Peanut skins can supply both protein and energy to ruminant diets, but their high tannin content is detrimental to cattle performance when they are included above 10% in beef cattle diets and above 16% in dairy diets. It is necessary to raise the protein content of the diets using natural or artificial sources of nitrogen to overcome the binding effects of peanut skins tannins and to prevent protein deficiencies that can cause severe depressions in performance and even death (Hill, 2002). In lambs, peanut skins could be included at up to 20% without adverse effects (Abdelrahim et al., 2012).
Peanut skins can be used in diets for lactating cows without impairing milk performance, but should be limited to about 16% of the diet, and diets should exceed the recommended minimum protein content. Higher inclusion rates of peanut skins caused a decline in ruminal ammonia and protein digestibility, probably related to the formation of indigestible tannin-protein complexes (West et al., 1993).
Several experiments in the USA concluded that peanut skins could be utilized to feed dairy and beef cattle provided that the diet contains enough protein, usually exceeding requirements. Feedlot cattle can be given high protein diets containing up to 10% peanut skins or 15% ammoniated peanut skins, or 15% peanut skins with urea. Grazing cattle can consume high-protein forages such as rye, ryegrass, or wheat supplemented with peanut skins and maize fed in equal portions at about 2 kg/d (Hill, 2002). Feedlot heifers fed 10% peanut skins showed depressed protein digestibility and feedlot performance: the average daily gain with 10% skins was half that of the gain obtained with the control diet. However, feedlot steers fed 9% peanut skins maintained growth. This inconsistency appears to be related to the amount of consumed tannins relative to the amount of consumed protein (McBrayer et al., 1983). Steer calves fed pellets made of Bermuda grass and 10% peanut skins gained 27% faster than control animals with not difference in feed intake and feed efficiency. However, levels higher than 5% decreased pellet durability and reduced the acceptability of the pellet for feeding and mechanical handling (Utley et al., 1985). In feedlot steers, increasing dietary protein level to 16%, in 15% peanut skin diets, using soybean meal or a soybean meal-urea combination, was effective in overcoming the detrimental effects of peanut skin tannins (Hill et al., 1986a). Ammonia treatment of peanut skins prior to feeding may provide a method of increasing their feeding value, while eliminating the need for additional supplemental protein (Hill et al., 1986b). Increasing dietary urea was not effective in overcoming detrimental effects of peanut skin tannins on digestibility and performance of feedlot steers fed diets containing 15% peanut skins (Hill et al., 1987). In finishing steer diets including 15% soybean hulls, peanut skins could be substituted for 50% of the soybean hulls where the diet contained 10.5% protein, and they could completely replace soybean hulls where the diet contained 15.5% protein (Utley et al., 1993).
In Gulf Coast ewe lambs fed peanut skins up to 40% dietary level, peanut skins could replace a portion of maize and soybean meal without any adverse effects on carcass characteristics or lambs performance, though the rib eye area was greater in lambs fed the control diet or 20% peanut skins, than in lambs fed 40% peanut skins (Abdelrahim et al., 2012).