Postpartum performance in a diallel cross among lines of mice selected for litter size and body weight

Postpartum dam performance was studied in a complete diallel design involving five lines of mice. The selection criterion in each line was: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and random (K). Females from the five lines and 20 reciprocal F1 crosses were mated to sires of a randomly selected control line (CC). Correlated responses in average direct genetic and average maternal genetic effects for dam body weight and litter size at parturition persisted throughout lactation, indicating important pleiotropic effects. Major correlated responses occurred for litter weight, feed intake and litter feed efficiency, primarily due to average direct genetic effects. Using general combining ability and net line effects as criteria for choosing among lines, L+ had a distinct advantage if the objective was to increase litter size in a crossing program. If the objective was to maximize litter weaning weight, then W+ would be favored for net line effects, while L+ and W+ would be about equivalent for general combining ability. None of the lines had an advantage for litter feed efficiency. Direct heterosis for dam weight at 12 and 21 d of lactation averaged 2.7 and 1.9%, while for litter size the respective averages were 7.4 and 7.3%. The W+ X L+W- cross exhibited overdominance for litter size. Direct heterosis was moderate for feed intake and litter weight, but was negligible for litter feed efficiency because of the mathematical relationship among the three traits. Maternal heterosis for preweaning progeny growth was suppressed because of heterosis for litter size in the dam. Grand-maternal effects on growth of the young were small and would not be an important consideration in choosing among these lines in a crossbreeding program.     

Direct and maternal genetic differences between lines of mice selected for body weight and litter size: traits of dams

Genetic differences in performance of dams were estimated by linear contrasts using means of two selected lines of mice and reciprocal F1's, F2's and backcrosses. The lines were selected for increased 6-wk body weight (W) or increased litter size (L). Genetic differences estimated were direct average (gD), direct heterosis (hD), maternal average (gM), progeny average (gP), and progeny heterosis (hP). For dam weight and feed consumption from 12 to 21 d postpartum (pp), gD was the largest genetic difference and favored line W. For litter size, litter weight at birth, litter efficiency (litter weight gain/dam feed consumption) from birth to 12 d pp and within litter mortality from 1 to 21 d pp, gD favored L and, except for hD in litter efficiency, was the most important genetic difference for these traits. Direct heterosis was the only significant difference for litter weight at 21 d pp, litter efficiency from 12 to 21 d pp and within litter mortality at parturition. The gM were larger in W than in L for dam weight and feed consumption, and for litter size and weight at birth, but they were usually of smaller magnitude than gD. The gP were significant only in litter traits measured before 12 d pp and favored W. For no trait measured was hP of consequence. Line differences in dam and litter weight accounted for genetic differences in dam feed consumption. Genetic differences in litter size at birth were not due to line differences in dam weight. The lower mortality within litters nursed by crossbred dams was responsible for hD on litter weight and litter efficiency. Within but not among lines, higher mortality rates were associated with larger litters.     

Reproductive performance of chimeric mice produced from genetic lines that differ in litter size

A population of chimeras was made by aggregating 8- and 16-cell embryos from two mouse strains: a randomly bred line (C) and a selected line characterized by large litters (JU), with litter sizes of 7.7 and 13.5, respectively. The two genotypes were developmentally "balanced", as judged by the high frequency (90%) of chimeras with an intermediate or high degree of coat-color chimerism, a chimeric sex ratio of 2.2:1 males:females, and a high percentage of chimeras (31% of males, 71% of females) with germ cells of both strains. Litter size characteristics, including ovulation rate, implantation rate, rates of pre- and postimplantation embryo survival and number born were studied in the female chimeras and compared with the performance of both parent lines and to the genetic cross of the two lines. Values for JU females exceeded those for C females for all parameters studied except postimplantation embryo survival, which was the same for both lines in second litters and was lower for JU's third litters. For most traits, means for genetic crossbreds and chimeras were similar, regardless of whether the means were at or above the midparent average. In contrast, for ovulation rate and body weight, genetic crossbreds and chimeras clearly differed, with chimeric females being similar to the JU line and genetic crossbred females exhibiting additive inheritance. Because of phenotypic differences between experimental chimeras and crossbreds produced from the same two lines, chimeras may provide a useful model for studying the physiologic basis for expression of genetic differences in quantitative traits.     

