an average live weight of 30±2.50 kg were used in a completely randomized design with four treatments and seven replications. The experimental diets were PWF included in the diet at levels 0 (control), 4, 8, and 12% DM and were fed to lambs for 60 days. Diet nutrient digestibility was measured using acid-insoluble ash as an internal marker on the 43^rd day of the experiment. Determination of the total rumen antioxidant capacity was performed on the 45^th day of the experiment and 3 hours after morning feeding. The feeding behavior of fattening lambs was determined visually on the 47^th day of the experiment for 24 hours.
Results and discussion: The contents of DM, crude protein, crude ash, crude fat, neutral detergent fiber, acid detergent fiber, non-fibrous carbohydrates, and total phenolic compounds of PWF were 92±2.22, 22.8±0.46, 16.5±0.26, 1.28±0.016, 25.7±0.53, 19.1±0.33, 34±0.57, and 21.5±0.35% DM, respectively, and metabolizable energy content was 2.4±0.075 Mcal/kg DM. Using different levels of PWF in the diet had no significant effect on nutrient intake, growth performance parameters, nutrient digestibility, and eating and rumination behavior (minutes per day) of fattening lambs (P>0.05). By increasing the level of PWF in the diet up to 12%, the total antioxidant capacity of the rumen increased, but the chewing behavior (minutes per day) in fattening lambs decreased compared to the control treatment (P<0.05).
Conclusions: The results generally indicated that the use of peanut waste up to 12% DM is recommended in the diet of fattening lambs.