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1.
Summary The aim of this study was to investigate the accuracy of ultrasound muscle (UMD) and fat depth (UFD) measurements as well as live EUROP conformation class (LEUROP) in predicting carcass composition and conformation in lambs. Measurements of 5993 lambs were analysed applying a multi‐trait animal model and the Restricted Maximum Likelihood (REML) method to obtain variance components for scanning live weight (SLW), UMD, UFD and LEUROP. The data were field records of Finnsheep and a small number of lambs from other breeds, from over 30 flocks between 1997 and 1999. The lambs were measured close to 120 days of age. Scanning was behind the last rib and at the third lumbar vertebra. Just before slaughter, scanning was repeated with a subset of lambs, whose half carcasses (n = 224) were dissected for lean, fat and bone. The UMD (third lumbar) and SLW together accounted for 51% of the variance in lean weight in the model in Finnsheep. The UFD alone explained 21% of the variance in lean percentage, UMD was a better predictor for carcass conformation than LEUROP. The estimates of heritability for SLW, UMD, UFD and LEUROP were 0.44, 0.46, 0.39 and 0.27 (with standard errors of 0.03 each), respectively. High positive genetic correlations, ranging from 0.49 to 0.69, were obtained between the four traits. Selection for UMD has resulted in genetic improvement of 0.06 mm/year (1%) in a Finnsheep nucleus flock. Conformation score of live animals could be considered to be included in the breeding programme if uniformity of assessment is assured by continued training.  相似文献   

2.
T. Kvame  O. Vangen 《Livestock Science》2007,106(2-3):232-242
Genetic parameters for carcass traits in lambs at weaning (average age of 128 days) measured by ultrasound (n = 1821) and computer tomography (CT) (n = 234), and response to selection for ultrasound eye muscle depth (UMD) and carcass LEAN weight, were estimated. The research flock comprised a meat line (ML) and a control line (CL) of Norwegian White Sheep. The ML was crossed with Texel from 1998, and selected for UMD from 1993 to 2001, and for LEAN weight from 2001 to 2004. For CT scanning, a mean of 23 images was taken per animal. Genetic parameters were estimated with univariate and bivariate mixed-animal models using AIREML, including all animals with records and their relatives. The statistical models included fixed effects, live weight or age of lamb at weaning (covariate), and a random genetic effect.

Heritability estimates for weight of LEAN, FAT and BONE were 0.57, 0.29 and 0.51 using model corrected for live weight. The heritability estimates were lower when these traits were adjusted for age. High genetic correlation was found between LEAN and UMD (0.70), and between carcass FAT and ultrasound fat depth (UFD) (0.82). The genetic trend for UMD regressed on year of birth was significantly greater for ML than CL in 2004.  相似文献   


3.
Small ruminants are affected by gastrointestinal nematode (GIN) infection. A promising alternative strategy for control of GIN infection is to increase the level of resistance in the population by taking advantage of the host's immune response. Immunoglobulin A (IgA) and E (IgE) are known to be involved in immune response to GIN. The aim of this study was thus to investigate genetic parameters of IgA and IgE responses against Haemonchus contortus in Creole kids naturally challenged at pasture and to determine the relationship with other resistance criteria such as faecal egg counts, packed-cell volume, eosinophil counts and bodyweight. Variance and covariance components for genetic and residuals effects for each trait were estimated on 3862 males at 11 months of age. Heritability estimates for IgA and IgE ranged between 0.15 and 0.57. Strong positive genetic correlations were observed between either IgE or IgA responses against L3 and adult excretory/secretory products (ESP) antigens of H. contortus, suggesting that the humoral immune response is not specific to the life cycle stage of the parasite suggesting that there is substantial cross recognition between the different parasite antigens. Heritability estimates for faecal egg count (FEC), packed-cell volume (PCV) and bodyweight (BW) were in accordance with previous results in Creole kids. Blood eosinophil counts were found moderately heritable and negatively correlated with FEC, suggesting that this cell population plays a role in resistance to nematode parasite infection in Creole goats. IgA response was positively correlated to FEC, in contrast with the negative correlation between IgE against L3 of H. contortus and FEC. In Creole goats, IgA response against L3 or ESP of H. contortus would rather be associated with the worm burden than an immune protective response. The immune response involving activity of IgE against L3 of H. contortus may be one important pathway for development of resistance to gastrointestinal nematode infections in Creole goats.  相似文献   