Fertility, embryo survival and litter size in lines of Targhee sheep selected for weaning weight or litter size

Conception rate, prenatal survival and litter size were recorded for 444 ewes of two age groups from five lines of grade Targhee sheep: two unselected control lines, HC1 and DC(C); two lines selected for 20 yr for increased 120-d weight, HW and DH(W); and a line selected for 18 yr for increased multiple births, T. Line T was equal or superior to the control lines in conception rate, prenatal survival and litter size in both age groups, although most of the differences were not significant. The W selected lines were inferior to the C and T lines in fertility and tended to be lower in prenatal survival, among mature ewes, resulting in a significantly lower number of lambs born per corpus luteum in the W lines than in the other two groups. Among yearlings, C ewes were non-significantly lower in fertility than T and W ewes, while W ewes were significantly lower than C and T ewes in prenatal survival. The T line ewes had higher overall reproductive performance than either of the other two groups. Ewes with two ovulations had a significantly higher conception rate than ewes with single ovulations. Gestation period was exceptionally uniform with a coefficient of variation of 1.3% and little difference due either to line or litter size. It was concluded that selection for multiple births improved overall reproductive performance, whereas selection for increased growth rate had an adverse effect on several components of reproduction, leading to a net decline in fitness.     

Effects of selecting for litter size and body weight on the components of litter size in mice

Divergent selection for the total number of young born in the first three litters (TNY-3) and for 6-week body weight in mice resulted in different changes in the components of first litter size.Selection for large TNY-3 increased the number of ova shed while pre-natal losses were not modified. Selection for small TNY-3 caused both a decrease in ovulation rate and an increase in post-implantation mortality. Divergent selection for body weight modified ovulation rate in the same direction as body weight. Embryo survival declined in both lines selected for body weight. That decline was caused by an increase in pre-implantation mortality in the case of the high line, and by an increase in post-implantation mortality in the low line.     

Reallocation of body resources in lactating mice highly selected for litter size

The present study investigated differences in the allocation patterns of body stores in lactating female mice from a line selected for high litter size at birth (S-line, average litter size of 20) and dams from a nonselected control line (C-line, average litter size of 10). Body weight, litter size, litter weight, and absolute and relative lipid and protein mass were measured at peak lactation (2 wk in lactation) and at weaning (3 wk in lactation). Body size in S-line females has been increased as a correlated effect of selection for high litter size at birth, allowing for larger litters and higher absolute milk production. However, these dams produce larger litters relative to their own body weight. At peak lactation, lipid and protein percentage did not differ between lines. At weaning, S-line females had a higher protein percentage (P < 0.001) and lower lipid percentage (P < 0.05) than C-line females. Apparently, S-line females produce more offspring but at a greater cost to their own metabolism. This process was insufficient to supply the offspring with adequate resources, resulting in reduced (P < 0.0001) pup development and increased (P < 0.0001) preweaning mortality rates.     

