Effect of diets with different digestible energy content
on the performance of rabbit does
J.J. Pascual
a, C. Tolosa
b, C. Cervera
b,*, E. Blas
b,
J. FernaÂndez-Carmona
baUnidad de ProduccioÂn Animal, Universidad Miguel Hernandez, Escuela Politecnica Superior de Orihuela,
Carretera de Beniel, km 3.5/03312 Orihuela (Alicante), Spain
bDepartamento de Ciencia Animal, Universidad Politecnica de Valencia. P.O. Box 22012, Valencia 46071, Spain
Received 13 October 1998; received in revised form 19 February 1999; accepted 20 April 1999
Abstract
One hundred and ninety-two lactations from a total of 59 New ZealandCalifornian rabbit does
were used to study the influence of the dietary energy content on the reproductive performance of rabbit does. Three experimental diets (L, M and H) were formulated to give the same fibre content and different digestible energy (DE) content (9.9, 11.1 and 12.2 MJ DE kgÿ1
DM) using cereal starch as the main energy source. Primiparous does given diet H showed a higher live weight during the first gestation (p< 0.01), but no differences in the live weight were found at partum. Primiparous does on diet H showed significantly higher DE intake and live weight gain (p< 0.01) during lactation, but their milk yield was lower (p< 0.05) than those given diets L and M. Rabbit does showed a higher live weight at the second mating when the dietary energy content was increased (p< 0.001), and this was maintained subsequently. Diet H decreased the food intake of multiparous does throughout the reproductive cycle, and especially during lactation (p< 0.001). Milk yield during the last two weeks was lower for multiparous does given H diet (p< 0.01). Neither the size nor the weight of litters was significantly affected by the type of diet during lactation, but mortality at partum was higher for H diet (p< 0.05). Thus, the high starch diet increased the live weight and the DE intake of primiparous rabbit does during lactation, but it did not improve the performance of their litters and could induce an excessive live weight of gestating rabbit does.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Dietary starch; Energy intake; Rabbits; Milk yield; Litter mortality Animal Feed Science and Technology
81 (1999) 105±117
* Corresponding author. Tel.: +34-963-877432; fax: +34-963-877439
E-mail address:ccervera@dca.upv.es (C. Cervera)
1. Introduction
Recent studies have shown a clear energy deficit during lactation of does in highly productive situations (Partridge et al., 1986), under conditions of heat stress (FernaÂndez-Carmona et al., 1996) or in the first lactation (Parigi-Bini et al., 1990, 1991). Voluntary food intake is a main limiting factor in the energy balance of lactating does (Xiccato, 1996) and a stimulation of food ingestion would reduce the negative energy deficit of does.
In long-term experiments, some performance traits have been improved with high energy diets (Maertens and de Groote, 1988; Castellini and Battaglini, 1991; Barreto and de Blas, 1993; Cervera et al., 1993). The main dietary energy sources are cereals (starch) and fats of animal or vegetal origin. However, based on results obtained their effects on the voluntary food intake, productivity and energy balance of reproductive does seem to be different.
The addition of fat allows an increase in the energy content of diets without decreasing the fibre content and seems to increase substantially the digestible energy (DE) intake and subsequent utilization of lactating does, improving some performance traits like litter size and weight (Fraga et al., 1989; Cervera et al., 1993; Fortun-Lamothe and Lebas, 1996; Pascual et al., 1998a, 1999). However, it does not seem to reduce the usual negative energy balance of lactating rabbit does (Xiccato et al., 1995; Parigi-Bini et al., 1996). Other studies have increased the dietary energy by the inclusion of high levels of starch (Butcher et al., 1983; Xiccato et al., 1995; Fortun-Lamothe and Lebas, 1996; Lebas and Fortum-Lamothe, 1996), showing that energy intake is maintained in spite of a reduction in food intake of lactating rabbits. However, the effects of these diets on the productivity and body condition of rabbit does have not been established.
The results of all these studies have been obtained with diets in which DE and crude fibre (CF) contents are inversely related, and FernaÂndez-Carmona et al. (1995) observed that fibre itself could have some effect on ingestion and production of does fed ad libitum; in these studies, the different fibre content of the experimental diets could mask the actual effect of the high-energy diets. Therefore, the aim of the current study was to evaluate the effect of dietary energy content on the reproductive performance of commercial rabbit does, using diets with cereals as main dietary energy source and a similar fibre content.
