RESUMEN

From 84 to 93% of New Zealand's annual production from livestock is exported to over 100 markets throughout the world. This export dependence has produced production systems that are low-cost because the Mediterranean maritime climate allows animals to graze outdoors throughout the year without provision for housing and with minimal requirements for cropping, harvesting, and forage storage. These systems exploit the inherent tendencies for ruminants to have annual production cycles that can be synchronized to use the seasonal availability of pasture, but this means that processing facilities must handle peak supply for brief periods. Processing technology can reduce the impact of peaks in supply that may not match market demand. The disadvantages of seasonality in processing costs are outweighed by lower production costs, as well as by the opportunity to manage large numbers of animals per labor unit. Cooperative structures that are owned by livestock producers are a common feature, especially in New Zealand's dairy industry. This continued preference for cooperatives may reflect the need to have a guaranteed processor for a perishable product such as milk, as well as sharing the risk in an export industry that has scant control over prices received. In addition, management systems for ruminant livestock can only respond slowly to changes in market demand because their production cycles last at least 12 mo and only one or two offspring are produced in each cycle. Export marketing of livestock products is complicated by trade barriers and by dumping of subsidized surpluses. Negotiations to eliminate these practices may mean that livestock production systems in many countries will have to adopt some principles similar to those developed in New Zealand, not because of export dependence but because this dependence has created low-cost systems.

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RESUMEN

Three commercially available electronic lamb carcass grading probes (Hennessy Grading Probe, AUS-Meat Sheep Probe, Swedish FTC Lamb Probe) and one developmental probe (Ruakura GR lamb probe) were assessed for accuracy and suitability for use on-line on the lamb dressing chain for objectively classifying lamb carcasses. GR is the total tissue thickness over the 12th rib taken at a distance 11 cm from the mid-line, used to define fatness in lamb carcass grading in New Zealand. Probe measurements were compared with manually measured GR (sometimes used at present) and Toland probe measurements (total tissue depth between the ribs) for accuracy of predicting both GR on the right side of the carcass and also carcass water (indicating muscle) and fat content. Probes were tested on six occasions, each having approximately 50 lambs. All probes combined with carcass weight accounted for over 70% of the variation (R(2)) of GR right, with GR left accounting for 92% of the variation of GR right. Inclusion of a quadratic probe term was not quite as useful as inclusion of carcass weight for predicting GR right. The three commercial electronic probes individually when combined with carcass weight could account for 36-49% of the variation in the percentage of water and fat in the carcass, with the manual GR probe (right) on the chilled carcass accounting for 55% of the variation in water and 58% of the variation in fat percentages. Chilled carcass measurements are expected to give better results than readings on hot carcasses. The use of a quadratic probe coefficient instead of carcass weight with the probe readings gave similar accuracy of prediction of carcass composition. There was little difference between the two sides in the accuracy of prediction. Small differences were found between regressions relating probe readings to GR and composition for the different probing occasions. The electronic probe results from this trial are consistent with overseas results where probes are in use for objectively grading the carcasses of meat animals.

RESUMEN

Young bulls from an Angus yearling-weight selection herd (ASl) and from the contemporary control herd (ACO), differing in average slaughter weight by 16·8%, were allocated for slaughter on one or six occasions between 7·5 and 25 months of age. The M. longissimus lumborum from the left side of each animal was measured for cholesterol, fatty acid composition, and protein, fat and ash contents in both raw and cooked samples; the pH and tenderness were also recorded. All meat was generally lean, averaging 4% fat in raw samples and 2·4% fat in cooked samples. There was a trend, though not significant, for a slightly lower percentage of fat at a fixed age in raw and cooked meat from the AS] herd than from the A CO herd. There were no significant selection effects on cholesterol content or fatty acid content, in either raw or cooked meat samples. The pH was significantly, higher in meat from the ASl than the A CO herd, although the difference was small (0·11 units), and there were no significant herd differences in tenderness. Overall, the herd effects on chemical composition and tenderness were very small and unlikely to be detected by consumers.

