Yearling Fleece Weight Research Articles

Characterizing the vaginal microbiota of high and low producing Poll Merino and White Suffolk ewes.

There is a substantial, and growing, body of research focused on manipulating gastrointestinal microbes to affect health and production. However, the maternal vaginal microbiota and its effects on neonatal inoculation and lifetime production have received little attention. We aimed to characterize the vaginal microbes of domesticated sheep to determine whether they differ across sheep breeds with differing meat and wool growth potentials and to determine a link between vaginal microbes and high and low producing animals. A flock of White Suffolk (n = 136) and Poll Merino (n = 210) ewes were sorted by the Australian Sheep Breeding Values (ASBV), for yearling fleece weight in the Merino and by post-weaning weight in the Suffolk ewes. The top and bottom ASBV sheep were selected for sampling and the resulting treatment groups were; High Suffolk (n = 12), Low Suffolk (n = 12), High Merino (n = 12), and Low Merino (n = 12) ewes. A double guarded culture swab was used to sample from the surface of the vaginal epithelium. Diversity profiling analysis of vaginal bacterial communities was conducted using 16S rRNA amplicon sequencing. Breed and ASBV group differences in bacterial communities were tested. Within breed, there were no significant differences in ewe vaginal bacterial communities associated with ewe production parameters; however, there was a significant difference in ewe vaginal bacterial communities between breeds. We have been able to characterize the normal vaginal microbiota of nonpregnant ewes and demonstrate a rich microbial community.

Genetic analysis of parent-of-origin effects on growth traits and yearling greasy fleece weight in Raeini Cashmere goat

Pedigree on 7253 individuals and data information on growth traits and greasy yearling fleece weight collected from 1979 to 2013 at the Breeding Station of Raeini Cashmere goat, south-east of Iran, were used for genetic analysis of parent of origin effects for these traits using a gametic relationship matrix. The studied traits included birth weight (BW; 4747 records), weaning weight (WW; 3268 records), six months weight (6 MW; 2855 records), nine months weight (9 MW; 1407 records), yearling weight (YW; 1013 records), and yearling greasy fleece weight (YFW; 1272 records). Models including or excluding imprinting (maternal and paternal) effects were compared by applying Akaike Information Criterion (AIC). Paternal imprinting effects did not influence any of the studied traits. Maternal imprinting effects explained 9%, 6%, 9%, 18%, and 6% of phenotypic variances for WW, 6 MW, 9 MW, YW, and YFW, respectively. By including the maternal imprinting effects in the model used for genetic analysis, direct heritability estimates for WW (from 0.04 to 0.01), 9 MW (0.24–0.15), YW (from 0.31 to 0.14), and YFW (0.18–0.09) were decreased, implying a considerable proportion of the maternal imprinting effects for these traits may overlap with direct additive genetic effects. BW did not influence by imprinting effects. Strong maternal imprinting correlations among body weights at different ages (except for BW) showed that WW, 6 MW, 9 MW, and YW share similar genes with maternally imprinted effects. It means that the imprinting effects of genes are not limited to a specific stage of life and can be active in different stages of growth. Maternal imprinting correlation estimates between YFW and other traits were not statistically significant. Therefore, imprinting effects may be crucial for the genetically evaluating of these traits in the Raeini Cashmere goat.

Genome-Wide Association Studies Identify Candidate Genes for Coat Color and Mohair Traits in the Iranian Markhoz Goat.