2. Material and methods
2.1. Diets
treatment). Does were kept in individual metabolism cages and, after a seven-day adaptation period, their faeces were collected individually for five days. Diets L, M and H had 9.9, 11.1 and 12.2 MJ DE kgÿ1
DM, respectively and 117, 148 and 146 g digestible protein (DP) kgÿ1
DM, respectively. Pelleted diets were manufactured and analysed three times during the experimental period. Diets were offered ad libitum to both does and litters during the experimental period.
Chemical analysis of diets and faeces followed the method of the Association of Official Analytical Chemists (1984) for DM, CP and crude fibre, and Van Soest et al. (1991) for ADF with a thermostable amylase pre-treatment. Gross energy was determined by adiabatic bomb calorimetry. Dietary starch content was determined according to a two-step enzymatic procedure, using a thermostable amylase followed by amylogluco-sidase (Tecator, application note 85/86), the resulting glucose being measured by the hexokinase/glucose-6-phosphate dehydrogenase/NADP system (Boeringher).
Table 1
Main ingredients (g kgÿ1), chemical composition (g kgÿ1DM) of experimental diets: low (L), medium (M) and high (H) energy content
acid detergent fibre (ADF) 192 198 182
starch 86 111 282
digestible protein (DP)c 117 148 146
digestible energy (DE; MJ kgÿ1DM)c 9.9 11.1 12.2
aAll diets contain 66 ppm robenidine.
bContains (g kgÿ1): thiamin, 0.25; riboflavin, 1.5; calcium pantothenate, 5; pyridoxine, 0.1; nicotinic acid, 12.5; retinol, 2; cholecalciferol, 0.1; a-tocopherol, 15; phytylmenaquinone, 0.5; cyanocobalamin 0.006; choline
chloride, 100; MgSO4H2O, 7.5; ZnO, 30; FeSO47H2O, 20; CuSO45H2O, 3; KI, 0.5; CoCl26H2O, 0.2; Na2SeO3, 0.03.
cValues experimentally determined in 15 females of three months of age fed ad libitum.
2.2. Animals
One hundred and ninety-two lactations (67 for each of diets L and H and 58 for diet M) from a total of 59 New ZealandCalifornian rabbit does (21, 20 and 18 for diets L, M and H, respectively) housed in a traditional building were studied during a period of two years.
Nulliparous does were presented to the male at ca. 4.5 months of age and with a live weight no less than 3.2 kg. Until mating, all does received the same commercial diet. Subsequently, does were housed in individual cages and had free access to one of the experimental diets. The experimental does were maintained for up to six reproductive cycles.
Lactating does were presented to the male 14 days after parturition, and if necessary each week thereafter until a mating took place. Fourteen days after mating, the does were tested for pregnancy by palpation, and non-pregnant does were remated. Does were discarded for two reasons: pathology or fertility (three consecutive sterile matings or six consecutive male refusals). Milk production was measured daily using the weigh (doe)± suckle±weigh (doe) method. To prevent free nursing, does were placed in a cage next to the nest box. Suckling took place once a day (ca. 9 : 00 a.m.) in the nest box for a short period. Food intake and weight of does were recorded weekly during the experiment. The size and weight of litters were noted weekly during lactation. Suckling pups were allowed to eat the same diet as their mothers from the 21st to the 35th day of lactation, when they were weaning. During this period, solid food intake of litters was recorded.
3. Statistical analysis
Data were analysed by variance analysis, using the general linear GLM procedure of SAS (Statistical Analysis Systems Institute, 1990), except for the number of dead pups, which was analyzed using a non-parametric procedure (NPAR1WAY), and for mean separation, where a2test was used. Data were initially analysed according to a repeated
measures design (REPEATED procedure; Table 2). As differences throughout time were principally due to the differences between primiparous and multiparous rabbit does, data were analysed independently of each other. So, data of primiparous rabbit does were analysed according to a model including the effect of the diet (L, M and H). However, data of multiparous does were analysed according to a split-plot design including the effect of diet, the effect of rabbit doe within diet (error to test the diet effect), the effect of parity (2±6), the effect of lactation±gestation overlapping (0±3 weeks) and their interactions. For the live weight, milk yield and food intake analyses the size of the litters was added as a covariate.
