Relationships between ovulation rate and litter size in purebred Landrace and Yorkshire gilts

The aim of the present study was to investigate the ovulation rate and its relationship to number of total piglets born in purebred gilts under tropical climatic conditions. This study was conducted in two swine breeding herds (A and B) in the northeastern part of Thailand. The sources of swine genetic material originate from West Europe. Gilts were mated (AI) on the second or later observed estrus at a body weight of at least 130 kg. In most cases, they were mated at third estrus. One hundred and twenty-seven gilts, 24 Landrace and 24 Yorkshire from herd A, and 42 Landrace and 37 Yorkshire from herd B were used. Gilts were examined once by laparoscopy under general anesthesia between days 8 and 15 after mating. The ovaries were examined and the pathological findings were recorded. The number of corpora lutea was counted, and was assumed to equal the ovulation rate. Subsequent mating results and farrowing data were recorded. The data were analyzed with analysis of variance. Single or double unilateral cysts and par-ovarian cysts did not affect mating results. Landrace gilts were significantly younger at first mating than Yorkshire gilts (244 versus 249 days, P < 0.05). At first mating, Yorkshire gilts had a significantly higher ovulation rate compared to Landrace gilts (15.3 versus 13.8, P < 0.001). There was no difference in the number of total piglets born per litter between the two breeds, but the total prenatal loss from ovulation to farrowing was significantly higher in Yorkshire than in Landrace gilts. Both the low ovulation rate and the high prenatal loss contribute to the low litter size in gilts raised under tropical climatic conditions.     

Age at puberty and first litter size in early and late paired rats

The rate of sexual maturation among female Sprague-Dawley rats was measured in a variety of intraspecific social environments. It was found that females of this strain differ from at least one other strain of laboratory rat in that neither age at vaginal perforation nor age at first estrus was affected in Sprague-Dawley females by the presence or absence of male, regardless of his age or breeding history. Sizes of first litter among females who mated at their first estrus were compared with those among females who were first inseminated at older ages. On average, females bred at first estrus produced litters that contained more than 3 fewer pups than females mated at older ages. This observation suggests that female Sprague-Dawley rats do not attain full reproductive competence until sometime after the onset of puberty.     

Correlated responses on litter size traits and survival traits after two-stage selection for ovulation rate and litter size in rabbits

Farmer profit depends on the number of slaughter rabbits. The improvement of litter size (LS) at birth by two-stage selection for ovulation rate (OR) and LS could modify survival rate from birth to slaughter. This study was aiming to estimate direct and correlated response on LS traits and peri- and postnatal survival traits in the OR_LS rabbit line selected first only for OR (first period) and then for OR and LS using independent culling levels (second period). The studied traits were OR, LS measured as number of total born, number of kits born alive (NBA) and dead (NBD), and number of kits at weaning (NW) and young rabbits at slaughter (NS). Prenatal survival (LS/OR) and survival at birth (NBA/LS), at weaning (NW/NBA) and at slaughter (NS/NW) were also studied. Data were analysed using Bayesian inference methods. Heritability for LS traits were low, 0.07 for NBA, NW and NS. Survival traits had low values of heritability 0.07, 0.03 and 0.03 for NBA/LS, NW/NBA and NS/NW, respectively. After six generations of selection by OR (first period), a small increase in NBD and a slight decrease in NBA/LS were found. However, no correlated responses on NW/NBA and NS/NW were observed. After 11 generations of two-stage selection for OR and LS (second period), correlated responses on NBA, NW and NS were 0.12, 0.12 and 0.11 kits per generation, respectively, whereas no substantial modifications on NBA/LS, NW/NBA and NS/NW were found. In conclusion, two-stage selection improves the number of young rabbits at slaughter without modifying survival from birth to slaughter.     

