Clean Fleece Weight Research Articles

Fat depth, muscle depth, fat score and wool growth in Merino dams selected for high or low clean fleece weight and bodyweight

Concerns exist that selection for increased clean fleece weight (CFW) is expected to reduce body fatness. Such an effect is likely to impact on reproduction; however, all previous studies have examined non-reproductive yearlings or hoggets. The present study, using adult reproductive dams examined the impact of phenotype [based on high or low phenotypic CFW and bodyweight (BWT) performance], stocking rate (high or low) and litter size on body composition and wool traits. High CFW dams were heavier (P < 0.01) with lower fat depth (P < 0.01) and muscle depth (P < 0.05). The high CFW twin-weaning dams had a lower fat score from lamb marking to pre-joining (P < 0.05), but tended to replete fat reserves faster (P < 0.1) between weaning and pre-joining. At these times of repletion these animals grew longer wool staples (P < 0.05). High BWT ewes had reduced staple length (P < 0.01), and when adjusted for maternal liveweight also reduced fat depth (P < 0.001) and muscle depth (P < 0.05). We conclude that the CFW phenotype impacts on fat reserves but that management of dams in groups according to their CFW performance is not warranted.

Effects of feeding fresh citrus pulp to Merino wethers on wool growth and animal performance

Two studies were conducted to determine the effects of replacing lupins with fresh citrus pulp in Merino wethers diets: (i) an in vitro study, which measured ruminal fermentation; and (ii) an in vivo study in which 18 mature Merino wethers were fed dietary treatments (n = 3) over 56 days to evaluate effects on performance [i.e. DM intake, average daily gain and wool growth]. In both the in vitro and in vivo studies, the control treatment consisted (in diet DM) of lucerne chaff (69.9%), lupins (30.1%) and phosphate (0.3%), whereas the citrus pulp treatments (n = 2; replacing lupins on 20 and 30% DM basis, respectively) consisted of lucerne chaff (61.7 and 63.3%), lupins (18.5 and 6.3%), phosphate (0.34 and 0.33%) and fresh citrus pulp (19.5 and 30.1%). Data were analysed using the MIXED model of SAS and orthogonal polynomial contrasts were used to determine linear (L) and quadratic responses to the level of citrus pulp. In the in vitro study, gas production, net total volatile fatty acid production as well as in vitro DM digestibility were similar (P > 0.05) among the dietary treatments. Ammonia production in citrus pulp treatments were twofold lower compared with the control (L, P < 0.01). The addition of citrus pulp to the diet increased the molar proportions of acetic acid and decreased that of butyric, branched-chain volatile fatty acids, and valeric acids (all L, P < 0.01) compared with the control diet. In the in vivo study, DM intake, average daily gain and feed conversion were similar among treatments (P > 0.52). Wool production parameters including clean fleece weight, yield and staple length were not different between diets (P > 0.30). Hence, fresh citrus pulp can be included up to 30% on a DM basis replacing lupins without detrimental effects on wool production and animal performance.

Relationships of subjectively assessed wool and conformation traits with objectively measured wool and live weight traits in the Tygerhoek Merino flock

Records of the Tygerhoek Merino resource flock were used to estimate genetic, phenotypic and environmental parameters between subjective wool and conformation traits with objective wool and live weight traits. The database contained records of 4 495 animals, the progeny of 449 sires and 1 831 dams, and born from 1989 to 2004. On the genetic level (rg) live weight was favourably related to regularity of crimp (ROC) (0.20), woolly face score (WFS) (0.21), general head conformation (GEN) (0.67), conformation of the hind legs (HOCKS) (0.36), conformation of the front legs (FQ) (0.42), topline (TOPL) (0.25) and total fold score (TOT). Estimates of rg were favourable for clean yield with wool quality (QUAL) (0.30), wool colour (COL) (0.45), wool oil (OIL) (-0.44), staple formation (STAPL), belly and points (BANDP) (0.24), face cover score (FCS) (0.18), GEN (0.25), HOCKS (0.19), TOT (-0.26) and FQ (0.18). Clean fleece weight (CFW) was favourable correlated `to QUAL (0.18), STAPL (0.39), BANDP (0.48) and GEN (0.23). Staple length was favourably related to COL (0.16), BANDP (0.40) and WFS (0.16) and negatively related to OIL (-0.33). Staple strength was favourable correlated to ROC (0.33) and FQ (0.39). Fibre diameter was favourable correlated with QUAL (-0.32), ROC (-0.28), FCS (-0.32), pastern score (PS) (-0.16) and TOPL (-0.18). Coefficient of variation of fibre diameter (CVFD) was favourably correlated with QUAL (-0.50), ROC (-0.73), HOCKS (-0.17), FQ (-0.33) and TOPL (-0.25). In contrast, unfavourable correlations occurred for SS with TOT (0.25), for FD with STAPL (0.59), BANDP (0.37), HOCKS (0.13) and TOT (0.13). Other unfavourable genetic correlations were between CFW and TOT (0.28) and between CVFD and STAPL (0.49). The results showed that selection for LW and objective wool traits will not seriously compromise subjective wool and conformation traits, barring a few exceptions.

