The basal toughness of unaged lamb.

Identification of the commencement of aging in relation to the rigor process was determined on lamb loin muscles by injecting a zinc-TRIS solution, which inhibits meat aging, into the muscle over the period when the pH was falling. Aging was evaluated by measuring the tenderness of cooked meat samples using a MIRINZ tenderometer. When zinc was injected into muscle above pH 6·5, the sarcomeres shortened and the cooked meat had an average shear force of 19 kgF (shear force is the force required to shear through at 1 cm cross-section sample). When sinc was injected into the muscle at pH values below 6·5 the sarcomeres did not shorten, and down to the ultimate pH, the shear force remained at approximately 15 kfF. Aging did not take place pre-rigor. The same relationships occurred for electrically stimulated muscle. The data indicate that the basal shear-force value of lamb loin prior to aging, i.e. the basal toughness level, is 15 kgF.

The effect of growth rate and ultimate pH on meat quality of lambs.

Entire male Romney lambs (n = 60) were grown slowly (67 g/day) and slaughtered at 14 months of age at an anticipated carcass weight of 18 kg. Another group of ram lambs (n = 15) from the same genetic background (born 7 months later) were grown rapidly (162 g/day) for 7 months and slaughtered at the same time and at a similar carcass weight. Preslaughter shearing (20 days prior to slaughter) and swim washing (3 times) were variously imposed upon the 14-month old lambs to give them a graded preslaughter stress. The lambs were head-only electrically stunned and slaughtered. Dressed carcasses were electrically stimulated at 20 min post mortem for 90 s at 14·3 pulses/s, 1·8-2 A and 1130 V peak, then held at 12°C for 2 h and frozen so that the deep leg reached -4°C in 12 h. The ultimate pH was measured for the longissimus dorsi, and loin samples were assessed by tenderometer and a sensory panel. The groups with the greatest stresses imposed had the highest ultimate pH. The most tender meat came either from carcasses with an ultimate high pH greater than 6·3 or from young lambs with an ultimate pH from 5·5-5·7. While 7-month old lambs were slightly more tender than the 14-month old lambs of iso pH, the 14-month old lambs of high pH were the most tender. This suggests that age-related connective tissue effects were minimal for the loin. The shear force values and taste panel tenderness scores were linearly related. When the shear force and panellists' tenderness scores were expressed in relation to ultimate pH, there was a decreased acceptance of meat with a moderate ultimate pH between 5·8 and 6·0. Panel texture assessments showed a less clearly defined, but statistically significant decrease in acceptance at pH 5·8-6·0. Other sensory attributes of flavour, juiciness and aroma were uniform across the whole ultimate pH spectrum.

Onset of insensibility at slaughter in calves: effects of electroplectic seizure and exsanguination on spontaneous electrocortical activity and indices of cerebral metabolism.

Cerebral venous and femoral arterial blood samples were collected from 21 young calves either during electrical stunning and recovery or electrical stunning and slaughter by carotid severance or slaughter without stunning. The blood samples were analysed for PO2, PCO2, pH, glucose and lactate. The results were compared with simultaneous recordings of spontaneous electrocortical (ECOG) activity. Calves subjected to head-only electrical stunning and slaughter became permanently insensible at the time of the stun. The six calves slaughtered without stunning lost sensibility within 10 seconds. One calf, in which a clot formed in the carotid arteries inhibiting bleeding, maintained some evidence of cortical activity beyond 52 seconds; this was high amplitude low frequency activity and analysis by Fast Fourier Transform showed sensibility was not regained. In the remaining calves the ECOG activity was lost on average within 49 +/- 3.5 (SEM) seconds after slaughter. The cerebral extraction of metabolites increased after carotid severance, indicating inadequacy of cerebral bloodflow after slaughter. No correlations were found between indices of cerebral metabolism and the time of loss of cortical function.

The cumulative effect of nutritional, shearing and preslaughter washing stresses on the quality of lamb meat.

Carcass and meat characteristics were measured in lambs exposed to combinations of nutritional, shearing and preslaughter washing treatments. Both shearing and a low plane of nutrition reduced carcass weight (P < 0·001) and increased carcass leanness (P < 0·01). Tenderness and colour of M. longissimus dorsi were not significantly influenced by treatments even though there were substantial responses in meat pH. In lambs subjected to all three stressors pH was 0·40 units above control levels, significantly more than the sum of individual effects (P < 0·05), demonstrating a cumulative effect of stressors on meat pH.

Electroencephalographic studies of calves associated with electrical stunning, throat cutting and carcass electro-immobilisation.

