María-Luz García

Background: Selection for increased homogeneity of litter size has been proposed to improve resistance to stress and diseases in animals. Previous studies have shown that lines selected for decreased litter size variability (L lines) have higher litter sizes at parity than lines selected for increased litter size variability (H lines), possibly due to higher embryo survival in the oviduct. Thus, the study aimed at examining the effect of the line selection on the oviduct environment and its contribution to embryo development, particularly via extracellular vesicles (EVs). Oviductal EVs (oEVs) and their molecular cargo play essential roles in supporting early embryo development in different species, but little is so far known in rabbits. Results: Oviductal fluid was collected by flushing oviducts from pregnant (with embryos at 72 h p.c., P) and control does (non-ovulated/non-pregnant, NO) from the two lines, resulting in 4 experimental groups: pregnant H line (H_P); pregnant L line (L_P); non-pregnant H line (H_NO); non-pregnant L line (L_NO). Oviductal EVs were isolated and characterized. RNA cargo of oEVs was analyzed by RNA-sequencing, revealing a high number of differential abundant (DA) genes between P vs. NO does in both lines (1223 DA genes in H line and 1519 in L line, FDR < 0.1%). Additionally, 27 and 25 miRNAs were found as DA between P vs. NO in H and L lines, respectively. Interestingly, functional enrichment analysis of DA genes and predicted target genes of identified miRNAs revealed biological terms such as embryo development, epithelium morphogenesis and differentiation, and cilium movement, which were only associated to L line for P and NO groups. Furthermore, the comparison between H and L lines identified 169 DA RNAs in NO does, but without significant differences in P does. For miRNAs, no differences were detected in H vs. L lines in P or NP does. Conclusions: This is the first study unveiling the differential oEV RNA cargo between lines selected for low versus high variation in litter size, and in each line, between P and NO does. The changes in protein-coding RNA and miRNA cargo might reflect the different maternal support to the early embryo development in the different lines.

The aim of this study is to examine the influence of food restriction on rabbit ovarian functions. A total of eight females were fed ad libitum (NF), while eight females were subjected to 50% food restriction (RF). One month later, all females were euthanized. Weights and lengths of ovaries and uterine horns were measured. Representative parts of the ovaries were subjected to histomorphometry analysis of folliculogenesis. Granulosa cells were isolated and cell viability, proliferation (accumulation of PCNA, cyclin B1, and BrdU-positive cells), apoptosis (accumulation of bax, caspase 3, and DNA fragmentation) were evaluated. Granulosa cells were subjected to proteomic analysis by using the nano HPLC-Chip-MS/MS method. Estradiol and progesterone release by ovarian and granulosa cells was assessed by ELISA. Ovarian and uterine horn weights were lower in RF than NF. The diameter of follicles and oocytes and the thickness of the theca and granulosa cells were higher in RF than NF. RF showed a lower percentage of cells containing bax and caspase 3, occurrence of DNA fragmented cells, and estradiol and progesterone. RF had higher incorporation of BrdU, a higher proportion of cells containing PCNA and cyclin B1, and a lower percentage of viable cells. RF produced more specific proteins than NF, including peptides involved in cell differentiation, proliferation/division, mitotic cell cycle, and GTP-ase activity. In conclusion, food restriction can activate reproduction by (1) selection of the growing primordial follicles, (2) better transformation of secondary to preovulatory follicles, (3) increasing growth of oocytes, (4) increasing proliferation and decreasing apoptosis in granulosa cells, (5) changes in ovarian secretory activity, and (6) changes in the number of peptides.

A divergent selection for resilience was carried out in rabbits over 12 generations. The selection criterion was increased (the HO line) and decreased litter size variability at birth (the HE line). The HO line (more resilient) shows higher litter size than the HE line (less resilient). The HO line sows higher litter size and embryo development than the HE line. The aim of this work is to investigate the plasma organic acid profile in both lines at mating and early gestation in order to analyze the effect of selection by resilience in the ovulation rate and early gestation. A total of 19 and 18 nonlactating multiparous females from the HE and HO lines were used. The ovulation rate, normal embryos, and percentage of compacted morulae at 72 h post-coitum (hpc) were studied, and blood samples were obtained at mating and 72 hpc. The organic profile was determined by HPLC. Bayesian methodology was used for statistical analysis. The HE line had 1.5% fewer normal embryos and 12.3% fewer compacted morulae than the HO line. The ovulation rate was similar in both lines. α-ketoglutaric acid and cis-aconitic acid were higher in the HE line than in the HO line. Citric acid, lactic acid, and pyruvic acid were higher at mating than at early gestation. In conclusion, the lower efficiency in the utilization of energy sources in the HE line could explain the reduced embryo production observed. The organic profile varies depending on the reproductive state in the female.

