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1.
A complete diallel cross involving 3 maternal lines of rabbit was performed to estimate cross-breeding parameters for functional longevity. This trait was defined as the ability to delay involuntary culling. The lines considered, A, V, and Prat, had all been selected by litter size at weaning for a long period. Data were related to a total of 653 does belonging to the 9 genetic types from the diallel cross; does were reared and bred on the same commercial farm. Survival analysis was performed using a Cox proportional hazard model. The model incorporated time-dependent factors, such as year-season, litter size, and the interaction between cycle and physiological status of the female; time-independent factors, such as the genetic type of the doe; and sire and dam random factors. Crossbreeding parameters were estimated from the solutions obtained for the type of doe and its estimated variance-covariance matrix, using a generalized least squares procedure. The estimated parameters were the differences between lines in direct genetic effects and maternal genetic effects and individual heterosis. Relevant differences were observed in direct genetic effects between lines A and Prat but not in any maternal effects. Heterosis was found to be significant and favorable between lines A and Prat, and between the lines V and Prat. The magnitude of this effect was variable but important, especially in the first cross. Results stress the importance of using crosses between specialized lines to produce does for intensive meat rabbit production.  相似文献   

2.
Variance components were estimated in 3 lines of rabbits selected for litter size at weaning (A, Prat, and V) to test one of the assumptions of the models used for selection: that litter size data at different parities are repeated measurements of the same trait. Multiple-trait analyses were performed for the total number of kits born (TB), the number of kits born alive (BA), and the number of kits weaned (NW) per litter. Estimates were obtained by REML in multivariate analyses, including all of the information of the selection criteria, under a repeatability model or a multiple-trait model, considering litter size at the first, second, and subsequent parities as different traits. Models included the fixed effects of the physiological status of the female and the year-season of mating day, buck and doe random permanent environmental effects, and doe additive genetic effects. Results indicated that prolificacy was determined mainly by doe components and that the service sire had a very small effect. Heritabilities for the first and second parities were greater than the estimates obtained under the repeatability model (0.04 to 0.14 for the repeatability model). In the A and V lines, similar values of heritability were found at the first and second parities, but in the Prat line heritability at the second parity was always greater than at the first and greater parities (values of 0.21, 0.17, and 0.15 for TB, BA, and NW, respectively, in second parities of the Prat line). Genetic correlations between the same traits at different parities were approximately 0.8 for all traits in line A, but much lower in the other 2 lines. On average, the values were 0.64 for TB, 0.48 for BA, and 0.39 for NW between the first and second parities, and 0.65 for TB, 0.56 for BA, and 0.45 for NW between the first and third and greater parities. Genetic correlations between the second and greater parities showed the greatest values (approximately 0.8) in lines A and Prat for all traits, but they were lower in line V (0.63 for BA and 0.37 for NW). The heterogeneity of heritabilities and genetic correlations between parities lower than 0.9 suggests that litter size at different parities could be considered as different traits when genetic evaluations are performed. However, when the accuracies of predicted breeding values under a multiple-trait and a repeatability model were calculated, assuming the first to be the true model, the values obtained were nearly the same for all traits in all lines.  相似文献   

3.
Data from the National Pork Producers Council Maternal Line National Genetic Evaluation Program were used to compare longevity of sows from 6 commercial genetic lines and to estimate the phenotypic associations of sow longevity with gilt backfat thickness, ADG, age at first farrowing, litter size at first farrowing, litter weight at first farrowing, average feed intake during lactation, and average backfat loss during lactation. The lines evaluated were American Diamond Genetics, Danbred North America, Dekalb-Monsanto DK44, Dekalb-Monsanto GPK347, Newsham Hybrids, and National Swine Registry. The data set contained information from 3,251 gilts, of which 17% had censored longevity records (sows lived longer than 6 parities). The line comparison was carried out by analyzing all lines simultaneously. Because the survival distribution functions differed among genetic lines, later analyses were carried out separately for each genetic line. All analyses were based on the non-parametric proportional hazard (Cox model). Dekalb-Monsanto GPK347 sows had a lower risk of being culled than sows from the other lines. Moreover, the shape of the survival distribution function of the Delkab-Monsanto GPK347 line was different from the other 5 lines. The Dekalb-Monsanto 347 line had lower culling rates because they had lower gilt reproductive failure before the first parity than gilts from the other lines. Within line, sows with lower feed intake and greater backfat loss during lactation had a shorter productive lifetime. Thus, producers should implement management practices having positive effects on sow lactation feed intake. Additionally, the swine genetics industry is challenged to simultaneously improve efficiency of gain of their terminal market pigs and to obtain high feed intake during lactation of their maternal lines for future improvement of sow longevity. Recording sow feed intake and backfat loss during lactation in nucleus and multiplication breeding herds should be considered. Between-line differences in this study indicate that it is possible to select for sow longevity, but more research is needed to determine the most efficient selection methods to improve sow longevity.  相似文献   

