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Genetic parameters for carcass composition and meat quality traits were estimated in Scottish Blackface sheep, previously divergently selected for carcass lean content (LEAN and FAT lines). Computerized X-ray tomography (CT) was used to obtain non-destructive in vivo estimates of the carcass composition of 700 lambs, at ca. 24 weeks of age, with tissue areas and image densities obtained for fat, muscle and bone components of the carcass. Comprehensive measures of meat quality and carcass fatness were made on 350 male lambs, at ca. 8 months of age, which had previously been CT scanned. Meat quality traits included intramuscular fat content, initial and final pH of the meat, colour attributes, shear force, dry matter, moisture and nitrogen proportions, and taste panel assessments of the cooked meat. FAT line animals were significantly ( P , 0·05) fatter than the LEAN line animals in all measures of fatness (from CT and slaughter data), although the differences were modest and generally proportionately less than 0·1. Correspondingly, the LEAN line animals were superior to the FAT line animals in muscling measurements. Compared with the LEAN line, the FAT line had lower muscle density (as indicated by the relative darkness of the scan image), greater estimated subcutaneous fat (predicted from fat classification score) at slaughter, more intramuscular fat content, a more 'yellow' as opposed to 'red' muscle colour, and juicer meat (all P , 0·05). All CT tissue areas were moderately to highly heritable, with h 2 values ranging from 0·23 to 0·76. Likewise, meat quality traits were also moderately heritable. Muscle density was the CT trait most consistently related to meat quality traits, and genetic correlations of muscle density with live weight, fat class, subcutaneous fat score, dry matter proportion, juiciness, flavour and overall liking were all moderately to strongly negative, and significantly different from zero. In addition, intramuscular fat content was positively genetically correlated with juiciness and flavour, and negatively genetically correlated with shear force value. The results of this study demonstrate that altering carcass fatness will simultaneously change muscle density (indicative of changes in intramuscular fatness), and aspects of intramuscular fat content, muscle colour and juiciness. The heritabilities for the meat quality traits indicate ample opportunities for altering most meat quality traits. Moreover, it appears that colour, intramuscular fat content, juiciness, overall liking and flavour may be adequately predicted, both genetically and phenotypically, from measures of muscle density. Thus, genetic improvement of carcass composition and meat quality is feasible using in vivo measurements.

This study examined the temporal relationships between behavioural activity and hormones associated with stress in gilts farrowing in two environments. Thirty-one Large White × Landrace gilts with indwelling jugular catheters were blood sampled daily (08.00 and 16.00 h) from 10 days before their expected parturition date (EPD). Five days before EPD they were moved to either a farrowing crate (C) with no bedding, or a pen (P) (2·5 m × 3·0 m) with straw provided and were blood sampled daily at 08.00, 12.00 and 16.00 h. Around 12 h before the onset of farrowing an extension was fitted to the catheter and blood samples were taken remotely at 30-min intervals. The posture of the gilts was recorded using 5-min scan samples over the 24 h pre-farrowing. The proportion of scans standing (an index of activity) was strongly affected by time (P < 0·001) with peak levels at approximately 8 h pre-farrowing in both treatments, and by treatment (0·25 v. 0·33 (s.e.d. 0·03) for C and P gilts respectively; P < 0·05). Plasma cortisol concentrations also increased before farrowing (P < 0·001) reaching a peak at 12 to 6 h pre-farrowing. Crated gilts had higher cortisol concentrations than, penned gilts (overall mean 41·5 v. 30·7 (s.e.d. 3·8) [μg/l for C and P gilts respectively; P < 0·05) at 24 to 12 (P < 0·05), 12 to 6 (P < 0·01) and 6 to 2 (P < 0·05) h pre-farrowing. Plasma ACTH concentration showed a similar pattern to cortisol over the pre-parturient period, peaking at 12 h pre-farrowing in both treatments (time: P < 0·001); crated gilts had significantly higher concentrations of ACTH at 6h pre-farrowing only (P < 0·05). Plasma β-endorphin concentrations also showed a gradual rise (P < 0·001) towards parturition; however no treatment differences were seen. These results suggest that the pituitary-adrenal (PA) axis is stimulated during pre-farrowing activity irrespective of farrowing environment. Crates, without bedding, further stimulate the PA axis over the pre-farrowing period perhaps by preventing nest-building. The rise in Q-endorphin may be involved in an endogenous defence against parturition pain.

ContentsSows are routinely housed in behaviourally restrictive crates when giving birth. In the UK there has been considerable public concern over the use of these parturition (or farrowing) crates. In attempting to objectively assess the stress experienced by sows in farrowing crates it has been necessary to consider the potential inter-relationships between behaviour, stress and the physiology associated with parturition. Evidence from behaviour and the hypothalamic-pituitary-adrenal (HPA) axis suggests that farrowing crates elicit a stress response, indicated by raised plasma cortisol, by interfering with pre-parturient maternal behaviour (nest-construction). Cortisol concentrations, however, also rise during parturition irrespective of whether sows are housed in crates or in pens that allow greater behavioural freedom, which may indicate that parturition itself has stress-inducing aspects. The hormone oxytocin, released from the posterior pituitary is fundamentally involved in the parturition process. Recently it has become apparent that opioids play a significant role in regulating oxytocin release both centrally and at the level of the pituitary. The interaction between opioids and the oxytocin system allows for the possibility that stress can influence oxytocin release. An acute midpartum stress is highly effective at restraining oxytocin and slowing delivery rate in rats and pigs, an effect that appears largely opioid-mediated. The work reviewed here suggests that opioids also strongly regulate oxytocin release in pigs farrowing under undisturbed conditions as the opioid-antagonist naloxone elevates oxytocin in sows farrowing in crates and pens. The function of this opioid-restraint of oxytocin during normal deliveries remains unclear. The crate environment itself appears to be associated with a weak opioid-restraint of oxytocin during the late delivery phase, which may reflect a mild adverse response to giving birth in the crate. Overall, the results suggest that crates do not act to strongly elevate hypothalamicopioid tone to inhibit posterior pituitary release of oxytocin. By inference the evidence suggests that farrowing crates are not a potent source of stress for sows during actual delivery.