Ultrasound measurements of perirenal fat thickness to estimate the body condition of reproducing rabbit does in different physiological states.

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.

Section: Environmentsmentioning

confidence: 99%

Environmental sensitivity differs between rabbit lines selected for reproductive intensity and longevity

Savietto

Cervera

Blas

et al. 2013

“…The average of the left-and right-side PFT was used for further calculations. The evolution of the estimated body energy (EBE) content of does was determined from live weight (LW) and PFT of does, using the equations proposed by Pascual et al (2004) for body energy estimation at different physiological states.…”

Section: Methodsmentioning

confidence: 99%

Differences in productive robustness in rabbits selected for reproductive longevity or litter size

Theilgaard

Baselga

Blas

et al. 2009

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; 1128 g; P , 0.05), PFT (10.47 mm; P , 0.05) and estimated body energy (EBE; 10.29 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 LW 0.75 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 LW 0.75 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 (1210 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 (16 g DM/kg LW 0.75 day; P , 0.05) and milk yield (127 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 (1206 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.

“…In both lactations, the female rabbit's LW was measured at 0, 7, 14, 21 and 28 dpp, and perirenal fat thickness (PFT) at 0, 14 and 28 dpp, using the ultrasound method described by Pascual et al (2004). Dry matter intake was monitored weekly during both lactations and during the weaning to parturition intervals.…”

Section: Environmentsmentioning

confidence: 99%

Different resource allocation strategies result from selection for litter size at weaning in rabbit does

Savietto

Cervera

Ródenas

et al. 2014

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 shortterm environmental fluctuations (less severe) that frequently occur in the environment where this line has been selected.