4.
Offspring-dam regression was used to estimate the heritability of strongyle faecal egg counts (FEC) of traditionally raised West African N'Dama cattle in the Central River Division in The Gambia. Faecal samples were taken monthly from June-October 1992, and again from July-October 1993, including 179-463 dams and their calves sampled on each occasion. The only proven genetic relationship was the dam-offspring relationship. Gastrointestinal strongyle FEC was expressed as epg (eggs per gram faeces). Regression of offspring FEC on dam FEC, showed a heritability (h(2)) of 0.18 (95% Confidence Limits 0.10, 0.25). Heritabilities were higher at the beginning and end of the rainy season than during the months of the peak rainy season. This is in line with earlier suggestions that genetic control of faecal egg counts is most effective during periods of low parasite transmission. There was a significant (p<0.001) increase in heritability of 0.086+/-0.018 with each year of age of the corresponding offspring. In view of the virtual absence of national cattle breeding systems in West Africa, which are a precondition for exploitation of heritable traits in cattle, integrated control using improved management and strategic prophylaxis remain the methods of choice to control gastrointestinal nematodes in the given conditions.  相似文献   

5.
Genetic and phenotypic parameters were estimated for production and disease traits (including dagginess) from about 2 million pedigree-recorded animals born between 1990 and 2008 in New Zealand dual-purpose ram breeding flocks. This is the most comprehensive study of genetic parameter estimates for the New Zealand sheep industry to date and includes estimates that have not previously been reported. Estimates of heritability were moderate for BW at 8 mo (LW8), fleece weight at 12 mo (FW12), dagginess score at 3 and 8 mo (DAG3, DAG8; 0.31 to 0.37), typical for weaning weight (WWT), fecal egg count in summer (FEC1) and autumn (FEC2), and analogous Nematodirus counts (NEM1, NEM2; 0.17 to 0.21), and low for number of lambs born to ewes (NLB; 0.09). The genetic correlations among production traits, WWT, LW8, and FW12, were positive and moderate to high. Correlations of DAG3 and DAG8 with production and disease traits were low and mostly negative. The NLB had low, but typically positive, correlations with other traits. Disease traits also had low, but positive, correlations with production traits (WWT, LW8, and FW12), and were highly correlated among themselves. In general, the heritability estimate for BW and dagginess were greater than what is currently used in the New Zealand genetic evaluation service (Sheep Improvement Limited), and the availability of accurate estimates for dagginess plus parasite resistance and their genetic correlations with production traits will enable more accurate breeding values to be estimated for New Zealand sheep.  相似文献   

