Lamb survival in Australian Merino sheep: a genetic analysis.

Direct and maternal components of variance for lamb survival to birth, 7 d, and weaning (110 d) were estimated by REML procedures in a flock of Australian Merino sheep. A total of 14,142 lambs, the progeny of 421 sires and 3,666 dams, born between 1975 and 1983 were available for analysis. The study has produced some of the most precise estimates of genetic parameters for lamb survival in the Australian Merino. Very low heritabilities for lamb viability (0.03) and the performance of the dam or ewe rearing ability (0.07) suggest that genetic solutions to lamb survival are unlikely to be significant. But, despite the low heritabilities, there is still potential for improvement through selective breeding. The estimated repeatability of at least 0.10 shows that multiple records on the rearing ability of a ewe over its lifetime can increase selection accuracy. More importantly, such repeatabilities indicate that current generation improvement can be achieved by culling ewes from the breeding flock with poor rearing ability. Despite maternal bond score and lamb birth weight being highly repeatable and moderately heritable traits, correlations with lamb survival were essentially zero. These traits therefore have no value as indirect selection criteria for Merino lamb survival.

Phenotypic aspects of lamb survival in Australian Merino sheep.

Lamb survival in Australian Merino sheep was investigated using survival records from 14,142 lambs born between 1975 and 1983. This data set included roll calls of live lambs at birth, 7 d, marking (30 d), and weaning (110 d), which allowed 4 binomial traits (alive or dead) to be recorded for each lamb at each time interval. The average survival to weaning was 72.4% with 23% of singles, 32% of twins, and 45% of multiple-born lambs not surviving to weaning. The timing of lamb loss was consistent across birth types; 6% died within 24 h of birth, a further 14% by 7 d, 3% between 7 and 30 d, and 8% between 30 and 110 d. Partitioning of phenotypic variation revealed that after the first postpartum week, mothering ability of Australian Merino ewes is not an important factor in lamb survival. Some ewes repeatedly lose lambs at birth and in the early postnatal period, but the intraclass correlation decreased by a factor of 10 for survival after 7 d of age (0.096 at birth and 0.100 at 7 d, falling to 0.009 at marking and 0.018 at weaning). This study examined the relationships of lamb survival with lamb birth weight and found varying relationships at each time period. Whereas birth weight had a highly significant curvilinear relationship with survival to weaning, the relationship was flatter for survival to 24 h with only small differences between average birth weights and the birth weight at which survival was optimized (-0.04, 0.28, and 0.54 kg for single-, twin-, and multiple-born lambs, respectively). This suggests that any management interventions to increase birth weight may increase the risk of death to both lamb and ewe during the lambing process due to dystocia. Among twin-born lambs there was a carryover effect of losses at birth on subsequent loss in the first week of life. Survival to 7 d of age was highly dependent on the survival of the littermate, favoring those whose littermate survived, but after the first week, this trend was reversed. Lamb birthcoat score had a small positive impact on survival only at birth.

Genetic parameters for carcass and meat quality traits and their relationships to liveweight and wool production in hogget Merino rams.

Genetic parameters for carcass and meat quality traits of about 18-month-old Merino rams (n = 5870), the progeny of 543 sires from three research resource flocks, were estimated. The estimates of heritability for hot carcass weight (HCW) and the various fat and muscle dimension measurements were moderate and ranged from 0.20 to 0.37. The brightness of meat (colour L*, 0.18 +/- 0.03 standard error) and meat pH (0.22 +/- 0.03) also had moderate estimates of heritability, although meat relative redness (colour a*, 0.10 +/- 0.03) and relative yellowness (colour b*, 0.10 +/- 0.03) were lower. Heritability estimates for live weights were moderate and ranged from 0.29 to 0.41 with significant permanent maternal environmental effects (0.13 to 0.10). The heritability estimates for the hogget wool traits were moderate to high and ranged from 0.27 to 0.60. The ultrasound measurements of fat depth (FATUS) and eye muscle depth (EMDUS) on live animals were highly genetically correlated with the corresponding carcass measurements (0.69 +/- 0.09 FATC and 0.77 +/- 0.07 EMD). Carcass tissue depth (FATGR) had moderate to low genetic correlations with carcass muscle measurements [0.18 +/- 0.10 EMD and 0.05 +/- 0.10 eye muscle area (EMA)], while those with FATC were negative. The genetic correlation between EMD and eye muscle width (EMW) was 0.41 +/- 0.08, while EMA was highly correlated with EMD (0.89 +/- 0.0) and EMW (0.78 +/- 0.04). The genetic correlations for muscle colour with muscle measurements were moderately negative, while those with fat measurements were close to zero. Meat pH was positively correlated with muscle measurements (0.14 to 0.17) and negatively correlated with fat measurements (-0.06 to -0.18). EMDUS also showed a similar pattern of correlations to EMD with meat quality indicator traits, although FATUS had positive correlations with these traits which were generally smaller than their standard error. The genetic correlations among the meat colour traits were high and positive while those with meat pH were high and negative, which were all in the favourable direction. Generally, phenotypic correlations were similar or slightly lower than the corresponding genetic correlations. There were generally small to moderate negative genetic correlations between clean fleece weight (CFW) and carcass fat traits while those with muscle traits were close to zero. As the Merino is already a relatively lean breed, this implies that particular attention should be given to this relationship in Merino breeding programmes to prevent the reduction of fat reserves as a correlated response to selection for increased fleece weight. The ultrasound scan traits generally showed a similar pattern to the corresponding carcass fat and muscle traits. There was a small unfavourable genetic correlation between CFW and meat pH (0.19 +/- 0.07).