4.
Reproductive and maternal performance of a line of mice selected for large first parity litter size (L+) and a control line (K) were compared under two mating systems: (1) postpartum mating (PP), in which females undergo concurrent gestation and lactation, and (2) postweaning mating (PW), in which females wean their litter before being remated. Females were evaluated in their first two parities. Litters in each line were standardized at birth to 4, 8, 12 or 16 pups in parity 1, and to 10 pups in parity 2. Concurrent gestation had no adverse effect on postnatal maternal performance in parity 1 of either line. In parity 2, both L+ and K declined in reproductive and postnatal maternal performance in PP compared with PW. The pattern of delayed implantation as number of pups nursed increased was similar in both lines under the PP regimen. Several interactions indicated that reproductive performance of L+ was more adversely affected than in K under postpartum mating. Pup mortality was greater in L+ than K under PP but not under PW. In the PP regimen, L+ dams nursing 12 and 16 pups had a lower mating success rate and dams nursing 16 pups had a smaller litter size and higher pup mortality than did K dams. Thus, when L+ dams nurse their natural litter, frequently exceeding 16 pups, their reproductive advantage over K dams observed in PW would be eliminated in PP. If the differences in the first two litters reflect subsequent parities, lifetime reproductive performance in the PP environment would be reduced in the high fecundity line. High fecundity appears to depend upon the environment of selection.  相似文献   

5.
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6.
Reproductive performance was evaluated on lines of rats selected 34 generations for up (U) and down (D) 3- to 9-wk weight gain and from a control (C). Direct response to 3- to 9-wk weight gain was 16% in U and -8% in D lines. Inbreeding was similar among lines. Both selection lines were poorer in percentage of fertile pairs than the C line, especially so in D (P less than .10). The lines differed (P less than .05) in litter size born with means of 11.4, 10.4 and 9.6 for U, C and D, respectively. The significant positive correlated response in litter size corresponded to that expected from intraline association with female body weight. Selection for increased postweaning gain resulted in 5% earlier age but little change in weight at vaginal opening. The D line was similar to C in age, but 7% lighter in weight at vaginal opening. The U line was significantly higher (14, 12 and 69%) for ovulation rate, number of fetuses and post-implantation losses, but not for pre-implantation losses. The D females were similar to C females in all components of litter size. Males of all lines were similar in age at first mating, but U males were 22% heavier than C males in weight at first mating. A positive correlated response in weight of testes at 91 d of age disappeared when adjusted for intraline association with body weight.  相似文献   

7.
Annual performance measurements, age structures of female pig inventories, and by-parity culling rates were abstracted from data files of 110 herds that participated in a data-share program in Japan. Parity at culling was used as a prime measurement of longevity, whereas pigs weaned x mated female(-1) x year(-1) (PWMFY) was a prime measurement of reproductive efficiency. High or low longevity herds were based on the greatest 50% of the herds or the remaining herds ranked by parity at culling, whereas high or low reproductive efficiency herds were grouped according to the greatest 50% of the herds or the remaining herds ranked by PWMFY. Measurements were analyzed as a 2 x 2 factorial arrangement, using the main effects of the 2 herd groups of longevity (high or low) and reproductive efficiency (high or low). Means of parity at culling and PWMFY were 4.6 (SD = 0.82) and 21.2 (SD = 3.02), respectively. The high longevity group had 1.27 greater parities at culling than the low longevity group (P < 0.05), but no differences between the high and low longevity groups were found in PWMFY (P = 0.21). No differences between the high and low efficiency groups were found in parity at culling (P = 0.50). No interactions between the longevity and efficiency groups were found on any longevity or efficiency measurement (P > 0.20). In herd management, the percentage of reserviced females and the percentage of multiple matings were associated with the longevity group and the efficiency group (P < 0.05). The high longevity group had lower culling rates in parity 0 to 6 than the low longevity group (P < 0.05), whereas no differences between the low and high efficiency groups were found in culling rates in parity 0 to 2 (P > 0.20). This study suggests that measures to achieve longevity and high reproductive efficiency in breeding herds do not conflict and that high reproductive efficiency and high longevity can be achieved.  相似文献   

