Dietary guanidinoacetic acid increases the longissimus dorsi muscle depth of finishing pigs without requiring a higher standardised ileal digestible methionine + cysteine concentration

The objective of this study was to evaluate the interaction of guanidinoacetic acid (GAA) with standardised ileal digestible methionine + cysteine (SID Met + Cys) levels in finishing pig diets on the performance, carcase characteristics, pork quality, blood variables, gene expression of creatine transporter (SLC6A8) and oxidant and antioxidant action. The experimental design (n = 32) was in randomised blocks arranged in a 2 × 2 factorial scheme, consisting of two levels of guanidinoacetic acid (0.00% and 0.05%) and two levels of SID Met + Cys (0.44% and 0.50%). There was no interaction of SID Met + Cys and GAA levels on the performance variables, carcass characteristics, pork quality and creatine transporter gene expression (p ≥ .05), except for plasma lactate dehydrogenase (LDH) (p = .016), wherein at the highest SID Met + Cys level the GAA supplementation (0.05%) showed lower plasma LDH concentration in relation to non-supplementation. Longissimus dorsi muscle depth (MD) (p = .001) showed an isolated effect for the evaluated GAA levels, in which the supplementation increased the MD. Blood urea presented an isolated effect (p = .040) for SID Met + Cys levels, showing lower plasma concentration for the highest dietary level. It was concluded that GAA does not require a higher intake of SID Met + Cys in finishing pig diets and its supplementation improved the depth of Longissimus dorsi muscle, without changing the performance, meat quality and gene expression of the SLC6A8 transporter in the liver.Highlights Higher levels of SID Met + Cys reduced homocysteine concentration, and GAA supplementation reduced plasma lactate dehydrogenase concentration at higher dietary SID Met + Cys level. GAA supplementation improves the depth of Longissimus dorsi muscle and did not affect the post-mortem glycolysis. Higher concentration of SID Met + Cys in finishing pig diets do not affect the gene expression of the creatine transporter (SLC6A8) in the liver