This study aimed to analyze the effect of reducing litter size variability on growth rate, carcass traits, and meat quality in rabbits. Two divergent lines selected by litter size variability were compared: a line selected to reduce litter size variability (HO) and one selected to increase litter size variability (HE). All animals were fed the same commercial diet and kept under identical rearing conditions. The HO line had lower live weight at weaning compared to the HE line (p ≤ 0.05), but the growth rate was higher in the HO line than in the HE line (p ≤ 0.05). Carcass weight and composition were similar between the lines. No differences in meat pH at 45 min and 24 h post-mortem were found between lines. However, the HO line had a higher lightness (L*) value at 45 min post-mortem than the HE line (p ≤ 0.05). The HO line showed higher Ca concentrations than the HE line (p ≤ 0.05). The HO line also had higher protein content and lower saturated fatty acid content than the HE line (p ≤ 0.05). No differences in fat oxidation were observed among the lines. In conclusion, the selection to reduce litter size variability did not negatively impact growth rate and had a favorable effect on protein content, as well as a reduction in saturated fatty acid content in carcass.

The preweaning weight of kits has been related to their mortality during the suckling period. Selecting rabbit kits for individual body weight in the first days of life could be interesting; however, better knowledge of body weight’s heritability during the preweaning period is necessary to determine the opportune moment for selection. A total of 1696 growth records of kits from 81 females of the ITLEV2006 synthetic line were analysed in order to estimate the genetic and non-genetic parameters for individual body weight at birth as well as at 5, 7, 14, 21, 28, and 35 days of age. The estimates of heritability (h²) for individual weight were between low (0.11 at birth, 0.16 at 5 days, and 0.17 at 7 days) and moderate (0.21, 0.21, 0.24, and 0.21 at 14, 21, 28, and 35 days, respectively). Weight at birth showed a strong and positive genetic correlation with weight at 5 days (+0.79) and 7 days of age (+0.78), but the correlation was low for the rest of the weight measurements (+0.41, +0.49, +0.54, and +0.54 with weight at 14, 21, 28, and 35 days, respectively). Weight at 5 days and 7 days displayed strong and positive genetic correlations with the rest of the weight measurements (higher than +0.83). The values of the common litter effect (c²) were high, and they increased with age from 0.43 at birth to 0.66 at 35 days of age. The values of the maternal permanent effect (p²) were low compared to those of the common litter effect (c²), varying between 0.04 and 0.11. In conclusion, opting to select for body weight at 5 or 7 days of age would yield a greater response compared to selecting for birth weight. This approach would indirectly increase the kits’ weight at birth and at weaning, thereby reducing preweaning losses.

The aim of this work is to study changes in body weight, perirenal fat thickness (PFT), and non-esterified fatty acid (NEFA) and leptin concentrations throughout the reproductive life of the rabbit female and their correlations when a semi-intensive reproductive rhythm is applied. A total of 46 lactating females were used. Body weight, PFT, and NEFA and leptin concentration were recorded at 12 weeks of age, at first mating and delivery, and at second, third, and fourth mating, 12th d of gestation, and delivery. The highest body weight was detected on the 12th d of any gestation, around 4280 g, and the lowest weight was at delivery, around 4030 g. PFT increased until third mating. NEFA and leptin concentration showed a cyclical pattern throughout the reproductive lifespan of the females. NEFAs presented the highest concentration at delivery within each reproductive cycle and levels decreased over the course of the deliveries (0.423 mmol/L at first delivery, 0.406 mmol/L at second delivery, 0.371 mmol/L at third delivery, and 0.309 mmol/L at fourth delivery). Similar NEFA concentrations at mating and on the 12th d of gestation were obtained. Leptin showed the highest concentrations at mating within each reproductive cycle. Leptin decreased between mating and delivery in all reproductive cycles and it was close to 1 ng/mL HE. Low or null correlations were shown between body weight, PFT, and NEFA and leptin concentration at mating, 12th d of gestation, and delivery. In conclusion, females are able to maintain a semi-intensive reproductive rhythm across four parities weighing around 4 kg from first mating. Females had an increased perirenal fat thickness until third delivery, and their NEFA concentration was maximum at delivery and leptin concentration was maximum at mating. Body weight, PFT, and NEFA and leptin concentration should be measured during critical moments of reproductive life in order to determine body condition and energy mobilization, due to their low or null correlations.