Some factors that influence semen characteristics in rabbits.

The aim of this study, based on a five-year-long experiment, was to analyse some of the factors that influence rabbit sperm production. A total of 174 bucks between 23 and 44 weeks of age from five successive groups were used for semen collection one day per week, two times, at a 15 min interval (ejaculates of rank 1 and 2), over a period of 21 weeks. Immediately after collection, pH, mass motility, volume and concentration were measured using classical methods, and a set of motility parameters were recorded by a computer-assisted semen analysis system. Between groups, the number of motile sperm per ejaculate, considered as a synthetic criterion combining both qualitative and quantitative aspects of semen characteristics, varied from simple to double (from 150 to 326×10(6)), reflecting the strong influence of uncontrolled environmental factors. Adult (37-43 weeks old) expressed a higher number of motile sperm/ejaculate than younger bucks (300 vs. 205×10(6)). In autumn the number of motile sperm/ejaculate was higher than in summer (287 vs. 188×10(6)). Sperm production was higher on average for the first ejaculate compared to the second one (270 vs. 167×10(6)). For several semen characteristics, the effect of the collector was significant but without any repercussion on sperm production. Bucks born to nulliparous or primiparous does had higher performances. This study highlights the high variability of rabbit semen characteristics and the multitude of factors involved, either controlled or uncontrolled.

Selection for litter size in pigs. II. Efficiency of closed and open selection lines.

A selection experiment on litter size in the pig was carried on for seventeen generations in an Inra experimental herd. The founder population was made up of 10 males and 120 females from the Large White breed. Selection was first performed for ten generations in a closed line, compared to a control line derived from the same founder population. Selection was carried on within sire family on the total number of piglets born in the first two litters of the dam (TB1 + TB2). After ten generations, the selection criterion became dam TB1 only. The control line was then discontinued and a panel of frozen semen from the 11th generation boars was created for later comparisons. The selected line was opened to gilt daughters of hyperprolific boars and sows, at a rate of 1/8 per generation, and the same selection procedure was applied irrespective of the origin of the gilt. During the whole experiment, the number of ova shed (OS) and the number of live embryos (LE) at 30 days in the 3rd pregnancy were recorded. These two parts of the experiment were analysed using REML estimation of genetic parameters and a BLUP-Animal Model in order to estimate the responses to selection. Significant heritabilities for TB1, TB2, OS and LE were obtained, i.e. 0.10, 0.05, 0.43 and 0.19, respectively. Significant common environment variances and covariances were estimated for nearly all traits. Significantly positive BLUP responses per generation were observed from G0 to G17 for TB1 (+0.086), TB2 (+0.078), OS (+0.197) and LE (+0.157). However, the responses were 3- to 4-fold higher in the G12-G17 interval compared to G0-G11, and they were also in fair agreement with previous estimates based on standard least-squares procedures, using the control line and the control frozen semen panel. Since G11, the selection intensity was increased by nearly 80 p. cent compared to the previous generations, and the proportion of hyperprolific ancestry increased up to 65 p. cent in the sows of the last generation. The total genetic gain of about 1.4 piglets at birth per litter could be shared between a gain due to immigration, of about 0.8 piglets per litter, and a within-line selection gain of about 0.6 piglets. Thus by combining selection and immigration in the second part of the experiment, advantage could be taken from both the genetic superiority of the immigrants and the higher internal selection intensity made possible by immigration.

Divergent selection for uterine capacity in rabbits.

To examine the genetic and phenotypic parameters of uterine capacity and its components in rabbits, we performed a divergent selection experiment for uterine capacity. Rabbit does were unilaterally ovariectomized, and a laparoscopy was performed at midgestation to count the number of corpora lutea and implanted embryos. Selection was performed on litter size in all parities. Genetic parameters were estimated by residual maximum likelihood. For most traits, phenotypic and genetic correlations were in the same range. In unilaterally ovariectomized rabbit does, litter size had a low genetic (.34) and phenotypic (-.08) correlation with ovulation rate, a high genetic (.71) and phenotypic (.60) correlation with the number of implanted embryos, and a high genetic correlation (.89) and moderate phenotypic correlation (.51) with fetal survival. Embryonal survival had a low phenotypic (-.26) or genetic (.12) correlation with fetal survival. A component of uterine capacity, fetal survival in one overcrowded uterine horn, had a low heritability (.05), and consequently limited possibilities for improvement by selection. Uterine capacity, estimated as litter size in one overcrowded uterine horn, had a moderately low heritability (.16). Divergent selection on uterine capacity was effective and a correlated response was found in implanted embryos. No correlated response was found in fetal survival and number of dead fetuses between implantation and birth.

Effect of acrosome defects and sperm chromatin decondensation on fertility and litter size in the rabbit. Preliminary electron-microscopic study.

Sections of ejaculated spermatozoa from rabbits with known fertility were observed by transmission electron microscopy. Acrosome defects, odd head shapes, the presence of spermatids and the decondensation of sperm nuclei were recorded. The fertility negatively correlated with the number of acrosomal defects, while litter size was negatively related to nuclear decompaction. Sperm nuclear decondensation was present in all ejaculates. Its frequency was correlated with that of spermatids in ejaculates.

[Reproduction of French Angora rabbits: ovulation in the female, semen production in the male]. / La reproduction du lapin Angora de souche française: ovulation chez la femelle, production de semence chez le mâle.

