Selection for ovulation rate in rabbits

An experiment of selection for ovulation rate was carried out. Animals were derived from a synthetic line first selected 12 generations for litter size, then 10 generations for uterine capacity. Selection was relaxed for 6 generations. Selection was based on the phenotypic value of ovulation rate with a selection pressure on does of 30%. Males were selected from litters of does with the highest ovulation rate. Males were selected within sire families in order to reduce inbreeding. Ovulation rate was measured in the second gestation by a laparoscopy, 12 days after mating. Each generation had about 80 females and 20 males. Results of three generations of selection were analyzed using Bayesian methods. Marginal posterior distributions of all unknowns were estimated by Gibbs sampling. Heritabilities of ovulation rate (OR), number of implanted embryos (IE), litter size (LS), embryo survival (ES), fetal survival (FS), and prenatal survival (PS) were 0.44, 0.32, 0.11, 0.26, 0.35, and 0.14, respectively. Genetic correlation between OR and LS was 0.56, indicating that selection for ovulation rate can augment litter size. Response to selection for OR was 1.80 ova. Correlated responses in IE and LS were 1.44 and 0.49, respectively. Selection for ovulation rate may be an alternative to improve litter size.     

Direct and correlated responses to two-stage selection for ovulation rate and number of fully formed pigs at birth in swine

Our objectives were to estimate responses and genetic parameters for ovulation rate, number of fully formed pigs at birth, and other production traits following two-stage selection for increased ovulation rate and number of fully formed pigs. Eight generations of selection were practiced in each of two lines. One selection line was derived from a line that previously selected eight generations for an index to increase ovulation rate and embryonic survival (the IOL pigs). The other selection line was derived from the unselected control line of the index selection experiment (the COL pigs). The control line (C) was continued with random selection. Due to previous selection, Line IOL had greater ovulation rate (4.24 +/- 0.38 and 4.14 +/- 0.29 ova) and litter size (1.97 +/- 0.39 and 1.06 +/- 0.38 pigs) at Generation 0 of two-stage selection than did Lines COL and C. In Stage 1, all gilts from 50% of the largest litters were retained. Approximately 50% of them were selected for ovulation rate in Stage 2. Gilts selected for ovulation rate were mated to boars selected from the upper one-third of the litters for litter size. At Generations 7 and 8, differences in mean EBV for ovulation rate and litter size between Lines IOL and C were 6.20 +/- 0.29 ova and 4.66 +/- 0.38 pigs; differences between Lines COL and C were 2.26 +/- 0.29 ova and 2.79 +/- 0.39 pigs; and differences between Lines IOL and COL were 3.94 +/- 0.26 ova and 1.86 +/- 0.39 pigs. Regressions of line mean EBV on generation number were 0.27 +/- 0.07 ova and 0.35 +/- 0.06 pigs in Line IOL; 0.30 +/- 0.06 ova and 0.29 +/- 0.05 pigs in Line COL; and 0.01 +/- 0.07 ova and 0.02 +/- 0.05 pigs in Line C. Correlated responses were decreased age at puberty and increased number of pigs born alive, number of mummified pigs, prenatal loss, and individual and litter birth weight. Two-stage selection for ovulation rate and number of pigs per litter is a promising procedure to improve litter size in swine.     

Divergent selection for uterine capacity in rabbits. II. Correlated response in litter size and its components estimated with a cryopreserved control population

Our objective was to evaluate the correlated responses to selection for litter size and its components after 10 generations of divergent selection for uterine capacity (UC). A total of 294 intact females from the 11th and 12th generations of divergent selection for high and low UC and from a cryopreserved control population was used (139, 112, and 43 females, respectively). Uterine capacity was assessed as litter size in unilaterally ovariectomized females. Traits recorded on females for up to five parities were litter size (LS) and number born alive (NBA). Laparoscopy was performed in all females at d 12 of their second parity, and the ovulation rate (OR) and number of implanted embryos (IE) were recorded in these females. Embryo survival (ES = IE/OR), fetal survival (FS = LS/IE), and prenatal survival (PS = LS/OR) were computed. Correlated responses in LS and in its components were inferred using Bayesian methods. Correlated responses in LS were asymmetric. The divergence between high and low lines was 2.35 kits, mainly because of a higher correlated response in the low line (1.88 kits). The lower LS in the low line was associated with a lower PS (control - low = 0.14), because of decreases in ES and FS.     