Electroencephalographic (EEG) recordings were made on 34 calves (two days to six weeks old, 30-50 kg) during the slaughter process. The calves, supported in a V-shaped box or polypropylene net, were either head-only electrically stunned (50 Hz, 1.0 A) across the head and allowed to recover, head-only stunned followed by throat cutting or head-only stunned followed by throat cutting and electro-immobilisation. All time intervals were measured from the commencement of the stun. The electro-immobilisation (80 V peak, 14.3 Hz, 5 ms square wave) at 15-26 seconds post-stun was applied through electrodes attached to nose and anus, for periods ranging from 5-60 seconds. The head only stun produced an elevated EEG amplitude of the electroplectic fit which lasted approximately 34 seconds followed by a quiescent period before the EEG amplitude again became elevated above normal. A normal pre-stun pattern was not reached until many minutes had elapsed. Following the stun, the forelegs were usually flexed and then extended, gradually becoming part of the paddling movements commencing as early as eight seconds post-stun. Such movements were taking place while the animal was still stunned. With a head-only stun followed by throat cutting, the electroplectic fit was reduced to about 23 seconds and the amplitude of the EEG fell to about 10 microV after 50-73 seconds and breathing was inhibited for at least 20 seconds after stun commencement. If inadvertently only one carotid was severed, the EEG did not fall as rapidly as when both carotids were cut. The increase in amplitude of the EEG tracings was caused by stunning but the reduced duration of this increase in calves in which the throat was cut, suggests that there is an impairment of recovery of brain function from the moment of cutting and recovery of sensibility is unlikely. In reviewing the criteria of sensibility, we believe that insensibility can be presumed to continue from stun initiation, through the throat cut until the EEG falls below 10/microV provided that there is no resurgence of activity and the EEG amplitude continually falls rapidly enough. By this criteria, calves which are electrically stunned and rapidly exsanguinated remain permanently and irreversibly insensible. The addition of at least 15 seconds electro-immobilisation causes an even more rapid fall in the amplitude of the EEG (<10 microV at 50 seconds) making insensibility more certain as well as abolishing animal movement.

The effect of electrical stunning and slaughter on the electroencephalogram of sheep and calves.

To study the application of electroencephalography (EEG) for the assessment of insensibility during stunning and slaughter, recordings were made on sheep that were slaughtered by throat cutting, electrically stunned head-only and allowed to recover, electrically stunned head-only followed by throat cutting or electrically stunned head-to-back. The same experiments were repeated on calves (1-6 weeks old) except some calves were stunned and allowed to recover before final stunning and throat cutting. After the throat cut, sheep became insensible (i.e. EEG < 10 µV) at 8-22 s but the calf EEG did not fall below 10 µV until 79 s after the cut. With head-only stunning/recovery, high-amplitude EEG waves (electroplectic fit) continued for 47 s (sheep) and 33 s (calves) post stun. A quiescent period followed, which then developed into a period of moderate-amplitude EEG signals, so that, at 50 s post stun, the EEG usually exceeded 50 µV and often had bursts of 150 µV activity. After head-only stunning/throat cutting, the electroplectic fit was shortened (39 s in sheep, 23 s in calves) and the EEG took at least 50 s to fall below 10 µV. With sheep stunned head-to-back, which stops the heart, and thus should cause immediate, permanent insensibility, the EEG took longer to fall below 10 µV (52 s) than after throat cutting. These results suggest that electrical stunning of sheep and calves causes a prolonged increase in the post-stun EEG amplitude. Therefore, during slaughter, stunned animals have larger amplitude EEG signals than unstunned animals, and EEG criteria developed for judging the sensibility of unstunned animals cannot be used for those that are electrically stunned.

Post-mortem changes in cytoskeletal proteins of muscle.

Progressive changes have been identified in the solubility of muscle-cell proteins during post-mortem muscle ageing, particularly the cytoskeletal proteins, desmin and connectin. Ox sternomandibularis muscle was sampled immediately post mortem and up to six days later. It was homogenised and separated into three salt-soluble fractions: phosphate soluble, concentrated KI soluble and guanidine-HCl soluble. Proteins in each fraction were analysed on sodium dodecylsulphate polyacrylamide gels. Changes reported previously by other authors were confirmed. In addition desmin, which was restricted to the guanidine fraction, disappeared, apparently due to proteolysis during storage. Connectin was also partly lost from the guanidine fraction, possibly through increased solubility in the KI fraction. In this respect an unidentified polypeptide of 110 000 D appeared during storage. Desmin extracted from ox muscle was partially purified and identified by amino acid analysis. It apparently occurs in vivo as a network of linked collars around the Z-discs and its loss during post-mortem storage probably accounts for the ease with which stored muscle disintegrates into individual myofibrils on homogenisation. The disintegration of the cytoskeletal network can account for the post-mortem changes in the physical properties of muscle for the increased tenderness after cooking of stored meat. However, factors other than those related to changes in cytoskeletal proteins are responsible for the toughness of cooked, cold-shortened muscle since cold shortening prior to storage did not affect the distribution of proteins among the three salt fractions, nor the patterns obtained in gel analyses.