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Three groups (n = 147) of New Zealand mixed breed lambs averaging 170 d of age and 31.7 kg in weight were killed after a diet of pasture to determine whether the total depth of soft tissues over the 12th rib 11 cm from the dorsal midline (GR) could be measured in live lambs with sufficient accuracy to warrant its use as a selection tool for breeding flock replacements. Relationships among live and carcass measurements and carcass chemical composition also were determined. An ultrasonic measurement of GR in the live lambs was a more accurate predictor of carcass GR (r = .87) and percentage carcass fat (r = .80) than was a measurement of GR made with a needle (r = .80 and .67, respectively). Both measurements were sufficiently accurate to permit culling of over-fat lambs from breeding flock replacement prospects. The best single indicator of percentage carcass fat (r = .87) was a shoulder fat measurement, followed closely by carcass GR (r = .85). Both were superior to USDA yield grade for estimating carcass chemical composition in these young, lightweight lambs. These two measurements also were most highly related to percentage carcass protein (r = -.78 and r = -.77, respectively). These results indicate possibilities for improving the method of evaluating the composition of U. S. lamb carcasses.

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Carcass data from more than 4,400 Southdown x Romney ewe and wether lambs collected over a 16-yr period were analyzed for the effects of sex, rearing status, and growth rate. Ewe lambs grew more slowly than wethers and had .78 kg less carcass weight at the same age. The carcass weight advantage for wethers was nearly all caused by heavier fat-free weight. Based on fat depths, the fat on ewe lambs was distributed in more anterior and ventral parts of the carcass relative to wether lambs. Lambs reared as twins had 1.73 kg less carcass weight and correspondingly reduced carcass measurements compared with lambs reared as singles. Sex and rearing status interacted for some traits. However, in no case was a significant sex difference reversed in single- and twin-related lambs. Growth rate effects were determined by regressing average change in carcass measurements on average carcass weight gain over a 5-wk period. When carcass weight remained constant over a 5-wk period, fat weight increased by .12 kg, fat-free weight and muscle measurements decreased, and bone lengths increased. For each kilogram of increase in 5-wk carcass weight gain, the marginal increase in fat weight was .41 kg and that of fat-free weight was .59 kg. At the average 5-wk carcass weight gain of 1.4 kg, fat and fat-free gains were As carcass weight gain increased above 1.4 kg, fat-free gain exceeded fat gain.

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Approximately 4,400 crossbred lambs from Southdown sires and Romney ewes were slaughtered at approximately 18, 23, and 28 wk of age over a 16-yr period. Live weights, carcass measurements, and chemical percentages were analyzed to estimate genetic and phenotypic parameters. Heritabilities of postweaning weights and gains were about .20. Heritabilities of fat and water percentages were about .35 adjusted for age. Heritability of kidney fat percentage was .53. Heritabilities of fat depth and muscle measurements ranged from .21 to .37. Crutch depth (h2 = .73) and cannon bone length (h2 = .74) were the most highly heritable carcass measurements. The genetic correlation between carcass fat and fat-free weight was .47 when lambs were slaughtered at a constant age. Fat-free weight was nearly uncorrelated with percentages of fat, water, and protein when lambs were slaughtered at the same age. Carcass measurements increased accuracy of selection for fat-free weight at a constant age very little compared with using only carcass weight. However, this does not mean that additional measurements are useless. The addition of carcass measurements to the selection criteria would result in correlated responses in chemical composition that more closely resembled direct selection for fat-free weight. Carcass weight would be of little value when used by itself to reduce fat weight adjusted for carcass weight. Direct measurement of carcass composition resulted in 1.6 to 2.6 times more predicted response for reduced fat weight than any combination of carcass weight and one fat depth measurement.

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Left sides of 36 bulls, 22 cows, 57 steers and 38 heifer carcasses were weighed hot (HCWL) and were probed with the Hennessy Grading Probe (HGP) at five sites to give four subcutaneous fat depths, two M. longissimus dorsi depths and one total tissue depth measurement. A fat depth (GR) over the 10th rib was also measured by ruler probe. The left sides were later separated by knife into saleable eat (90% visual lean), fat trim and bone. Probe readings of subcutaneous fat thickness at the fatter rump sites (BF, 5-7 cm lateral to the perianal region over the M. biceps femoris; SC8, 8 cm lateral to the prominence of the sacral crest) were smaller than ruler measurements at the same sites. Probe eye muscle depth measurements were smaller than measurements taken at the same site by ruler. The BF measurement taken by probe, combined with HCWL, gave the best prediction of percentage fat trim (RSD = 2·0% for steers and 2·2% for heifers) and edible meat yield (RSD = 2·0% for steers and 2·6% for heifers) in the left sides of all the measurements studied, either singly or in combination. A major problem was to find a measurement site where subcutaneous fat was not removed from some carcasses during hide removal.

