Peanut meal is a good source of protein for ruminants and there are no restrictions on its use, provided that it is not contaminated by aflatoxins. It is a potential alternative to soybean meal or cottonseed meal. Non-dehulled peanut cake has a high fibre content that makes it a useful corrective for cattle feeding grass that is low in fibre (Göhl, 1982). However, it has been observed that it was preferable to mix peanut meal with other protein sources for better growth and milk yield (Martin, 1991; Sheely et al., 1942). It is possible that the sometimes contradictory results obtained with peanut meal are caused by undetected aflatoxin contaminations.
Peanut meal is not widely exported and its use for ruminants in developed countries has declined, but it is widely used as a protein source in tropical countries where it is an indigenous crop (Blair, 2011). In India, for instance, peanut meal is fed to cattle, buffalo, sheep and goats (NDDB, 2012). In studies conducted in these countries, peanut meal is sometimes the protein source used as the standard in comparative studies. Recent studies involving peanut meal in ruminant diets are rarely available since developed countries stopped using it, although in Brazil researchers are showing renewed interest in this resource.
Aflatoxin contamination has been shown to be lethal, or at least very detrimental to cattle, particularly to young stock. Administration of 1 mg/kg of aflatoxin B1 in the diet of 6-month old steers for 133 days resulted in death or in reduced live weight gains. Administration of 0.2 mg/kg aflatoxin B1 in the diet of calves also reduced live weight gains. Dairy cows fed diets containing 13-20% aflatoxin-contaminated peanut meal showed significant reductions in milk yield (McDonald et al., 2002).
Digestibility and degradability
Peanut meal is highly digestible in ruminants, with OM digestibility values above 80% (Sauvant et al., 2004). Its energy value is about 89-92% that of soybean meal (Sauvant et al., 2004; NRC, 2001). Peanut meal protein is highly degradable (N effective degradability comprised between 72 and 90%).
Peanut meal was recommended in the USA in the 1940s for its palatability and nutritive value, which was described as comparable to that of other oil meals with similar protein contents (Sheely et al., 1942). A more recent trial found that a diet containing 21% peanut meal fed to dairy cows, during periods of heat stress, resulted in better milk yield and DM intake than that obtained with a diet containing 16% peanut meal or a soybean meal-based control diet (Hamid et al., 1989). In the UK, several trials in the 1970s concluded that peanut meal was a suitable protein supplement for dairy cows fed grass silage. Dairy cows fed high digestibility perennial ryegrass silage ate more silage and gave more milk when supplemented with peanut cake, rather than barley (1 kg supplement per 10 kg milk) (Castle et al., 1976).
In Brazil, crossbred dairy cows grazing Guinea grass and supplemented with peanut cake (from biodiesel production), totally replacing soybean meal, had DM intakes, digestion, blood parameters and feeding behaviours similar to cows fed soybean meal (Neto et al., 2015). Peanut cake replaced up to 100% soybean meal in a supplement, given to lactating crossbred cows at pasture, without altering their feeding behaviour or physiological parameters (Costa et al., 2015). In The Gambia, lactating cows grazing local pasture supplemented with peanut cake, at 425 or 850 g/day for the last 3 or 5 months of the dry season, showed increases in milk yield, in growth rate of the sucking calves, and decreases in losses of cow live weight (Little et al., 1991).
In India, pre-ruminant calves were reared successfully on a calf starter in which peanut meal replaced fish meal, with only a slight decrease in average daily gain and feed efficiency (Sahoo et al., 1998).
Early experiments in the USA demonstrated that peanut meal was an excellent protein supplement of high palatability and valuable for growing animals, fattening steers and breeding animals (Sheely et al., 1942). In Brazil, a more recent trial showed that the replacement of soybean meal with peanut cake, from biodiesel production, at up to 100% in the diet of feedlot-finished young bulls did affect carcass traits and beef quality, although it modified the fatty acid profile of the longissimus thoracis, with a beneficial increase in the levels of polyunsaturated fatty acids (Correia et al., 2016). In Chile, finishing beef heifers fed a diet containing 21% peanut cake had daily live weight gain and carcass results similar to those obtained with a diet containing 17% soybean meal (Rojas et al., 2011). In Mauritius, crossbred bulls fed urea-molasses and either leucaena or peanut cake (2% live weight or ad libitum) did not consume the groundnut cake well and performance with leucaena was better than with groundnut cake (Hulman et al., 1978). In Australia, however, the supplementation of weaned steers grazing native pastures with leucaena, peanut meal (680 g/d), or a combination of both, improved the body weight performance of the steers over the post-weaning winter and the following autumn, the best performance being obtained with the leucaena/groundnut combination (Addison et al., 1984).
In India, there have been early attempts at treating peanut meal with formaldehyde to protect its protein in the rumen. In calves fed a diet containing 48.5% peanut meal, replacing half of untreated peanut meal with formaldehyde-treated peanut meal (1.5 g/100 g protein) resulted in better N retention (Gupta et al., 1984).
In India, sheep fed a basal diet of wheat straw supplemented with either sunflower cake or peanut cake (at the maintenance requirement for protein) had similar intakes of various nutrients (Dutta et al., 2002). In Brazil, peanut cake added to the diet of lambs, partially or totally replacing soybean meal, did not affect the physical and chemical characteristics of the meat. However, the total replacement of the soybean meal altered the proximate composition and fatty acid profile of the meat (Bezerra et al., 2016), in ways similar to those observed in beef cattle (Correia et al., 2016). Another Brazilian trial reported that peanut meal fully replaced soybean meal in the diets of crossbred lambs with no effect on intake and health parameters (Duarte et al., 2015). In Nigeria, a comparison of peanut cake and palm kernel cake, fed ad libitum as supplements to West African Dwarf sheep, found that peanut cake resulted in much lower daily gains and feed efficiency than palm kernel meal (Martin, 1991).
In India, goats fed a basal diet of wheat straw supplemented with either sunflower cake or peanut cake (at the maintenance requirement for protein) had similar intakes of various nutrients (Dutta et al., 2002). In Cameroon, West African Dwarf goats, fed fresh Guatemala grass and various combinations of cassava flour and peanut cake, had maximum live weight gains with either 200 g/d cassava + 100 g/d peanut cake or 200 g/d cassava + 150 g/d peanut cake (Njwe et al., 1989). In Ethiopia, Somali goats fed Hyparrhenia rufa hay, supplementation with a mixture of peanut meal and wheat bran improved feed intake, DM and protein digestibility, and N retention (Betsha et al., 2009). Two trials in Brazil led to mixed conclusions: partial substitution of soybean meal with peanut meal in the diets of crossbred kids reduced intake and daily gain (Silva et al., 2015), but it had no effect on carcass characteristics and quality, and on the fatty acid profile of the meat (Silva et al., 2016).