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* Research Institute of Animal Husbandry, 8203 AD Lelystad, The Netherlands;
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Hybro, 5830 AA Boxmeer, The Netherlands;
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Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands; and
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Department of Animal Sciences, Wageningen Institute of Animal Science, Wageningen University and Research Center, 6700 AH Wageningen, The Netherlands
Correspondence:
P.O. Box 2176 (E-mail:
J.M.Rommers{at}PV.AGRO.NL).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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4000 g), medium (BW 3500 to 4000 g), and small (BW < 3500 g). Among does that kindled, differences in BW at first insemination were related to differences in voluntary feed intake and body growth rate during rearing. Heavy does consumed more feed per day (+ 45 g/d, P < 0.001) and had a higher BW gain (+ 12 g/d, P < 0.001) than small does from weaning (4.5 wk) to 14.5 wk of age. Body weight at first insemination did not affect BW, feed intake, and culling rate during the first two parities. Heavy does were heavier at first insemination and remained so throughout the reproductive period, but they followed a similar BW curve as medium and small does. A higher BW at first insemination (14.5 wk of age) improved litter size in the first parity (8.9, 7.7, and 6.4 for heavy, medium, and small does, respectively, P < 0.05). Extra BW at start of reproduction improves litter size in the first parity but does not contribute to an improved feed intake or increased BW development during reproduction.
Key Words: Body Weight • Rabbits • Rearing Techniques • Reproduction
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Likewise does are often fed to appetite during rearing, and first insemination is recommended at approximately 75 to 80% of mature BW (Lebas et al., 1986). In modern management, young does are not inseminated at a fixed BW but at a fixed age. Under ad libitum feeding conditions during rearing, does can develop according to their growth potential, and BW differences at first mating (at a fixed age) will be substantial. At the same age, heavy does can benefit from the extra amount of BW at the end of rearing to withstand the energy deficit during first lactation. The consequence of variation in BW at first mating (at a fixed age) on feed intake, body development, and prolificacy in subsequent reproductive life is unknown.
Therefore, the objective of this study was to evaluate relationships between BW at first mating and subsequent body development, feed intake, and reproductive performance in does given ad libitum access to feed during rearing. To understand the causes of BW differences at first mating, BW, feed intake, and gain/feed ratio during rearing were also studied.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Data from does fed to appetite during rearing were obtained from three subsequent experiments (Rommers et al., 2001b and a set of unpublished data). The experiments were performed from April 1997 to May 2001 with a strain of New Zealand White rabbits bred at the Institute of Animal Husbandry. The Use and Care Committee of the Research Institute of Animal Husbandry approved all protocols.
Rearing Period. Experiments varied in condition during the preweaning period. In Exp. 1 and 2, does were held in litter sizes of six, nine, or 12 kits, whereas in Exp. 3, does were held in litters of nine kits. After weaning (4.5 wk of age), does were reared similarly. In Exp. 1, 48 does, in Exp. 2, 42 does, and in Exp. 3, 52 does were put into individual cages (50 x 60 x 30 cm) of galvanized wire net, equipped with an automatic drinker, and a manual feeder in identical deep-pit compartments. Does had free access to a standard commercial diet, containing 10.3 MJ ME/kg, and 17% CP (ABCTA Lochem, The Netherlands). The first 2 wk after weaning, a minimum ambient temperature of 18°C was maintained. From 2 wk after weaning onward, the minimum ambient temperature was set to 16°C. Does were submitted to a photoperiod of 12 h. Rearing period ended at 14.5 wk of age.
Reproductive Period. The reproductive period included the first two parities of each doe until weaning of the second litter. Does were housed in the same cages as during rearing. A minimum ambient temperature of 16°C was maintained, and does were submitted to a photoperiod of 16 h.
At 14.5 wk of age (end of rearing), receptive does were inseminated. Does were scored receptive if the vulva was red or purple-colored and swollen. For the second parity, does were inseminated 10 to 12 d after kindling (semi-intensive breeding rhythm).
Inseminations were performed with fresh-mixed sperm from 12 bucks, selected for growth performance. On each insemination date, one mixed and diluted semen dose was prepared. Dilution was performed using a commercial extender (Galap, IMV, L’Aigle Cedex, France) according to the method developed by Zöldágh et al. (1988). A GnRH analogue was administered i.m. (0.2 mL containing 0.0042 mg Buseriline-acetate/mL; Receptal, Intervet, Boxmeer, The Netherlands) immediately after insemination to induce ovulation.
