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Genetic variability of functional longevity in five rabbit lines
- A. G. EL Nagar, J. P. Sánchez, M. Ragab, C. Mínguez, M. Baselga
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The objectives of this study were to analyse the differences in the genetic determination of functional longevity in five Spanish lines of rabbits and to check how different systematic factors might affect this genetic determination. Four of the lines were maternal (lines A, V, H and LP), these lines were established selecting base generation animals according to different criteria, but in the subsequent generations all of them were selected for litter size at weaning. The other is the paternal line R, this line was constituted by selecting animals with an outstanding daily growth rate. The trait analysed, length of productive life, was the time in days between the date of the first positive pregnancy test and the date of culling or death of a doe. Four models extended from the Cox proportional hazard model were used to analyse data of each line separately and jointly. The complete model (Model 1) included the fixed effect of year-season (YS) combination, positive palpation order (OPP), that is, reproductive cycle, physiological status of the doe (PS) at service and number of kits born alive (NBA) in each kindling as time-dependent factors. The inbreeding coefficient was fitted as a continuous covariate and the animal’s additive genetic effect was also fitted to the model (Model 1). The other models were identical to Model 1 but excluding OPP (Model 2) or PS (Model 3) or NBA (Model 4), which were explored to assess the consequence on additive variance estimates of not correcting for these animal-dependent factors. Estimated effective heritabilities of longevity were 0.07 ± 0.03, 0.03 ± 0.02, 0.14 ± 0.09, 0.05 ± 0.04, 0.02 ± 0.01 and 0.04 ± 0.01 for lines A, V, H, LP, R and for the merged data set, respectively. Removing the PS from the model led to an increase in the estimated additive genetic variance in all lines (0.17 ± 0.05, 0.05 ± 0.03, 0.29 ± 0.19, 0.29 ± 0.20, 0.07 ± 0.04 and 0.05 ± 0.02 for lines A, V, H, LP, R and the merged data set, respectively). The highest hazard of death and/or culling was observed during the first two parities and decreased as the order of parity progressed. Does non-pregnant-non-lactating had the highest risk of death or culling. The does that had zero kits born alive incurred the highest risk, and this risk decreased as the NBA increased. In conclusion, the consideration of longevity as selection criterion for the studied rabbit lines is not recommended.
Crossbreeding effects on rabbit reproduction from four maternal lines of rabbits
- M. Ragab, J. P. Sánchez, C. Mínguez, M. Baselga
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Litter size is essential for an efficient production of rabbit meat. A diallel cross between four maternal lines was carried out and the analysis of the components of litter size has been already done. This paper presents the analysis of litter size traits themselves (total born (TB), number born alive (NBA), number weaned (NW)) and kindling interval (KI), that complete the analysis of the reproductive performance. The 16 genetic groups were distributed in four Spanish farms. The V line was present in all farms in order to be used as reference group. A total of 34 546 parities from 7111 does, were analysed. The crossbreeding parameters were estimated according to Dickerson model. The differences between lines performance were of low magnitude and not significant for litter size traits. The LP line showed the shortest KI followed by H respect to lines A and V. These differences reflected the differences between direct and maternal genetic effects. The differences between the average of all crosses and line V were found to be significant and seemed to be important, being 0.46 for TB, 0.56 for NBA, 0.75 for NW and −2.21 days for KI. The differences between reciprocal crosses for litter size were of low magnitude and non-significant, which indicate that the maternal effects are not important between these lines. In general, the lines did not show significant differences in direct and maternal genetic effects for TB, NBA and NW but there were some significant differences for KI, which ranged from 1.54 to 6.85 days in direct effects and from 0.63 to 3.38 days for maternal effects. A positive and, in some cases, relevant heterosis was found. The largest heterosis was for TB in the HV cross (1.05 rabbits), followed by the AH (0.74 rabbits), AV (0.57 rabbits) and LH (0.55 rabbits) crosses. For NBA, significant heterosis was found in HV (1.11 rabbits) and AV (0.49 rabbits) and for NW in AV (0.90 rabbits), LH (0.70 rabbits) and LV (0.58 rabbits). Favourable and significant heterosis for KI was found in AV and LV crosses, whereas it was unfavourable in AL and in LH. The more recommended crosses were AV and LH, showing the greatest performances on NW, while the cross HV, which shows the greatest performances an NBA, could be highly recommended when cross-fostering is practised to equalise litter sizes after birth, in this situation the lower NW performance observed could be improved.