The Markhoz goat provides an opportunity to study the genetics underlying coat color and mohair traits of an Angora type goat using genome-wide association studies (GWAS). This indigenous Iranian breed is valued for its quality mohair used in ceremonial garments and has the distinction of exhibiting an array of coat colors including black, brown, and white. Here, we performed 16 GWAS for different fleece (mohair) traits and coat color in 228 Markhoz goats sampled from the Markhoz Goat Research Station in Sanandaj, Kurdistan province, located in western Iran using the Illumina Caprine 50K beadchip. The Efficient Mixed Model Linear analysis was used to identify genomic regions with potential candidate genes contributing to coat color and mohair characteristics while correcting for population structure. Significant associations to coat color were found within or near the ASIP, ITCH, AHCY, and RALY genes on chromosome 13 for black and brown coat color and the KIT and PDGFRA genes on chromosome 6 for white coat color. Individual mohair traits were analyzed for genetic association along with principal components that allowed for a broader perspective of combined traits reflecting overall mohair quality and volume. A multitude of markers demonstrated significant association to mohair traits highlighting potential candidate genes of POU1F1 on chromosome 1 for mohair quality, MREG on chromosome 2 for mohair volume, DUOX1 on chromosome 10 for yearling fleece weight, and ADGRV1 on chromosome 7 for grease percentage. Variation in allele frequencies and haplotypes were identified for coat color and differentiated common markers associated with both brown and black coat color. This demonstrates the potential for genetic markers to be used in future breeding programs to improve selection for coat color and mohair traits. Putative candidate genes, both novel and previously identified in other species or breeds, require further investigation to confirm phenotypic causality and potential epistatic relationships.

Sheep of divergent genetic merit for wool growth do not differ in digesta kinetics while on restricted intakes

Sheep selected for high wool growth were previously shown to exhibit higher microbial protein outflow from the rumen and higher uptake of amino nitrogen in portal blood than those selected for low wool growth. This suggests that genetic selection for wool growth may induce changes in foregut physiology. This study was undertaken to determine whether differences in digesta kinetics, especially mean retention mime (MRT), are associated with differences in fleece production between sheep with low or high estimated breeding values (EBVs) for fleece weight. Twenty mature Merino wethers with uniform EBVs for liveweight were allocated to two groups of 10 animals on the basis of high or low EBVs for yearling fleece weight. Five sheep with low-EBVs and five sheep with high-EBVs for fleece weight groups were allocated in a crossover design to low and high feeding-level treatments, which comprised a blended hay diet fed at maintenance or 1.5 times maintenance. All sheep were given single doses of chromium-mordanted fibre and cobalt-EDTA as inert, non-digestible markers. Digesta kinetics was determined by analysis of the faecal marker excretion patterns using a compartmental model. Higher feed intakes from animals fed 1.5 times maintenance were associated with higher rates of wool growth and higher masses of indigestible fibre in the gut, but reduced MRT of digesta. Although sheep with higher EBVs for fleece weight had higher wool growth rates, there was no indication that these wool growth differences were associated with differences in digesta kinetics. The lack of interaction between feeding level and genotype suggests that MRT did not contribute to genotype differences in wool growth in sheep fed restricted intakes. The differences in wool growth among commercial Merino sheep with divergent fleece weight EBVs achieved by multi-trait selection are not attributable to differences in digesta kinetics, at least when feed is not available ad libitum.

Evaluation of insulin-like growth factor-I gene polymorphism on growth traits and yearling fleece weight in goats

The PCR–SSCP analysis of the 5′ flanking region of the goat insulin-like growth factor-I gene (gIGF-I) was used to screen polymorphisms in a total of 296 goats belonging to two breeds of goats (Markhoz and Kurdi) reared in the Kurdistan province in Iran. The PCR products of different electrophoresis patterns were sequenced and aligned. Sequencing revealed a novel G to A transition at position 422bp upstream from the ATG codon (g.1617 G>A), according to the GenBank sequence D26119.2. PCR–RFLP analysis of part of intron 4 and exon 4 of the goat IGF-I gene was used to identify associations between the intron 4/HaeIII polymorphism and economic traits. Results of fixed model analysis revealed that the intron 4/HaeIII polymorphism was significantly associated with yearling weight (YW), post-weaning average daily gain from 3-months to 12-months (ADG4), 6-months to 12-months (ADG6), 9-months to 12-months (ADG7), and first shearing fleece weight (FSFW) (P≤0.05). Animals that possessed the GG genotype for the intron 4/HaeIII mutation appeared potentially more favorable for all mentioned traits. These results suggest that variation in the caprine IGF-I gene is associated with growth traits and yearling fleece weight in Markhoz goats.