Genetic parameter estimation of 16-month live weight and objectively measured wool traits in the Tygerhoek Merino flock

Genetic evaluation systems require the accurate estimation of genetic parameters. The genetic, phenotypic and environmental parameters for live weight and objectively measured wool traits were estimated for a South African Merino flock. Records of the Tygerhoek Merino resource flock were used to estimate these parameters. The database consisted of records of 4 495 animals, the progeny of 449 sires and 1 831 dams born in the period 1989 to 2004. The pedigree records used have been collected between 1969 and 2004. Direct heritability estimates (h²a) for 16-month live weight (LW) and objectively measured wool traits ranged from 0.20 for staple strength (SS) to 0.68 for fibre diameter (FD). Maternal heritability estimates ranged from 0.05 for LW and FD, to 0.10 for clean fleece weight (CFW). The proportion of the total phenotypic variance due to the maternal permanent environment variance (c²pe) amounted to 5% for fleece weights. The genetic correlation between animal effects for LW, greasy fleece weight (GFW) and CFW were -0.28, -0.65 and -0.70 respectively. The genetic correlation between LW and CFW was positive, but low at 0.14. The other important genetic correlations among the wool traits ranged from low to high, and were variable in sign ((for GFW with CFW (0.87) and with staple length (SL – 0.18); CFW with clean yield (CY – 0.33) and with SL (0.29); FD with CY (-0.09), with SL (0.15), with SS (0.40) and with standard deviation of FD (SDFD – 0.38): CY with SL (0.33) and with SDFD (0.10); SS with coefficient of variation of FD (CVFD – -0.57) and with SDFD (-0.28); CVFD with SDFD (0.87)). These results suggested that worthwhile responses in the objectively measured traits can be achieved through direct and indirect selection.

Genetic parameters for visually assessed traits and their relationships to wool production and liveweight in Australian Merino sheep