4. Results
4.1. Effect of parity
Table 2
Effect of parity on the performance of rabbit does and their litters
Parity SEa Significanceb
1 2 3 4 5 6 Pc PDd covariate
No. of observations 59 40 29 29 18 17
Interval between parturitions (days) Ð 59.0a 50.8b 49.4b 48.3b 51.2b 2.42 *** NS Does' weight (g) at
mating 3672a 4037b 4124b 4179b 4184b 4095b 48.9 *** ***
partume 3739a 3899b 3913b 3928b 3918b 3952b 41.5 *** ** NS
weaningf 4249a 4413b 4436b 4447b 4416b 4466b 47.8 ** ** ***
Does' weight gain (g) during
gestatione 562.1b 388.1a 294.1a 265.4a 210.2a 347.5a 59.25 *** NS ***
lactationg 160.0 132.8 129.9 115.8 86.7 110.1 55.09 NS * NS
DEhintake of does (kJ DE kgÿ0.75dayÿ1) during
1±35 days of lactationg 1265 1321 1311 1264 1243 1282 27.5 NS *** NS
Means within a row with different letters are significantly different (p< 0.05). aStandard error.
b*p< 0.05; **p< 0.01; ***p< 0.01; NS not significant. cEffect of parity.
dEffect of the interaction between parity and diet. eCovariate: Litter size total at partum.
fCovariate: Litter size at 35 days. gCovariate: Litter size at 21 days. hDigestible energy.
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male (Table 2). Whereas 65% of multiparous rabbit does were mated before 21 days postpartum, only 37% of primiparous does were mated in this period. Because of primiparous does are still growing, they showed a higher live weight gain during the gestation (p< 0.001) than that shown in the following cycles.
On the other hand, there was a significant interaction between diet and parity in the live weight of does (p< 0.01) and in the live weight gain of does during lactation (p< 0.05), with higher figures for H diet in the first lactation and similar figures for all diets during the following lactations. The significant interaction between parity and diet in the DE intake of lactating does was related to differences in this trait for the different diets between primiparous and multiparous does. Consequently, the results for the effect of diet were considered independently of each other.
4.2. Effect of diet
4.2.1. Primiparous does
Data in Table 3 show that there were no significant differences in the parturition interval and live weight at mating of primiparous does (3660 g). However, some differences in live weight (Fig. 1(a)) and in food and DE intake were noticed during the first reproductive cycle. Pregnant does given H diet showed a higher DE intake (only significant during the 2nd week, p< 0.05) and a greater live weight at 21st day of gestation (p< 0.05) than does given L and M diets, although food intake was generally higher with L diet (p< 0.01). However, does given H diet had a lower DE intake during the last days of gestation (only significant during the last three days,p< 0.05), showing live weight losses. So, no significant differences in the live weight of does at partum (3721 g) and in the total weight gain during gestation were found.
Does given L diet showed a higher food intake in lactation than does given M and H diets, but does on H diet showed a significantly higher DE intake (especially during the first three weeks;p< 0.05). Live weight of lactating rabbit does on H diet was higher than on L and M diets, showing a greater total weight gain during the first lactation (p< 0.01). Type of diet had a significant effect on milk yield, although it was not consistent throughout lactation (Fig. 2): does on H diet had higher milk yield during the 3rd week (p< 0.01) and lower milk yield during the first and last weeks of lactation (p< 0.05) than does on L and M diets. The total milk production was significantly lower for does given H diet (5.74, 5.43 and 5.24 for L; M and H diets, respectively;p< 0.05).
4.2.2. Multiparous does
Similar to the first reproductive cycle, there were no significant differences in the parturition interval for the different diets, this being shorter than for primiparous does (50.0 vs. 59.0 days).
In contrast to the results for primiparous, when the dietary energy content was increased, multiparous does showed a higher live weight at mating, especially for H diet (3777, 3889 and 4291 for the L, M and H diets, respectively;p< 0.001), and this was maintained throughout the reproductive cycle (Fig. 1(b)).