Five days before kindling, each doe had free access to a nestbox that was put in front of the cage. The first day after kindling, litter size was standardized at eight kits in the first parity and nine kits in the second parity. Nestboxes were removed 3 wk after kindling, and kits were put in the cage with the doe to stimulate solid-feed intake. Kits were weaned at 4.5 wk of age.
After first insemination, does were fed the same diet as during rearing. Experiments varied in feeding level during first gestation. In Exp. 1, and 2, does were fed to appetite, whereas in Exp. 3 does were fed according to the recommendation of Maertens (1993) (first 21 d of gestation: 0.400 kJ ME/BW0.75 + 0.38 MJ ME/BW0.75 per day, from 21 d onward: 0.400 kJ ME/BW0.75 + 1.13 MJ per day). After the first kindling, all does were allowed to consume their feed on an ad libitum basis.
Measurements
The following separate phases were used for measurements: rearing period (from weaning at 4.5 wk until first insemination at 14.5 wk), first gestation period (from first insemination to first kindling), first lactation (from kindling to weaning [30 d]), weaning to kindling interval (12 d), and second lactation (from second kindling to weaning of the second litter [30 d]).
Rearing Period
Body Weight, Feed Intake, and Gain/Feed Ratio. Does were weighed weekly from weaning (at 4.5 wk of age) until first insemination at 14.5 wk of age. Feed intake was determined by weighing the feeder at the beginning and end of each week, and the weight of all feed supplies given within a week were recorded. If wastage occurred, period and cage were recorded, and the feed intake for this period was scored as missing value. Body weight and feed intake were used to calculate gain/feed ratio (g gain/g feed).
Reproductive Period
Body Weight and Feed Intake. In the first and second parities, BW was determined at the first day after kindling, at d 16, and at d 30 of lactation. Feed intake was determined for the first gestation period, from kindling until d 16 of lactation, from d 16 until d 30 of lactation for both the first and second parities, and from weaning to second kindling. Feed intake was determined by weighing the feeder at the beginning and end of each reproductive stage, and all feed given within each stage was recorded.
Reproductive Performance. Kindling rate was calculated as the number of does kindled divided by the number of does inseminated. The number of live and stillborn kits (total litter size), the number of kits at d 16 and d 30 of lactation, together with the litter weight at d 16 and d 30, were recorded. The average kit weight at d 16 was used as an estimate for milk production, because in our system we observe that kits start eating solid feed from d 17 onward (Rommers, personal communication).
Culling of Does. The number of does culled and the reason of culling was recorded. Dissections were performed on dead and diseased does.
Treatments
Body weight at first insemination at 14.5 wk of age was used to assign each doe to one of the following three groups: 1) heavy: BW 4,000 g, 2) medium: BW 3,500 and < 4,000 g, 3) small: BW < 3,500 g. The mature BW of medium-sized hybrid rabbits, as used in our study, varies from 4.5 to 5 kg. In rabbit production, first insemination is recommended at 75 to 80% of mature BW. In general, does smaller than 3,500 g are considered too small, whereas does heavier than 4,000 g are considered too fat for first insemination. Body weight ranges were based on this principle. The number of does in the second parity did not permit more than three groups for statistical analysis.
Statistical Analysis
Body Weight, Feed Intake, and Gain/Feed Ratio During Rearing. Data of does that kindled after the first insemination at 14.5 wk of age were used for analysis. Body weight, feed intake, and efficiency were analyzed for the total rearing period. To understand the causes of BW differences at first mating, BW, feed intake, and gain/feed ratio were also calculated for each of the 10 successive weeks of rearing. For analysis of gain/feed ratio, individual gain/feed ratio deviating more than three times the standard deviation from the mean was scored as missing value (n = 4).
To test differences among groups during the total rearing period and the 10 successive weeks of rearing, the following model was used: Yij = µ + Ei + Gj + (E x G)ij + eij [model 1], where Yij is dependent variable; µ = overall mean; Ei = Exp. 1, 2, and 3; Gj = group H, M, and S; and eij is the residual error. In all analysis, nonsignificant interactions were deleted from the model. All statistical analysis was performed with the GLM procedure of SAS (SAS Inst. Inc., Cary, NC).
Body Weight, Weight Gain, and Feed Intake During the Reproductive Period. Data were used of does that kindled. To analyze the effect of treatment, model 1 was used.