Heritability was estimated for a range of visually assessed traits recorded on Merino sheep, together with the phenotypic and genetic correlations among the visually assessed traits and correlations of the visually assessed traits with measured wool production traits and liveweight. Data were derived from four research resource flocks, with a range of 12 958 to 57 128 records from animals with 478 to 1491 sires for the various traits. The estimates of heritability were high for the wool quality traits of handle, wool character and wool colour (0.33–0.34) and the conformation traits of face cover, neck wrinkle and body wrinkle (0.42–0.45), moderate for front leg structure (0.18) and low for back leg structure (0.13). Fleece rot score had low heritability (0.14), while classer grade was moderately heritable (0.20). Estimates of genetic correlations among the visually assessed wool quality traits were low to moderate in size and positive (0.17–0.47). Genetic correlation estimates among the assessed conformation traits were generally very low, except for the genetic correlations between scores for neck and body wrinkle (0.92 ± 0.01) and front and back leg structure (0.31 ± 0.09). Fleece rot score had low positive genetic correlations with neck and body wrinkle scores (0.18 ± 0.05 and 0.15 ± 0.05, respectively) and classer grade (0.26 ± 0.06). Classer grade was slightly positively correlated with the wool quality traits (0.17–0.45) and leg structure traits (0.21–0.25). The genetic correlations among the visually assessed traits were generally neutral to favourable. The visually assessed wool quality traits had low to moderate favourable genetic correlations with mean and coefficient of variation of fibre diameter (0.19 –0.47), but negative correlations with clean wool yield (–0.26 to –0.37). Face cover was unfavourably correlated with staple length (–0.27 ± 0.04) and liveweight (–0.23 ± 0.02). Neck and body wrinkle scores were genetically associated with higher greasy (0.33–0.39) and clean fleece weights (0.19–0.22), greater coefficient of variation of fibre diameter (0.24–0.26) and fibre curvature (0.27–0.28), but with reduced yield (–0.26 to –0.28) and staple length (–0.34 to –0.41). Fleece rot score was genetically correlated with clean fleece weight (0.26 ± 0.05) and coefficient of variation of fibre diameter (0.27 ± 0.04). Classer grade was favourably correlated with greasy and clean fleece weights (–0.41 to –0.43), staple length (–0.29 ± 0.04), liveweight (–0.36 ± 0.03) and coefficient of variation of fibre diameter (0.27 ± 0.03). Most genetic correlations between the visually assessed traits and the measured production traits and liveweight were close to zero and less than 0.2 in magnitude. This study provides accurate values for the parameter matrix required to incorporate visually assessed traits into breeding objectives and the genetic evaluation programs used in the Australian sheep industry, allowing the development of breeding objectives and indexes that optimally combine visually assessed performance and measured production in Merino sheep.

Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 4. Genetic relationships between and within wool traits

The aim of this paper was to describe the genetic relationship among expressions at different ages of seven wool traits: greasy and clean fleece weights, fibre diameter, coefficient of variation of fibre diameter, staple length and strength, and mean fibre curvature. Genetic correlations among measurements at different ages for the same trait were moderate to high, and ranged from ~0.6 for both fleece weights to 0.9 and higher for mean fibre diameter and curvature. Generally, low to moderate genetic correlations (0.3–0.4) were estimated between fleece weights and fibre diameter, clean fleece weight and staple length, and fibre diameter and staple strength. Small positive genetic correlations (0.2) were estimated between greasy and clean fleece weight with fibre diameter coefficient of variation, and between fibre diameter and staple length. Mean fibre curvature had a negative genetic correlation (approximately –0.4) with most other wool traits, the exceptions were staple strength (~0.0) and coefficient of variation of fibre diameter (approximately –0.1). Fibre diameter, staple length and staple strength had negative genetic correlations with coefficient of variation of fibre diameter (–0.15, –0.10, and –0.61, respectively). The results indicate that for most wool traits only one measurement across ages is required to make accurate selection decisions. The relationships between traits are generally moderate to low suggesting that simultaneous genetic improvement is possible.

Genetic correlations between early growth and wool production of crossbred ewes and their subsequent reproduction

Genetic correlations between reproductive and productivity traits of ewes and their early growth, wool production and worm resistance traits were estimated among 2460 crossbred ewes. The ewes were progeny of 74 maternal breed sires and mainly Merino dams. The ewes were born over 3 years and had three joinings with a total of 6824 ewe joining records. The reproductive and ewe productivity traits included: (i) fertility (ewes lambing per ewe joined); (ii) litter size (number of lambs born per ewe lambing); (iii) rearing ability or lamb survival (lambs weaned of lambs born for lambing ewes); (iv) number of lambs born (NLBj) per ewe joined; (v) number of lambs weaned (NLWj) per ewe joined; (vi) total litter weight weaned (TWWj) per ewe joined; and (vii) the component trait average lamb weaning weight in the litter (AWW). The growth traits included the weight of the ewe at birth (BWT), weaning (WWT) and postweaning (PWWT), as well as growth rate pre- and postweaning. The wool traits included greasy (GFW) and clean fleece weight (CFW), yield and average fibre diameter (FD) at their first adult shearing. Worm egg count (WEC) during their first year was also recorded. Bivariate mixed models analyses using ASReml procedures were used to estimate the genetic correlations. The genetic correlations between TWWj and growth traits were positive and moderate to high and ranged from 0.34 for BWT to 0.61 for PWWT. Those for the other composite reproductive traits were slightly lower and ranged from 0.27 to 0.54 for NLWj and from 0.07 to 0.46 for NLBj. The genetic correlations between the overall measures of reproduction (NLBj, NLWj and TWWj) and GFW, CFW and FD were negative and generally low to moderate (–0.21 to –0.52). The correlations were generally larger for NLBj than for NLWj and TWWj. The genetic correlations between the reproductive traits and WEC were close to zero, except between AWW and WEC (0.42). The phenotypic correlations between the reproductive traits and the growth, wool and WEC traits were all close to zero. The genetic correlations were generally favourable between ewe reproduction and growth, with early selection for traits such as WWT and PWWT likely to give some improvement in subsequent reproduction and ewe productivity. In contrast, there appears to be a slight antagonism between reproduction and wool production. This study provides estimates of genetic correlations from crossbred ewes that add to the limited knowledge of these parameters that will improve the accuracy of genetic evaluation and prediction of the outcomes from breeding programs for meat and wool objectives that include reproduction.