Reproductive performance in mice selected for divergence in body fat content

SUMMARY: Correlated responses in female reproductive performance were studied in lines of mice selected for high (HF) and low (LF) fat content relative to a randomly selected control line (RC). Selection was based on an indicator trait of body fat percentage in males (epididymal fat pad weight as a percentage of body weight at 12 weeks of age). LF mice showed a positive correlated response (P < 0.05) in number of pups born (NB), whereas HF showed no significant change. The increase in NB could be explained partially by an increase in ovulation rate (adjusted for body weight at mating; P < 0.01), measured as number of corpora lutea (CL) 16 days postcoitus (P < 0.05) or number of ova (OR) shed 2 days postcoitus (P < 0.01). Asymmetry was observed for CL (P < 0.05) and OR (P < 0.01); the major correlated response was observed in the LF line. Preimplantation and total embryo survival were higher (P < 0.01) in LF than in HF mice, whereas no significant divergence was found for post-implantation embryo survival. Reciprocal crosses of HF and LF lines allowed partitioning of divergence in OR into maternal (P < 0.10) and individual (P < 0.10) effects with LF being larger than HF. No significant heterosis was found for OR or mating weight. Body weight at mating was larger in HF females than in RC controls, while LF females were larger than controls in one experiment and not different from controls in a second experiment. Therefore, body weight at mating did not explain the positive correlated response in ovulation rate observed in the LF line. ZUSAMMENFASSUNG: Reproduktion in gegens?tzlich auf K?rperfett selektierten M?usen Korrelierte Selektionswirkungen auf weibliche Reproduktion wurden in Linien untersucht, die auf hohen (HF) oder niedrigen (LF) Fettgehalt selektiert worden waren, relativ zu einer zufallsgepaarten Kontrolle. Selektion beruhte auf Nebenhodenfett, korrigiert auf 12 Wochengewicht, als Indikator-merkmal. LF M?use hatten signifikant h?here Zahl geborener Junge (NB), HF zeigten keine signifikanten Wirkungen. Die Steigerung von NB kann teilweise durch hochsignifikante Steigerung der gewichtsadjustierten Ovulationsrate, gemessen als Zahl von Gelbk?rper (CL) 16 Tage postcoitus oder Zahl Eier (OR) 2 Tage pc, erkl?rt werden. Asymmetrie zeigte sich für CL (p < .01) und OR (p < .1), aber keine signifikanten Unterschiede zeigten sich für Post-Implantations überleben. Reziproke Kreuzungen von HF und LF erlaubten Aufteilung der OR Unterschiede in maternal (p < .1) una individuell verursachte (p < .1) Wirkungen, wobei LF gr??er als HF waren, aber sich keine Heterosis für OR oder Gewicht bei der Paarung ergab. Dieses war in HF Tieren h?her als in RC Kontrollen, was bei LF Tieren in einem, aber nicht im zweiten Versuch zutraf, so da? K?rpergewicht nicht die korrelierte Wirkung auf OR erkl?ren kann.     

Heterosis and combining ability for body weight in a diallel cross of three chicken genotypes

The aim of the study was to evaluate heterotic and combining ability effects for growth in nine chicken genotypes. A 3?×?3 complete diallel mating system involving two indigenous breeds named Venda (V) and Naked Neck (N) and one commercial broiler breed named Ross 308 (R) were used. The nine genetic groups of crosses were reared up from hatch to 13 weeks of age in deep litter open house. Body weights of 180 chicks (20 chicks per genetic group), recorded at 0, 3, 5, 7, 9, 11, and 13 weeks of age, were used to estimate heterosis, general combining ability (GCA), and specific combining ability (SCA). Results showed that the Ross 308 had the heaviest body weight at all weeks of measurement except for hatch. With respect to crosses, the V × R and its reciprocal cross, R × V had the heaviest body weights at 13 weeks. Heterosis estimates for body weight were higher in the Venda male × Ross 308 female and Venda male and Naked Neck female crosses. GCA was significant (P?≤?0.01) for body weight from hatch to 13 weeks of age while SCA and reciprocal effects were both significant (P?≤?0.05) for body weight at all ages of measurement except for hatch. The Ross 308 gave the highest positive effect of GCA for body weight except for hatch. V × N gave the highest and positive effects of SCA for body weight.     

Effect of selection for litter size and body weight on hormone-induced ovulation rate in mice.