Selection for yearling fleece weight and its effect on fleece shedding in New Zealand Wiltshire sheep

A flock of New Zealand Wiltshire sheep was divided into two lines and selected for increased greasy fleece weight or decreased greasy fleece weight as yearlings. Wiltshires shed their fleece annually, and although these yearlings may have expressed shedding as lambs in the preceding summer, they were shorn in autumn at 5 months and again in spring at 12 months of age to determine fleece weight before the subsequent shedding. A rapid separation in fleece weight was observed within 8 years, with ewe (0.89 kg) and ram yearlings (0.92 kg) selected for increased fleece weight producing significantly more wool (P < 0.001) than ewe (0.43 kg) or ram yearlings (0.39 kg) from the line selected for decreased fleece weight. There was no significant difference between sexes, and the sex × line interaction was not significant. Clearly this was very low wool production, but fleece weight was heritable (h2 = 0.57 ± 0.04). Shedding was scored from 0 (not shed) to 5 (completely shed) for all animals (n = 2505 records) and was found to be heritable in December (h2 = 0.39 ± 0.04) and again in January (h2 = 0.52 ± 0.05), but less so in September at shearing (h2 = 0.24 ± 0.03). Fleece weight in spring was negatively correlated with shedding score in January, both phenotypically (–0.52 ± 0.02) and genetically (–0.81 ± 0.04). Selecting yearlings for low fleece weight developed a shedding sheep with negligible fleece, which may not require shearing. Selecting for shedding of lambs in January would likely achieve a similar outcome.

Selection response to fleece weight, wool characteristics, and heritability estimates in yearling Romney sheep

The juvenile live weights, yearling fleece weight and wool characteristics of 2987 Romney progeny of 114 sires born over 9 breeding seasons in a fleece-weight-selected and a random control line were analysed. The high fleece weight-selected flock performance was higher (P < 0.001) for weaning weight and spring weight (6.9 and 8.4%), higher (P < 0.001) for greasy and clean fleece weight (23.8 and 24.3%), and also higher (P < 0.001) for FD by 1 μm, staple length by 6 mm, and wool yellowness by 0.3 unit than random control yearling sheep. Heritability estimates for weaning and spring live weight, greasy fleece weight, clean fleece weight, yield, fibre diameter, staple length, staple strength, loose wool bulk, brightness and yellowness were 0.15, 0.51, 0.35, 0.36, 0.40, 0.57, 0.41, 0.24, 0.46, 0.12 and 0.14 respectively. The heritability estimates are within the range of the long wool sheep breeds studied previously. The high selection differential achieved in the initial screening commercial flocks however facilitated to approach a selection response peak in a shorter selection duration and thus resulted in a non-significant genetic gain in greasy fleece weight when averaged over the 9 years of selection.

Genetic and Phenotypic Parameter Estimates of Body Weight at Different Ages and Yearling Fleece Weight in Markhoz Goats

