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.     

Experimental Brucella ovis infection in pregnant ewes.

Forty yearling Brucella-free ewes were inoculated with Brucella ovis by the conjunctival route in mid or late first pregnancy. Only a few ewes excreted B ovis during pregnancy and gave birth to stillborn lambs, but most of them excreted the organism at lambing or during lactation. One of the 11 lambs which were born alive but died before they were weaned was found to be infected postmortem. In contrast, none of the 46 surviving lambs which were reared in isolation until adulthood, was found to be infected. At weaning, the 40 ewes were mated again with five Brucella-free rams. Although many of the ewes excreted B ovis, none of the rams was found to be infected when necropsied after mating. Most of the ewes that became pregnant, all having excreted B ovis during their first pregnancy, cleared the infection during the second pregnancy. However, three remained persistently infected and excreted B ovis in their milk throughout the second lactation. None of the lambs born to these three ewes was found to be infected when necropsied at weaning.     

Elliptical selection experiment for the estimation of genetic parameters of the growth rate and feed conversion ratio in rabbits

Two elliptical selection experiments were performed in two contemporary sire lines of rabbits (C and R) in order to optimize the experimental design for estimating the genetic parameters of the growth rate (GR) and feed conversion ratio (FCR). Twelve males and 19 females from line C, and 13 males and 23 females from line R, were selected from an ellipse defined by a quadratic index based on these traits. Data from 160 rabbits of each of the parental generations of lines C and R and their offspring (275 and 266 animals, respectively) were used for the analysis. A Bayesian framework was adopted for inference. Marginal posterior distributions of the genetic parameters were obtained by Gibbs sampling. An animal model including batch, parity order, litter size, and common environmental litter effects was assumed. Posterior means (posterior standard deviations) for heritabilities of GR and FCR were estimated to be 0.31 (0.10) and 0.31 (0.10), respectively, in line C and 0.21 (0.08) and 0.25 (0.12) in line R. Posterior means of the proportion of the variance due to common litter environmental effects were 0.14 (0.06) and 0.21 (0.06) for GR and FCR, respectively, in line C and 0.17 (0.06) and 0.22 (0.06) in line R. Posterior means of genetic correlation between both traits were -0.49 (0.25) in line C and -0.47 (0.32) in line R, indicating that selection for GR was expected to result in a similar correlated response in FCR in both lines.     

The effect of divergent selection for uterine capacity on fetal and placental development at term in rabbits: maternal and embryonic genetic effects

The aim of this work was to study the effects of the genotype of the dam, the embryo, or their interactions on prenatal growth by performing double-reciprocal embryo transfers between two lines of rabbits divergently selected for uterine capacity. Females from high (n = 53) and low (n = 48) lines were slaughtered at 72 h of gestation, and recovered embryos were transferred to the oviducts of recipient does from the high (n = 23) and low (n = 19) lines. Each recipient doe received eight embryos from the high line into one oviduct and eight embryos from the low line into the other. Recipient does were slaughtered on d 28 of gestation. The percentages of live fetuses at 28 d of gestation were 89.2 and 74% for high and low recipient lines, respectively. Length and weight of the empty uterine horn and weight of the full uterine horn were not affected by either the recipient or by donor line. Fetal weight was affected by the recipient line but not by the donor line. Fetuses gestated in high recipient does were 7% heavier (P < 0.10) than those in the low recipient does. There was a donor and a donor x recipient interaction effect on fetal placental weight. Fetal placental weight was heavier (7%, P < 0.01) for embryos from the low line. Embryos from the high line gestated in low-line uteri showed a lower fetal placenta weight than did low-line embryos gestated in high-line uteri and low-line uteri (P < 0.05). Linear regression coefficients of fetal weight at term on fetal placental weights differed (P < 0.05) for the high and low donors (4.33 +/- 0.28 and 3.41 +/- 0.29 respectively). A significant effect of the donor genotype on individual placental length was observed (P < 0.05), which might have resulted from a smaller individual placental length of low-line embryos gestated high-line uteri (P < 0.10). Neither donor nor recipient lines affected maternal placental weight or available space for fetuses. Fetuses and their fetal placentae were heavier when receiving more than four blood vessels than when receiving less than three blood vessels (13 and 17% respectively, P < 0.05). Neither recipient nor donor genotype affected the number of blood vessels arriving at each live fetus. Thus, fetal weight depends on the maternal genotype, whereas fetal placental weight depends on the embryo genotype in these two lines of rabbits divergently selected for uterine capacity.     

Specificity dependence between serological tests for diagnosing bovine brucellosis in Brucella-free farms showing false positive serological reactions due to Yersinia enterocolitica O:9

When brucellosis false positive serological reactions happen in cattle, the serial use of pairs of specificity-correlated serological tests (rose bengal, complement fixation, competitive ELISA) results in specificities lower than expected. In this situation, highly specific tests, such as the indirect ELISA used alone, may be more adequate than serial testing.     

