Poultry offal meal is a suitable source of protein for ruminants (El-Sayed et al., 1997). Particularly, the heat treatment applied to poultry by-products during processing makes the final meal a valuable source of rumen undegraded proteins for ruminants.
Degradability and digestibility
The effective crude protein degradability of poultry by-product meal is lower than that of soybean meal (Silva et al., 1999; Souza et al., 2000; Kamalak et al., 2005) and rapeseed meal (Mustafa et al., 2000), with a ratio of 0.7-0.8, and much lower than that of whole cottonseed (ratio of 0.6-0.7) (Ilghami et al., 2008). However, it is higher than that of meat and bone meal (Klemesrud et al., 1997), feather meal (Klemesrud et al., 1998), blood meal and corn gluten meal (Bonhert et al., 1998). Protein digestibility is also lower than that of soybean meal but higher than that of meat and bone meal (Klemesrud et al., 1997). Additional processes can modify protein degradability: it increased after enzymatic or NaOH treatment of spent hen meal (Kim et al., 2003), and decreased when sulfite liquor is applied to the carcasses of laying hens (Wilson et al., 1998).
As a consequence of its low degradability, dietary use of poultry by-product meal increases the duodenal flow of amino acids (Bonhert et al., 1998; Bonhert et al., 1999). However, it may be necessary to add a source of soluble nitrogen in the diet to maintain microbial synthesis in the rumen (El-Sayed et al., 1997).
Poultry by-product meal can be used as a protein supplement for dairy cows. Daily amounts of 0.5 to 0.7 kg have been recommended (Schroeder, 1999). Including up to 1 kg/day in a maize silage diet increased milk yield and improved milk composition (Gonzalez et al., 2007). However, lower inclusion rates may be necessary due to palatability issues. The use of poultry by-product meal in prepartum diets is also possible and allows normal reproductive performance and milk production. (Yazdi et al., 2009). It is also better to include poultry by-product meal in a total mixed ration rather than adding it to the diet (Schroeder, 1999).
Beef cattle and growing cattle
Poultry by-product meal fully replaced soybean meal (on a protein basis) in the diets of steers without negative effects on consumption or diet digestibility (Silva et al., 2002) and with similar (Bonhert et al., 1998) or higher (Klemesrud et al., 1998) results for daily gain and feed efficiency.
Adding poultry by-product meal in the diets of finishing steers increased metabolizable protein supply better than urea supplementation. The difference in protein efficiency is due to the amount of metabolizable methionine. However, when using poultry by-product meal, tryptophan may be the first limiting amino acid for steers (Klemesrud et al., 1997).
In Holstein calves, supplementation with poultry by-product meal at 10% resulted in higher growth performance and economic efficiency (Al-Saiady et al., 1997).
Poultry by-product meal was found to be a useful and cheaper protein substitute for soybean meal in rations for growing lambs. It improved daily gain without altering feed conversion efficiency, and decreased feed cost when added to whole chopped sugarcane-based diets (Lallo et al., 1994). Including poultry by-product meal up to 10% in high-concentrate rations enhanced growth performances and feed efficiency (Al-Saiady et al., 1996; Alshaikh et al., 1997) and increased energy retention (Kraidees et al., 1996).
Other poultry processing by-products
Wastewater from poultry processing can be purified by the dissolved air floatation technique, and the resulting sludge can be further processed and dried, yielding a product called ‘secondary protein nutrients’ which contains about 47% protein (DM basis). This product can be included in diets of steers in order to supply up to 25% of supplemental nitrogen without a negative impact on performances. It can also be included at up to 40% of the supplemental N in meat goat rations (Freeman et al., 2008).
The substitution of 60% of soybean meal protein by protein of a coextruded blend of the hard tissue fraction from spent hens with soybean hulls increased DM intake and nitrogen retention in growing goats (Freeman et al., 2009).