Age at puberty, fertility and litter size of ewe lambs reared under different photoregimens

Age at puberty, fertility and litter size of ewe lambs of synthetic sire and dam strains raised under different photoregimens were determined. The lambs were bred during January, May or September at 30 to 32 weeks of age. Irrespective of birth date, the lambs were reared under continuous light from birth to 5 weeks of age. From 5 to 20 weeks of age, they were kept under 16 hours of light dairy (16L:8D; Treatment A), 8 hours of light daily (8L:16D; Treatment B), or a split photoperiod of 8 hours total light daily (7L:9D:1L:7D; Treatment C). Subsequently, all lambs were exposed to 9 hours of light daily until after breeding. Lambs were exposed to rams for two estrous periods after treatment with fluorogestone acetate-impregnated intravaginal sponges and pregnant mares' serum gonadotropin (PMSG) to induce synchronized estrus. Although the age at puberty (174 days) was similar among treatments, the incidence of puberty prior to progestagen sponge treatment was higher ( approximately 50%) for lambs reared under Treatments A and C than under Treatment B. Fertility and litter size of lambs were not influenced by the previous photoperiod history or by sexual maturity, i.e., puberal or prepuberal, at the start of the sponge treatment. However, strain, age and weight of lambs at breeding influenced significantly the reproductive outcome.     

Effects of lactation length and weaning-to-service interval on subsequent farrowing rate and litter size in Landrace and Yorkshire sows in Thailand

The aim of the present study was to investigate the influence of lactation length (LL) on weaning-to-service interval (WSI), and the effect of LL and WSI on the subsequent farrowing rate and litter size among purebred Landrace and Yorkshire sows under tropical conditions. The variation in litter weight at weaning (LWW) was also studied. Data were analyzed from three purebred sow herds located in the central part of Thailand, including sows weaned during the period from January 1993 to December 1996. Data were analyzed with analysis of variance using SAS software. The procedure MIXED was used for analysis of the continuous outcome variables (namely LL, LWW, WSI, number of total born and number of live born piglets). The GLIMMIX macro was used for analysis of the categorical outcome variable, farrowing rate (FR). In the statistical analyses, WSI was grouped into 7 groups, when it was an independent variable, as follows: 1 to 4, 5, 6, 7, 8, 9, to 10, and 11 to 21 days. Lactation length was grouped into 4 groups as follows: 17 to 24, 25 to 27, 28 to 30 and 31 to 35 days. Parities were grouped into 4 groups as follows: 1, 2, 3 + 4, and 5 to 8. Landrace sows had significantly higher LWW (P < 0.001) compared with Yorkshire sows (56.1 vs. 53.6 kg). The LL was significantly (P < 0.05) shorter during the cool season than during the other seasons while no difference was found in LWW between the hot and the cool season. The LL had no effect on WSI, FR and litter sizes. The FR was significantly lower when the WSI was 7 to 10 days than when the WSI was 1 to 6 days. An increase in WSI between Days 9 to 10 and Day 21 resulted in a significant increase in FR. Subsequent litter size decreased by about 0.5 piglets when the WSI increased from 1 to 5 days to 6 to 7 days. Thereafter, litter size increased as the WSI increased from 9 to 10 days to 21 days.     

The influence of ovulation rate on subsequent litter size in sows

Data were collected from 318 pregnant sows (Large White, Landrace or crossbred), which had been weaned from their first litter, to determine the relationship between ovulation rate (OR) and subsequent litter size (total born alive - TBA). Laparoscopy was performed on sows 7 to 14 days after mating to determine OR, and subsequent litter size (TBA) was recorded. Mean (+/-SE) ovulation rate, litter size (TBA) and foetal survival (FS) was 14.56+/-0.19, 9.00 +/- 0.16 and 63.5+/-1.1%, respectively. Regressions of TBA against OR and FS against OR were best fitted by a linear function which indicated that litter size of first-litter sows was limited by ovulation rate up to at least 23 ova. The respective linear regressions were:     