Table 3
Effect of diet on live weight, intake and milk yield of primiparous and multiparous rabbit does (Llow, Mmoderate and Hhigh energy diets)
Primiparous Significancea Multiparous Significancea
L M H SEb diet covariate L M H SEb diet covariate
No. of observations 21 20 18 46 38 49
Interval between parturitions (days) 61.3 58.7 57.3 3.26 NS 52.4 49.0 48.6 1.95 NS Does' weight (g) at
mating 3610 3604 3781 87.4 NS NS 3777A 3889B 4291C 25.6 *** 21st day of gestationc 4048a 4013a 4324b 85.6 * * 4065A 4175B 4471C 8.2 * * pre-partumc 4235 4125 4282 73.1 NS ** 4232A 4227A 4616B 41.7 ** *** partumc 3734 3635 3800 69.7 NS NS 3722A 3713A 4101B 24.0 ** NS 21st day of lactationd 3703a 3664a 4032b 72.7 ** NS 3836A 3817A 4200B 121.3 * NS weaninge 3785a 3744a 4218b 80.2 *** NS 3901A 3879A 4252B 124.2 * NS Does' weight gain (g) at
gestationc 624.7 521.4 500.7 62.65 NS NS 441.6 299.2 308.1 16.26 NS * lactationd 51.2a 118.1a 387.3b 71.99 ** NS 101.8 96.2 80.0 62.52 NS ** Food intake (g DM dayÿ1kgÿ0.75)
Pregnant doesc
mating to 21st day 75.63b 65.74a 67.08a 3.187 ** NS 78.19 76.71 63.02 3.917 NS NS 22nd day to partum 46.99b 43.16b 34.44a 3.194 ** * 60.44C 50.96B 41.22A 3.908 ** NS Lactating does
partum to 21st dayd 116.6b 104.3a 103.8a 4.30 ** * 131.8C 114.3B 96.9A 5.42 *** NS 22nd day to weaninge 137.4b 118.4a 116.2a 4.77 *** * 135.4B 119.9AB 100.7A 5.44 *** NS Energy intake (g DE dayÿ1kgÿ0.75)
Pregnant doesc
mating to 21st day 748.7 729.6 818.4 35.55 NS NS 774.1 851.5 768.8 36.15 NS NS 22nd day to partum 465.3 479.0 419.7 34.51 NS * 598.3B 565.6AB 502.9A 32.88 * NS Lactating does
partum to 21st dayd 1154a 1158a 1266b 46.3 * * 1306B 1268AB 1181A 60.4 * NS 22nd day to weaninge 1360 1315 1418 53.2 NS * 1340 1331 1227 60.7 NS NS Milk yield (g dayÿ1) 164.0b 155.2ab 149.8a 7.59 * *** 174.3 154.5 156.9 11.83 NS ***
a,b,c Means for the effect of diet on primiparous does lacking a common letter differ (p< 0.05). A,B,C Means for the effect of diet on multiparous does lacking a common letter differ at (p< 0.05). a*p< 0.05; **p< 0.01; ***p< 0.001; NS not significant.
bStandard error.
cCovariate: Litter size total at partum. dCovariate: Litter size total at 21 days. eCovariate: Litter size total at 35 days.
intake of does was lower for H diet during the last days of gestation (p< 0.05) and during lactation (only significant for the first three weeks;p< 0.05). Neither the live weight gain of multiparous does during gestation nor during lactation was affected by diet. Type of diet did not affect the milk yield of multiparous does during the first three weeks of lactation (Fig. 2), but it was lower for does given H diet than for those given L and M diets during the last two weeks (p< 0.001 and p< 0.01, respectively).
4.3. Litters
There was no interaction between parity and diet in the litter performance, so the effect of diet is shown in Table 4 for all reproductive cycles. At parturition, the number of alive pups (9.16) was similar for the different diets, but mortality at partum was higher on H Fig. 1. Evolution of average live weight of primiparous (a) and multiparous (b) rabbit does with the different experimental diets throughout reproductive cycle (ÐÐÐ L, - - - M and H).
diet than on L and M diets (p< 0.05). Neither the size nor the weight of litters was affected by diet, so litter size (7.57) and weight (5212 g) at weaning did not differ between diets. A lower solid food intake of litters on H diet during the last week of lactation (p< 0.05) was compensated for its higher DE, being DE intake similar in the three groups at this time (504.7 kJ DE kgÿ0.75
dayÿ1
).
