Effect of different dietary levels of DL-methionine and the calcium salt of DL- 2-hydroxy-4-[methyl] butanoic acid on the growth performance, carcass yield and meat quality of broiler chickens Einfluss unterschiedlicher Zulagen von DL-Methionin und dem Kalziumsalz von DL-2- Hydroxy-4-[Methyl] Butter

Introduction Methionine is the first limiting amino acid in common broiler chicken and turkey diets. Dietary supplementation with methionine increases protein utilisation and consequently feed utilisation and improves performance. A study of fast-growing turkeys, conducted by KUBIŃSKA et al. (2014), demonstrated that immune system function can be modulated by increasing dietary methionine concentrations. However, if the dietary supply of methionine is low, the body synthesises adequate quantities of the semi-essential amino acid cysteine from methionine and both amino acids participate in protein synthesis (GARDZIELEWSKA et al., 2005). According to many authors, methionine as well as methionine + cysteine levels in poultry diets are too low (WALLIS, 1999; CAFÉ and WALDROUP, 2006). Recent studies have shown that a dietary methionine deficiency significantly inhibits broiler growth, compared to a deficiency of other essential amino acids (CAREW et al., 1997; ELWERT et al., 2008), whereas excess methionine intake decreases feed intake, thus reducing the body weight gains of birds (HESABI et al., 2006; CENGIZ et al., 2008). The above indicates that adequate dietary methionine levels are required to increase lean carcass content and to reduce abdominal fat deposition in broilers (LIU et al., 2010). In all poultry production systems, feed cost is the largest single cost item accounting for up to 70–75% of total production costs per bird. Thus, it is important to find cost-effective feed ingredients for poultry. The optimum level and source of methionine have important implications for the growth performance of broilers. Economically optimal methionine levels in poultry diets should be determined in view of the maximum performance of birds, current feed prices and the income from meat sales. Over the last few decades, DL-methionine (DLM) and DL-2-hydroxy-4-[methyl] butanoic acid (DL-HMB), known as liquid methionine hydroxy-analogue free acid (MHA-FA), have been the main sources of methionine in poultry diets. Liquid MHA-FA contains approximately 12% water and 88% MHA molecules, mostly monomers (65%) as well as dimers and trimers (23%). The calcium salt of DL-HMB has recently been introduced to the feed industry. Methionine hydroxy-analogue calcium salt (MHA-Ca) is a powder containing at least 84% monomeric hydroxyanalogue, 14% calcium and 2% water (LEMME et al., 2007). According to the literature, the average relative bioavailability of MHA products compared to DLM is approximately 75–80% on an equimolar basis (BAKER, 2006; SAUER et al., 2008). Whereas L-methionine and D-methionine are actively absorbed (transported against a concentration gradient), MHA is absorbed by the H+ dependent system which is slower than the Na+ system in DLMet (MAENZ and ENGELE-SCHAAN, 1996a). MITCHELL and LEMME (2008) demonstrated that the use of MHA products in less efficient polymeric forms is the major reason for their lower bioavailability relative to DLM forms. According to Europ.Poult. Sci., 79. 2015, ISSN 1612-9199, © Verlag Eugen Ulmer, Stuttgart. DOI: 10.1399/eps.2015. 114