The influence of pre-slaughter stress on the meat quality and carcase yield of prime lambs

Summary

​Understanding the impact of acute and chronic stress incurred during the pre-slaughter period is important to maximise lamb meat quality and yield as well as maintaining high animal welfare.

This study utilised 2877 lambs of the Meat and Livestock Australia Genetic resource flock. Plasma indicators of acute and chronic stress were quantified at slaughter and analysed for their association with meat quality and carcass yield traits. Production factors had the largest impact on indicators reflecting acute stress, feed deprivation, dehydration, muscle activity and damage, the majority of which were elevated above normal range at slaughter.

Phenotypically leaner lambs also demonstrated greater fat metabolism and lower rates of glycogen turnover at slaughter. Loin ultimate pH demonstrated a positive association with slaughter levels of plasma glucose and lactate, indicating that acute pre-slaughter stress has an impact on glycogen turnover and ultimate pH in lamb. 

Kill order was associated with an increase in loin Warner Bratzler shear force, which indicates that a greater exposure to stress decreases tenderness. Feed deprivation up to 48 hours under resting and commercial conditions resulted in up to 35% higher adipose tissue response in Merino sired lambs compared to Terminal sired lambs, a response that was also influenced by selection for increased genetic growth and leanness. 

Feed deprivation beyond 36hrs had a negative impact on ultimate pH of the M. Semitendinosus in Merino lambs and caused a 3% reduction in carcass weight.  Further work is required to understand methods of mitigating acute pre-slaughter stress in order to minimise high ultimate pH and reduced tenderness. In addition, it has been demonstrated that Merino genotypes have a significantly higher fat turnover in response to feed deprivation and stress, and indicates that shorter duration of curfew and lairage may be beneficial in minimise carcass losses and meat quality.