8.
The objective of this study was to determine the effect of some factors on the length of productive life (LPL), the number of parities (NP), and the culling interval (CI) of sows. The information from 2003 to 2009 of 3,746 sows with LPL and NP records and 5,819 sows with CI records from the four farms of Yucatan, Mexico was used. LPL was defined as the number of days between the first farrowing and culling or death and CI as the number of days between the last farrowing and culling. To determine the effects of farm, litter size at first farrowing (LSF1) and age at first farrowing (AF1) on LPL and NP, and of farm, LSF1 and culling reason on CI general linear models were used. Means and standard errors for LPL, NP, and CI were 496.4 ± 8.42 days, 3.35 ± 0.04 parities, and 48.3 ± 0.52 days, respectively. All factors had significant effects (P < 0.05) on LPL, NP, and CI. The sows from farm 2 stayed longer (806.0 days) and had more parities (5.25) than the sows from the other farms. Sows with the smallest litters (≤8 piglets) at first farrowing stayed the least time in the farm (675.1 days) and had the fewest parities (4.49). Gilts farrowing the first time before 331 days of age stayed longer time in the farm (726.4 days) and had more parities (4.81) in comparison with 331–348 and more than 348 days age groups. With respect to CI, the sows in farm 3 stayed the longest time in the farm. Sows with more than five parities were culled sooner after their last farrowing. In conclusion, differences between farms for LPL, PN, and CI were found. Females that farrowed at a short age and those with large litters stayed longer in the herd. Old sows and those culled for reproductive reasons stayed the least time in the herd after their last farrowing.  相似文献   

9.

A study on the growth and reproductive performance of two rabbit breeds was undertaken. Data on 588 kits and 97 does of California White and 574 kits and 90 does of New Zealand White rabbits reared under hot and humid environment in Ghana were taken. The reproductive performance of the two breeds, in terms of litter size at birth and weaning, litter weight at birth and weaning, kindling interval, age at sexual maturity, and gestation length as influenced by breed, season of kindling (rainy and dry), year of kindling (2005–2012), and parity (first to sixth and over) were determined. The performance of California White in terms of litter size at birth, at weaning, kit weight at birth, and age at first kindling was 5.9?±?0.2, 4.6?±?0.1, 54.7?±?0.4 g, and 159.8?±?0.2 days, respectively. That of New Zealand White was 5.9?±?0.1, 5.1?±?0.1, 55.2?±?1.0 g, and 159.9?±?0.2 days, respectively. The results obtained also showed a significant breed effects on kit weight at birth, litter weight at weaning, and mortality; whereas no significant differences (p?>?0.05) were observed between the two breeds regarding the other traits measured. Parity had significant effects (p?<?0.05) on all the growth and reproductive parameters measured with the exception of age at first kindling. Year of kindling also had significant effect on litter weight at birth, kit weight at birth, and at weaning (p?<?0.05) but did not have any significant effect on the age at sexual maturity and mortality. Season also had significant (p?<?0.05) effects on kit weight at birth, gestation length, kindling interval, and mortality with better performance experienced during the rainy season.

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10.
The aim of this experiment was to investigate the effect of body condition and selection for prolificacy on the reproductive life span of female rabbits. The body condition was obtained by ultrasound measurement of the perirenal thickness of 166 crossbred does at day 10 after parturition in 6 consecutive parities. Two genetic groups were included: the current generation of does crossbred between two lines, both selected within line for number of pups at weaning, and a control group consisting of animals from the same cross but from 12 generations earlier. This control population was obtained by use of cryopreservation techniques, and made a simultaneous comparison between animals of different generations possible. A proportional Cox model was used to obtain estimates of survival characteristics. Twelve generations of selection for litter size at weaning did not significantly affect reproductive life span. Animals in poor body condition were found to have a significantly (P < 0.05) higher risk of dying than animals in better condition. Also, animals with high body fat mobilisation had a higher risk of culling (P < 0.05) than animals with intermediate mobilisation. Animals with zero pups born alive were also found to have a high risk of culling (P < 0.001).  相似文献   