Programming sheep production on saltbush: adaptations of offspring from ewes that consumed high amounts of salt during pregnancy and early lactation

We investigated if feeding a high salt diet (pellet containing 14% NaCl) or saltbush (Atriplex nummularia) to ewes between day 60 of gestation and day 21 of lactation would allow their offspring to gain more weight, and produce more wool, when grazing saltbush as adults compared to offspring from ewes that were fed a control diet (2% NaCl) or grazed pasture. At 10 months of age, offspring grazed saltbush for 8 weeks then dry pasture for 2 weeks. Throughout this time, liveweights, plasma renin activity and wool growth (g/day) were measured. Greasy and clean fleece weights, and fleece characteristics were measured at 14 months of age, and greasy fleece weight was measured again at 22 months after grazing pasture. Offspring from ewes that consumed the high salt pellet had an 8 and 10% increased fleece weight at 14 and 22 months of age, respectively (P ≤ 0.01). Offspring of ewes that consumed saltbush also showed an 8% increase in greasy fleece weight at 22 months of age (P ≤ 0.05). Offspring from ewes that consumed saltbush had lower plasma renin activity and gained tissue weight when grazing saltbush (P ≤ 0.05), whereas the other three treatment groups all lost weight (P > 0.05). Grazing pregnant ewes on saltbush induces important adaptations in plasma renin activity of their offspring, which allows them to gain weight when grazing saltbush as adults and may also increase the density of their wool follicles. Grazing pregnant ewes on saltbush can profit farmers in three main ways: (i) ability to utilise salt-affected land; (ii) increase weight gain of sheep when grazing saltbush; and (iii) increase fleece weight.

Heterogeneity of lifetime reproductive performance, its components and associations with wool production and liveweight of Merino ewes

The heterogeneity in lifetime (2–6 years of age) reproductive performance within three research flocks maintained at the Agricultural Research Centre, Trangie, in central-western New South Wales, was used to establish the potential to improve flock reproductive performance by identifying performance segments for either selection or for differential management. The data comprised a total of 32 716 records from 7322 ewes, collected over the period from 1977 to 2003. Within each of the flocks, there were large differences (P < 0.001) in lifetime net reproduction rate, and each of its components (fertility, fecundity and lamb survival), between each of the net reproduction rate quartiles. The difference in net reproduction between the ewes in the top quartile and those in the bottom quartile was equivalent to an additional lamb per ewe annually. These differences in reproduction rate between the quartiles were not related to pre-joining liveweight or condition score. Higher reproductive rates were associated with a cost to clean fleece weight, although the estimated effects on fibre diameter were small. Opportunities to use this variation to improve reproduction rates are discussed and include retaining high-performing ewes longer in the breeding flock, removing poor performers and targeting management interventions towards ewes that will yield the largest responses.