Selection for ovulation rate in rabbits: Direct and correlated responses estimated with a cryopreserved control population

The aim of this work was to evaluate the response in 10 generations of selection for ovulation rate in rabbits using a cryopreserved control population. Selection was based on the phenotypic value of ovulation rate estimated at d 12 of second gestation by laparoscopy. To produce the control population, embryos from 50 donor females and 18 males, belonging to the base generation of the line selected for ovulation rate, were recovered. A total of 467 embryos (72-h embryos) were vitrified and stored in liquid N(2) for 10 generations. The size of both populations was approximately 10 males and 50 females. The number of records used to analyze the different traits ranged from 99 to 340. Data were analyzed using Bayesian methodology. A difference between the selected and the control populations of 2.1 ova (highest posterior density interval (HPD(95%))[1.3, 2.9]) was observed in ovulation rate (OR), but it was not accompanied by a correlated response in litter size (LS; -0.3; HPD(95%) [-1.1, 0.5]). The number of implanted embryos (IE) increased with selection in 1.0 embryo (HPD(95%) [-0.6, 2.0]), but this increase was not relevant. Prenatal survival, embryonic survival, and fetal survival (FS) were calculated as LS/OR, IE/OR, and LS/IE, respectively. Prenatal survival was reduced with selection (-0.12; HPD(95%) [-0.20, -0.04]), basically because of a decrease in FS (-0.12; HPD(95%) [-0.19, -0.06]). Embryonic survival could have slightly decreased (-0.05; HPD(95%) [-0.12, 0.02]). In summary, comparison with a control population showed that ovulation rate in rabbits increased with selection without any correlated response in litter size, basically because of a decrease in fetal survival.     

Alternative methods of selection for litter size in mice: II. Response to thirteen generations of selection

Selection was conducted on an index of components of litter size (I = 1.21 x ovulation rate + 9.05 x ova success; ovulation rate measured by number of corpora lutea and ova success measured as number of pups born + number of corpora lutea), on uterine capacity (measured as number of pups born to unilaterally ovariectomized dams) and on litter size concurrent with an unselected control for 13 generations. Selection criteria (IX = index, UT = uterine capacity, LS = litter size and LC = control) were applied in each of three replicates. In an evaluation after five generations, IX and LS each exceeded LC by about .5 pups, with no response in UT. After 13 generations, mean ovulation rate, ova success and litter size (measured as number of fetuses at 17 d gestation in intact females) were, for IX, 14.25, .84, 11.95; for LS, 14.15, .82, 11.64; for UT, 12.61, .86, 10.77; and for LC, 12.27, .82, 9.98. The regression of number born (litter size in IX, LS and LC; uterine capacity with only a functional left uterine horn in UT) on cumulative selection differential across 13 generations was .12 +/- .01, .09 +/- .02 and .08 +/- .02 for IX, LS and UT, respectively. The regression of breeding value for litter size on each selection criterion, estimated as response in the generation-13 evaluation divided by cumulative selection differential, was .11 +/- .02, .08 +/- .01 and .05 +/- .03 for IX, LS and UT, respectively. Regression of response in number born on generation number was .17 +/- .01, .15 +/- .04 and .10 +/- .02 for IX, LS and UT, respectively. Selection in IX was promising relative to LS, and selection in UT changed number born.     