6.
This study describes responses to artificial infection with Haemonchus contortus in ewes and lambs of 50% Dorset, 25% Rambouillet, and 25% Finn-sheep ancestry and provides estimates of genetic parameters for measures of parasite resistance. One hundred ninety-eight ewes out of 64 sires, and 386 lambs out of 25 sires were evaluated in autumn and spring of 2 yr. Ewes were dewormed shortly after weaning their lambs and lambs were dewormed at about 120 d of age. One week after deworming, ewes and lambs were dosed with approximately 10,000 infective larvae of H. contortus. After infection, BW, fecal egg counts (FEC), and packed cell volume (PCV) were measured weekly for 7 wk in lambs kept in drylot and fortnightly for 11 wk in ewes on pasture. Summary traits were defined as initial PCV, mean BW across all times, and means for PCV (MPCV) and log-transformed FEC (MLFEC) at wk 3 to 7 after infection for lambs and wk 3 to 11 after infection for ewes. Ewes and lambs did not lose weight overall in any year or season, but there was no consistent effect of year or lambing season on mean LFEC or mean PCV during infection in either ewes or lambs. Yearling ewes were less resistant to infection than older ewes, with lower PCV (P < 0.05) and higher LFEC (P < 0.05). During infection, PCV was positively correlated with BW and negatively correlated with LFEC in both ewes and lambs. In lambs, heritabilities were 0.39 (P < 0.01) for PCV, 0.10 (P < 0.05) for LFEC across all measurement times, and 0.19 (P < 0.01) for three measures of LFEC taken at the peak of infection. Heritability estimates for ewes were 0.15 (P < 0.05) for PCV and 0.31 (P < 0.01) for LFEC. Repeatabilities for LFEC and PCV across measurement times were moderate in ewes and lambs. Correlations between dam and lamb records for MLFEC were generally low, suggesting different mechanisms of resistance in lambs and nonlactating ewes. Ewes with higher genetic merit for growth as lambs were less resistant to infection as adults, but genetic merit for fertility and prolificacy were not related to parasite resistance. Lambs with higher genetic merit for body weight were more resistant to infection. Selection for resistance to H. contortus is therefore possible and should not adversely affect growth of lambs and fertility of ewes in this production environment.  相似文献   

7.
An experiment was conducted over two successive years (2002 and 2003) to investigate the effects of grazing improved permanent pasture (mainly perennial ryegrass/white clover) by cattle or sheep, either sequentially or mixed, on the faecal egg counts and growth rates of weaned lambs when treated with anthelmintics. The grazing season was divided into two parts, May-July then July-October, relating to the pre- and post-weaning of the lambs. Four grazing regimes, replicated three times, were compared: (1) sheep only from May to October (SS); (2) cattle May to July followed by lambs until October (C/S); (3) cattle and sheep May to July followed by lambs until October (C+S/S); and (4) cattle and sheep May to July followed by cattle and lambs until October (C+S/C+S). Sward height was maintained at 6 cm using a "put and take" stocking system. At weaning, lambs were weighed and treated with an anthelmintic (0.08% ivermectin drench, Oramec) before being allocated to plots. They were then weighed and drenched every 28 days until the end of the experiment (Day 84). Faecal egg counts (FEC) were measured in all lambs immediately prior to each anthelmintic treatment. In 2002 and 2003, there were differences between the groups in FEC, with the SS lambs having the highest values and C/S lambs the lowest (P<0.01). There were also differences in the rate of liveweight gain of the lambs in each of the study years: for this parameter SS lambs had the lowest growth rate but the fastest growth was in C+S/C+S lambs not C/S lambs (P<0.01), indicating that these differences were due to factors other than parasite infection. Overall, sequential grazing of pastures with cattle then sheep reduced the faecal egg counts in lambs regularly treated with anthelmintics when compared with lambs grazing in mixed systems with cattle and sheep or with sheep only systems, however, the highest growth rates were observed in lambs in the mixed cattle/sheep grazing system throughout.  相似文献   

8.
Horses, mules and donkeys are indispensable farming and working animals in many developing countries, and their health status is important to the farmers. Strongyle parasites are ubiquitous in grazing horses world-wide and are known to constitute a threat to equine health. This study determined the prevalence of strongyle infection, the efficacy of ivermectin and fenbendazole treatment, and strongyle re-infection rates of working horses during the dry months in Nicaragua. One hundred and five horses used by farmers for transport of people and goods were randomly allocated into three treatment groups, i.e., the IVM group treated with ivermectin, the FBZ group treated with fenbendazole and the control group treated with placebo. Determined by pre-treatment faecal egg counts (FECs), horses showed a high prevalence (94%) of strongyle parasites with high intensities of infection (mean FEC of 1117 eggs per gram (EPG) with an SD of 860 EPG, n=102). Body condition scores of all horses ranged from 1.5 to 3.5 with a mean of 2.4 (scales 1-5). Fourteen days after treatment faecal egg count reductions (FECRs) were 100% and 94% in the IVM and the FBZ groups, respectively. The egg reappearance period (ERP) defined as the time until the mean FEC reached 20% of the pre-treatment level, was estimated as 42 days for the FBZ group and 60 days for the IVM group. Individual faecal cultures were set up and the larval differentiation revealed a 36% prevalence of Strongylus vulgaris before treatment (n=45). In the FBZ group, 25% of the horses were S. vulgaris-positive 70 days post treatment compared to 11% in the IVM group. Our results indicate that strongyle infection intensities in Nicaragua are high and that S. vulgaris is endemic in the area. Furthermore, efficacies and ERPs of IVM and FBZ were within the expected range with no signs of anthelmintic resistance.  相似文献   