Influence of SLA haplotype on ovulation rate and litter size in miniature pigs

Systemic blood was collected from and surgery performed on sows of 3 strains of miniature swine bred for specific SLA (swine MHC) haplotypes (a, c and d) from Day 2 to Day 6 after mating (first day of mating = Day 0). Ovulation rate was determined by counting corpora lutea and embryos were flushed from the uterus. Progesterone, oestradiol-17 beta and oestrone were quantitated in blood plasma and uterine flushings by RIA. SLAd/d females had a higher ovulation rate than SLAa/a or SLAc/c females (11.50 +/- 0.87 vs 9.11 +/- 0.68 and 8.17 +/- 0.83, respectively; P less than 0.01). Oestrone was higher than oestradiol-17 beta in systemic plasma (56.5 +/- 6.4 vs 33.0 +/- 4.7 pg/ml, P less than 0.01) while oestradiol-17 beta was higher than oestrone in uterine flushings (19.8 +/- 1.4 vs 14.9 +/- 1.5 pg/horn, P less than 0.10). Systemic progesterone concentration was correlated with day after mating (r = 0.93, P less than 0.01). There was no effect of haplotype on any of the hormone concentrations measured. Litter size was analysed from 99 matings amongst SLAa/a, SLAa/c, SLAa/d, SLAd/c and SLAd/d sires and dams. Litter size from -/d and d/d sows or from d/d boars were larger (P less than 0.05) than for all other matings. Although ovulation rate was higher in SLAd/d sows, the significant effect of sire SLA genotype on litter size suggests an additional effect of the d haplotype on embryonic survival.     

Ovulation rate, litter size and prenatal losses in hair sheep of the French West Indies

Ovulation rate (OR) and litter size (LS) were recorded in local hair sheep of Martinique and in local x Lacaune-viande crossbreeds, in order to assess prenatal losses. Local hair sheep LS and OR were 1.91 and 2.41, respectively. Prenatal losses increased with OR, from 0.22 (OR = 2) up to 1.50 (OR > 3). The ewes (69.7%) with LS = 1 had actually lost at least one ovum, against 25.9% of the ewes with LS > 1. Ewes grazing Cynodon nlemfuensis (Stargrass) had lower LS than those grazing Digitaria decumbens (Pangola), in relation with a lower nutritional level and, maybe, more parasitism effects. No seasonal or age at lambing effect was shown. The OR and LS were dramatically decreased on local x Lacaune-viande crossbred ewes (minus 1.32 and 0.67 unit, respectively, P < 0.05). This suggests a possible negative effect of the tropical environment on the crossbreeds' reproductive function.     

LH receptor induction and ovulation rate in mice selected for litter size and body weight

Female mice from lines which had undergone long-term single trait and antagonistic index selection for litter size and body weight were analysed for ovulation rate and LH receptor induction. Compared to randomly selected controls, selection for large litter size increased ovulation rate (60%; P less than 0.001) and decreased LH receptor induction per microgram ovarian DNA (87%; P less than 0.01). Selection for large body weight increased ovulation rate (18%; P less than 0.001), but did not lead to a significant correlated response in LH receptor induction. Index selection for large litter size and small body weight increased ovulation rate (14%; P less than 0.01) and decreased LH receptor induction (72%; P less than 0.01), while index selection for small litter size and large body weight did not significantly alter either ovulation rate or LH receptor induction. LH receptor quantities in testes of males from the 5 lines did not exhibit the among-line profile which was observed in ovaries of females. These results confirm the role of ovulation rate in mediation of the positive genetic correlation between litter size and body weight in mice. Increased ovulation rate in mice selected for large litter size may be due to mechanisms associated with LH receptors as well as factors related to growth. In contrast, increased ovulation rate in mice selected for large body weight may be due exclusively to factors related to growth.     

Effect of chlortetracycline supplementation during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival and fetal development in gilts

A total of 166 crossbred gilts weighing approximately 87 +/- 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 +/- 1 d of age until 15 d after breeding. These gilts were slaughtered at 31 +/- 1 or 71 d +/- 1 d of gestation for evaluation of reproductive performance. Age (190 +/- 3 d vs 195 +/- 3 d) and body weights (106 +/- 2 kg vs 106 +/- 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 +/- 0.7 vs 12.9 +/- 0.9, P = 0.31) and 71 d (13.9 +/- 0.6 vs 12.4 +/- 0.5, P = 0.10) of gestation. There was an increase (P = 0.04) in the number of live embryos for CTC-fed gilts at 31 d (12.1 +/- 0.7 vs 9.7 +/- 0.7) but not at 71 d (10.0 +/- 1.1 vs 9.6 +/- 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding CTC during prebreeding and early gestation did not influence the proportion or age of gilts at puberty. However, CTC feeding may have influenced a trend to-ward an increased ovulation rate and increased number of live embryos in gilts.     