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Divergent selection for uterine capacity in rabbits. III. Responses in uterine capacity and its components estimated with a cryopreserved control population

This work evaluated the response to 10 generations of divergent selection for uterine capacity (UC) in rabbits to determine whether this response was symmetric by contrasting both lines against a cryopreserved control population. Animals came from the 13th generation of an experiment of divergent selection for UC and from a cryopreserved control population. The two UC lines were divergently selected for 10 generations, and selection was relaxed from the 11th generation until the 13th generation. Uterine capacity was estimated as litter size (LS) in unilaterally ovariectomized (ULO) does. To create the control population, embryos from the base generation were vitrified and stored in liquid N2 for 10 generations. Data from 461 pregnancies produced by 134 ULO does were used: 62 does from the high UC line, 55 females from the low UC line, and 17 females from the control line. The following traits were analyzed: ovulation rate (OR); number of implanted embryos (IE); (UC), estimated as total number of rabbits born; number born alive (NBA); prenatal survival (PS), estimated as UC/OR; embryo survival (ES), estimated as IE/OR; and fetal survival (FS), estimated as UC/IE. Ovulation rate, IE, PS, ES, and FS were measured by laparoscopy only in the second parity. Uterine capacity and NBA were measured over four parities. Responses in UC and its components were estimated as differences between the selected lines and the control line using a Bayesian approach. Selection for UC led to differences of 1.01 kits between the high and low lines, but this response was asymmetric. No differences were found between the high and control lines (high - control = -0.08), whereas the low and control lines differed by 1.08 kits, with a probability of the difference being greater than zero of 0.98. Difference between the high and low lines and between the control and low lines was one-half of the difference reported for correlated response in LS in previous studies. No differences in OR were detected among lines. The control and low lines differed by 1.06 IE, with a probability of the difference being higher than zero of 0.84. Prenatal survival for the low line was less than that of the control line. In summary, selection for UC was asymmetric, which was mainly due to a correlated response in PS. Response in UC was one-half of the difference reported for correlated response in LS in previous studies.     

OVULATION RATE AT FIRST MATING AND REPRODUCTIVE PERFORMANCE OF GILTS

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.     

Responses in ovulation rate, embryonal survival, and litter traits in swine to 14 generations of selection to increase litter size

Eleven generations of selection for increased index of ovulation rate and embryonal survival rate, followed by three generations of selection for litter size, were practiced. Laparotomy was used to count corpora lutea and fetuses at 50 d of gestation. High-indexing gilts, approximately 30%, were farrowed. Sons of dams in the upper 10% of the distribution were selected. Selection from Generations 12 to 14 was for increased number of fully formed pigs; replacements were from the largest 25% of the litters. A randomly selected control line was maintained. Responses at Generation 11 were approximately 7.4 ova and 3.8 fetuses at 50 d of gestation (P < .01) and 2.3 fully formed pigs (P < .01) and 1.1 live pigs at birth (P < .05). Responses at Generation 14 were three fully formed pigs (P < .01) and 1.4 live pigs (P < .05) per litter. Number of pigs weaned declined (P < .05) in the index line. Total litter weight weaned did not change significantly. Ovulation rate and number of fetuses had positive genetic correlations with number of stillborn pigs per litter. Significantly greater rate of inbreeding and increased litter size at 50 d of gestation in the select line may have contributed to greater fetal losses in late gestation, greater number of stillborn pigs, and lighter pigs at birth, leading to lower preweaning viability. Heritabilities of traits were between 8 and 25%. Genetic improvement programs should emphasize live-born pigs and perhaps weight of live-born pigs because of undesirable genetic relationships of ovulation rate and number of fetuses with numbers of stillborn and mummified pigs and because birth weight decreased as litter size increased.     