9.
AIM: To assess the in vivo anthelmintic activity of condensed tannins (CT) in the forage species Dorycnium rectum and Medicago sativa, and in an extract from grape (Vitus vinifera) seeds (GSE), against two species of parasite, Teladorsagia (Ostertagia) circumcincta and Trichostrongylus colubriformis, at different stages of their life cycle, in sheep that were parasite-na?ve or previously exposed to nematodes. METHODS: In Trial 1, a factorial treatment structure was used to compare faecal nematode egg counts (FEC) and worm burdens in 40 weaned Romney lambs fed either the CT-containing forage D. rectum (12% dry matter; DM) or M. sativa (lucerne; 0.2% DM). Twenty na?ve and 20 previously-exposed lambs were drenched free of parasites then reinfected with known species and numbers of parasites, and housed in pens indoors on a diet of lucerne pellets and chaffed hay. Groups of lambs (n=5 lambs per group) were fed one of the forages over one of two time periods within the parasite's life cycle. Six to nine days after the last feeding of fresh forages, faecal samples were collected for FEC, and all lambs were slaughtered and worm counts conducted. In Trial 2, 12 Suffolk x Romney lambs were surgically implanted with an abomasal cannula and then housed indoors in metabolism crates. After infection with parasites, six lambs were infused continuously over a 14-day period with a commercially available CT GSE (96% DM, made up to 34 g/L in water); the remaining lambs were infused with water. During infusion, samples were collected for egg hatch and larval development assays. After infusion, samples were collected for FEC, and all lambs were slaughtered and worm counts conducted. RESULTS: In Trial 1, there was a significant (p<0.001) difference in burdens of O. circumcincta between na?ve lambs and those previously exposed to parasites, but no other differences were recorded. In Trial 2, lambs infused with GSE had significantly (p<0.05) fewer T. colubriformis at slaughter and significantly (p<0.001) fewer eggs hatched in the egg hatch assay (EHA) than for lambs infused with water. Overall, the differences attributable to GSE were small in magnitude, being an 11% drop in egg hatch, and an 18% drop in numbers of adult T. colubriformis after 14 days of continuous infusion. No other differences were recorded. CONCLUSION: The results indicate that the in vivo anthelmintic activity of these CT sources is, at best, modest and is unlikely to be of any practical value. Further, these data emphasise that in vitro activity is an unreliable indicator of in vivo efficacy for CT-containing forages and extracts.  相似文献   