11.
An experiment was carried out to evaluate the response obtained in a three‐way cross of rabbits when the lines involved had undergone within‐line selection for litter size or postweaning daily gain. The interaction between the level of nutrition and genetic level of the crossbreds was also studied. Using frozen embryos, old (H1) and current (H2) crossbred does and young were compared contemporarily. Does were fed a standard diet or a diet having high digestible energy and protein. The difference in the number of generations between lines used to produce both crosses were: 13 or 0 for the maternal lines, and 12 for the paternal line. The traits studied in the crossbred does were: daily feed intake during gestation, during the first 3 weeks of lactation and during the last week before weaning; doe weight at mating and at kindling; litter weight at birth and at weaning; total litter size, number born alive and litter size at weaning. The recorded traits for the young were: individual weight at weaning and at 63 days; individual daily gain after weaning; daily feed intake and feed conversion index. The last two traits were recorded as averages per cage. A total of 1161 litters from 190 does were involved. Significant differences in litter‐size traits, between H1 and H2 does, were observed and were higher than the expected from the within‐line response. The doe effect was not significant for other doe traits, adjusted to a constant litter size. The estimated difference in postweaning daily gain between H1 and H2 young was significant and in favour of H2, but the value was considerably lower than expected. The effect of type of feed and the interaction with the type of doe was not significant for any doe trait. The type of feed consumed by the doe was significant for postweaning daily gain, and the interaction with the type of crossbreds was significant for this trait and for individual weight at 63 days.  相似文献   

12.
The objective of this study was to evaluate the effect of dystocia on the reproductive performance and functional longevity in Iranian Holsteins. Data consisted of 1 467 064 lactation records of 581 421 Holstein cows from 3083 herds which were collected by the Animal Breeding Center of Iran from April 1987 to February 2014. Reproduction traits in this study included interval from first to second calving, days open and days from first calving to first service. The generalized linear model was used for the statistical analysis of reproductive traits. Survival analysis was performed using the Weibull proportional hazards models to analyse the impact of dystocia on functional longevity. The incidence of dystocia had an adverse effect on the reproductive performance of dairy cows. Therefore, reproductive traits deteriorated along with increase in dystocia score (p < 0.05). The culling risk was increased along with increase in the score of dystocia (p < 0.0001). The greatest culling risk was observed in primiparous cows, small herds and low‐yielding cows (p < 0.0001). Also, the lowest culling risk was found for cows calving at the youngest age (<27 months), and cows with age at first calving >33 months had the greatest risk (p < 0.0001). The results of current study indicated that dystocia had important negative effects on the reproductive performance and functional longevity in dairy cows, and it should be avoided as much as possible to provide a good perspective in the scope of economic and animal welfare issues in dairy herds.  相似文献   

13.
An evaluation of a new maternal line (LP) of rabbits was carried out. This new line was founded following a scheme similar to that applied in the selection for hyperprolificacy in rabbits or pigs. In this case, the selection criteria were hyperlongevity and an independent culling level near the average for prolificacy. Evaluation was carried out by comparison of the reproductive and longevity performance of the LP line with another maternal line recognized for good reproductive performance and standard longevity (V line). The results indicate that the LP line could be a valuable resource for inclusion in the current 3-way cross schema used in rabbit production, because females showed better survival ability and nearly the same prolificacy as the well-reputed V line. A V doe was 1.3 times more likely to leave the herd than an LP doe, and the probability of the differences in prolificacy between lines being greater than 0 was not extreme (no more than 0.22). Differences in relative performance of the lines were observed across farms for prolificacy, longevity, cumulative production, and fertility; however, based on deviance information criterion results, the data supported the hypothesis of only these differences being generated under a genotype x environment interaction for prolificacy traits. The longer productive life of LP females could partially be understood as an indication of success of the selection procedure during the foundation of this line.  相似文献   