The objective of the present study was to estimate genetic parameters for economic traits in Markhoz goats. Data collected from 1993 to 2006 by the Markhoz goat Performance Testing Station in Sanandaj, Iran, were analyzed. The traits recorded as body weight performance at birth (BW), weaning (WW), six month (6MW), nine month (9MW), yearling (YW) and yearling fleece weight (YFW) were investigated. Least square analyses were used for estimation of environmental effects. Genetic parameters were estimated with single and multi trait analysis using restricted maximum likelihood (REML) procedures, under animal models. By ignoring or including maternal additive genetic effects and maternal permanent environmental effects, five different models were fitted for each trait. The effects of sex, type of birth, age of dam and year of birth on the all body weights were significant (p<0.01), but had no effects on YFW except year of birth. Age of kids had significant influences on WW and 6MW (p<0.01). A log likelihood ratio test was carried out for choosing the most suitable model for each trait. Total heritability estimates for YFW and growth traits varied from 0.16 for YFW and WW to 0.41 for YW. For all traits, maternal heritability was lower than direct heritability, ranging from 0.06 for BW to 0.01 for 6MW and 9MW. The magnitude of c 2 was more substantial for BW than the others, and relative importance was reduced from 0.12 for BW to 0.04 for 9MW. The direct additive genetic correlations estimates were positive and varied from 0.21 between BW-YW to 0.96 between WW-6MW. Direct additive genetic correlations between YFW and body weight traits were positive and ranged from 0.14 between BW-YFW to 0.67 between 6MW-YFW. For all traits, the corresponding estimates for phenotypic correlation were positive and lower than genetic correlations. The maternal additive genetic correlations between various traits were varied and ranged from -0.19 between 9MW-YFW to 0.96 between 6MW-9MW. The estimates of the maternal permanent environmental correlations between various traits were positive and ranged from 0.33 between WW-YFW to 0.93 between WW-6MW. Also, the environmental correlations between various traits ranged from 0.01 between BW-YFW and WW-YFW to 0.70 between 9MW-YW. Estimates of genetic parameters for various traits in this study confirm that selection should be applied on WW for genetic improvement in Markhoz goats.

Breeding objectives for Targhee sheep1

Breeding objectives were developed for Targhee sheep under rangeland production conditions. Traits considered were those for which EPD were available from the US National Sheep Improvement Program and included direct and maternal effects on 120-d weaning weight (WW and MM, respectively); yearling weight (YW); yearling fleece weight, fiber diameter, and staple length; and percent lamb crop (PLC), measured as the number of lambs born per 100 ewes lambing. A bioeconomic model was used to predict the effects of a change of 1 additive SD in EPD for each trait, holding all other traits constant at their mean, on animal performance, feed requirements, feed costs, and economic returns. Resulting economic weightings were then used to derive selection indexes. Indexes were derived separately for 3 prolificacy levels (1.41, 1.55, and 1.70 lambs/ewe lambing), 2 triplet survival levels (50 and 67%), 2 lamb pricing policies (with or without discounting of prices for heavy feeder lambs), and 3 forage cost scenarios (renting pasture, purchasing hay, or reducing flock size to accommodate increased nutrient requirements for production). Increasing PLC generally had the largest impact on profitability, although an increase in WW was equally important, with low feed costs and no discounting of prices for heavy feeder lambs. Increases in PLC were recommended at all 3 prolificacy levels, but with low triplet survival the value of increasing PLC eventually declined as the mean litter size increased to approximately 2.15 lambs/ewe lambing and above. Increasing YW (independent of WW) increased ewe maintenance costs and reduced profitability. Predicted changes in breeding values for WW and YW under index selection varied with lamb pricing policy and feed costs. With low feed costs or no discounts for heavy lambs, YW increased at a modest rate in association with increasing WW, but with high feed costs or discounting of heavy lambs, genetic trends in WW were reduced by approximately 50% to constrain increases in YW. Changes in EPD for MM or fleece traits generally had smaller effects on profitability than changes in PLC, WW, and YW. Two indexes designed to address current rangeland production conditions (low forage costs and discounting of heavy feeder lambs) or more intensive and integrated production with retained ownership and value-based marketing of lambs (higher forage costs and no discounting of heavy lambs) were anticipated to meet the needs of most Targhee producers.

Responses of Romney sheep to selection for resistance or susceptibility to nematode infection

