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The aim of this work was to evaluate the growth performance, carcass characteristics, 12th rib tissue composition, haematological and serum biochemical parameters, as well as the presence of gossypol residues in the meat of Santa Inês lambs fed cotton crop by-products. For an experimental period of 90 days, 24 intact male Santa Inês lambs (bodyweight (BW): 20.6 ± 1.9 kg; 4 months old) were fed a 50 : 50 forage : concentrate diets fed ad libitum. Chopped Coast cross (Cynodon dactylon (L.) Pers) hay was used as forage. The animals were then allocated into four treatments, according to the cotton crop by-product included in the concentrate formulation: Control (CON) – No cotton crop by-product used in formulation; Whole cottonseed (WCS); Cottonseed cake (CSC); and Cottonseed meal (CSM). The animals were weighed and blood collected every 15 days. At the end of the experimental period, the lambs were slaughtered and the evaluations of carcass characteristics, 12th rib tissue composition and presence of gossypol residues in the meat were carried out. Dry matter intake was higher (P < 0.05) for the diets containing cotton crop by-products, but BW gains were not different (P > 0.05). Despite these results the animals fed the highest level of gossypol (WCS) had lower (P < 0.05) carcass yield resulting in lower (P < 0.05) carcass weight, suggesting a possible negative effect of gossypol on carcass development. Serum urea was elevated on all treatments including CON, otherwise haematological and biochemical parameters were within reference ranges. No gossypol residues in meat were detected by the method used here, which had a minimum detection limit of 20 ppb. It is concluded that the cotton crop by-products may have impaired carcass production but did not leave gossypol residues in lamb meat.

Gossypol easily pairs with lysine side chains and enzymes involved in the cellular growth process. The effect of gossypol (a compound present in cotton co-products) in ruminant metabolism and meat quality is not yet clear. This study was undertaken in order to evaluate the effects of cotton co-products in lamb muscle proteome. Twenty-four Santa Inês ram lambs, 5-months old (20.6 ± 1.9 kg), were randomly assigned to four treatments: control (without cottonseed), whole cottonseed, cottonseed meal and high oil cottonseed meal. At 95 days into the experiment, lambs were slaughtered and samples from Longissimus dorsi were collected. Proteins were extracted and analyzed by 2-D electrophoresis. Spots showing a significant effect from the treatment (the "treatment effect") and present in more than 90 % of the samples were identified using mass spectrometry. Cotton co-products decreased the abundance of aldehyde and malate dehydrogenases, creatine kinase M-type and Adenosine triphosphate (ATP) synthase. They also increased four proteins related to muscle contraction. Thus, feeding cotton co-products to lambs changed the abundance of important muscle proteins. A cotton co-product diet induced a negative impact on the energy supply of muscle cells and, consequently, the abundance of ATP dependent proteins (contractile apparatus) increased, probably in order to offset and maintain muscle function. These proteomic changes can promote our understanding of alterations in the sensorial properties of meat due to cotton co-product diets in further investigations.

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