Effects of intrauterine crowding on available uterine space per fetus in rabbits

The aim of this study was to examine the effects of uterine crowding on available uterine space per fetus and fetal development at 18 days of gestation in unilaterally ovariectomized and intact does from the sixth generation of a divergent selection experiment on uterine capacity. Uterine capacity was estimated as litter size in unilaterally ovariectomized (ULO) does. Records from 37 ULO and 26 intact does were used. All does were slaughtered on d 18 of gestation. Ovulation rate per side in ULO does was almost twice as much as intact does (12.41 ova vs. 6.47 ova, P < 0.001). ULO does showed higher intrauterine crowding at implantation than intact does (9.36 implanted embryos/uterine horn vs. 5.31 implanted embryos/uterine horn, P < 0.001) and a lower available uterine space per live fetus (3.60 cm vs. 4.44 cm, P < 0.001). The available uterine space per embryo decreased quadratically with the number of implanted embryos (b₁ = − 2.46 ± 0.18, b₂ = 0.13 ± 0.01), and showed a negative linear regression coefficient with number of dead fetuses (− 0.18 ± 0.08). The available uterine space affects quadratically the development of the maternal placenta, and to a lesser extent is linearly related to the development of the fetus and its fetal placenta. The coefficients of these regressions were higher in ULO does than intact does, due to the higher degree of uterine overcrowding in these females.

Although the fetal position within the uterus did not affect the proportion of dead embryos, the uterine position could affect the survival of fetuses with a lower available uterine space. A poor blood supply had a negative effect on survival of the fetus and its development. Probability of death for fetuses with placenta receiving less than 3 blood vessels was higher than those receiving more than 3 blood vessels in both ULO and intact does (75.61% vs. 7.32%). Probability of survival asymptotically increases with available uterine space, as a result of the greater availability of uterine space which allows more blood vessels to reach each implantation site. The uterine overcrowding of ULO does was therefore associated with less uterine space and blood supply available at each implantation site, which could be related to higher fetal mortality in these females. Blood supply also affects fetal development. The implantation sites receiving less than 3 blood vessels showed lighter placentas (1.31 g vs. 1.41 g, P < 0.05) and fetuses (2.02 g vs. 2.12 g, P < 0.05) than those receiving more than 3 blood vessels in both ULO and intact does. These results suggest that available uterine space is a limitation component of fetal survival, which is related to an adequate vascular supply for nutrient exchange from the maternal to fetal blood streams and an adequate surface area for development of the placenta.     

Biofortification of Se and induction of the antioxidant capacity in lettuce plants

The aim of the present work is to analyse the way in which Se fertilization in both Se forms applied at different rates can affect the production and accumulation of Se and the foliar antioxidant capacity in lettuce plants Lactuca sativa L. cv Philipus. After different rates of sodium selenate and selenite were applied (5, 10, 20, 40, 60, 80, 120 μmol L⁻¹), the foliar biomass, lipid peroxidation, Se accumulation, antioxidant compounds, and the antioxidant capacity were analysed. Our results indicate that the less toxic form was selenate, as it induced greater biomass, higher Se accumulation, and more antioxidant compounds than did selenite. The treatment of 40 μmol L⁻¹ proved the most suitable for lettuce plants, as the antioxidant capacity and Se accumulation augmented without diminishing biomass, and making the two these lettuce plants healthier than control plants for human consumption, in comparison to control. Finally, regarding the antioxidant capacity test used (the ferric reducing ability of plasma [FRAP], 2,2-diphenyl-1-picryl-hydrazyl [DPPH] and reducing power), only FRAP showed a significant relationship with the different antioxidant compounds, while ascorbate best reflected the effect of Se on the antioxidant capacity under our experimental conditions.     

Performance of skin tests with allergens from B. melitensis B115 and rough B. abortus mutants for diagnosing swine brucellosis

Swine brucellosis by Brucella suis biovar 2 is an emerging disease whose control is based on serological testing and culling. However, current serological tests detect antibodies to the O-polysaccharide (O/PS) moiety of Brucella smooth lipopolysaccharide (S-LPS), and thus lack specificity when infections by Yersinia enterocolitica O:9 and other gram-negative bacteria carrying cross-reacting O/PS occur. The skin test with the protein-rich brucellin extract obtained from rough B. melitensis B115 is assumed to be specific for discriminating these false positive serological reactions (FPSR). However, B115 strain, although unable to synthesize S-LPS, accumulates O/PS internally, which could cause diagnostic problems. Since the brucellin skin test has been seldom used in pigs and FPSR are common in these animals, we assessed its performance using cytosoluble protein extracts obtained from B. abortus rough mutants in manBcore or per genes (critical for O/PS biosynthesis) and B. melitensis B115. The diagnostic sensitivity and specificity were determined in B. suis biovar 2 culture positive and brucellosis free sows, and apparent prevalence in sows of unknown individual bacteriological and serological status belonging to B. suis biovar 2 naturally infected herds. Moreover, the specificity in discriminating brucellosis from FPSR was assessed in brucellosis free boars showing FPSR. The skin test with B. abortus ΔmanBcore and B. melitensis B115 allergens performed similarly, and the former one resulted in 100% specificity when testing animals showing FPSR in indirect ELISA, Rose Bengal and complement fixation serological tests. We conclude that O/PS-free genetically defined mutants represent an appropriate alternative to obtain Brucella protein extracts for diagnosing swine brucellosis.