Reproductive Performance. For the first parity, data were used of does that kindled after the first insemination at 14.5 wk of age. For the second parity, does were used that kindled after the first insemination 10 to 12 d postpartum. Differences in kindling rate and percentage of stillborn kits among groups were analyzed with a chi-square test. To analyze the effect of treatment, model 1 was used.
Culling Rate of Does During the First Two Parities. Data of all does were used for analyses of culling rate. Differences in culling rate among groups were analyzed with a chi-square test.
Experiment included variation due to differences in litter size in the preweaning period. The number of does that were raised in litters of 6, 9, and 12 kits before weaning for each group is included in Table 1
. To test the effect of litter size in which kits were reared in the preweaning period on subsequent body development, feed intake, and reproductive performance, the above analysis (see model 1) was performed on data of kits raised in litters of 9 kits in the three experiments. At weaning, similar differences in BW among weight groups were found, and effects on body development and feed intake during rearing and reproduction were similar compared with analysis performed on all data. Therefore, we feel confident that the effect of litter size in the preweaning period did not affect subsequent results.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The change in number of does during the experiments for each group is given in Table 1
. No culling occurred during rearing. During the reproductive period, no difference in culling of does among treatments was found. The total percentage of does culled was 11.9, 12.5, and 11.3% for heavy, medium, and small does, respectively. No specific differences for culling reasons among groups were found. The percentage of does that succeeded the reproductive rhythm during the first 2 parities did not differ among groups. The percentage of does that kindled after the first insemination at 14.5 wk of age and after the first inseminations 10 to 12 d after kindling in the first and second parities was 38.1, 38.6, and 37.7% for heavy, medium, and small does, respectively.
Body Weight, Feed Intake, and Gain/Feed Ratio During Rearing
Body weight, weight gain, feed intake, and gain/feed ratio for the total rearing period (from weaning until first insemination) for does that kindled after the first insemination at 14.5 wk of age are presented in Table 2. Feed wastage was observed in 2 small does and 1 heavy doe. No interaction was found between experiment and group. For the total rearing period, groups differed (P < 0.001) in BW at weaning, BW at insemination, body growth, and feed intake. Heavy does at first insemination were does with the heaviest BW at weaning, the fastest weight gain, and the highest feed intake during rearing, whereas small does at first insemination were smallest at weaning, grew slowest, and ate the lowest amount of feed during rearing. Gain/feed ratio was similar for all treatment groups.
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Analysis of BW, and feed intake per week revealed that differences among groups remained throughout the rearing period, and gain/feed ratio for the three groups followed the same curve until 14.5 wk of age.
Body Weight, Body Growth, and Feed Intake During Reproduction
The number of does that kindled to the second service was 20 for heavy, 34 for medium, and 16 for small does (see Table 1). Body weight during the successive periods of reproduction for these does is presented in Figure 1. Weight gain during reproduction is given in Table 3. Although does in Exp. 3 were feed restricted instead of ad libitum, no differences in BW and weight gain during first gestation were found among experiments. Therefore, average BW of the three experiments is presented for each group. For one medium doe, weighing of the doe and feeder was missed at 16 d of first lactation. One small doe failed to nurse the kits in the first lactation; the number of kits at d 16 and 30 of lactation was scored zero, and feed intake was scored as missing value. The figure shows that heavy, medium, and small does had similar BW curves during reproduction. If BW during reproduction was corrected for difference in BW at first insemination, no differences in BW at the different stages of reproduction among experiments were found. This implies that groups followed the same BW curve independent of their BW at start of reproduction.
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). Small does grew 306 ± 52 g, medium does grew 167 ± 39 g, whereas heavy does lost -45 ± 60 g during first gestation (P < 0.001). After two parities, small does remained smaller than medium and heavy does (4,057, 4,448, and 4,758 g respectively, P < 0.001).
Feed intake during the successive periods of reproduction for the heavy, medium, and small does is given in Table 4. Feed wastage was observed in the weaning to kindling interval (first to second parity) in one small doe, and feed intake was scored as missing value. During first lactation, no difference in feed intake among experiments was found. Therefore, average feed intake of the 3 experiments for each group is presented from first kindling onward. No differences in feed intake among groups were found during the first parity. In the first 16 d of the second lactation heavy does consumed more feed than small does, whereas feed intake of medium does was intermediate (402, 383, and 367 ± 11 g/d for heavy, medium, and small does, respectively).