4.4. Effect of overlapping
Data presented in Table 5 show some significant differences in the live weight and food intake for the different overlapping periods. There was a tendency to a lower live weight and to a higher food intake of gestating does when overlapping period increased. As a consequence of this, food intake in pregnant does which overlapped two or three Table 4
Effect of diet on the performance of litters (Llow, Mmoderate and Hhigh energy diets)
Diets SEa Significanceb
L M H diet covariate
No. of observations 67 58 67
Size at
alive at partum 9.40 9.09 8.99 0.634 NS
7th day 8.45 8.17 8.16 0.525 NS
14th day 8.12 7.91 7.88 0.508 NS
21st day 7.96 7.78 7.76 0.505 NS
28th day 7.85 7.69 7.66 0.507 NS
35th day (weaning) 7.72 7.47 7.51 0.508 NS
Mortality (%)
at birth 1.662a 1.755a 4.469b 1.3525 *
from birth to weaning 17.55 17.49 16.46 3.8057 NS Weight (g) at
alive at partumc 483.3 499.4 488.6 14.75 NS ***
7th dayd 1055 1081 1043 36.3 NS ***
14th daye 1758 1808 1777 64.4 NS ***
21st dayf 2440 2417 2476 88.1 NS ***
28th dayg 3756 3816 3630 156.7 NS ***
35th day (weaning)h 5461 5741 5183 167.4 NS ***
Solid food intake (g DM dayÿ1kgÿ0.75)
22±28 daysg 40.43 39.51 38.03 3.389 NS *
28±35 daysh 86.75b 84.14b 74.82a 3.383 * NS
Solid energy intake (kJ DE dayÿ1kgÿ0.75)
22±28 daysg 400.7 438.8 463.4 38.08 NS *
28±35 daysh 859.5 933.9 912.5 35.88 NS NS
a,b Means within a row with different letters are significantly different (p< 0.05). aStandard error.
b*p< 0.05; ***p< 0.01; NS not significant. cCovariate: Litter size alive at partum. dCovariate: Litter size at 7 days. eCovariate: Litter size at 14 days. fCovariate: Litter size at 21 days. gCovariate: Litter size at 28 days. hCovariate: Litter size at 35 days.
weeks with the previous lactation was higher during the last 10 days of gestation (p< 0.001) than those overlapping zero or one week. However, in spite of their higher food intake, gestating does with long overlapping period showed lower live weight at 28th day of gestation (p< 0.001), at prepartum and at partum (p< 0.05), and lower number of pups alive at birth (p< 0.05).
5. Discussion
In recent years, most of the studies of the reproductive performance of rabbit does have tried to improve productivity and body condition by using high energy diets. The addition of fat to the diet seems to stimulate the DE intake and milk yield of does, inducing a higher litter weight gain (Fraga et al., 1989; Cervera et al., 1993; Xiccato et al., 1995; Pascual et al., 1998b, 1999), but it does not seem to affect significantly the body condition of lactating does (Xiccato et al., 1995; Pascual et al., 1998b).
All authors have showed that the use of high starch diets implied a decrease in the food intake and similar DE intake (Butcher et al., 1983; Xiccato et al., 1995; Lebas and Fortum-Lamothe, 1996; Fortun-Lamothe and Lebas, 1996), but different results for the effect on the performance of rabbit does have been found. Milk output did not increase in the studies of Butcher et al. (1983) and Xiccato et al. (1995), and was lower in the Table 5
Effect of lactation and gestation overlapping on the performance of gestating multiparous rabbit does Overlapping (weeks) SEa Significanceb
0 1 2 3 Oc O
Dd covariatee
No. of observations 42 13 18 60
Live weight of does (g) at
7th day of gestation 4090 Ð Ð Ð 13.6
14th day of gestation 4209 4185 Ð Ð 42.1 NS NS NS
21st day of gestation 4329b 4225b 4018a Ð 8.2 NS * NS 28th day of gestation 4376b 4297b 4054a 4138a 18.6 *** NS **
prepartum 4497b 4476b 4204a 4310a 41.7 * NS **
partum 3965c 3924c 3683a 3824b 24.0 * NS NS
Food intake of does (g DM kgÿ0.75dayÿ1)
mating to 7th day of gestation 78.22 Ð Ð Ð 18.027
7±14 days of gestation 89.48 68.86 Ð Ð 9.111 NS NS * 14±21 days of gestion 69.30 67.82 86.24 Ð 17.291 NS NS NS 21±28 days of gestation 45.91a 50.74ab 55.82b 55.45b 14.964 *** NS NS 28th day of gestation to prepartum 45.95a 50.88ab 55.35b 54.32b 13.790 *** NS NS Litter size alive at birth 9.15b 9.94b 7.38a 8.47a 0.861 * NS Litter weight (g) alive at birth 508.9 487.9 522.8 486.8 6.28 NS NS *** a,b,c Means within a row with different letters are significantly different (p< 0.05).
aStandard error.
b*p< 0.05; **p< 0.01; ***p< 0.001; NS not significant. cEffect of overlapping.
experiment of Lebas and Fortum-Lamothe (1996). Furthermore, growth of litters followed a similar trend. In relation to the body condition, Butcher et al. (1983) and Fortun-Lamothe and Lebas (1996) recorded an increase in the live weight of does given high starch diets or the weight of their adipose tissues, but Xiccato et al. (1995) did not find any significant change in body condition.
