Indicadores de bem-estar e qualidade da carne de suínos pesados submetidos a diferentes períodos de descanso

Abstract

Intensive genetic selection of pigs for higher growth rate and lean meat yield has resulted in fast-growing animals that the cutting and processed meat industry has been slaughtering at higher final weights. In tropical climates, this accelerated growth, combined with higher slaughter weight, increases susceptibility to thermal and social stress during pre-slaughter handling, reinforcing the need to reassess lairage protocols at slaughter plants, integrating animal welfare indicators and technological meat quality traits. The aim of this dissertation was to integratively evaluate the influence of different pre-slaughter lairage durations on welfare and on meat and carcass quality in pigs, combining a systematic review with meta-analysis (Chapter 1) and a controlled experiment (Chapter 2). In Chapter 1, a systematic review was conducted according to PRISMA 2020 guidelines, with searches in Scopus and Web of Science and selection of 13 experimental studies that isolated pre-slaughter lairage time as the main independent variable. Data was extracted on physiological stress indicators and on meat and carcass quality responses. Random-effects models indicated that moderate increases in lairage duration significantly reduced cortisol (SMD = −0.42; p = 0.001), lactate (SMD = −0.31; p = 0.018) and CK (SMD = −0.27; p = 0.032). Meta-regression identified an approximate interval of 1–3 h as more favorable to attenuate stress and improve early quality parameters, whereas prolonged lairage periods (> 6–8 h) were associated with a higher risk of DFD meat and skin lesions. In Chapter 2, 180 heavy pigs (130 ± 5.0 kg, halothane-negative genotype) were assigned to four lairage times (0, 30, 60 and 120 min). Physiological variables (blood glucose, lactate, cortisol, blood gases), thermal variables (surface temperature and respiratory rate), behavioral measures and meat quality traits were evaluated and analyzed using mixed models, mean comparisons and regression (α = 0.05). Blood glucose showed a quadratic response, with the lowest estimated value at around 60 min, suggesting better metabolic stabilization in this interval. Serum cortisol concentrations also fitted a quadratic model, but with a monotonically decreasing pattern between 0 and 120 min. Surface temperature assessed by thermography showed a significant interaction between lairage time and assessment time, with stability at 30 and 60 min and progressive increase at 120 min. Muscle pH at 45 min post-mortem differed between treatments, but all values remained within the expected range for this time point, with no relevant effect on 24 h pH. Cooking loss decreased as lairage time increased. Integration of the literature evidence with the experimental study indicates that, in heavy pigs reared in tropical climates, a pre-slaughter lairage period of about 60 min represents a balance point between physiological recovery, welfare and meat quality, whereas 120 min may provide modest additional technological gains at the cost of greater surface heating and stronger dependence on strictly controlled environmental and management conditions.