Genetic differences in natural vs hormone-induced ovulation rates were compared in immature female mice from five lines that had undergone long-term single-trait and antagonistic index selection for litter size and(or) 6-wk BW. Lines used were control (K); high litter size (L+); high BW (W+); low litter size and high BW (L-W+); and high litter size and low BW (L+W-). Natural ovulation rate at a mean age of 34.3 d and hormone-induced (5 IU of pregnant mare's serum gonadotropin followed 2 d later by 5 IU of human chorionic gonadotropin) superovulation rate at a fixed age of 31 d were obtained. Total number of eggs ovulated was affected by line (P less than .001), treatment (P less than .001), and line x treatment interaction (P less than .001). Line differences were subsequently tested within treatment because of the significant line x treatment interaction. Line differences were important (P less than .001) for natural ovulation, hormone-induced ovulation, and response to hormones. Mean natural ovulation rates for K, L+, W+, L-W+, and L+W- were 14.1, 19.8, 15.1, 13.6, and 16.4, respectively. Selection changed ovulation rate by 40, 16, 7, and -4% in the L+, L+W-, W+ and L-W+ lines, respectively (P less than .01). Hormone-induced ovulation rates in K, L+, W+, L-W+, and L+W- were 32.3, 24.6, 19.6, 20.9, and 22.1, respectively. Exogenous hormones increased ovulation by 18.2, 4.8, 4.6, 7.3, and 5.7 ova for K, L+, W+, L-W+, and L+W-, respectively (P less than .001). Lines with lower natural ovulation rates had higher responses to superovulation. Increased ovulation rate due to treatment ranged from 24.3% in L+ to 129% in K. These results indicate significant differences among lines in ovarian response to exogenous hormones.     

Ovulation rate in sheep selected for weaning weight or litter size

Ovulation rate was measured by laparoscopy at two consecutive cycles on 366 ewes 2 yr old and over and 85 yearling ewes of five lines of Targhees from the base base population; 53 yearling linecross ewes were also included. The lines were two unselected controls (HCl and DC), two selected for 21 yr for increased 120-d weight (HW and DH) and one selected for 19 yr for multiple births (T). Ewes were synchronized in late July or early August at the start of the normal breeding season with intravaginal pessaries impregnated with 60 mg methylacetoxyprogesterone and examined at first and second estrus. Ovulation had occurred in both cycles in 327 (89%) and 177 (85%) of the mature and yearling ewes, respectively. Overall mean numbers of corpora lutea at first and second estrus were 1.42 and 1.63, respectively for ewes 2 yr and over and 1.20 and 1.44 for yearlings, indicating an effect of synchronizing treatment, season, flushing, or a combination of these. Among mature ewes, ovulation rate was higher (P less than .05) in DH (+.20), HW (+.19) and T (+.16) than in controls at first estrus, and in HW (+.29) and T (+.21) but not DH (-.04) at second estrus. Among yearlings, differences were significant only at second estrus (HW, +.40; T, +.35) and again not for DH (+.08). The failure of line DH to increase in ovulation rate from first to second estrus as did other lines was transmitted to linecross progeny. Body weight within line affected ovulation rate significantly, with a greater effect at second estrus, in both age groups. Adjustment for body weight removed the difference between HW and controls but not between T and controls. Repeatability of corpora lutea count was .27 and .25 for mature and yearling ewes, respectively.     

Effects of concurrent lactation and postpartum mating on reproductive performance in mice selected for large litter size

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.     

Hepatic 5'-deiodination in chickens from lines selected for high and low body weight and their F1 cross

1. Assay conditions for measuring hepatic 5'-deiodinase (5'D) activity at initial velocity, using reverse T3 as substrate, have been validated for adult chicken liver. 2. The characteristics of hepatic 5'D activity in adult chickens from lines selected for high (HW) and low (LW) juvenile body weight are similar to those in mammals and in the other birds that have been investigated. 3. Chickens from the HW line have significantly higher specific activity of hepatic 5'D, and thus potentially higher T3 production, than those from either the LW line or the F1 cross (HL) between the HW and LW lines.     