The results of the present study show that the high starch diet (H diet) seems to increase the DE intake of rabbit does during their first lactation. However, in contrast to that shown with high fat diets (Pascual et al., 1999), this high DE intake did not increase the milk yield nor the growth of litters, but rather induced a greater live weight gain of does in this period. These results suggest that, although live weight change is a poor indicator of body tissue mobilization (Partridge et al., 1983; Parigi-Bini et al., 1992), this diet with cereal starch as the main dietary energy source could reduce the current body-reserve depletion shown in primiparous rabbit does at the end of lactation (Partridge et al., 1983; Parigi-Bini et al., 1991; Xiccato et al., 1995). In fact, Fortun-Lamothe and Lebas (1996) have described recently how primiparous rabbit does given a diet supplemented with 140 g kgÿ1
of maize starch did not increase either the DE intake or milk yield, but the weight of adipose tissues tended to be higher (28 vs. 52 g of fat for the control and high starch diets, respectively). On the other hand, Xiccato et al. (1995) found that primiparous does given a high energy diet presented a lower body energy content when they were slaughtered at the second parturition. Thus, the use of high energy diets seems to improve the negative energy balance of primiparous rabbits when the main energy source is starch, but they were not able to improve productivity, in contrast to what has been observed when the main energy source is fat (Xiccato et al., 1995; Pascual et al., 1998b).
Primiparous rabbit does on H diet showed a different response from those on L and M diets, but the responses of does on L and M diets were similar in spite of their different dietary DE content. So, higher DE intake and live weight gain of rabbit does on H diet during their first lactation seem to be more related to its higher starch content.
Rabbit does given H diet presented a higher live weight at the end of the first lactation than those given L and M diets, and these differences were maintained during the following reproductive cycles. Multiparous rabbit does fed with H diet showed a lower DE intake throughout lactation, which could be the reason for the depletion in the milk yield of does during the last two weeks, and for the slightly lower litter weight at weaning. This is in agreement with the results obtained by Butcher et al. (1983) and Lebas and Fortum-Lamothe (1996) in multiparous rabbit does. The long-term preservation of a relatively constant body weight implies some long-term regulation of food intake.
Type of diet during pregnancy appeared to have no effect on litter size and weight at birth, but the incidence of pup mortality at birth increased markedly when does were fed with H diet. Partridge et al. (1986) found that pup mortality at birth was higher for does receiving a high energy diet during pregnancy than for animals fed with a low energy diet: a higher individual weight at birth should increase the incidence of dystocia (Partridge et al., 1985) or a build-up of fat in the abdominal cavity in the heaviest rabbit does (does given H diet), which could block foetal movement along the birth canal (Partridge et al., 1986).
On the other hand, in concurrently lactating-pregnant rabbit does energy requirements remain high due to the rapid development of the foetuses and uterine tissues (Xiccato, 1996), and normally this is responsible for a further reduction in the fat content and body energy levels. Consequently, pregnant does with long period of overlapping (two or three weeks) should show a higher food intake and a lower live weight after weaning. The results of the present study also show that multiparous rabbit does with a long overlapping period had smaller litters at partum than the rest of the groups. These results are in agreement with those of other workers who found a decrease in litter size alive at birth when the remating interval was shortened (Maertens et al., 1988; Cervera et al., 1993). For this reason, independently of the dietary energy level, the nutritional deficit caused by a longer overlapping period could be responsible for the poor body condition of gestating does, and consequently a reduction in the live weight of does and viability of pups at birth was found.
In conclusion, the results obtained in the present study showed that a large increase of dietary starch content increased the DE intake and the live weight gain of primiparous rabbit does during lactation. This could minimise the problem of their negative energy balance, but it could induce an excessive live weight of does. The inclusion of high levels of starch in the diet seems to stimulate fat deposition of primiparous does, but their higher DE intake did not improve either milk yield or performance of their litters, in contrast to what is observed when the main energy source is fat. High energy diets reduce the food intake of multiparous rabbit does during lactation, although this is due to their higher live weight, and consequently no improvements in the performance of their litters were found.
Acknowledgements
The present work was supported by a grant from CICYT (AGF97-1139).
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