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Reproductive performance in the first and second parities for each group is presented in Table 5. No interaction was found between experiment and group in either parity. No difference in kindling rate was found among groups after first insemination at 14.5 wk of age and after first insemination 10 to 12 d postpartum during first lactation.
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In the second parity, no differences among groups were found, except for the percentage of stillborn kits at kindling. Small does had a higher percentage of stillborn kits than medium and heavy does, but this was principally due to 2 does with 70 and 80% stillborn kits (P < 0.05).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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First, the causes of weight differences at first mating, BW, body development, feed intake, and feed conversion during rearing for does that were fed to appetite were evaluated. Data of the rearing period showed that heavy does can be characterized as does with a high growth rate and a high voluntary feed intake, whereas small does showed a 25% lower growth rate and consumed 25% less food per day. Gain/feed ratio among groups was equal. This indicates that in heavy does no additional fat deposits could have been formed. In general, forming of fat involves less binding with water than forming of protein. At the same level of feed intake, gain/feed ratio decreases when fat is being formed. This was not the case. Even when gain/feed ratio was corrected for BW at weaning, gain/feed ratio of heavy does was higher instead of lower than small does. Therefore, it can be assumed that heavy does had not formed relatively more fat tissue compared with medium and small does at 14.5 wk of age, and body composition among groups must have been similar. Heavy does were heavier as a consequence of a higher feed intake or a higher growth potential, but that overfattening had not occurred.
Second, the effect of BW at first insemination on subsequent body weight gain, feed intake, and reproductive performance was studied. If heavy does are able to benefit from the extra amount of BW, it should be expressed in either a decreased culling rate or improved reproductive performance. However, no difference was found among groups in the percentage of does culled during reproduction or percentage of does kindling to the second insemination.
Body weight at 14.5 wk did affect productive performance in the first parity. Heavy does produced 2.5 kits more than small does in the first parity. Rommers et al. (2001a) showed that at the same age, heavier does had larger uterine horns and more corpora lutea on the ovaries compared with small does. In that study, lower BW was caused by restricted feed intake during rearing and resulted in an average BW of 3,590 g for small does. BW at 14.5 wk of age for small does in this study was even 400 g lower.
Body weight at first insemination seems to affect milk production; heavy does had heavier kits at d 16 of lactation in the first parity. In the second parity medium and heavy does tended to have heavier kits at 16 d of lactation. However, in both parities the higher milk production did not result in a heavier weight of the kits at weaning. Kits of small does may have compensated for the lower amount of milk available to them by consuming more pelleted feed as found by Parigi-Bini et al. (1992) and Xiccato et al. (1995). In our study, feed intake of the kits was not recorded separately from the feed intake of the doe.
In the second parity, no difference among groups in reproductive performance was found anymore. The decreased kindling rate (average of 55%) might have been related to the body energy loss that occurs in the first parity (Parigi-Bini and Xiccato, 1993). Parigi-Bini and Xiccato (1993) found a lower litter size in the second parity, which was not the case in our study. A more intensive breeding rhythm was used in their study (does were remated 1 to 4 d after kindling), that could have resulted in a more negative energy balance during lactation. This might have affected litter size in the second parity in their study.
The fact that no difference was found in percentage of does that could follow the reproductive rhythm or percentage of does that was culled during reproduction can be explained by the feed intake and BW curve during reproduction. Although heavy does had a higher voluntary feed intake during rearing, no difference in feed intake during the first parity was found compared with small and medium does. Our data reveal that correlation between feed intake during rearing and feed intake during first lactation is low (r = 0.14). In the weaning-to-kindling interval and in the first 16 d of second lactation, heavy does had a higher feed intake than small does. Except for maintenance requirements, the extra feed intake seems to have been used for milk production. In several studies, an increased energy intake resulted in an increased milk production, whereas the weight gain of the doe was not affected (Fortun-Lamothe, 1997). Although heavy does were heavier at first insemination and remained heavier throughout the reproductive period, they followed a similar BW curve after weaning the first litter as small and medium does. This BW loss from weaning of the first litter to kindling of the second litter is related to the high energy demand for fetal growth (Parigi-Bini et al., 1990) and drop in feed intake during the last 10 d of gestation (Partridge et al., 1986; Maertens, 1993). Our findings indicate that heavy does do not seem to benefit from the extra feed intake capacity or the extra BW at start to increase BW development, improve feed intake, or decrease culling during reproduction.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Received for publication December 14, 2001. Accepted for publication April 5, 2002.
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Literature Cited |
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