Correlated response in litter size components in rabbits selected for litter size variability

A divergent selection experiment for the environmental variability of litter size (Ve) over seven generations was carried out in rabbits at the University Miguel Hernández of Elche. The Ve was estimated as the phenotypic variance within the female, after correcting for year‐season and parity‐lactation status. The aim of this study was to analyse the correlated responses to selection in litter size components. The ovulation rate (OR) and number of implanted embryos (IE) in females were measured by laparoscopy at 12 day of the second gestation. At the end of the second gestation, the total number of kits born was measured (TB). Embryonic (ES), foetal (FS) and prenatal (PS) survival were computed as IE/OR, TB/IE and TB/OR, respectively. A total of 405 laparoscopies were performed. Data were analysed using Bayesian methodology. The correlated response to selection for litter size environmental variability in terms of the litter size components was estimated as either genetic trends, estimated by computing the average estimated breeding values for each generation and each line, or the phenotypic differences between lines. The OR was similar in both lines. However, after seven generations of selection, the homogenous line showed more IE (1.09 embryos for genetic means and 1.23 embryos for phenotypic means) and higher ES than the heterogeneous one (0.07 for genetic means and 0.08 for phenotypic means). The probability of the phenotypic differences between lines being higher than zero (p) was 1.00 and .99, respectively. A higher uterine overcrowding of embryos in the homogeneous line did not penalize FS; as a result, this line continued to show a greater TB (1.01 kits for genetic means and 1.30 kits for phenotypic means, p = .99, in the seventh generation). In conclusion, a decrease in litter size variability showed a favourable effect on ES and led to a higher litter size at birth.     

饲喂大米草对波尔山羊产羔数、羔羊初生重和体尺指标的影响

文章旨在研究饲喂大米草对纯种波尔山羊的产羔数、羔羊初生重以及羔羊体尺指标的影响。结果表明:饲喂大米草对波尔山羊产羔数、羔羊初生重和羔羊体尺指标等具有一定的影响。其中试验组与对照组双羔的初生重和胸围指标达到差异显著水平(P<0.05)。     

Genetic determination of individual birth weight, litter weight and litter size in Mukota pigs

Genetic parameters for individual birth weight (IBWT), total number of pigs born (NBT), number of pigs born alive (NBA), number of pigs born dead (NBD) and litter weight at birth (LBWT) were estimated using 1961 Mukota pigs kept at the University of Zimbabwe Farm, Harare, Zimbabwe. Variance components were estimated for IBWT based on a direct-maternal genetic effects model. The genetic relationships among NBT, NBA, NBD and LBWT were assessed using a multi-trait direct effects model. For LBWT, the direct, maternal and common environmental litter proportions on the phenotypic variance were 0.090, 0.033 and 0.009, respectively. After adjustment of IBWT for NBA, phenotypic fractions were 0.091, 0.034 and 0.011 for direct, maternal and litter effects. The correlation between the direct and maternal genetic effects of IBWT was − 0.354 and − 0.295, with and without adjustment for NBT. Heritabilities for NBT, NBA, NBD and LBWT were 0.020, 0.030, 0.088 and 0.196, respectively. Differences in the maternal heritability and the heritability for LBWT, a trait of the dam, are different due to accumulation of observations per litter. Maternal genetic effects are, therefore, of less importance than in highly selected European breeds.     

Comparison of energy metabolism during the growing period in quail lines selected for body weight

1. The present study was conducted to compare body weight, daily weight gain, relative growth rate, food intake, food conversion efficiency, abdominal fat weight, thyroid weight, plasma T4 concentration, body temperature, oxygen consumption, carbon dioxide production and heat production among three Japanese‐quail lines selected for body weight: a random bred line (RR) and lines for large (LL) or small (SS) body weight.

2. T4 concentration increased in the order SS, RR, LL in both sexes and did not vary significantly between sexes; the SS line had a significantly higher value than that of the LL line.

3. The body temperatures of SS, RR and LL lines were 42.45, 42.03 and 41.25°C in males, and 42.7, 42.03 and 41.63°C in females.

4. The oxygen consumptions of SS, RR and LL lines were 63.4, 46.0 and 43–8 ml/kgW^0.75 min. in males, and 61.4, 44.8 and 37.2 in females. The value for SS was significantly higher than those of RR and LL lines in both sexes (P< 0.01). The carbon dioxide productions of SS, RR and LL lines were 31.8, 33.8 and 27–3 ml/kgW⁰⁷⁵ min. in males, and 31.2, 31.9 and 27.3 in females. In both sexes, that of the LL line was significantly lower than those of the SS and RR lines (P< 0–01).