Effects of weaner nutrition on sire and flock rankings: a re-analysis of historical data

Early work in the 1950s on the wool growth response of sheep from diverse genotypes for wool production in response to varying planes of nutrition at pasture did not show the significant genotype × environment interactions exhibited in later pen studies with the same or very similar genotypes. However, this early study used a log-transformation on all traits to adjust nutritional effects for scale. Re-analysis of the original (i.e. untransformed) data shows that superior genetic merit for clean fleece weight, different sire progeny groups or selection flocks is more apparent when hogget ewes are fed a high plane of nutrition at pasture. However, only in the case of flocks was the interaction statistically significant, and this interaction was insignificant when data were either log-transformed, or when an appropriate test that accounts for scale-type effects was applied. When left untransformed, the data are, thus, in agreement with the subsequent pen studies that examined data on untransformed clean wool production.

Across flock genetic parameter estimation for yearling body weight and fleece

Accurate genetic parameter estimates are needed upon which to perform multiple-trait across flock breed analyses. Genetic parameters for yearling body weight (BW), clean fleece weight (CFW) and mean fibre diameter (MFD) were estimated using records of 107 389 individuals (the progeny of 1 530 sires and 45 178 dams) collected between 1992 and 2004 in the South African Dohne Merino population. Fixed effects included in the model were flock-year-season-sex-management group (1 594 classes), type of birth (singles, multiples), age of dam (2 - 7+ years) and age at measurement, fitted as a linear covariate (385 ± 12 days). Six different single-trait animal models were fitted, where different combinations of the following random effects were fitted: direct additive, the sire-flock interaction, the sire-flock-year-season interaction (SFYS), the dam genetic effect, the direct-maternal correlation and the dam permanent environmental effect. These analyses were followed by a three-trait analysis structured according to the log likelihood ratios obtained for the single-trait analysis. This analysis allowed the calculation of relevant correlations among traits together with their respective standard errors. Direct heritability estimates from the three-trait analysis were 0.17 for BW, 0.19 for CFW and 0.45 for MFD. Maternal heritability estimates were 0.01 for BW and 0.006 for CFW, with corresponding dam permanent environmental ratios of respectively 0.03 and 0.02. The genetic correlation between animal effects amounted to 0.48 for BW. Derived proportions of the total phenotypic variance due to SFYS were 0.02, 0.02 and 0.02, respectively. Genetic correlations of BW with CFW and MFD were 0.11 and 0.13, respectively, and of CFW with MFD 0.16. It was concluded that the inclusion of some form of a genotype by environmental interaction as part of the national evaluation is essential, although it controlled only a modest portion of the overall phenotypic variation.

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).

The impact of clean fleece weight and bodyweight selection in Merinos on meat traits in the progeny

The carcasses of 136 Merino wether lambs from a single bloodline were studied to determine the impact of phenotypic selection for clean fleece weight (CFW) and bodyweight (BWT) on meat quality characteristics. The lambs were the progeny of sires and dams that were selected for high or low CFW and high or low BWT using hogget phenotypic data, where the dams were managed at 10 or 15 dry sheep equivalent/ha during gestation and from marking to weaning. Maternal stocking rate was found to have no significant effect on any meat traits, except to reduce fatness in high BWT lambs. High CFW selection led to increased glycolytic activity in muscle reflected by lactate dehydrogenase (LDH) activity. Phenotypic BWT selection increased hot carcass weight and decreased fatness, lowered temperature at pH 6.0, and showed considerable variation in LDH activity and the ratio of LDH to isocitrate dehydrogenase. It is clear from this study that the stocking rate of the dam during gestation and lactation, and her selection on the basis of CFW or BWT phenotype had no large negative impact on the meat traits of her male progeny.

Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 1. Description of traits, model comparison, variance components and their ratios

Both wool and sheep meat industries are interested in sheep that have a high reproduction performance and are resistant to internal parasites, in addition to the traditional traits. There is considerable interest in breeding sheep for wool, carcass, reproductive and internal parasite resistance traits simultaneously. The objective of this study was to estimate single trait genetic parameters for 40 traits recorded in Merino sheep, covering bodyweight, carcass, wool, reproduction and internal parasite resistance traits. This also involved determining the appropriate models. The results from this study will be used to review the genetic parameters used in the routine genetic evaluations conducted by Sheep Genetics. The most appropriate models included a maternal genetic effect and covariance between direct and maternal genetic effects for most of the bodyweight traits, greasy and clean fleece weight, fibre diameter and coefficient of variation of fibre diameter. The permanent environment due to the dam was not included for any trait. There was considerable genetic variation in most traits analysed; lowest heritabilities (0.09–0.10) were found for number of lambs born and weaned per lambing opportunity, and highest heritabilities (0.62–0.77) for fibre diameter. The estimated heritabilities and genetic variances, in combination with the estimated correlations, indicate that there is potential to make genetic improvement in most traits currently recorded in Australian Merino sheep.