Different resource allocation strategies result from selection for litter size at weaning in rabbit does
- D. Savietto, C. Cervera, L. Ródenas, E. Martínez-Paredes, M. Baselga, F. J. García-Diego, T. Larsen, N. C. Friggens, J. J. Pascual
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This study examined the effect of long-term selection of a maternal rabbit line, solely for a reproductive criterion, on the ability of female rabbits to deal with constrained environmental conditions. Female rabbits from generations 16 and 36 (n=72 and 79, respectively) of a line founded and selected to increase litter size at weaning were compared simultaneously. Female rabbits were subjected to normal (NC), nutritional (NF) or heat (HC) challenging conditions from 1st to 3rd parturition. Animals in NC and NF were housed at normal room temperatures (18°C to 25°C) and respectively fed with control (11.6 MJ digestible energy (DE)/kg dry matter (DM), 126 g digestible protein (DP)/kg DM, and 168 g of ADF/kg DM) or low-energy fibrous diets (9.1 MJ DE/kg DM, 104 g DP/kg DM and 266 g ADF/kg DM), whereas those housed in HC were subjected to high room temperatures (25°C to 35°C) and the control diet. The litter size was lower for female rabbits housed in both NF and HC environments, but the extent and timing where this reduction took place differed between generations. In challenging conditions (NF and HC), the average reduction in the reproductive performance of female rabbits from generation 16, compared with NC, was −2.26 (P<0.05) and −0.51 kits born alive at 2nd and 3rd parturition, respectively. However, under these challenging conditions, the reproductive performance of female rabbits from generation 36 was less affected at 2nd parturition (−1.25 kits born alive), but showed a greater reduction at the 3rd parturition (−3.53 kits born alive; P<0.05) compared with NC. The results also showed differences between generations in digestible energy intake, milk yield and accretion, and use of body reserves throughout lactation in NC, HC and NF, which together indicate that there were different resource allocation strategies in the animals from the different generations. Selection to increase litter size at weaning led to increased reproductive robustness at the onset of an environmental constraint, but failure to sustain the reproductive liability when the challenge was maintained in the long term. This response could be directly related to the short-term environmental fluctuations (less severe) that frequently occur in the environment where this line has been selected.
Environmental sensitivity differs between rabbit lines selected for reproductive intensity and longevity
- D. Savietto, C. Cervera, E. Blas, M. Baselga, T. Larsen, N. C. Friggens, J. J. Pascual
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To better understand the mechanisms that allow some animals to sustain their productive effort in harsh environmental conditions, rabbit does from two selection lines (LP and V) were housed in normal (NC), nutritional (NF) or heat (HC) challenging environmental conditions from first to third partum. The LP line (n=85) was founded on reproductive longevity criteria by selecting does from commercial farms that had a minimum of 25 partum with more than 7.5 kits born alive per parity. Line V (n=79) was constituted from four specialised maternal lines into a composite synthetic line and then selected by litter size at weaning for 36 generations. Female rabbits in NC and NF environments were housed at normal room temperature (18°C to 24°C) and fed with control [11.6 MJ digestible energy (DE)/kg dry matter (DM)] or low-energy diets (9.1 MJ DE/kg DM). HC does were housed at high room temperatures (25°C to 35°C) and fed the control diet. Female rabbits in the HC and NF environments ingested 11.5% and 6% less DE than NC does, respectively (P<0.05). These differences between environments occurred in both lines, with the differences being higher for LP than for V does (+6%; P<0.05). Milk yield responses followed those of energy intake also being higher for LP does (+21.3 g/day; P<0.05). The environmental conditions did not affect the perirenal fat thickness (PFT), but a genotype by environment interaction was observed. In NC and HC, the PFT was higher for line V (+0.23 and +0.35 mm, respectively; P<0.05) than for LP does, but this was not the case at NF (−0.01 mm). Moreover, the PFT evolution was different between them. In the NC environment, LP does used the accreted PFT in late lactation (−0.29 mm), whereas V does did not (−0.08 mm). Conversely, in the HC environment, LP does showed a flat PFT evolution in late lactation, whereas V does accumulated PFT. In the NF environment, LP and V does had a similar PFT evolution. There was also a litter size reduction for V does of −2.59 kits total born in HC and −1.78 kits total born in NF environments, whereas this was not observed for LP does. The results for LP does indicate a direct use of DE ingested for reproduction with little PFT change, whereas V does actively use the PFT reserves for reproduction.