Selection for ovulation rate in rabbits: genetic parameters and correlated responses on survival rates

The aim of this work was to evaluate the correlated responses on survival rates after 10 generations of selection for ovulation rate (OR). Selection was based on the phenotypic value of ovulation rate estimated at d 12 of second gestation by laparoscopy. Traits recorded were litter size (LS), estimated as total number of rabbits born per litter in up to 5 parities; OR, estimated as the number of corpora lutea in both ovaries; the number of implanted embryos (IE), estimated as the number of implantation sites; the number of right and left IE (RIE and LIE); ovulatory difference (OD), defined as the difference between the right and the left OR, expressed as an absolute value; implantatory difference (ID), defined as the difference between RIE and LIE, expressed as an absolute value; embryonic survival (ES), calculated as IE/OR; fetal survival (FS), calculated as LS/IE; prenatal survival (PS), calculated as LS/OR. A total of 1,081 records were used to analyze ES, and 770 were used to analyze FS and PS. The number of records used to analyze the other traits ranged from 1,079 for ID to 3,031 for LS. Data were analyzed using Bayesian methodology. Genetic parameters of OR, OD, and LS were estimated in a previous paper. Estimated heritabilities of IE, ID, ES, FS, and PS were 0.11, 0.03, 0.09, 0.24, and 0.14, respectively. Estimated repeatabilities of IE, ID, and ES were 0.22, 0.12, and 0.20. Estimated phenotypic correlations of OR with ES, FS, and PS were -0.07, -0.26, and -0.28, respectively. Their estimated genetic correlations with FS and PS were negative (probability of being negative 1.00 and 0.98, respectively). Nothing can be said about the sign of the genetic correlation between OR and ES. Ovulation rate was phenotypically uncorrelated with ID. Their estimated genetic correlation was positive (probability of being positive 0.91). The genetic correlation of ID with PS and LS was not accurately estimated. Phenotypic and genetic correlations between LS and survival rates were positive (probability of being positive 1.00). In 10 generations of selection, FS decreased around 1% per generation. No correlated response in ES was observed. In summary, the decrease in FS in rabbits selected for OR seemed to be responsible for the lack of correlated response observed in LS.     

Duration of estrus in relation to reproduction results in pigs on commercial farms.

This research was conducted to determine factors that influence duration of estrus, AI strategy, and reproduction results between and within commercial swine farms that use AI. Data from 15,186 sows and gilts on 55 farms for a period of 6.1+/-4.2 mo per farm were used in this study. The average duration of estrus was 48.4+/-1.0 h, ranging from 31 to 64 h, and was consistent from month to month within a farm (repeatability of 86%). Differences in duration of estrus between farms accounted for 23% of the total variation in duration of estrus. On most farms (n = 45), gilts showed a shorter (P < .05) duration of estrus than sows (40.8+/-1.1 h vs 48.5+/-1.0 h). The duration of first estrus after weaning was longer (P < .0001) compared with that of repeat-breeder sows (50.2+/-1.0 h vs 46.8+/-1.0 h). Duration of estrus decreased (P < .05) when interval from weaning to estrus increased from 4 to 6 d (56.0 +/- 1.2 h vs 45.8 +/-1.2 h). The regression of interval from onset to estrus to first AI and interval from weaning to estrus varied between farms and ranged from -7.4 to +1.3 h/d; four farms had a positive relationship. Farrowing rate decreased (P < .05) from 89.7+/-2.7% to 78.2+/-5.74 when the interval from weaning to estrus increased from 4 to 10 d. The litter size decreased (P < .05) from 11.7 to 10.6 pigs when the interval from weaning to estrus increased from 4 to 7 d. Compared with a single AI, double AI in sows and gilts resulted in a 4.3 and 7.0% higher (P < .05) farrowing rate, respectively. When the first AI was performed after expected ovulation, reproduction results were lower than when AI was performed before or at expected ovulation in sows. Duration of estrus was not related to farrowing rate or litter size in individual pigs. Number of inseminations per estrus, time of AI, and duration of estrus were correlated, which made it difficult to assess which of these factors was primarily related to the farrowing rate or litter size. Knowledge of average duration of estrus on farms and of factors that influence the duration of estrus on commercial farms can help to improve the efficiency of the AI strategy specific for each farm.     