10.
Fecal egg count (FEC) has been widely used as an indicator of host resistance to gastrointestinal parasites in sheep and has been shown to be a heritable trait. Two other possible indicators of parasites, dag score (DS; accumulated fecal material) and fecal consistency score (FCS), were investigated in this study, along with BW. All four traits were studied to see how heritability and genetic correlations varied with age from weaning (4 mo) to hogget age (approximately 400 d). More than 1,100 lambs, the offspring of 37 rams, were recorded eight times between weaning (3 to 5 mo of age) and hogget age (13 to 18 mo of age) on two farms. Sire models were fitted to the data from each trait at each recording and in a repeatability model involving the whole data set. Overall, the heritabilities were 0.28+/-0.072 (FEC), 0.11+/-0.036 (DS), 0.12+/-0.036 (FCS), and 0.23+/-0.070 (BW). By fitting random regression models to the time-series data, it was possible to see how these heritability values varied as the lambs aged, from weaning to hogget age. The heritability of FEC rose from 0.2 at weaning to 0.65 at 400 d. Dag score had a higher heritability (0.25) in the middle of the age range and a low value at weaning (<0.1) and hogget age (0.16). The heritability of FCS was low, with a value of 0.2 at weaning reducing to 0.05 as the animals aged. Body weight had zero heritability at weaning, which rose to greater than 0.6 at hogget age. Most traits had low genetic correlations between them, the only exception being that between FCS and DS (0.63). Most genetic correlations varied little over the age range with the exception of FEC and BW, which fell from 0 at weaning to -0.63 at hogget age. Whereas FCS and DS may be good indicators of scouring, they are very different from FEC as an indicator of host resistance to gastrointestinal parasites.  相似文献   

11.
Reasons for performing study: Increasing prevalence of anthelmintic resistance in equine nematodes calls for a reexamination of current parasite control programmes to identify factors influencing control efficacy and development of resistance. Objectives: To investigate if associations occur between prevalence of parasitic nematodes and management practices. Methods: German horse farms (n = 76) were investigated in 2003 and 2004. Information on farm and pasture management with respect to endoparasite control measures obtained using a questionnaire survey. Faecal examinations were performed in parallel. Results: Horses (n = 2000) were examined by faecal nematode egg counts, grouped into foals, yearlings and mature individuals for statistical analyses. Farms were categorised into 3 types, riding, stud farms and small holdings. Count regression models were used to analyse strongyle faecal egg count data. Following dichotomisation of faecal egg count (FEC) data, prevalence of strongyle and Parascaris equorum infections were assessed by logistic regression models as a function from various management factors. Yearlings on stud farms showed a 2‐fold higher risk of being positive for strongyle FEC, higher (i.e. ≥3 per year) anthelmintic drug treatment frequencies were associated with reduced strongyle infection rates only in mature individuals but not in foals or yearlings, foals on farms fertilising pastures with horse manure had a significantly higher risk of being P. equorum FEC positive and yearlings on stud farms were more often showing incomplete FECR following anthelmintic treatment compared to yearlings on other farm types. The mean yearly treatment frequencies per age group were: foals 4.52, yearlings 3.26 and mature horses 2.72 times, respectively. Conclusion and potential relevance: To delay the development of anthelmintic, resistance management should include additional nonchemotherapeutic parasite control strategies, FEC‐monitoring, controlled quarantine treatment of new arrivals and control of efficacy by the faecal egg count reduction test on a regular basis.  相似文献   

12.
A survey on the prevalence and intensity of infection with gastrointestinal helminths of Dorper sheep in relation to age and weather factors was carried out on a ranch in Kajiado district, a semi-arid area of Kenya for a period of 13 months (May 1999 to May 2000). Faecal samples from lambs (3 months to 1 year), yearlings (1-2 years) and adult breeding ewes (2-4 years) were examined for helminth egg output and helminth genus composition at 3-week intervals. The results indicated that the prevalence of strongyle and tapeworms infections were highest for lambs, followed by the adult breeding ewes and then for the yearlings. In all age groups the proportions of infected animals were higher during the wet season than in the dry season for both nematodes and tapeworms. The mean strongyle egg counts were higher during the dry season for lambs, but were higher during the wet season for the other age groups. Mixed strongyle infections were detected, with Trichostrongylus (55 %), Haemonchus (28 %), Cooperia (10.5 %) and Oesophagostomum (6.5 %) being the most frequently encountered genera throughout the study period. The trends in strongyle faecal egg counts indicated the occurrence of hypobiosis, with resumption of development towards the end of the dry season and at the onset of the short rains in October and November. Self-cure was also observed in September and November in all age groups, although less frequently in lactating ewes. The prevalence and intensities of infection with gastrointestinal helminths in this area appeared to be influenced by the age of the host and weather factors.  相似文献   