14.
Our objective was to examine whether mouse lines divergently selected for response to fescue toxicosis differed in the impact of increasing reproductive intensity on growth, final weight or first and second parity reproduction. Resistant (R) and susceptible (S) females were never mated (NR), mated only once (low reproduction, LR), mated after their first litter was weaned (moderate reproduction, MR) or paired continuously with a male (high reproduction, HR), allowing concurrent pregnancy and lactation. Final weight was significantly higher in mated than in not mated females (31.6 ± 0.6, 35.9 ± 0.6, 36.8 ± 0.6 and 37.2 ± 0.5 g for NR, LR, MR and HR females respectively), but the effect of increasing reproductive intensity was similar in both lines. Neither genetic line, reproductive treatment (LR and MR versus HR) nor their interaction affected first parity traits of dams or pups. In second parity, S dams produced larger litters at birth and weaning and heavier litters at birth than R dams, and MR dams produced more pups and heavier litters than HR dams. As with first litters, however, line by reproductive treatment interactions were not significant or important. Concurrent pregnancy and lactation (the HR treatment) had a similar dampening impact on the expected increase in litter size between first and second parity of both lines. Thus, lines divergently selected for toxicosis response did not differ significantly in the impact of increasing reproductive intensity on dam or pup growth, reproductive output through two parities or mature size. This conclusion should not be generalized. Selection responses in livestock should be monitored to ensure that improvement in one trait does not lead to deterioration in others.  相似文献   

15.
SUMMARY Laparoscopy was used to estimate ovulation rate at first mating in 460 Large White/Landrace gilts. For 385 gilts which farrowed litter size was recorded and the relationships between age and mating, maternal litter size, ovulation rate and reproductive performance were examined. The mean ovulation rate of the gilts which farrowed was 10.9 ± 0.14 corpora lutea and the mean first litter size was 8.0 ± 0.12 piglets born with 7.5 ≥.± 0.13 born alive. Ovulation rate was related to first litter size (r = 0.29, P < 0.001) but embryo loss was the major factor determining litter size, accounting for about 58% of the variation. None of the variable examined at the time of mating was sufficiently correlated with litter size to be useful as selection criteria for improving reproductive performance.  相似文献   

16.
Functional longevity (FL), measured as length of productive life (LPL) adjusted by production level, has been regarded as an important trait to measure the global functional aptitude of a cow, particularly when direct measures of the functional traits (health and reproductive performance) are not available. The objective of this study was to analyze the trait FL making use of survival analysis techniques in order to propose a model for the genetic evaluation of this trait in the Spanish Holstein Friesian population. The data set consisted of 133,629 registered cows of three regions; Andalusia, Basque Country and Catalonia. The hazard function was described as the product of a baseline hazard function and the time-independent effects of age at first calving, lactation number-stage of lactation, annual change in herd size, milk, fat and protein yield. Sire and maternal grandsire and herd-year-season of calving were considered as random effects. Percentage of right-censored data ranged from 41.9% to 52.7% for the analysed data sets. All the effects analyzed were significant (P < 0.0001) and had a great influence on the risk of culling of a cow, except for the age at first calving which showed a relatively small effect. Higher risk for factors such as age at first calving, change in herd size and relative level of milk production was associated with the more extreme classes. The consistency of the results among regional samples which represent diverse production systems in the population indicated that the proposed model could be applied at the national level. The relatively low heritability (0.048 to 0.074) suggests that genetic improvement of LPL could be effective if the direct evaluation is combined with indirect measures of LPL.  相似文献   

17.
Sustainability has come to play an important role in agricultural production. A way to combine efficiency with sustainability might be by searching for robust animals that can be selected for the homogeneity of certain traits. Furthermore, the optimization of feed efficiency is one of the challenges to improve livestock genetics programmes, but this might compromise reproductive efficiency. Animals from two divergent mouse lines, regarding variability of birthweight, were used to check whether homogeneity was also related to both feed and reproductive efficiency. The objective of this study was to use these divergent lines of mice to compare them with their feed efficiency and the reproductive capacity. Animal weight, weight gain, feed intake, relative intake and cumulated transformation index were considered as feed efficiency traits. Animals from the low line had both lower weight and feed intake from 21 to 56 days. They had a worse transforming index in the three last weeks when litter size was fitted as an effect of the model, but the lines become similar if the higher litter size of the low line was not included. Reproductively, the low line performed better considering the number of females having parturitions, the number of parturitions, and with higher litter size and survival in both parturitions. Hence, the low variability line was preferred because of reproductive efficiency without seriously affecting its feed efficiency. Homogeneity seemed to be related to robustness with similar feed efficiency but higher reproductive efficiency.  相似文献   