Progestagen supplementation during early pregnancy does not improve embryo survival in pigs

Progesterone supplementation during early pregnancy may increase embryo survival in pigs. The current study evaluated whether oral supplementation with an analogue of progesterone, altrenogest (ALT), affects embryo survival. A first experiment evaluated the effect of a daily 20-mg dosage of ALT during days 1-4 or 2-4 after onset of oestrus on embryo survival at day 42 of pregnancy. A control group (CTR1) was not treated. The time of ovulation was estimated by transrectal ultrasound at 12-h intervals. Altrenogest treatment significantly reduced pregnancy rate when start of treatment was before or at ovulation: 25% (5/20) compared to later start of treatment [85% (28/33)] and non-treated CTR1 [100% (23/23)]. Altrenogest treatment also reduced (p < 0.05) number of foetuses, from 14.6 ± 2.6 in CTR1 to 12.5 ± 2.5 when ALT started 1-1.5 days from ovulation and 10.7 ± 2.9 when ALT started 0-0.5 days from ovulation. In a second experiment, sows with a weaning-to-oestrous interval (WOI) of 6, 7 or 8-14 days were given ALT [either 20 mg (ALT20; n = 49) or 10 mg (ALT10; n = 48)] at day 4 and day 6 after onset of oestrus or were not treated (CTR2; n = 49), and farrowing rate and litter size were evaluated. Weaning-to-oestrous interval did not affect farrowing rate or litter size. ALT did not affect farrowing rate (86% vs 90% in CTR2), but ALT20 tended to have a lower litter size compared with CTR2 (11.7 ± 4.1 vs 13.3 ± 3.1; p = 0.07) and ALT10 was intermediate (12.3 ± 2.9). In conclusion, altrenogest supplementation too soon after ovulation reduces fertilization rate and embryo survival rate and altrenogest supplementation at 4-6 days of pregnancy reduces litter size. As a consequence, altrenogest supplementation during early pregnancy may reduce both farrowing rate and litter size and cannot be applied at this stage in practice as a remedy against low litter size.     

Reproductive performance in gilts through their first two parities

Fertility data were collected for 766 gilts from 12 breeding and commercial herds. The age at first breeding was 244.5 days and at first farrowing 363.2 days. The litter size was 9.91 piglets born (9.16 live). The farrowing rate at the first service was 87.8%. The total farrowing rate was 95.5% of the mated gilts and 88.4% of all the gilts. 9.8% were repeat breeders. 2.6% of the once mated gilts never returned to oestrus and still did not farrow. The culling rate was 11.6%. The major reason for culling was delayed puberty/anoestrus (7.7%). Of the 565 gilts having a first litter 85.3% were mated after weaning. The age at second farrowing was 541.7 days. The litter size was 10.9 piglets born (10.3 live). The farrowing rate after first service was 83.0%. The total farrowing rate of the 482 sows was 92.9% and of the 565 weaned sows 79.3%. 12.2% were repeat breeders. 4.8% of the sows once mated never returned to oestrus and still did not farrow. The culling rate was 20.7%. Culling because of anoestrus was 4.4%. The month of birth significantly influenced the number of gilts culled because of anoestrus, the age at first breeding and at first and second farrowing. The season also influenced the interval from weaning to service, the percentage of sows served within 7 days of weaning and culled because of anoestrus. No correlation between a high ultrasonic index and lowered fertility was found. The age at first breeding was 1.12 days younger per unit higher ultra-sonic index.     

