P. D. Warriss

Meat science : an introductory text

1. Producing and Eating Meat 2. The Growth and Body Composition of Animals 3. The Chemical Composition and Structure of Meat 4. The Slaughter of Animals 5. Post-mortem Changes in Muscle and its Conversion into Meat 6. Meat Quality 7. The Effects of Live Animal Handling on Carcass and Meat Quality 8. Post-mortem Handling of Carcasses and Meat Quality 9. Meat Hygiene, Spoilage and Preservation 10. Animal Welfare 11. The Improvement of Carcass and Meat Quality by Genetic Selection 12. Measuring the Composition and Physical Characteristics of Meat 13. Assessing Eating Quality.

The handling of cattle pre-slaughter and its effects on carcass and meat quality

Abstract Almost all cattle are eventually slaughtered for meat. Because the slaughtering industry is becoming centralised into fewer, larger plants, marketing times have increased, particularly for animals sold through live auctions or those reared under extensive systems. During marketing, cattle are subjected to various stressors which elicit specific behavioural and physiological responses. Typical stress responses such as elevation of heart rate and body temperature and increased circulating corticosteroid levels are seen. The natural patterns of behaviour of cattle, particularly their following and herding instincts, can be exploited to facilitate handling. Increased use of young bulls for beef production in many countries has highlighted the importance of good design of handling facilities. Pre-slaughter handling can affect both carcass and meat quality. Losses in carcass yield are caused by both mobilisation of tissues to provide energy for maintaining the vital functions of the body and the dehydration which often accompanies the inevitable period of food and water deprivation together with the stress of transport. The size and onset of these losses are as yet poorly defined for cattle, possibly because of the large influence of variation in environmental conditions. Reported losses in yield after a 48 h fast range from

Changes in the blood biochemical and haematological profile of neonatal calves with age.

Fourteen calves were used to investigate the changes from birth to 83 days of age in the concentrations of serum albumin, alkaline phosphatase, beta-hydroxybutyrate, plasma cortisol, serum creatine kinase, creatinine, iron, plasma fibrinogen, serum gamma-glutamyl transferase, plasma glucose, haptoglobin, serum non-esterified fatty acids, total protein, transferrin, triglycerides, urea and gamma globulin; the haematological variables measured were: basophils, eosinophils, haematocrit, haemoglobin, lymphocytes, mean cell haemoglobin, mean cell haemoglobin concentration, mean cell volume, monocytes, band neutrophils, neutrophils, platelets, red blood cells and white blood cells. The changes are presented as a series of graphs and the values are discussed in relation to the published reference ranges for adult cattle. Two populations of calves were identified which gave rise to a bimodal distribution for some of the variables. Differences in haematocrit, haemoglobin and red blood cell counts were apparent at birth, with raised values for these measurements being associated with an increased white blood cell and neutrophil count between three and 27 days of age.

Relationships between subjective and objective assessments of stress at slaughter and meat quality in pigs.

A study was carried out to relate subjective and objective measures of stress at slaughter and meat quality in pigs. Thirteen slaughter plants were visited. The systems used for handling the pigs pre-slaughter and the levels of stress experienced by the animals were subjectively assessed. The sound level immediately before stunning was also measured. Generally, systems that were rated as being most stressful also produced higher levels of sound, probably because of the vocalisations of the pigs. As the size of plant increased, there was a tendency for the level of stress, and the recorded sound level, to increase. This appeared to be because larger plants operated faster and were more likely to use restraining conveyors supplied by races to handle the animals before stunning. The restraint associated with these seems stressful to pigs. Five plants were selected for further study. Two had been assessed as having handling systems that produced a low level of stress in the pigs, one as having a system producing a medium level, and two as having poor systems producing high levels of stress. Blood samples were collected at exsanguination, and meat quality was assessed. As the level of subjectively assessed stress experienced by the pigs increased, so did the average blood levels of lactate and creatine phosphokinase (CPK). There was also a progressive increase in the potential incidence of pale, soft, exudative (PSE) and dark, firm, dry (DFD) meat in the plants using more stressful handling systems. Additionally, there were positive relationships between sound level and lactate and CPK, and sound level and indices of poorer meat quality. Cortisol concentrations were not different in pigs killed in the different systems and probably reflect events earlier in the handling process, such as in transport and lairage, rather than the stress experienced immediately before stunning. The overall conclusion was that subjective assessments of the stress suffered by pigs correlate well with objective measures and that higher stress levels are associated with poorer meat quality.