Correlated responses on growth traits after two-stage selection for ovulation rate and litter size in rabbits

Rabbit commercial maternal lines are usually selected for litter size (LS) and paternal lines for growth rate (GR). Line OR_LS was selected by ovulation rate (OR) and LS to improve LS more efficiently. In this study, growth traits of line OR_LS were evaluated by estimating the correlated response on weaning weight (WW), slaughter weight (SW) and GR during fattening period as well as their variability (DWW, DSW and DGR, respectively). Data were analyzed using Bayesian inference methods. Heritability estimates were low for growth traits (0.09, 0.13 and 0.14 for WW, SW and GR, respectively) and negligible for growth traits variability (0.01, 0.004 and 0.01 for DWW, DSW and DGR, respectively). Moderate common litter effect ratio (c²; 0.35, 0.28 and 0.27) and low maternal effect ratio (m²; 0.11, 0.05 and 0.01) were obtained for WW, SW and GR, respectively. Both c² and m² were lower at slaughter than at weaning. In addition, low common litter effect and negligible maternal effect were observed for growth traits variability. Genetic correlations between LS and both growth traits and their variability were close to zero. Positive genetic correlations were observed between OR and growth traits (0.19, 0.38 and 0.36 for WW, SW and GR, respectively) as well as between OR and growth traits variability (0.35, 0.62 and 0.20 for DWW, DSW and DGR, respectively). Positive correlated responses in both periods were obtained for growth traits, WW, SW and GR (0.037, 0.156 and 0.110 kg, respectively). The correlated response found in growth traits might be due to the positive genetic correlations between OR and these traits. However, selection for OR and LS using independent culling levels did not modify the growth traits variability. Therefore, no negative consequences on growth traits can be expected in current commercial maternal lines.     

A diet rich in n-3 polyunsaturated fatty acids reduced prostaglandin biosynthesis, ovulation rate, and litter size in mice

Successful cryopreservation is usually measured in terms of cell survival. However, there may also be more subtle effects within cells that survive. Previous studies on zebrafish have produced evidence of mitochondrial DNA (mtDNA) damage in cryopreserved embryonic blastomeres and, after exposure to cryoprotectants, alterations in mtDNA replication in embryos and decreased mitochondrial membrane potential, mtDNA and ATP production in ovarian follicles. This study shows that the decreased ATP levels previously observed in stage III zebrafish ovarian follicles exposed to ≥3 M methanol persisted in those follicles that subsequently developed to stage IV. However, the decreased mtDNA levels were restored in those follicles. In order to determine whether mitochondrial distribution and/or their transport network was affected by the methanol exposure, immunocytochemistry analysis of tubulin and mitochondrial cytochrome c oxidase I (COX-I) was performed, along with phalloidin staining of polymerized actin. Neat arrangements of all proteins were observed in control follicles, with COX-I and tubulin being colocalized near granulosa cell nuclei, while actin formed hexagonal and/or polygonal structures nearer granulosa cell membranes and projected into the oocyte surface. Exposure to methanol (2 to 4 M) disrupted the COX-I and tubulin arrangements and the hexagonal and/or polygonal actin distribution and actin projections into the oocyte. These effects were still observed in those follicles that developed to stage IV, although the severity was reduced. In summary, the disruption to function and distribution of mitochondria in ovarian follicles exposed to > 2 M methanol may be mediated via disruption of the mitochondrial transport system. Some recovery of this disruption may take place after methanol removal and subsequent follicle maturation.     

Numbers of litters, litter size and survival in two species of microtines at two elevations

The number of litters, litter size and survival of Clethrionomys gapperi and Microtus pennsylvanicus were documented at two elevations (1450 m; 2240 m) in the Canadian Rocky Mountains to determine if those life history traits changed with the length of the breeding season. The high elevation was colder, had fewer frost-free days, and more precipitation than the low elevation. The length of the breeding season of C. gapperi and M. pennsylvanicus averaged 8 d and 34 d longer, respectively, at the low elevation than at the high elevation. In both species and at both elevations, most females survived only long enough to produce one or two litters. Litter size was significantly greater at the high elevation than at the low elevation in M. pennsylvanicus , but not different in C. gapperi. Overall, nestling survival was greater at the low elevation than at the high elevation in M. pennsylvanicus , but not different in C. gapperi. Summer and winter survival rates were not different between elevations in either species. Differences in litter size and nestling survival between elevations in M. pennsylvanicus may be related to differences in habitat quality.     