Direct responses to selection for increased litter size, decreased age at puberty, or random selection following selection for ovulation rate in swine

Nine generations of selection for high ovulation rate were followed by two generations of random selection and then eight generations of selection for increased litter size at birth, decreased age at puberty, or continued random selection in the high ovulation rate line. A control line was maintained with random selection. Line means were regressed on generation number and on cumulative selection differentials to estimate responses to selection and realized heritabilities. Genetic parameters also were estimated by mixed-model procedures, and genetic trends were estimated with an animal model. Response to selection for ovulation rate was about 3.7 eggs. Response in litter size to selection for ovulation rate was .089 +/- .058 pigs per generation. Average differences between the high ovulation rate and control lines over generations 10 to 20 were 2.86 corpora lutea and .74 pigs (P less than .05). The regression estimate of total response to selection for litter size was 1.06 pigs per litter (P less than .01), and the realized heritability was .15 +/- .05. When the animal model was used, the estimate of response was .48 pigs per litter. Total response in litter size to selection for ovulation rate and then litter size was estimated to be 1.8 and 1.4 pigs by the two methods. Total response to selection for decreased age at puberty was estimated to be -15.7 d (P less than .01) when data were analyzed by regression (realized heritability of .25 +/- .05) and -17.1 d using the animal model. No changes in litter size occurred in the line selected for decreased age at puberty. Analyses by regression methods and mixed-model procedures gave similar estimates of responses and very similar estimates of heritabilities.     

Divergent selection for uterine capacity in rabbits. I. Genetic parameters and response to selection

A 10-generation divergent selection experiment for uterine capacity (UC) measured as litter size in unilaterally ovariectomized females was carried out in rabbits. A total of 2,996 observations on uterine capacity of does (up to four parities) was recorded. Laparoscopy was performed at d 12 of their second gestation, and ovulation rate (OR) and number of implanted embryos (IE) were recorded in 735 does. Prenatal survival (PS) was assessed as UC/OR, embryo survival (ES) as IE/OR, and fetal survival (FS) as UC/IE. Genetic parameters and genetic trends were inferred using Bayesian methods. Marginal posterior distributions of all unknowns were estimated by Gibbs sampling. Heritabilities of UC, OR, IE, ES, FS, and PS were 0.11, 0.32, 0.22, 0.04, 0.14, and 0.09, respectively. Genetic and phenotypic correlations between FS and ES were low, suggesting different biological mechanisms for the two periods of survival. After 10 generations of selection, the divergence was approximately 1.5 rabbits, or approximately 1% per generation. Approximately one-half of this response was obtained in the first two generations of selection, which may suggest the presence of a major gene segregating in the base population.     

Effect of soluble and insoluble dietary fiber on embryo survival and sow performance

Two experiments were conducted to evaluate the effects of soluble (SF) and insoluble (ISF) dietary fiber during gestation on embryo survival and sow performance. In Exp. 1, 43 gilts were assigned randomly to 1 of 4 experimental diets: a corn-soybean meal control (C; 1.16% SF, 9.98% ISF); a 30% oat bran high in SF (HS; 3.02% SF, 10.06% ISF); a 12% wheat straw diet high in ISF (HIS; 1.08% SF, 18.09% ISF); and a 21% soybean hull diet (HS + HIS; 2.46% SF, 24.55% ISF). Gilts were fed the experimental diets based on their initial BW to meet their daily nutrient requirements. At estrus, gilts were inseminated artificially 3 times using pooled semen. Reproductive tracts were harvested 32 d postmating (range = 28 to 35 d). Statistical analysis of data included the effects of diet with days of gestation as a covariate. There were no differences in ovulation rate among gilts fed the experimental diets (avg. = 14.1). Number of live embryos was less for HIS and HS + HIS gilts compared with C and HS (9.9 and 9.1 vs. 11.9 and 10.6, respectively; P < 0.05). Total embryo survival rate (P < 0.05) was less for gilts fed HS + HIS compared with those fed the C and HS diets. These results suggest that high dietary ISF might decrease the total embryo survival rate without affecting ovulation rate. In Exp. 2, 716 sows were used in 3 concurrent trials. In trial 1, diets included a corn-soybean meal control (C; 0.43% SF, 10.50% ISF; n = 122) or a 31% oat bran diet (HS; 1.93% SF, 8.87% ISF; n = 124). In trial 2, diets included a C (n = 97) or a 13% wheat straw diet (HIS; 1.10% SF, 17.67% ISF; n = 119), and in trial 3 sows were fed a C (n = 123) or a 21% soybean hull diet (HS + HIS; 1.50% SF, 17.77% ISF; n = 131). All diets were offered to sows beginning 2 d postmating. All sows had ad libitum access to a standard lactation diet. Statistical analysis included the effects of diet, parity group, genetic line, and season as well as their interactions. The inclusion of SF and ISF in gestation diets did not affect litter size. Sows fed the HS + HIS diet had a greater ADFI and lost less BW during lactation (P < 0.01) than sows fed C. Under the conditions of this study, feeding gestating sows increased levels of SF and ISF from d 2 after breeding to d 109 of gestation did not increase litter size.     