Ovulation rate and semen quality in French Angora rabbits were investigated to determine the potential of improving breeding practices in this breed. The proportion of does ovulating and their ovulation rate were studied in 40 females, as well as sexual behaviour and semen quality in 8 males. The experiments took place in autumn 1987 and were repeated in winter. Three groups of does were injected with 25, 50 IU hCG or 0.8 microgram GnRH (groups 1, 2 and 3, respectively). Another group was mated and served as a control (group 4). Hormonal treatments improved the proportion of does which ovulated (95, 90, 74 and 28% in groups 1-4, respectively; P less than 0.05) but did not change their ovulation rate (10.9 +/- 0.7, 10.7 +/- 0.7, 11.3 +/- 0.8 and 8.9 +/- 1.3 corpora lutea per ovulating female, groups 1-4, respectively; m +/- SEM, NS). In males, two ejaculates were collected twice weekly for 3.5 weeks from 8 bucks. Ejaculates obtained in March were better than those collected in November (volume: 0.33 vs 0.23 ml, P less than 0.01; raw motility: 5.2 vs 3.9, P less than 0.01; individual motility: 2.7 vs 2.1, P less than 0.05; number of living spermatozoa per ejaculate: 71 vs 28 x 10(6), P less than 0.01, respectively). These results suggest that artificial insemination may be utilized to improve reproductive performance in French Angora rabbits.

[Measurement of ovulation rate in rabbits by celioscopy]. / Mesure du taux d'ovulation par coelioscopie chez la lapine.

With the aim of determining the efficiency of a simple and non destructive method for measuring the ovulation rate, 20 doe rabbits were subjected to coelioscopy and slaughtered on day 14 of gestation. Among the 40 ovaries examined, 45% of corpora lutea counts were accurate and 35% approximate (+/- 1), i.e. a total of 80% acceptable counts. This percentage represented 96% when the number of corpora lutea per ovary did not exceed 8. As compared with a few control does, coelioscopy did not seem to have a significant unfavourable effect on embryonic survival rate on day 14 of gestation, but this result has to be checked. It may be concluded that this method can be used in further experiments.

Blockade of the final phase of ovulation has no effect on the post-ovulatory surge of serum FSH in the rabbit.

Mating induces a surge of both LH and FSH in the blood of female rabbits, followed 10-12 h later by a surge of FSH only, which begins at the time of ovulation. We have studied the effect of suppression of ovulation on the post-ovulatory surge of FSH. In the first experiment, follicular fluid and oocytes were withdrawn from the largest follicles 8 h after coitus. In the second experiment, ovulation was inhibited by injecting the rabbits with 25 mg indomethacin/kg body weight 7.5 h after mating. Levels of serum FSH and LH were measured for 24-48 h after mating. Control rabbits ovulated normally in both experiments. The treatments did not significantly affect the levels of serum FSH in either experiment, although the second surge of FSH was slightly higher after fluid had been aspirated from the preovulatory follicles. These observations show that the post-ovulatory surge of serum FSH is not dependent upon the completion of ovulation and that it is programmed before 7.5-8 h post coitum.

Effect of swine lymphocyte antigen haplotypes on birth and weaning weights in pigs.

Birth weights of 708 live piglets and weaning weights of 566 piglets were used to investigate the effect of the swine lymphocyte antigen (SLA) complex on these traits in Large White pigs. Piglets were from litters of a long-term selection experiment to measure response for selection to increase litter size. SLA haplotypes were determined using conventional class I antisera. A total of 14 haplotypes were detected. The effect of SLA haplotype on birth and weaning weights was investigated using a statistical model that included the effects of experimental group, sire, dam, sex and SLA haplotype. Results indicated that SLA class I haplotype 13.1.3 increased birth weights (P less than 0.10) and significantly increased weaning weights (P less than 0.01). This effect of haplotype 13.1.3 on weaning weight was 605 +/- 215 g (0.3 standard deviations). SLA class I homozygosity did not appear to affect birth and weaning weights. These results suggest that the SLA complex plays an important role in early growth in the pig and that further study of SLA effects on growth and reproduction are warranted.

[Influence of mineral diet of the sow on the sex ratio of the newborn]. / Influence de l'alimentation minérale de la truie sur le taux de masculinité à la naissance.

This paper reports a study on sows to check the theory of Stolkowski which hypothesizes that mineral imbalance in the diet of the female before fertilization affects the sex ratio of the progeny. Relative excess of Na+ and K+ ions (NaK diet) would favour the birth of males, while relative excess of Ca2+ and Mg2+ ions (CaMg diet) would favour the birth of females. We carried out two successive experiments. In the first, sows were given the diet for about 34 days, the molar Na + K/Ca + Mg ratios being 2.1 for the NaK diet and 0.7 for the CaMg diet. Out of a total of 677 births, the sex ratio was 55.7 with the NaK diet and 48.3 with the CaMg diet. In the second experiment, the sows were treated for about 53 days and the molar ratios were 3.9 for the NaK diet and 0.5 for the CaMg diet. Out of a total of 869 piglets, the sex ratios were 50 and 53.5, respectively. Thus, the difference observed in experiment 1 (0.05 less than P less than 0.10), which agrees with the above mentioned theory, was reversed in experiment 2, the diet-experiment interaction being significant (P less than 0.05). Overall, the diet did not affect the sex ratio; the contradictory results of the two experiments showed no reproducible effect of dietary mineral imbalance on the sex ratio in pigs. There was also a significant diet-experiment interaction (P less than 0.05) as to litter size, and a nearly significant negative relationship between sex ratio and litter size was observed.