Differences in productive robustness in rabbits selected for reproductive longevity or litter size
- P. Theilgaard, M. Baselga, E. Blas, N. C. Friggens, C. Cervera, J. J. Pascual
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The aim of this work was to evaluate the ability of a line selected for reproductive longevity (LP) to confront productive challenges compared to a line selected during 31 generations for litter size at weaning (V). A total of 133 reproductive rabbit does were used (72 and 61 from LP and V lines, respectively). Within each line, three groups with different levels of productive effort were planned: PP9, inseminated at day 4 after the first partum and with nine kits during the second partum, and inseminated after first weaning (30 days) and with nine (PW9) or five kits (PW5) during the second partum. The reproductive performance, body condition (perirrenal fat thickness (PFT)) and lipolytic response were controlled. LP does showed greater mean live weight (LW; +128 g; P < 0.05), PFT (+0.47 mm; P < 0.05) and estimated body energy (EBE; +0.29 MJ/kg; P < 0.01) than V does at second partum. However, LP does that mated at first post partum did not significantly differ in EBE relative to V does at second partum. During the first week of lactation, dry matter (DM) intake was similar for both lines (94 and 95 g DM/kg LW0.75 day for V and LP does, respectively). There was a significant difference in milk yield between both lines during the first week when litter size was nine (60 v. 54 g of milk/kg LW0.75 day for LP and V does, respectively; P < 0.01), but no difference when litter size was five. Consequently, when litter size was nine, LP does showed a lower recovery of PFT (0.6 mm less; P < 0.05) than V does during the first 10 days of lactation. However, when litter size was five, LP does showed a higher LW (+210 g; P < 0.05) than V does at 10 days of lactation and a similar recovery of PFT. During the last 3 weeks of the lactation, LP does showed a higher feed intake (+6 g DM/kg LW0.75 day; P < 0.05) and milk yield (+27 g/day; P < 0.001) than V does when litter size was nine, resulting in no significant differences in LW at 30 days of lactation. However, when litter size was five, both lines showed similar feed intake and milk yield, maintaining their differences in LW at 30 days of lactation (+206 g for LP does; P < 0.05). These results show that the rabbit line selected for reproductive longevity is more robust with respect to coping with productive challenges, than a line selected for reproductive intensity.
