Due to their high fibre content, peanut hulls can be used as a roughage source in ruminant diets, particularly for beef cattle, sheep and goats.
Digestibility and energy values
With their high fibre content, peanut hulls have a high potential as a low-quality roughage source, especially as an alternative to hay in hot and dry climates (Palmer, 2010; Aregheore, 2001). Their low bulk density makes them difficult to transport and many processors grind or pellet them. However, decreasing the particle length of the peanut hull decreases its effectiveness as a fibre source (Utley et al., 1973).
Peanut hulls have a very low digestibility. In vitro DM digestibility ranges from 16 to 25% (Barton et al., 1974), and in vivo OM digestibility is about 20% (Alibes et al., 1990). Many studies have tried to improve the digestibility of peanut hulls by chemical treatment with sodium chlorite, ammonia, sodium hydroxide, chlorine gas, calcium hypochlorite, and other more exotic chemicals. For instance, alkali treatment (6 kg NaOH per 100 kg of hulls) of peanut hulls was shown to increase the level of potentially digestible dry matter, while alkali treatment of fine-ground hulls reduced it in diets for steers (Maglad et al., 1986). Treatment with urea or fungus (Trichoderma viride) increased in vitro digestibility in sheep (Abo-Donia et al., 2014). However, these treatments may be costly and/or difficult to use due to the dangerous nature of the chemicals and lack of care in their use. Furthermore, many studies stress the resistance of peanut hulls to chemical treatments used to improve digestibility (Hill, 2002).
Peanut hulls are probably usable as a source of roughage for dairy cows, provided that no aflatoxin contamination is detected. However, only one study concerning peanut hulls was found. Different fibre sources were compared for lactating dairy cows, including a 50:50 mixture of peanut hulls and ground cardboard included at 20% of the diet. This mixture gave a similar response as the other fibre sources tested (cottonseed hulls and ground cardboard) (Van Horn et al., 1984).
Average daily gain and carcass characteristics were similar for steers fed diets containing from 5 to 30% peanut hulls, and slightly higher than for steers fed diets without peanut hulls (substituted by ground maize grain). However, concentrations of between 10 and 20% peanut hulls appeared to be better for promoting body weight gains compared to 0 or 30% peanut hull diets. Intake increased proportionately to the level of hulls in the diet (Utley et al., 1972). Other studies have shown that, if properly processed, and fed at an appropriate level in the diet, peanut hulls can be effectively utilized by all classes of beef cattle (Hill, 2002).
Compared to other crop residues (maize cobs or cassava peel), the inclusion of 30% of peanut hulls in maize based diets supplemented with urea enabled acceptable body weight gains, although slightly lower than with the other residues (31 vs. 41 g/day; Aregheore, 1996). In growing lambs, diets including 25% of urea-treated peanut hulls (4 g/kg DM urea added to the ensiled hulls 6 weeks before use) were supplemented with peanut cake, cotton seed cake or fish by-products. They were utilized more efficiently by sheep (higher feed intake, daily weight gain and final body weight) than the untreated basal diets (Abdel Hameed et al., 2013). When compared with no treatment or a urea-based treatment, a diet based on peanut hulls treated with fungus offered to Ossimi rams led to increased feed intake, nutrient digestibility, and nitrogen balance (intake and retention) (Abo-Donia et al., 2014).
Compared with other crop residues (maize cobs, cassava peel, cocoa pod husks), the inclusion of 30-35% of peanut hulls in the diet of goats led to similar digestibility, voluntary feed intake and growth rate (Aregheore, 1995; Aregheore, 1996). In Zambia, during the hot dry season, growth rate obtained with goats fed up to 46% of peanut hulls, in a maize based diet supplemented with urea, was comparable to that from Gwembe valley goats and Small East African goats during favourable climatic conditions (Aregheore, 2001). The voluntary intake and growth rate showed that, if the residues are properly processed, they can meet the nutritional requirements of livestock during adverse weather conditions.