Behaviour, growth performance and pork quality of pigs differing in porcine stress syndrome genotype receiving dietary magnesium aspartate hydrochloride

Frequency of behavioural activities, growth performance and pork quality were determined for pigs with homozygous-normal (NN) or heterozygous-carrier (Nn) genotypes for porcine stress syndrome receiving dietary supplementation of magnesium aspartate hydrochloride (MAH). One hundred and forty-two pigs, 67.2 ± 1.2 kg, were assigned by genotype and gender to one of three dietary treatments. The pigs were fed a conventional cereal-based pelleted diet (Control), supplemented with a long-term, low-level (LL-MAH; 5 mg kg −1 BW for 43 ± 3 d) or short-term, high-level (SH-MAH; 40 mg kg −1 BW for 7 d) of MAH before slaughter. Supplementation of MAH did not significantly affect the behaviour of pigs before or after transport for slaughter with the exception of SH-MAH-fed pigs showing a higher (P < 0.05) frequency of pre-transport aggression. Pigs with the Nn genotype were, in general, more active 1 h before slaughter showing a higher frequency (P = 0.001) of aggression. Average daily gain of LL-MAH-fed pigs was higher (P < 0.05) than for those pigs fed the Control and SH-MAH diets. Pigs receiving both levels of MAH had lower (P < 0.05) longissimus thoracis (LT) muscle lean depth. In terms of pork quality, there were significant diet-by-genotype interactions. For pigs with the NN genotype, SH-MAH caused higher (P < 0.05) ultimate pH, lower muscle temperature and lower shear value of the LT. For pigs with the Nn genotype, MAH at both levels lowered (P < 0.05) glycogen content and subjective structure score of the LT, but ultimate pH, muscle temperature and lactate content were higher (P < 0.05) than those of Controls. Efficacy of MAH supplementation to pigs appears to be highly dependent on diet and genotype.