Search

The aim of this experiment was to compare the effects of electrical stimulation and lamb age on the retail colour stability of lamb meat. Poll Dorset Merino crossbred lambs that were 5 months (‘suckers’, SU) and 12 months (‘carryovers’, CO) finished on the same green annual pasture were slaughtered at a commercial abattoir. Half of the carcasses in each age group (10) were either electrically stimulated (ES) or not stimulated (NES) post-dressing with a commercial high voltage electrical stimulation system. Luminescence (L), hue angle (indication of redness), chroma (intensity), and oxy/met (a measure of browning) values were measured at 0 h (0 days), 21 h (0.86 days), 93 h (3.88 days), and 166 h (6.91 days) after meat had been cut 1 day after slaughter, over wrapped, and put under simulated retail display conditions. Three muscles, m. longissimus thoracis et lumborum (LL), m. gluteus medias (GM), and m. rectus femoris (RF), were measured in this way. A linear mixed model was used to fit a repeated-measurements model to the light measurements of L, hue angle, chroma, and oxy/met. Oxy/met rate of change was compared by fitting splines to predict the time required for oxy/met to reach an arbitrary benchmark value of 3. Colour and rate of colour change during display were affected by both age class and electrical stimulation but these effects depended on the muscle. The LL was the darkest (lowest L) and reddest (lowest hue angle), whilst RF was the most stable in colour (lowest rate of change for oxy/met) of the 3 muscles tested. Age class had a greater effect on oxy/met rate of change for the LL and GM compared with RF. Oxy/met of LL changed more rapidly for CO than SU lambs. ES increased the time for oxy/met to reach 3 in RF and GM for SU only but did so for both age groups in LL. ES decreased this time in RF and GM for CO. CO meat contained a higher concentration of myoglobin than SU meat. Negative effects of electrical stimulation on colour stability are more likely to occur in older lambs and in the GM and RF rather than in the LL.

Combined actions of nutrition and genetic regulation of the growth rate of lambs as well as the physical, biochemical, and eating quality characteristics of their skeletal muscle were assessed in a major field experiment. Data arising were collated and integrated to consolidate findings made at the farm, animal, tissue, cellular, and gene expression levels. At the farm level, increased nutrient availability significantly increased the growth rate of crossbred lambs and increased the growth advantage resulting from the use of sires with high estimated breeding values (EBV) for growth. In contrast, the extra depth of the M. longissimus thoracis et lumborum (EMD) arising from sires with a higher EBV for this trait was constant irrespective of nutrition. Ewe liveweight and body condition were critical in determining the pre-weaning nutrition and growth of lambs, with the LOW plane of nutrition causing stunting of forelimb bones and changes to the allometric growth coefficients for carcass lean and fat. The EBV of the sire for muscling (PEMD) influenced several non-muscling traits, and interactions with nutrition suggested that on HIGH nutrition, absorbed nutrients were partitioned away from wool and fat accretion and towards protein accretion in lambs having superior muscling genetics. Expression levels of known myogenic factors in muscle, together with a suite of peptides and proteins whose identity and levels were determined by proteomic screening, contributed to improved understanding of the mechanisms underpinning nutritional and genetic regulation of skeletal muscle development. The study revealed the need for caution in the use of indirect markers of growth or composition, with their usefulness being constrained if the localisation of the response to selection is specific to parts of the carcass where the selection had initially been concentrated. As well, the possibility that much of the variation explained by potential physiological markers can be accounted for by non-invasive measures of growth and fatness currently used by Australian farmers must be considered.

This paper provides an introduction to the special edition of the Australian Journal of Agricultural Research dedicated to an integrated research program to understand the effects of genetic selection for live animal traits (growth, muscle, and fatness) that determine carcass and meat attributes. Combined with this are the effects of nutritional status of the dam and growing lamb. The reasons for, and general approach of, the research is outlined.

Ninety crossbred (Large White × Landrace) female pigs were used to compare the effects on ultimate pork quality of different magnesium (Mg) compounds [magnesium aspartate (MgAsp) and magnesium sulfate (MgSO4)], Mg dose (1.6 and 3.2 g elemental Mg), and Mg supplementation period (2 and 5 days) in pigs subjected to an acute stressor pre-slaughter. Pigs fed the Mg-supplemented diets had lower muscle lactic acid concentrations at 24 h post-slaughter than pigs fed the control diet. There were no significant differences in muscle glycogen concentrations in the Longissimus thoracis (LT) at 5 min, 40 min, or 24 h post-slaughter between the control and Mg-supplemented diets. Pigs fed the Mg-supplemented diets produced less pale colour pork (i.e. darker colour) and had reduced drip loss and reduced incidence of pale, soft, exudative (PSE) pork in the LT muscle compared with pigs fed the control diet. Within the Mg diets, pigs fed the MgAsp-supplemented diet produced less pale LT muscle colour than pigs fed the MgSO4-supplemented diet. There were no significant differences in LT pork quality parameters (colour and percent drip loss) regardless of whether the high or low Mg dose or the 2- or 5-day supplementation period was used. This experiment has shown that the use of dietary MgAsp supplementation at a dose of 1.6 g elemental Mg (20 g MgAsp) for 2 days prior to slaughter significantly improved pork quality and reduced the incidence of PSE pork.

Forty-eight crossbred (Large White × Landrace) boars were used in a 2 × 2 factorial design to determine the effects of mixing unfamiliar pigs during lairage and the use of electric goads just prior to slaughter on muscle glycogenolysis and subsequent pork quality. The treatments included 2 mixing treatments (familiar pigs kept together during lairage and unfamiliar pigs mixed during lairage) and 2 handling treatments [minimal handling and negative (electric goad) handling pre-slaughter]. Pigs mixed during lairage had lower muscle glycogen and lactic acid at 5 min, 40 min, and 24 h post-slaughter than familiar pigs kept together during lairage. Mixing of unfamiliar boars also resulted in higher ultimate muscle pH, a higher incidence of dark, firm, dry (DFD) pork, and a lower incidence of pale, soft, exudative (PSE) pork compared with familiar pigs kept together during lairage. The use of an electric goad prior to slaughter did not affect muscle glycogen in mixed pigs, but in unmixed pigs there were large numerical diffferences in glycogen concentrations. The negatively handled unmixed pigs had a trend for lower glycogen concentrations which did not reach significance. This was probably due to the small sample size. However, pigs negatively handled pre-slaughter had higher lactic acid concentration at 5 min post-slaughter compared with minimally handled pigs. This experiment has demonstrated that mixing of unfamiliar boars can have a major impact on pork quality, resulting in a high incidence of DFD pork and a reduced incidence of PSE.

Thirty-six crossbred (Large White × Landrace) boars were used to investigate the effect of positive and negative handling of pigs on-farm over a period of 5 weeks, and the effect of minimal and negative handling just prior to slaughter at the abattoir on the level of stress and meat quality of the carcass. There was no significant difference in adrenal gland weight and plasma cortisol concentration measured at slaughter between pigs negatively and positively handled on-farm. Pigs negatively handled on-farm had lower muscle glycogen 5 min and 40 min post slaughter in the Longissimus thoracis (LT) but muscle paleness and percentage drip loss of the LT were similar compared with pigs positively handled on-farm. Pigs negatively handled at the abattoir had lower muscle glycogen 5 min post slaughter in the LT; however, muscle paleness, percentage drip loss, ultimate pH, and incidence of pale, soft, exudative meat were similar compared with pigs that were minimally handled at the abattoir. This study has shown how the interaction between pigs and humans on-farm can influence the pig’s ‘stress’ response to pre-slaughter handling and, potentially, meat quality.