National Pork Producers Council Maternal Line National Genetic Evaluation Program: a comparison of sow longevity and trait associations with sow longevity

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.     

Genetic relationships between length of productive life and lifetime production efficiency in a commercial swine herd in Northern Thailand

Genetic parameters and trends for length of productive life (LPL), lifetime number of piglets born alive per year (LBAY), lifetime number of piglets weaned per year (LPWY), lifetime litter birth weight per year (LBWY) and lifetime litter weaning weight per year (LWWY) were estimated using phenotypic records of 3085 sows collected from 1989 to 2013 in a commercial swine farm in Northern Thailand. The five‐trait animal model included the fixed effects of first farrowing year‐season, breed group and age at first farrowing. Random effects were animal and residual. Heritability estimates ranged from 0.04 ± 0.02 for LBWY to 0.17 ± 0.04 for LPL. Genetic correlations ranged from 0.66 ± 0.14 between LPL and LBAY to 0.95 ± 0.02 between LPWY and LWWY. Spearman rank correlations among estimated breeding values for LPL and lifetime production efficiency traits tended to be higher for boars than for sows. Sire genetic trends were negative and significant for all traits, except for LPWY. Dam genetic trends were positive and significant for all traits. Sow genetic trends were mostly positive and significant only for LPWY and LBWY. Improvement of LPL and lifetime production efficiency traits will require these traits to be included in the selection indexes used to choose replacement boars and gilts in this population.     

Genetic factors contributing to variation in littersize in British Large White gilts

The number of ova released (ovulation rate) by 516 Large White gilts born between 1986 and 1989 was recorded. The weight of the gilt at birth, weaning and time of ovulation rate measurement and her number of teats were also recorded. Parrowing data (number born alive and litter weight at birth) corresponding to the ovulation rate were recorded from 382 of the gilts, enabling calculation of prenatal survival (number born alive/ovulation rate). The data were analysed using univariate and multivariate restricted maximum likelihood (REML) techniques with an individual animal model. The additive genetic direct and maternal components of variance and the common family and residual environmental components of variance and the additive genetic and residual environmental covariances between traits were estimated. The univariate REML analyses showed that the additive genetic direct component was a significant source of variation for gilt weight at birth and weaning, teat number, ovulation rate on the left hand side, total ovulation rate and litter weight at birth. Common family environmental effects were significant sources of variation for gilt weights and teat number. The multivariate REML analyses indicated that the genetic correlations between total ovulation rate and ovulation rate from the left and right ovaries were close to unity, with an estimate of the heritability of total ovulation rate of 0.37±0.09. In the data from gilts that farrowed, the heritabilities of ovulation rate, number born alive and prenatal survival were 0.30±0.10, 0.09±0.06 and 0.00±0.00, respectively. The genetic correlation between ovulation rate and litter size was close to unity, suggesting that genetic variation in ovulation rate explains virtually all of the genetic variation in number born alive in the population of Large White gilts understudy.     

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.