AbstractDivergent breeding lines of Romney sheep, selected as lambs for consistently low or high faecal worm egg count (FEC) following natural multispecific challenge by nematode parasites, have been maintained at Wallaceville Animal Research Centre since 1979. From the start of the trial until 1992, 821 and 736 experimental lambs in lines selected for increased resistance (R) and increased susceptibility (S), respectively, were generated, with the use of 44 different sires. In order to assess genetic responses to selection, FEC and productivity data were analysed using restricted maximum likelihood procedures. By 1988 the two lines had diverged in average loge (FEC+100) by 0·67 log units, and by 1992 divergence had increased to 1·48 log units, representing 2·90 genetic standard deviations of divergence. No significant correlated responses were observed in live weights. However, by 1992 the mean score for breech soiling (dags) in the R line was proportionally 0·41 greater than in the S line (F &lt; 0·001). Yearling fleece weight was proportionally 0·15 greater in S-line than in R-line animals when grazed together under identical levels of challenge (P &lt; 0·001) but the lines did not differ significantly in fleece weight when they were grazed apart. The R line had significantly higher reproductive success than the S line (P &lt; 0·05), as measured by lambs weaned per ewe mated (1·01 v. 0·92, respectively). It is concluded that selective breeding can change the degree of resistance or susceptibility to nematode infection in Romney sheep, and selection for productivity needs to be continued at the same time in any practical breeding programme.

Faecal egg count and food intake comparisons of Romney single‐trait selection and control lines

Abstract Two sets of correlated responses were studied in five Romney selection lines and their controls. The lines were from one experiment selecting for yearling body weight or yearling fleece weight since 1967, from a second experiment selecting for weaning weight or yearling fleece weight since 1973, and from a third experiment selecting for yearling body weight since 1973. Overall, the five selection lines were evaluated whilst being run together with controls at a single site. The responses were faecal egg count (FEC) after weaning, using lamb crops born in 1990–93, and food intake using 1993‐born 7‐month‐old ram lambs. Four or five new sires were used per line per year, with 1471 and 232 animals being recorded for FEC and food intake respectively. The three body weight lines were each 20–22% heavier than their respective controls in March (6 months of age) and May. Average FEC over this time period was significantly greater by 63% in one of these three lines whereas there was no difference from the...

Single trait selection for yearling fleece weight or liveweight in Romney sheep—correlated responses in liveweight, fleece traits, and ewe reproduction

Abstract An experiment was carried out to study direct and indirect responses to selection in Romney sheep. There were two selection lines, one selected for greasy fleece weight (GFW) and the other for liveweight (LW), maintained alongside a control line (CO). Data from lambs born in 1967–90 were analysed to quantify the correlated responses to selection. By 1990, there had been an average of nine generations of selection with an average generation interval of 2.7 years. The correlated responses analysed included yearling and ewe greasy and clean fleece weights, washing yield, yearling and ewe fleece quality traits (staple length, mean fibre diameter, fibre diameter variation, loose wool bulk, Commission Internationale de l'Eclairange (CIE) Y value (brightness) and CIE Y—Z value (yellowness)), birth weight, weaning weight, yearling liveweight, ewe pre‐mating weight, and ewe reproductive rate (fertility, litter size, weaning percentage, and lamb survival). Correlated responses were estimated as the deviati...

Genetic factors affecting antibody responses to four species of nematode parasite in Romney ewe lambs

Serum levels of antibodies (Ab) and immunoglobulin G 1 (IgG 1) to the larval (L3) stage of the internal parasites Cooperia curticei and Trichostrongylus colubriformis and levels of Ab to the L3 stages of Haemonchus contortus and Ostertagia circumcincta were determined in 1432 Romney ewe lambs which were born on one farm in 1990 and 1991 and were the progeny of 63 rams. The objectives were to estimate heritabilities of, and genetic correlations among, the serum concentrations in newly weaned lambs under commercial conditions and to estimate genetic correlations of Ab and IgG 1 with production traits. Lambs were exposed to a natural parasite challenge on pasture, following an anthelmintic drench at weaning. Blood and faecal samples from 4- to 6-month-old lambs were then taken when the mean faecal nematode egg count of a monitor group reached 800–1500 eggs g −1. Heritabilities for the serum levels of the four Abs ranged from 0.25 ± 0.05 to 0.37 ± 0.06. Heritabilities for the level of IgG 1 developed against C. curticei was 0.19 ± 0.04 and against T. colubriformis, 0.18 ± 0.05. Genetic correlations between Abs for the 4 species were high, averaging 0.84, and between the two IgG 1s it was 0.82. The genetic correlations between Ab or IgG 1 levels and weight or gain traits were negative (for the 6 significant values out of 18), with yearling fleece weight positive (for the 2 significant values out of 6), whilst those with log e faecal egg count were all negative (average −0.15). These results show that Ab and IgG 1 traits are heritable and the data suggest that ram selection based on average serum antibody levels would lead to modest reduction in faecal egg counts (about 20% of the genetic gain achievable from selection based on faecal egg count), reduced weaning weight and weight gain, but increased yearling fleece weight and breech soiling.