THE EFFECTS OF AGE AT SLAUGHTER, GENOTYPE AND FINISHING SYSTEM ON THE BIOCHEMICAL PROPERTIES, MUSCLE FIBRE TYPE CHARACTERISTICS AND EATING QUALITY OF BULL BEEF FROM SUCKLED CALVES

Muscle fibre characteristics and biochemical properties of muscle recovered from young bulls of two genotypes (Aberdeen Angus × and Charolais ×), reared on two different diets (silage-based and barley-based) and slaughtered at varying ages between 10 and 19 months of age were established. These analyses were restricted to samples ofm. longissimus lumborum (LI) recovered at 48 h post mortem, vacuum packed and stored at 2°C for 14 days. Biochemical measurements included intramuscular fat content, intramuscular collagen content and its solubility, haem pigment concentration, sarcomere length and myofibril fragmentation. Muscle fibre type was classified according to the contractile nature of thefibres and their metabolic properties. Intramuscular fat content increased ( P v. 295·8 mg/g dry matter, P P v. 3·59 mg/g for Angus × and Charolais × bulls; P × 0·01) and diet (3·97 v. 3·62 mg/g for bulls given barley and silage; P P P P v. 49·3%; P v. 18·9%; P P P

Effect of lairage time on levels of stress and meat quality in pigs

A total of 1580 pigs killed in three slaughter -plants were held in lairage for ≥ 1 h, 3 h or overnight before slaughter. Blood samples were collected at exsanguination and subsequent carcass and meat quality monitored. Longer lairage reduced stress levels based on the concentration of cortisol, lactate and creatine phosphokinase in the blood. It also reduced the prevalence of pale, soft, exudative (PSE) but increased the prevalence of dark, firm, dry (DFD) meat. Additionally, it produced progressively greater amounts of skin damage caused by fighting between unfamiliar pigs and an overnight lairage reduced carcass yield and backfat thickness. The overall conclusion ivas that a period of between 1 and 3 h rest in lairage was optimal. There was no evidence that leaner, potentially more stress-susceptible pigs reacted differently from fatter, potentially more stress-resistant animals with regard to the effects of lairage time.

Factors affecting the prevalence of foot pad dermatitis, hock burn and breast burn in broiler chicken

1. Standardised data on flock husbandry were recorded on 149 broiler farms during the 4 d prior to slaughter. 2. Birds were examined at the slaughterhouse for contact dermatitis lesions. Foot pad dermatitis score (FPDS) and hock burn score (HBS) were measured on five point scales. Carcase rejection data were also collected. 3. The mean percentage of birds in each flock with: moderate or severe foot lesions was 11·1% (range 0–71·5%); moderate or severe hock burn was 1·3% (range 0–33·3%); and, breast burn was 0·02%. 4. A general linear model was developed to examine factors associated with mean flock FPDS. Assuming a linear relationship, within the range of data collected and with all other factors remaining the same, every 1% increase in the proportion of Genotype A birds in the flock was associated with an increase in mean FPDS of 0·003, every one-point increase in litter score was associated with a 0·326 increase in mean FPDS and every one-point increase in flock mean HBS was associated with a 0·411 increase in mean FPDS. Flock mean FPDS was associated with feed supplier and was higher in winter. 5. The general linear model developed for flock mean HBS, found that every one-point increase in mean FPDS increased mean HBS by 0·090, every one-point increase in litter score increased HBS by 0·119 and, every 1% increase in small/emaciated birds decreased mean HBS by 0·333. Reduced HBS was also associated with increased final litter depth, younger slaughter age and an increased percentage of dietary wheat. For every 1% increase in Genotype A birds, a decrease in flock mean HBS of 0·003 would be expected. 6. An effect of hatchery was also identified.