Carcass characteristics and meat quality of progeny of five Merino dam lines, crossed with Dormer and Suffolk sires

This study details the slaughter traits of lambs born from a terminal crossbreeding experiment that involved five Merino type dam lines crossed with Dormer and Suffolk sires. Dam lines included dual purpose types; South African Mutton Merino (SAMM), Dohne Merino, SAMM rams crossed to commercial Merino ewes (SAMM cross) and specialist Merino lines selected either for clean fleece weight (FW+) or for an increased fertility (Rep+). Data include between 228 and 483 individual records, depending on the trait. The unadjusted fat depth 25 mm from the midline at the 13 th rib of lambs from dual-purpose ewes was between 22 and 32% greater than that of lambs from FW+ Merino ewes. Progeny from Rep+ Merino ewes showed a closer resemblance to the progeny of dual-purpose breeds than to those of FW+ Merino ewes in this instance. Adjustment for slaughter weight eliminated these differences. The initial pH of meat from progeny of FW+ Merino ewes was lower than that from progeny of dual-purpose ewes, and Rep+ Merino ewes. No differences in Warner-Bratzler shear values of the meat were found between the different crosses. Crossbred progeny of the Merino lines performed satisfactorily for all the traits considered, and will not be discriminated against in the market. No conclusive differences in favour of either sire breed were found.

Genetic analysis of faecal worm egg count in South African Merinos under natural challenge

Sheep from a Merino selection experiment at the Tygerhoek research farm in the Southern Cape provided material for this study. The selection lines involved included a line selected for clean fleece weight, a “Wet and Dry” line, a fine wool line and an unselected Control line. Rectal faeces samples were obtained from individual animals at 13 to 16 months of age, after drenching was withheld for at least 10 weeks. Nematode eggs in these samples were counted. Fitting the appropriate fixed effects, the heritability of untransformed, cube root transformed and log transformed faecal nematode egg count (FEC) was obtained from single-trait analyses. The effects of sex and birth year were involved in a significant interaction. Means for FEC were generally higher in ram progeny than in ewes, but the magnitude of the sex difference was not consistent. Multiple lambs had a slightly lower mean for FEC than singles, while FEC was unaffected by dam age. The heritability of FEC was estimated at between 0.14 for untransformed data and 0.18 for log transformed FEC. Genetic correlations of log transformed FEC with two-tooth staple strength (-0.49) and coefficient of variation of fibre diameter (0.30) were favourable. Clean fleece weight was unfavourably related to FEC on a genetic level (0.19). Selection for resistance to parasitic nematodes after natural challenge should thus be feasible in the Merino lines studied. Keywords : Fleece weight; genetic correlation; heritability; live weight; resistance South African Journal of Animal Science Vol. 37 (4) 2007: pp.237-247

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.

Responses of wool growth rate and body reserves to nutrition in Merino ewes: a potential biological link between production and fitness