Single trait selection for yearling fleece weight or liveweight in Romney sheep—direct responses

Abstract An experiment was carried out to study the responses to selection for yearling fleece weight and liveweight in Romney sheep. There were two selection lines, one selected for fleece weight (FW) and the other for liveweight (LW), and a control (CO) line was maintained. Data from lambs born 1967–90 were analysed to quantify the direct responses to selection. By 1990 there had been an average of 9 generations of selection with an average generation interval of 2.7 years. Realised heritabilities and selection responses were estimated from the deviation of the selected lines from a control line and by restricted maximum likelihood (REML) techniques. Realised heritabilities were 0.36 ± 0.04 for both fleece weight and liveweight respectively when estimated using the regression of response on selection differential. The corresponding REML estimates of heritabilities were 0.39 ± 0.03 for fleece weight using data from FW + CO and 0.42 ± 0.03 for liveweight using LW + CO. The direct responses to selection, d...

Effects of upgrading Turkish Angora goats with American Angoras

The objective was to estimate upgrading effects on BW and mohair traits in a herd of Turkish Angora goats that had been crossed with American Angoras. Birth weight, BW at 105 days and 6 months (3615 animals), BW at 12 months and yearling fleece weight (2384 animals), staple length and fibre diameter (1674 animals) were analyzed. Since American does were not represented, maternal population difference and heterosis were only estimable as a sum. Individual population difference and heterosis resulted in increase of birth weight by 30% of the mean of the Turkish breed. In older animals, individual population difference tended to be negative and, along with positive heterosis, resulted in small but negative total crossbreeding effects. Yearling fleece weight was increased by individual crossbreeding effects by 11% of the mean, mainly due to the population difference. Crossbreeding effects on staple length and fibre diameter were minimal, with a tendency towards a negative population difference. Maternal crossbreeding effects were minimal for all traits, which could be due to an antagonism between population difference and heterosis. On the individual level this had been observed for most traits. The experiment indicated that upgrading of the Turkish breed was unexpectedly poor, both in BW and mohair traits. It is questionable whether the costly import of American Angoras is justified to improve the Turkish goats. Further research and a more appropriate design is needed to clarify the role of recombination effects and to disentangle maternal population difference and heterosis.

Wool follicle development, wool growth and body growth in lambs treated from birth with recombinantly derived bovine somatotropin

AbstractThe effect of recombinantly derived bovine somatotropin (bST) administration on wool follicle populations, wool growth and body growth was examined in young lambs. Romney × (Border Leicester × Romney) lambs were treated with bST at doses of 0·1 or 0·3 mg/kg live weight per day, or with excipient, commencing on the day of birth and continuing at weekly intervals until the last injection was given at 11 weeks of age. Concentrations of immunoreactive somatotropin in plasma were 19·2 (s.e. 2·1), 65·2 (s.e. 2·8) and 74·7 (s.e. 4·8) μgll in the control, low dose bST and high dose bST groups, respectively. Somatotropin treatment did not alter the density of primary (P) or secondary (S) follicles in the skin, or the S/P ratio, as measured by histological examination of mid-side skin biopsy samples at 14 weeks of age. Mid-side greasy and clean wool growth during weeks 2 to 14 of the study were increased (P &lt; 0·05) in bST-treated lambs but treatment had no effect on wool growth during the immediate post-treatment period (weeks 14 to 22), or on yearling fleece weight or wool quality characteristics. Body growth was not altered by bST administration. It is concluded that bST treatment stimulates wool growth even in very young lambs but, contrary to the results of a previous study, does not alter the development of wool follicle populations.