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One-hundred-and-twenty lambs were divided into three equal groups which were subjected to head electrical anaesthesia before bleeding. The normal group was stunned and bleeding was initiated within 5 to 8 s. The light/normal group was partially stunned and then treated as the normal group after a delay of 10s. The double stunned group was electrically anaesthetised, allowed to recover and then restunned and bleeding was initiated within 5 to 8 s. The light/normal and double stunning procedures increased the incidence and severity of carcass blood splash compared with normal stunning but the increase was less than that sometimes seen in normal mobs of head-stunned sheep and which occurs for unknown reasons.

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Five hundred and fifty-nine Southdown-Romney cross lambs were used in a comparison of the efficiency of bleeding animals slaughtered by one of three different methods. The main comparison was between spear stuck lambs that had been electrically stunned by either head application or a head-back method. In addition, some unstunned lambs were slaughtered by the traditional New Zealand gash cutting method, no longer used by industry but known to produce well bled carcasses. There was no difference in blood obtained during a 120-s bleeding time between the unstunned and head stunned lambs. For the head-back stunned lambs little, if any, of the blood not collected at bleeding remained in the carcass after dressing despite the fact that these animals released only 46% of the weight of blood recorded from the head stunned lambs during the bleeding time. The head-back stunning method markedly decreased the incidence of carcass blood splash in comparison with the splash observed in lambs stunned by the head application method.

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Three-hundred-and-three lambs were divided into three equal groups. Half the lambs in each group were not weaned before slaughter and the weaned half were slaughtered a week later. Lambs in one group were head stunned electrically before slaughter; in the second group lambs were stunned with a captive bolt pistol and in the third group they were percussion stunned before slaughter. Carcasses, gall-bladders, hearts and duodenums were inspected for blood splash after slaughter. A few small haemorrhages were detected in 57% of the electrically stunned lambs, in 30% of the captive bolt stunned lambs and in only 16% of the percussion stunned animals. Although no splash of commercial significance was found in any carcass, 25% of the electrically stunned lambs had detectably splashed carcasses, whilst only 1% of percussion-stunned lambs had splashed carcasses with captive bolt stunned lambs being intermediate in carcass splash incidence. These results show that stunning method affects the incidence of blood splash.

RESUMEN

A study based on 84 electrically stunned lambs showed that those gash stuck (transverse incision of the extended neck which almost simultaneously severs the trachea, oesophagus, common carotid arteries and jugular veins and the spinal cord at the occipito-atlantal junction; Blackmore & Newhook, 1976) immediately after removal of the electrical applicator had a lower incidence of blood splash than lambs gash stuck 5-8 sec r stunning. Lambs whose throats were cut immediately before the application of the electrical current had the lowest incidence of blood splash. None of the splash observed was of commercial significance. Systolic blood pressure recordings were made on a further 12 lambs of a similar age, 10 of which were electrically stunned and two shot with a captive bolt pistol. Blood pressure changes observed were related to the blood splash results obtained in the first trial. Electrical stunning raised blood pressures to an average of 3·5 times normal in lambs allowed to recover from stunning. A further seven young unweaned lambs which were electrically or percussion stunned showed a similar pattern of blood pressure change to that reported for older lambs following stunning, except that lower maximum pressures were reached. The authors interpret the results of the present trials as indicating that the application of electrical current to the heads of lambs results in damage to small vessels prior to the elevation of blood pressure. This damage may become apparent in the dressed carcass and organs as small haemorrhages. The subsequent rise in blood pressure following stunning then exacerbates the leakage of blood into tissues and it becomes more apparent in the form of discrete haemorrhages or blood splash.

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