6. The heat productions of SS, RR and LL lines were 1.178, 0.994 and 0.842 k]/kgW^01b min. in males, and 1.142, 0.879 and 0.736 in females. In both sexes, the heat production of the SS line was higher than those of the RR and LL lines (P< 0–01).

7. It was demonstrated that selection for body weight in Japanese quail was accompanied not only by changes in growth rate and conversion efficiency but also by changes in thyroid function and energy metabolism.     

Relationship between litter birth weight and litter size in six breeds of sheep

Metabolizable energy requirements of the ewe increase during pregnancy due to increases in fetal and maternal metabolism. Fetal metabolism is related to total weight of the fetuses. Fetal number is a primary contributor to fetal weight. Litter birth weight represents the culminated fetal growth of the litter and can be used to estimate the effect of fetal metabolism on energy requirements of the ewe. We hypothesized that litter weight in sheep would increase at a decreasing rate with increasing litter size. Birth weights of lambs born to yearling (11 to 15 mo) and mature ewes (> 34 mo) were collected on litters born to Dorset, Rambouillet, Suffolk, Finnsheep, Romanov, and Composite III ewes mated to produce straightbred lambs. Litter birth weight expressed as a function of litter size increased at a decreasing rate and the quadratic term differed from zero for mature Rambouillet, Suffolk, Finnsheep, Romanov, and Composite III litters (P < 0.042). The quadratic coefficient differed among breeds. In yearlings, litter weight increased at a decreasing rate for Suffolk ewes (P = 0.002). The quadratic term for the relationship between litter weight and litter size did not differ from zero for Finnsheep (P = 0.39) or Romanov litters (P = 0.07). The hypothesis that litter weight increases at a decreasing rate with increased litter size is supported by experimental results.     

Genetic analysis of litter size in mice

We performed quantitative trait locus (QTL) mapping analysis for litter size (total number of pups born and/or number of pups born alive) in 255 backcross mice derived from C57BL/6J and RR/Sgn inbred mice. We identified one significant QTL on chromosome 7 and 4 suggestive QTLs on chromosomes 3, 5, 10 and 13. In addition, two suggestive QTLs were identified on chromosomes 1 and 4 for the number of stillbirth. These results suggested that both litter size and number of stillbirth were heritable traits, although they were controlled by distinct genes. The RR allele was associated with reduced litter size and increased stillbirth at all QTLs. Therefore, RR mothers were observed to have reduced prolificacy in this particular genetic cross.     

Renewed selection for heat loss in mice: direct responses and correlated responses in feed intake, body weight, litter size, and conception rate

Divergent selection in mice was renewed in 3 independent replicates for high (MH) and low (ML) heat loss. An unselected control (MC) was maintained in all replicates. Heat loss was measured for individual male mice for 15 h, overnight in direct calorimeters. After 16 initial generations of selection followed by 26 generations of relaxed selection, divergent selection resumed for 9 generations. The realized selection applied was very close to the maximum possible selection according to the criteria and protocol. Selection differentials were greater for high than for low selection due to greater variation in the MH line. When corrected for SD, standardized selection differentials were similar for MH and ML selection. Unintended selection in MC was negligible. Realized heritability for divergence was 0.14 +/- 0.01, which was considerably less than that realized during the initial generations of selection (0.28 +/- 0.03). Realized heritabilities for MH selection (0.16 +/- 0.05) and for ML selection (0.07 +/- 0.06) were less, especially for ML selection, than were observed in the earlier generations. The difference in heat loss between MH and ML males was 55.7% of the MC mean at generation 51, compared with a difference of 53.6% in generation 15; this difference had decreased to 34.4% at the end of the relaxed selection (generation 42). For feed intake between 8 and 11 wk, MH and ML males differed by 34.0% of the MC mean by the end of the selection process. Body weight at 12 wk for MH and ML males was less than for MC males. Litter size response was positively related to the heat loss response. Conception rate was poorer in MH matings than in MC and ML matings.