This study examined whether the low body-fat reserves in sheep with high estimated breeding values (EBVs) for clean fleece weight (CFW) reported previously are affected by nutritional history, and second whether the effect may be related to differences in the variation in fibre diameter (CVfd). Groups of 11 20-month-old Merino ewes with high and low EBVs for CFW and for CVfd were compared in a 2 × 2 design at low bodyweight, then fed ad libitum for 100 days and re-measured. The response of wool growth rate to feed supply (WRF) was estimated as the slope of the regression against time of clean wool mass collected from mid-side patches at intervals of 30–40 days throughout the experiment. High CFW sheep had greater feed intake relative to liveweight and liveweight gain (P = 0.02), but did not differ significantly in other characteristics from low CFW sheep. High CVfd sheep had lower plasma concentrations of insulin (P = 0.02), IGF-1 (P = 0.03), and albumin (P = 0.02) throughout the study, and had less fat when in poor body condition (P = 0.02). The WRF was greater in both the high CFW (P = 0.003) and the high CVfd (P = 0.004) genotypes. When studied in poor body condition, sheep with a high WRF had lower liveweight (P < 0.001), lower body condition score (P < 0.001), lower plasma albumin (P < 0.001), and higher plasma growth hormone (P = 0.02), but these relationships weakened or disappeared after ad libitum feeding. Sheep with high WRF also had lower plasma concentrations of insulin (P = 0.002) and IGF-1 (P = 0.008) throughout the study, which may have brought about the increased responsiveness of protein and energy metabolism to nutrition. The results indicate that genetic selection for wool characteristics can affect the responsiveness of wool growth rate to nutrient supply. Sheep that are highly responsive grow more wool when offered abundant feed, but may have lower body nutrient reserves when on limited feed.

Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects

Accurate estimates of adjustment factors for systematic environmental effects are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate genetic parameters and investigate the significance of various environmental factors for production traits in Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, with over 2700 sires and 25 000 dams. Univariate linear mixed animal models were used to analyse 6 wool, 4 growth, and 4 reproduction traits. This first paper outlines the data structure and the non-genetic effects of age of the animal, age of dam, birth-rearing type, sex, flock, bloodline, and year, which were significant with few exceptions for all production traits. Age of dam was not significant for reproduction traits and fleece yield. Generally, wool, growth, and reproduction traits need to be adjusted for age, birth-rearing type, and age of dam before the estimation of breeding values for pragmatic and operational reasons. Adjustment for animal age in wool traits needs to be applied for clean fleece weight (CFW), greasy fleece weight (GFW), and fibre diameter (FD) with inclusion of 2 age groups (2 years old and >2 years old), but for reproduction traits, inclusion of all age groups is more appropriate. For GFW, CFW, and hogget weight (HWT), adjustment for only 2 dam age groups of maiden and mature ewes seems sufficient, whereas for birth (BWT), weaning (WWT), and yearling (YWT) weights, adjustments need to be applied for all dam age groups. Adjustment for birth-rearing type (single-single, multiple-single, multiple-multiple) is appropriate for wool, growth, and reproduction traits. The implications of adjustment for non-genetic effects are discussed.

Protein synthesis rates in skin components and skeletal muscle of sheep selected for divergent clean fleece weight in response to below- and above-maintenance nutrition

Protein metabolism in skin and muscle was studied in Merino wethers selected for high (F+, n = 10) or low (F–, n = 10) estimated breeding values for clean fleece weight, but with similar estimated breeding values for liveweight and fibre diameter, raised to 20 months of age under the same conditions, and then offered two levels of nutrition (0.8 or 1.8 × maintenance) for 37 days. Over 37 days, F+ sheep had greater rate of wool production, liveweight gain, and had greater eye-muscle and fat depth than F– sheep (P < 0.05). Fractional synthesis rates of protein (%/day) in the epidermis, dermis, whole skin and muscle were affected by both feeding level (P < 0.05) and genotype (P < 0.05). The fractional synthesis rates of protein were greater (P < 0.05) in F+ sheep at both levels of intake. There was an interaction (P < 0.01) between genotype and feeding level for the protein fractional synthesis rate in muscle, where F+ sheep were more responsive to higher feed intake. Muscle of F– sheep responded to increased amino acid supply by reducing the rate of protein degradation without altering synthesis rate; whereas muscle of F+ sheep responded by increasing the rates of both protein synthesis and degradation. The overall muscle fractional synthesis rate (1.6%/day) was ~7-times lower than the skin fractional synthesis rate (10.8%/day) in these animals (P < 0.01). F+ sheep had a higher rate of protein synthesis in dermis and whole skin to support their higher wool protein accretion at both levels of feed intake. Muscle protein synthesis rate was greater in F+ sheep offered above-maintenance metabolisable energy (ME) intake than those given below-maintenance ME intake but was unaffected by ME intake in F– sheep. The results indicate that selection for wool growth not only affects production of wool and the wool follicle, but also affects the rate of protein turnover in components of the skin and skeletal muscle.