The influence of insulin administration after weaning the first litter on ovulation rate and embryo survival in sows

Primiparous crossbred sows (n = 43), lactating for an average of 21.1 +/- 0.1 d and weaning 8.7 +/- 0.1 pigs, were used to evaluate the influence of insulin on ovulation rate and embryo survival. The sows were maintained on 2.3 kg/head/d of a 14% protein gestation diet during pregnancy, fed ad libitum during lactation, given 2.7 kg/head/d from weaning until re-breeding and fed 2.3 kg/head/d after mating. Beginning the day after weaning (Day 0) sows were treated with 0.4 IU/kg body weight (BW) insulin (n = 21) or were administered an equivalent volume of saline (n = 22) for 4 d. Beginning on Day 3 and continuing until Day 14 after weaning, the sows were checked for estrus twice daily and were artificially inseminated using pooled semen from 2 fertile boars. At slaughter (days 30 to 40 of gestation), ovaries and uteri were collected, and the ovulation rate, embryo number and viability, and uterine weight and length were evaluated and recorded. Use of insulin decreased the average interval from weaning to estrus compared with saline by increasing percentage in estrus by Day 14 after weaning (5.0 +/- 0.57 vs 6.9 +/- 0.56 d, respectively; P < 0.03). Ovulation rate, number of embryos, embryo survival, and average uterine length and weight were not influenced by insulin treatment. Overall, insulin affected reproductive efficiency in primiparous sows by increasing the percentage of sows in estrus.     

Geographic variation in litter size in the cotton rat (Sigmodon hispidus): factors influencing ovulation rate

Litter size in many mammalian populations varies along a gradient of latitude or altitude. This investigation tested the hypothesis that geographic variation in litter size among populations of the cotton rat is the result of differences in ovulation rate. Oviducts and uteri of virgin and recently mated lab-reared descendants of cotton rats from Kansas (KS), Texas (TX), and Tennessee (TN) were flushed on the day following the last day of estrus. Ovulation rates differ significantly among the three populations for both virgins (mean +/- SEM, KS = 5.3 +/- 0.3, TX = 4.6 +/- 0.5, and TN = 4.0 +/- 0.5) and for females that have recently copulated (KS = 6.5 +/- 0.3, TX = 5.7 +/- 0.7, and TN = 3.7 +/- 0.4; P less than 0.001). These nonvirgin females have significantly higher ovulation rates than virgins for KS and TX (P = 0.01 and 0.05, respectively), but there is no significant effect of copulation on TN. In all populations, ovulation rates of rats that release ova from both ovaries (KS = 6.1 +/- 0.2, TX = 5.9 +/- 0.4, and TN = 5.1 +/- 0.5) are significantly higher than those that use only one ovary (KS = 4.4 +/- 0.4, TX = 3.3 +/- 0.4, and TN = 3.2 +/- 0.3; P less than 0.001). The number of ovaries ovulating differs significantly between populations (P = 0.002). The effect of copulation on the number of ovaries ovulating is marginally significant (P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovulation rate, embryo survival and ovarian sensitivity to gonadotrophins in mice selected for litter size and body weight

Single trait selection of mice for either large body size or large litter size resulted in an increased ovulation rate because of possible enhanced ovarian sensitivity to gonadotrophins. There was no difference in pre-implantation embryonic survival in either of the selected lines when compared to control mice. Selection for body weight did not alter post-implantation embryo survival, but fewer fetuses were lost after implantation in the litter size line compared to the control line. Index selection for large body size and small litter size did not change ovulation rate but increased pre- and post-implantation embryonic mortality. Selection for small body size and large litter size increased ovulation rate and decreased early embryonic death.