Heritability of and genetic correlations among faecal egg counts and productivity traits in Romney sheep

Abstract A total of 2611 spring-born Romney ewe lambs, the progeny of 60 sires over 3 years, were studied on a Hawke's Bay farm to estimate the heritability of faecal egg count (FEC), and correlations between FEC and production traits. Weaning weight, an autumn weight, the weight gain between these 2 times, and yearling fleece weight were recorded in each of 3 years. A dag score was obtained in the final 2 years. An anthelmintic drench was administered to 1987-born lambs in mid January after which further treatment was withheld until April. In the 2 subsequent years, drench treatment was administered in the first week of December and further treatment withheld until the mean FEC in a small monitor group reached a target value of 1000-1500 eggs/g. Once the target value was reached, a faecal sample was obtained from all animals for an FEC, the dag score and autumn liveweight were taken, and routine drenching was then resumed. Variance components were estimated using a multivariate restricted maximum likelihood (REML) procedure, with a sire model. Heritabilities were low for the liveweights and gain traits (0.08 ± 0.04 to 0.13 ± 0.04), and moderate for fleece weight (0.41 ± 0.09), dag score (0.24 ± 0.08), and both FEC and loge (FEC + 1) (0.34 ± 0.08 and 0.27 ± 0.07 respectively). Phenotypic correlations between loge (FEC + 1) and all production traits were negative, but very low (−0.01 to −0.05). The corresponding genetic correlations were also negative and ranged from −0.05 to −0.36. Broadly similar correlations occurred between productivity traits and untransformed FEC. Phenotypic and genetic correlations between FEC or loge (FEC + 1) and dag score were positive, and thus favourable. Overall, the results demonstrate that breeding for low nematode egg output in lambs (and thus by implication improved resistance to nematode establishment) is feasible in a commercial ram breeding enterprise. However, to achieve any substantial improvement in growth rates or dag scores of lambs under untreated exposure to worm infection, an independent culling approach incorporating these traits is probably the simplest method at present.

Analysis of records of a Perendale flock

Phenotypic relationships were analysed between traits assessed at 14 months of age and for the next four consecutive years in Perendale sheep. Records from 458 sheep born between 1957 and 1967 were studied. Correlation coefficients indicated that yearling (hogget) fleece weight, quality number, fibre diameter, and staple length were good indicators of the level of these traits for the next four years. The results indicated that a weak relationship existed between hogget body weight and number of lambs weaned by the ewe over four lambings. A regression analysis of hogget traits on lifetime economic productivity of the ewe, estimated by applying various price functions to levels of production, indicated that fleece weight and hogget body weight had the greatest influence on lifetime economic productivity. Implications of the results are discussed with reference to culling of hoggets.

Environment and genetic factors affecting wool production from sub-tropical coarse wool sheep

SUMMARYWool production from different flocks of Ossimi, Rahmani and Barki Egyptian local sheep, raised at six different locations in the country was studied. Different genetic parameters for greasy fleece weight of the three breeds were estimated.Location was of significant effect on annual greasy fleece weight of Rahmani sheep only. With the adjustment for differences in yield percentages, differences in clean wool production from one location to another were slight for the three breeds. Age of ewe was of highly significant effect on annual greasy fleece weight.Heritability estimates of annual greasy fleece weight of the ewes were found to be generally low in the three breeds (range 0·00–0·34). The estimates differed markedly with age; those of the yearling fleece weight of Rahmani and Barki ewes were the highest, being 0–19 and 0–34, respectively.Repeatability estimates of annual greasy fleece weight were also low, being 0·11–0·04 and 0·29 for Ossimi, Rahmani and Barki ewes, respectively.Estimates of genetic correlation between yearling greasy fleece weight of the Ossimi and Rahmani ewes and their weaning and yearling body weights were high and positive. Those between annual greasy fleece weight of the ewes and their reproductive performance traits differed greatly in the two breeds.