Genetic evaluation for semen characteristics in a crossbreeding project involving Saudi and Spanish V-line rabbits
- M. H. Khalil, K. A. Al-Sobayil, A. M. Al-Saef, M. L. García, M. Baselga
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Two parallel schemes of crosses were practised involving the Spanish maternal line called V-line (V) and Saudi Gabali (S) rabbits. The first scheme began by crossing Saudi Gabali bucks with V-line does to get the F1 cross (½S½V), then does of this F1 were backcrossed with bucks of V-line to get ¾V¼S, then the progenies of the backcross were inter se mated to get (¾V¼S)2, followed by two more generations of inter se mating of (¾V¼S)2 to get a new synthetic maternal line named Saudi 2. The second scheme began by crossing V-line bucks with Saudi does to get the F1 cross (½V½S), then does of this F1 cross were backcrossed with Saudi bucks to get ½S½V, then progeny of this backcross were inter se mated to get (¾S¼V)2, followed by two generations of inter se mating of (¾S¼V)2 to form a new synthetic paternal line named Saudi 3. A generalised least-square procedure was used to estimate differences between lines in direct and maternal additive effects, direct and maternal heterosis, and direct recombination losses. A total number of 2497 ejaculates of 642 bucks were evaluated for ejaculate volume (VE), pH of semen, sperm concentration (SC), percentage of motile spermatozoa (MS), percentage of spermatozoa with abnormal form (AS), percentage of dead spermatozoa (DS) and libido score (LS). The estimates of direct additive effect for DS (14.2%), SC (12.4%) and AS (12.0%) were moderate and favourable to Saudi rabbits. Maternal additive effects for VE (11.7%) were in favour of genes of V-line carried by the dams of bucks, while these estimates were in favour of Saudi genes for DS (18.6%), AS (13.2%), MS (10.8%) and SC (10.0%). Positive estimates of direct heterosis recorded for SC (13.5%), VE (10.6%) and MS (10.5%) and the negative estimates recorded for AS (−21.5%) and DS (−20.3%) were moderate and well disposed to semen parameters of crossbred bucks. Positive estimates of maternal heterosis for VE (24.0%), MS (21.8%), SC (10.3%) and LS (10.2%) of bucks, and the negative estimates for percentage of DS (−14.7%) and AS (−9.6%) were also significantly favourable. Estimates of direct recombination losses for the majority of semen traits were always not significant.
Long-term effect of selection for litter size and feeding programme on the performance of reproductive rabbit does 2. Lactation and growing period
- F. Quevedo, C. Cervera, E. Blas, M. Baselga, J. J. Pascual
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- Animal Science / Volume 82 / Issue 5 / October 2006
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- 09 March 2007, pp. 751-762
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- October 2006
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A total of 166 crossbred does were used to study the possible long-term effect of two types of crossbred does (H1 v. H2, old and current generations, respectively) from the cross of different generations of lines selected for litter size, the use of a rearing programme based on a low-energy diet, and the administration of a high-energy diet during reproductive life, on the performance and body condition of lactating rabbit does and their litters until slaughter. The body condition of the reproductive rabbit does increased in the successive cycles to the fourth parturition, being maintained from this moment on. Animals more selected for litter size at weaning presented a greater food intake (+3%; P<0·05) and milk yield (+6%; P<0·05) during the first 21 days of lactation, which could be related to greater maternal aptitude. The difference in the weight of pups at slaughter time (+24 g for H2 respect to H1 pups) was one third lower than that expected from the generation response of the paternal line (0·45 g/day), perhaps related to the different enteropathy incidence depending on the genetic type. The use of a high-energy diet during the reproduction period increased the milk yield (+22%; P<0·05) of does, as the growth (+16 g at weaning day; P<0·05) and survival index (+2%; P<0·05) of the litters during lactation, but could produce a more sudden weaning of pups as a consequence of their lower pre-weaning food intake (−42%; P<0·05), which has been related with a greater health risk index during the growing period (+4·2%; P<0·05). Reproductive does given a high fibre diet during the rearing period (from 3 kg live weight to 28th day of the first pregnancy) reached parturition with a higher live weight than does that received a moderate energy diet restricted during this same period (+142 g; P<0·05). All other parameters controlled for the lactating does and their litters were not affected by the type of diet received during the rearing period. Females that were not effectively mated at first AI (11 days post partum) showed a greater increase in their perirenal fat thickness between partum and the 11th day of lactation than those lactating females that showed an effective mating (+0·22 v. +0·37 mm, respectively; P<0·05).