13.
Genetic parameters of resistance to gastrointestinal nematodes were estimated in Rh?n sheep, a local sheep breed in Germany. In the first year, a total of 131 lambs (born between January and February 1998) from five rams were evaluated. Faecal egg counts (FEC) (n=1528) were measured in all lambs every 2 weeks until 4 months of age and every 4 weeks until 12 months of age in female lambs. In the second year, a total of 129 lambs (born between January and February 1999) from the same rams were evaluated. FEC (n=645) were measured in the lambs every 4 weeks until 5 months of age. Blood was taken in both years at the time of faecal sampling from the jugular vein and haematocrit was measured. Heritabilities for log(10)(FEC+25) were between 0.11 and 0.44. Heritabilities for the corresponding haematocrits were between 0.19 and 0.26 depending on the number of samples taken in account. A significant negative correlation was estimated for the parameters of FEC and daily weight gain (r=-0.57). The results confirm the feasibility of genetic selection in Rh?n sheep for resistance to nematode parasites in an environment where Trichostrongylus spp./Teladorsagia spp., Haemonchus contortus and Cooperia spp. are the dominant species. Breeding decisions can be based on one or two samples depending on the mean values and ranges of FEC and haematocrit, respectively.  相似文献   

14.
In order to explore genetic variability of wool production and other quantitative traits, an 8-cohort divergent selection experiment for total fleece weight (TFW) was carried out in French Angora rabbits. Studies were made on the wool production of 669 female rabbits born between 1994 and 2001 and having produced wool from the third to 12th harvests. The aim of the selection experiment was to obtain two divergent lines (low and high) on total fleece weight. The studied traits included total fleece weight, weight of the two qualities of wool (WAJ1 and WAW1), homogeneity (HOM), live body weight at ages of 4 (LW4), 8 (LW8), 12 (LW12), 16 (LW16), and 20 (LW20) weeks and then 9 weeks before each harvest (9LW). A preliminary analysis of non-genetic factors was done with the GLM procedure. The genetic parameters and genetic trends were analysed using a BLUP animal model. Heritability estimates for TFW, WAJ1, WAW1, HOM, LW4, LW8, LW12, LW16, LW20 and 9LW were 0.38, 0.30, 0.10, 0.06, 0.30, 0.09, 0.14, 0.32, 0.39 and 0.45, respectively. Genetic and phenotypic correlations between TFW and WAJ1 were high (0.98 ± 0.01 and 0.89 ± 0.01, respectively). There was a low genetic correlation between TFW and 9LW (0.26 ± 0.12). After eight cohorts of selection, the divergence between the lines was approximately three genetic standard deviations. Selection for total fleece weight had a generally beneficial effect on fleece quality.  相似文献   

15.
Genetic breed differences, heterosis, recombination loss, and heritability for reproduction traits, lamb survival and growth traits to 90 days of age were estimated from crossing D'man and Timahdite Moroccan breeds. The crossbreeding parameters were fitted as covariates in the model of analysis. The REML method was used to estimate (co)variance components using an animal model. The first estimation of crossbreeding effects for Timahdite and D'man breeds shows that breed differences in litter traits are mainly of maternal genetic origin: +1.04 lambs, +1.88 kg, +0.60 lambs, and +2.23 kg in favour of D'man breed for litter size at lambing, litter weight at lambing, litter size at weaning, and litter weight at 90 days, respectively. The breed differences in lamb growth and survival are also of maternal genetic origin for the majority of traits studied, but in favour of the Timahdite breed: +3.48 kg, +45 g day−1 and +0.19 lambs for weight at 90 days, for average daily gain between 30 and 90 days of age, and for lamb survival to 90 days, respectively. The D'man direct genetic effect was low and negative for survival and birth weight of lambs during the first month of life. All traits studied showed positive heterosis effects. Recombination loss effects were not significant. Therefore, crossbreeding of Timahdite with D'man breeds of sheep can result in an improved efficiency of production of saleable lambs. Heritability estimates were medium for litter size but low for the other reproduction traits. Direct heritabilities were low for body weights and lamb survival at 90 days and the corresponding maternal heritabilities showed, however, low to moderate estimates. For litter traits, the estimates of genetic and phenotypic correlations were positive and particularly high for genetic correlations.  相似文献   