18.
Factors affecting longevity in maternal Duroc swine lines   总被引：3，自引：0，他引：3  
A competing risks approach was used to evaluate the influence of several pre-farrowing factors on risk of culling due to different causes in Duroc swine, these having low fertility, low productivity, lameness and mortality. Culling due to low fertility increased for average daily gains during the growth test lower than 585 g/day, whereas culling due to low productivity and mortality increased with low levels of backfat thickness at the end of the growth test. Lesser loin depths at first farrowing reduced culling due to low productivity but increased culling due to lameness. Furthermore, a higher average daily gain from the end of the growth test to first mating increased culling by all causes. A complementary analysis was carried out to evaluate the influence of these factors on risk of culling without taking into account the specific reason of failure. In this second analysis, the factors were included as time-dependent covariates whose relative importance changed throughout the sows' productive life. Expected survival functions and replacement rates have been calculated in different hypothetical situations in order to determine the optimal animal body type at first farrowing to maximise longevity, which under our production conditions is independent of average daily gain from birth until the end of the growth test, but from the end of the growth test to first mating average daily gain should not be over 485 g/day; backfat thickness should be more than 16 mm at the end of the growth test and maintain this level until the first parturition without exceeding 19 mm; loin depth should be kept below 45 mm at first farrowing.  相似文献   

19.
The objectives of this study were 1) to investigate if there were differences in the relation between temperature and reproductive performance traits in 2 different sow lines, a Yorkshire line producing mainly in temperate climates and a Large White line producing mainly in warm climates, and 2) to determine the upper critical temperature (UCT) for the reproductive performance of these 2 lines. Sows are exposed to heat stress when temperature exceeds the UCT of the thermo-neutral zone. Data included 32,631 observations on reproductive performance from 11,935 sows on 20 farms in Spain, collected from 2003 to 2005. Sows belonged to 2 different purebred sow lines, named D (Yorkshire sow line, producing mainly in temperate climates) and I (Large White sow line, producing mainly in warm climates). Only first insemination records per parity were used and were combined with the maximum outside temperature at day of insemination. Upper critical temperatures were studied for 3 reproduction traits: farrowing rate (0 or 1), litter size (range from 1 to 25), and total number of piglets born per first insemination (combination of farrowing rate and litter size, range from 0 to 25). Data were corrected for fixed effects, which included parity, service sire, and an interaction between farm and year. Corrected data were used as observations in the models to study the effect of outside temperature on reproductive performance. Two models were compared for goodness of fit: a linear regression model and a plateau-linear model with the plateau representing the thermo-neutral zone and a linear decrease above that zone. Farrowing rate of I-line sows was not affected by temperature. For litter size and total number born per first insemination of I-line sows no UCT could be estimated. These traits were linearly affected by temperature. For all 3 reproduction traits of the D-line the best model was the plateau-linear model; the UCT for the D-line sows was estimated to be 19.2 degrees C for farrowing rate, 21.7 degrees C for litter size, and 19.6 degrees C for total number born per first insemination. The decrease in reproductive performance of I-line sows with increasing outside temperature was less than in D-line sows. From this study it can be concluded that there are differences in heat stress tolerance between sow lines as measured by the differences in reproductive performance. These differences are an indication of genetic differences in heat stress tolerance in sow lines.  相似文献   

20.
Ewes from lines selected for high and low reproductive rate and a control line bred and selected randomly were endoscopically examined 3 to 5 d after breeding to determine ovulation rates in the fall of 1985, 1986 and 1987. Fertility (ewes lambing per ewe exposed), lambing rate (lambs born per ewe exposed) and litter size (lambs born per ewe lambing) were evaluated at lambing in the spring of each year. Embryonic survival was estimated as the number of lambs born per corpora lutea. Ovulation rates were 1.28, 1.73 and 1.46 for low, high and control lines, respectively. More (P less than .01) single ovulations occurred in low-line ewes than in the other two lines; high-line ewes had more (P less than .01) twin ovulations than did low- or control-line ewes. Fertility did not differ among lines. Selection line affected (P less than .01) lambing rate at first and all services. Control-line ewes had mean lambing rates at first and all services that were intermediate between those of the low and high lines, which were different from each other. Line x age of ewe interactions existed (P less than .01) for lambing rate at all services and litter size at first and all services. High-line ewes had lower lambing rates and litter sizes as 2-yr-olds than other lines, but their performance increased steadily to 6-yr-olds, whereas the low and control lines remained relatively constant. Embryo survival differed (P less than .10) between lines, being 74%, 63% and 67% for low, high and control lines, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

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