Long-term effect of selection for litter size and feeding programme on the performance of reproductive rabbit does 1. Pregnancy of multiparous does
- F. Quevedo, C. Cervera, E. Blas, M. Baselga, J. J. Pascual
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- Animal Science / Volume 82 / Issue 5 / October 2006
- Published online by Cambridge University Press:
- 09 March 2007, pp. 739-750
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- October 2006
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A total of 166 crossbred does were used to study the possible long term effect of two types of crossbred does (H1 v. H2, old and current generations, respectively) from the cross of different generations of lines selected for litter size, the use of a feeding programme based on a low-energy diet during the rearing and the administration of a high-energy diet during reproductive life, on the performance and body condition of multiparous pregnant does. Selection did not affect the live weight (LW) of does at the effective artificial insemination (AI; 4257 g), the LW change (+12·3 g/day) and food intake (172 g dry matter (DM) per day) until the 28th day of pregnancy. However, H2 does showed greater LW losses during the pre-partum period than H1 does (120+g; P<0·05), perhaps related to their higher prolificacy (+1·1 total pups born; P<0·05). H2 does showed a higher perirenal fat thickness (PFT) at first AI (+0·12 mm; P<0·05) than H1 does, these differences disappearing at effective AI. Females given a high-energy reproduction diet showed a lower LW at effective AI than those receiving a medium-energy diet (4210, 4305 g, respectively; P<0·05). However, type of reproduction diet did not affect the LW and PFT changes of pregnancy does, reaching partum with a similar PFT (8·83 v. 8·93 mm) and maintaining the differences in LW. Pregnant does given high-energy diet consumed 20 g DM and 1·4 g digestible protein per day less than does receiving medium-energy diet until the 28th day of pregnancy, but their digestible energy (DE) intake was significantly higher (+78 kJ DE per day; P<0·05). Does given high-energy diet showed a significantly lower litter size at birth (−0·7 pups; P<0·05), although there were no significant differences in the number of pups born alive (9·54 and 9·76 pups for high and medium-energy diets, respectively). Pups from does given high-energy diet were slightly weightier than those from medium-energy diet (+5·4 g; P<0·05). Multiparous pregnant does that received a low-energy diet ad libitum during the rearing period and first pregnancy showed a higher LW at effective AI (+137 g LW; P<0·05) but a lower PFT (−0·26 mm; P<0·05) than those females that received a medium-energy diet restricted during this same period. These differences were maintained at parturition (+142 g LW and −0·20 mm; P<0·05). Feeding programme during rearing affected neither the food intake of multiparous pregnant does until the 28th day of pregnancy, nor the litter size and weight at birth. The interval between parturitions was not affected by the selection for litter size or the reproduction diet received, but was longer for does that received the low-energy diet ad libitum during the rearing period (+2·9 days; P<0·05). In conclusion, rabbit selection programmes by litter size seem to be working well, but high energy reproduction diets, frequently used to cover their higher energy requirements, must be used carefully out of lactation in the long term to avoid a reduction in litter size.
Effect of selection for litter size and feeding programme on the performance of young rabbit females during rearing and first pregnancy
- F. Quevedo, C. Cervera, E. Blas, M. Baselga, C. Costa, J. J. Pascual
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- Journal:
- Animal Science / Volume 80 / Issue 2 / April 2005
- Published online by Cambridge University Press:
- 09 March 2007, pp. 161-168
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- April 2005
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A total of 166 crossbred young female rabbits were used to study the effect of two types of crossbred does (H1 v. H2, old and current generations, respectively) from the cross of different generations of maternal lines selected for litter size, the use of a feeding programme based on a low energy rearing diet (F) and the presentation of a high-energy diet pre-partum (E) on the performance of young rabbit females until their first parturition and on the main litter traits at first kindling. Perirenal fat was thicker at the age of 3 months for H2 than for H1 does, but this difference disappeared at the first insemination (4·5 months). H2 does had a significantly larger total number and number of live pups at birth (+2·06 live pups) than H1, higher than expected (+1·06). As this greater foetal growth was obtained for a similar energy intake of does, possible differences may exist in partitioning and/or effficiencies of dietary and body energies in favour of foetal growth as the genetic propensity for litter size increased. The use of a low-energy diet significantly reduced the growth of does during the rearing period (−294 g), but they showed a greater compensatory growth during the first 4 weeks of gestation (+79 g) as a consequence of their higher energy intake, without any retardation in their reproductive development. Does receiving diet F until 28th day of gestation showed a significantly greater pre-partum energy intake and their number of pups born alive was lower (−1·3 pups). Finally, the litters of females receiving diet E pre-partum and during lactation had lower mortality during the 1st week (26·9 v. 42·9% dead pups) and throughout lactation than those receiving a moderate energy diet.