16.
A mathematical model was developed to investigate the impact of level of Teladorsagia circumcincta larval pasture contamination and anthelmintic treatment on genetic parameter estimates for performance and resistance to parasites in sheep. Currently great variability is seen for published correlations between performance and resistance, with estimates appearing to vary with production environment. The model accounted for host genotype and parasitism in a population of lambs, incorporating heritable between-lamb variation in host-parasite interactions, with genetic independence of input growth and immunological variables. An epidemiological module was linked to the host-parasite interaction module via food intake (FI) to create a grazing scenario. The model was run for a population of lambs growing from 2 mo of age, grazing on pasture initially contaminated with 0, 1,000, 3,000, or 5,000 larvae/kg DM, and given either no anthelmintic treatment or drenched at 30-d intervals. The mean population values for FI and empty BW (EBW) decreased with increasing levels of initial larval contamination (IL(0)), with non-drenched lambs having a greater reduction than drenched ones. For non-drenched lambs the maximum mean population values for worm burden (WB) and fecal egg count (FEC) increased and occurred earlier for increasing IL(0), with values being similar for all IL(0) at the end of the simulation. Drenching was predicted to suppress WB and FEC, and cause reduced pasture contamination. The heritability of EBW for non-drenched lambs was predicted to be initially high (0.55) and decreased over time with increasing IL(0), whereas drenched lambs remained high throughout. The heritability of WB and FEC for all lambs was initially low (～0.05) and increased with time to ～0.25, with increasing IL(0) leading to this value being reached at faster rates. The genetic correlation between EBW and FEC was initially ～-0.3. As time progressed the correlation tended towards 0, before becoming negative by the end of the simulation for non-drenched lambs, with increasing IL(0) leading to increasingly negative correlations. For drenched lambs, the correlation remained close to 0. This study highlights the impact of IL(0) and anthelmintic treatment on genetic parameters for resistance. Along with factors affecting performance penalties due to parasitism and time of reporting, the results give plausible causes for variation in genetic parameter estimates previously reported.  相似文献   

17.
Strongyle parasites are ubiquitous in grazing horses and constitute a potential threat to equine health. Feces were collected from six horses four times daily over a period of 5 days. Fecal egg counts (FECs) were performed to identify any diurnal rhythms in strongyle egg shedding and to quantify variability at the different levels: individual horses, repeated counts, repeated subsamples, different time points, and different days. No significant differences in FECs were found between the different time points (P = .11). The variables—horse, day, subsample, and egg count—accounted for a variance of 104.83, 0.10, 7.24, and 5.61, respectively. The apparent lack of additional variability between the four different time points suggests that time of the day chosen for collecting fecal samples does not constitute a source of error in field studies. The majority of variability exists between different subsamples and repeated egg counts on the same subsamples, whereas the variability of FECs between following days can be considered negligible. The findings of this study have implication for designing and performing field surveillance of strongyle FEC levels and applying the FEC reduction test for evaluating anthelmintic efficacy.  相似文献   