Effects on cattle of transportation by road for up to 31 hours

The physiological and behavioural effects on cattle of transporting them for periods of 14, 21, 26 and 31 hours, including a stop for a rest and drink on the lorry after 14 hours, were studied in 120 transported animals and 48 control animals. The physiological measurements indicated that a journey lasting 31 hours was not excessively physically demanding, but many of the animals chose to lie down after approximately 24 hours. The animals that lay down had higher plasma cortisol levels than those that remained standing. Many animals chose not to drink during the rest stop. Physiological measurements made after the journeys indicated that 24 hours in lairage, with hay and water freely available, allowed the animals to recover substantially, although not completely, irrespective of the journey time.

Meat quality in pigs subjected to minimal preslaughter stress

The experiment compared meat quality in carcasses from pigs subjected to the absolute minimum of stress preslaughter with that from carcasses of pigs subjected to simulated commercial handling. A total of 120 pigs (85 kg) were used. They were a commercial hybrid and were processed in six equal batches. The minimal stress group were slaughtered with as little stress as possible. The simulated commercial handling group were mixed and transported for 2hr (80 km) and lairaged for 30 min. Simulated commercial handling increased plasma cortisol, plasma lactate, CPK and beta-endorphin. Muscle temperature measured in the m. longissimus dorsi (LD) at 45 min increased as did the ultimate pH in the m. adductor (AD). Overall eating quality was not affected. There were batch affects on most variables. Males were leaner and produced meat that had greater abnormal fat odour, darker cooked colour, poorer pork flavour, lower overall acceptability and was tougher.

Effects of stocking density, flock size and management on the welfare of laying hens in single-tier aviaries

1. Management practices, stocking rate and flock size may affect laying hen welfare but there have been few replicated studies in commercial non-cage systems that investigate this. This study used a broad range of physical and physiological indicators to assess the welfare of hens in 36 commercial flocks. 2. Six laying period treatments were examined with each treatment replicated 6 times. It was not possible to randomly allocate treatments to houses, so treatment and house were largely confounded. 3. Three stocking rates were compared: 7 birds/m2 (n = 2450), 9 birds/m2 (n = 3150) and 12 birds/m2 in either small (n = 2450) or large (n = 4200) flocks. In addition, at 12 birds/m2, in both small and large flocks, birds were subjected to either standard (SM) or modified (MM) management. MM flocks had nipple drinkers and no nest-box lights. 4. Bone strength, fracture incidence, heterophil:lympocyte (H:L) ratio, live weight, organ weights, serum creatine, serum osmolality, muscle pH and faecal corticosterone were measured on samples of birds at the end of the rearing period and at the end of lay. During the laying period, mortality, production and integument condition were recorded at regular intervals. 5 Birds housed at 9 birds/m2 had higher mortality than birds housed at 12 birds/m2 by the end of lay, but not higher than birds housed at 7 birds/m2. Birds housed at 7 and 9 birds/m2 had lower percent liver weight, and worse plumage condition than most of the 12 bird/m2 treatments. Modified management tended to improve plumage condition. There were no clear effects of flock size on the welfare indicators recorded. 6. At the end of the rearing period fracture incidence was almost negligible and H:L ratio was within a normal range. 7. By the end of lay fracture incidence was 60% and H:L ratio was high, with no treatment effect for either measure. This, together with information on faecal corticosterone, feather loss and mortality, suggests that the welfare of birds in all treatments was relatively poor by the end of lay.