Genetic correlations between ewe reproduction and carcass and meat quality traits in Merino sheep.

Genetic correlations between reproduction traits in ewes and carcass and meat quality traits in Merino rams were obtained using restricted maximum likelihood procedures. The carcass data were from 5870 Merino rams slaughtered at approximately 18 months of age that were the progeny of 543 sires from three research resource flocks over 7 years. The carcass traits included ultrasound scan fat and eye muscle depth (EMDUS) measured on live animals, dressing percentage and carcass tissue depth (at the GR site FATGR and C site FATC), eye muscle depth, width and area and the meat quality indicator traits of muscle final pH and colour (L*, a*, b*). The reproduction data consisted of 13 464 ewe joining records for number of lambs born and weaned and 9015 records for LS. The genetic correlations between reproduction and fat measurements were negative (range -0.06 +/- 0.12 to -0.37 +/- 0.12), with smaller correlations for live measurement than carcass traits. There were small favourable genetic correlations between reproduction traits and muscle depth in live rams (EMDUS, 0.10 +/- 0.12 to 0.20 +/- 0.12), although those with carcass muscle traits were close to zero. The reproduction traits were independent of meat colour L* (relative brightness), but tended to be favourably correlated with meat colour a* (relative redness, 0.12 +/- 0.17 to 0.19 +/- 0.16). There was a tendency for meat final pH to have small negative favourable genetic correlations with reproduction traits (0.05 +/- 0.11 to -0.17 +/- 0.12). This study indicates that there is no antagonism between reproduction traits and carcass and meat quality indicator traits, with scope for joint improvement of reproduction, carcass and meat quality traits in Merino sheep.

Genetic correlations among and between wool, growth and reproduction traits in Merino sheep.

Data from seven research resource flocks across Australia were combined to provide accurate estimates of genetic correlations among production traits in Merino sheep. The flocks represented contemporary Australian Merino fine, medium and broad wool strains over the past 30 years. Over 110,000 records were available for analysis for each of the major wool traits, and 50,000 records for reproduction and growth traits with over 2700 sires and 25,000 dams. Individual models developed from the single trait analyses were extended to the various combinations of two-trait models to obtain genetic correlations among six wool traits [clean fleece weight (CFW), greasy fleece weight, fibre diameter (FD), yield, coefficient of variation of fibre diameter and standard deviation of fibre diameter], four growth traits [birth weight, weaning weight, yearling weight (YWT), and hogget weight] and four reproduction traits [fertility, litter size, lambs born per ewe joined, lambs weaned per ewe joined (LW/EJ)]. This study has provided for the first time a comprehensive matrix of genetic correlations among these 14 wool, growth and reproduction traits. The large size of the data set has also provided estimates with very low standard errors. A moderate positive genetic correlation was observed between CFW and FD (0.29 +/- 0.02). YWT was positively correlated with CFW (0.23 +/- 0.04), FD (0.17 +/- 0.04) and LWEJ (0.58 +/- 0.06), while LW/EJ was negatively correlated with CFW (-0.26 +/- 0.05) and positively correlated with FD (0.06 +/- 0.04) and LS (0.68 +/- 0.04). These genetic correlations, together with the estimates of heritability and other parameters provide the basis for more accurate prediction of outcomes in complex sheep-breeding programmes designed to improve several traits.

Two traffic fatalities related to the use of difluoroethane.

The 18-year-old white male driver and 17-year-old white male passenger of an automobile were killed when their vehicle crossed the median of a 4-lane highway and collided with a minivan. A can of airbrush propellant was found in the automobile of the deceased. The only drug detected during initial toxicological analyses was 130 mg/L ethanol in the blood of the driver. When performing ethanol analysis by headspace gas chromatography, an unidentified peak was observed in the blood of both deceased. This peak was identified as difuoroethane (Freon 152), the propellant in the aerosol can found in the automobile. The concentrations of difluoroethane in the blood of the driver and passenger were 78 mg/L and 35 mg/L, respectively. Based on a literature search we believe that this is the first report of the quantitation of difluoroethane in biological samples.