18.
The number of eggs from gastrointestinal nematodes per gram of faeces (worm egg count WEC) is commonly used to determine the need for anti-parasite treatments and the breeding value of animals when selecting for worm resistance. Diarrhoea increases faecal moisture and may dilute the number of worm eggs observed. To quantify this effect, egg counts in sheep at pasture were simulated by dosing 15 animals with chromic oxide particles. The simulated WEC diminished as faecal moisture increased. When faeces were dried, simulated WEC per unit dry matter was not influenced by the amount of faecal moisture present prior to drying. The results suggest that adjustment for faecal moisture may provide an improved estimate of FEC. Drying faeces to calculate the WEC per unit dry matter would provide such an adjustment but may not be practical for industry application. In the past, the CSIRO McMaster Laboratory has used an adjustment factor developed by Gordon based on the classification of faecal consistency derived from the morphology of faeces. To examine the utility of an adjustment factor based on faecal consistency score (FCS), the relationships between FCS and simulated WEC and dry matter were examined. Dry matter and simulated WEC exhibited an exponential decline as FCS increased. The relationship between FCS and dry matter was further examined in 368 samples collected over 12 months from sheep at pasture, where it was observed that dry matter showed a linear decline as FCS increased. Adjustment factors based on dry matter were similar to those proposed by Gordon however adjustment factors predicted from simulated WEC diverged from the remainder for FCS>4. As no samples scored FCS 5 in the study of simulated FEC, the adjustment factors based on the larger study that included samples with FCS 5 was therefore considered more robust. Adjustment factors were given by the equation: WEC(estimated)=(WEC(observed)/(34.21-5.15 FCS))x29.06. This equation estimates for samples with FCS>1 the WEC that would be expected if the samples were FCS 1, the faecal consistency score for normal faeces. The impact of adjustment of observed WEC for faecal moisture predicted by FCS on decision points for treatment and on estimated breeding values requires further examination.  相似文献   

19.
Two digestibility experiments were carried out to comparatively measure true phosphorus (P) digestibility and the faecal endogenous P loss associated with soybean meal (SBM) and wheat middling meal (WM) for growing pigs by the simple linear regression analysis technique and the substitution method. Eight barrows, with an average initial body weight 21 kg, were randomly divided into two groups of four pigs with each group being fed four test diets according to a 4 × 4 Latin square design. Eight maize starch-based diets containing four levels (on dry matter basis) of P (0.20, 0.24, 0.36 and 0.42%) and P (0.181, 0.26, 0.36, and 0.43%) were formulated from SBM and WM as a sole source of P, respectively. Chromic oxide (0.30%) was used as a digestibility marker. Each experimental period comprised 8 d with a 4-d adaptation and a 4-d collection of faecal samples. Levels of the assay ingredient substitutions had no effects (P > 0.05) on true P digestibility and the endogenous P loss associated with SBM and WM measured by the substitution method. There were no differences (P > 0.05) between the regression technique and the substitution method in measuring the true P digestibility (SBM: 49.4 ± 3.51 vs. 50.6 ± 2.4; WM: 63.7 ± 5.0 vs. 63.2 ± 5.4%) as well as the faecal endogenous P loss (SBM: 0.62 ± 0.10 vs. 0.71 ± 0.11; WM: 0.65 ± 0.16 vs. 0.70 ± 0.17 g/kg dry matter intake) for the growing pig. Thus, true P digestibility and the faecal endogenous P loss in feed ingredients for pigs may be measured by using the regression analysis technique and the substitution method.  相似文献   

20.
Knowledge of horses that shed the same number of strongyle eggs over time can lead to the optimization of parasite control strategies. This study evaluated shedding of strongyle eggs in 424 horses on 10 farms when a selective anthelmintic treatment regime was used over a 3-year period. Faecal egg counts were performed twice yearly, and horses exceeding 200 eggs per gram (EPG) of faeces were treated. The results are presented as probabilities of the egg count outcome, when two previous egg counts are known. A horse with no strongyle eggs detected in the two previous faecal examinations had an 82% probability of a zero, and a 91% of being below 200 eggs per gram in the third examination. A horse with the two previous egg counts below 200 EPG had an 84% probability of being below 200 EPG the third time as well. When faecal egg counts exceeded 200 EPG on the previous two counts, the probability for a horse exceeding 200 EPG the third time was 59%. In conclusion, these data demonstrate consistent shedding from one grazing season to another in a majority of horses despite treatment of horses exceeding 200 EPG.  相似文献   

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