1158

Effect of Birth Weight and Litter Size on Productive Performance of Rabbits

C. Di Meo, M. P. Gazaneo, C. Racca1, F. Bovera, G. Piccolo and A. Nizza*

Dept. of Scienze Zootecniche e Ispezione degli Alimenti, Sezione B. Ferrara. Universit degli Studi di Napoli
Federico II, Via F. Delpino 1, 80137 - Napoli, Italy

ABSTRACT : This study chiefly aims to ascertain the effect of birth weight and litter size on productive performance in rabbits. After
delivery kits were removed from their mothers for individual weighing and randomly assigned to one of the following three
experimental treatments: Group (KT 6) with six tiny kits (about 45 g) per litter (21 litters); Group (KT 8) with eight tiny kits (about 45
g) per litter (17 litters); Group (KN8) with eight normal kits (about 70 g) per litter (20 litters). The litters, separated from their mothers
by putting them in a closed cage, suckled one time a day for 15 minutes. Daily milk production was measured by weighing the does
immediately before and after suckling; body weight of kits was measured on a weekly basis. At weaning 60 rabbits per group were
raised for six weeks to ascertain post-weaning performance and health. Compared with the two other groups, the kits of group KT8
ingested smaller quantities of milk both during the first 3 weeks (497.7 vs. 520.0 vs. 544.3 g, respectively for groups KT8, KN8, KT6)
and the following period (261.3 vs. 285.0 vs. 302.7 g, respectively for KT8, KN8, KT6). The differences between groups KT8 and KT6
were statistically significant (p<0.01) in the first period while in the second period also KN8 group showed milk intake different in
respect of KT8 (p<0.01) and KT6 (p<0.05) groups. Solid feed intake was significantly (p<0.05) lower in group KT6 (23.1 vs. 26.2 vs.
26.8 g/d, respectively for groups KT6, KN8, KT8). At weaning the kits of group KN8 always weighed more (966 vs. 894 vs. 888 g;
p<0.01, respectively for groups KN8, KT6, KT8). After weaning, no parameter considered (daily weight gain, feed intake, feed
conversion ratio, mortality and risk sanitary index) was affected by birth weight and litter size. (Asian-Aust. J. Anim. Sci. 2004. Vol 17,
No. 8 : 1158-1161)

Key Words : Rabbits, Birth Weight, Litter Size, Performance

INTRODUCTION nursing once a day from their mother.

The aim of this work was to establish whether by
In rabbits, individual birth weight is about 60-70 grams, reducing the size of litters formed by lighter kits we could
but can range from 35-40 to 80-90 grams. Generally, obtain similar productive performance at weaning and post
individually birth weight decreases with increase in litter weaning to that of rabbits with normal birth weight.
size. Kits of larger litters generally also show a lower
weight at weaning than the corresponding weight for kits of MATERIAL AND METHODS
smaller litters (Poigner et al., 2000). This is because their
weight gain depends on milk intake. Does milk production The test was conducted during the Spring of 2003 on
is positively related to litter size (De Blas and Galvez, 1973; litters obtained from multiparous Hyla hybrid females.
Torres et al., 1979; McNitt and Lukefahr, 1989; Sabater et After delivery, kits were removed from their mothers for
al., 1993; Ayyat et al., 1995). Nevertheless, kits of larger individual weighing and randomly assigned to one of the
litters consume less milk than those of smaller litters. following three experimental treatments:
This is why after delivery rabbit breeders equalize litters.
During the litters equalization, breeders also form litters Group KT 6 with six tiny kits (about 45 g) per litter (21
standardised by birth weight to eliminate the effect of litters)
imbalanced suckling by rabbits with different weights: in Group KT 8 with eight tiny kits (about 45 g) per litter
fact the heavier kits ingest more milk than lighter ones. In (17 litters)
this regard, it is necessary specify that the kit intake Group KN8 with eight normal kits (about 70 g) per litter
capacity is much higher than the milk available as reported (20 litters)
by Gyarmati et al. (2000). The authors showed that kits
suckling milk twice a day from two does increased milk Does and kits were housed in a commercial building (in
intake by 89%; consequently, weight gain improved and province of Avellino, Italy) with artificial ventilation and a
body weight was 70% higher at 21 days of age than kits 16 h light-8 h dark schedule. The does were fed ad libitum
* Corresponding Author: A. Nizza. Tel: +39-081-4421933, with commercially available pellets (diet D, Table 1), and
Fax: +39-081-292981, E-mail: nizza@unina.it water was available to the animals from self-drinkers.
1
ASL AV1 di Ariano Irpino, Dipartimento di Prevenzione, P.zza To maintain the standard litter size, any kits that died
Mazzini, 1 83031-Ariano Irpino (AV), Italy. were replaced with suckling rabbits of similar age and
Received November 7, 2003; Accepted April 27, 2004 weight previously not included in the experiment. The
 BIRTH WEIGHT AND LITTER SIZE ON PERFORMANCE OF RABBITS 1159

Table 1. Chemical composition of diets (g/kg)

Doe Weaner Finisher
Diets
(D) (W) (F)

Milk yield (g/d)

Dry matter 905 908 907
Crude protein 178 163 157
Ether extract 36 28 31
Ash 87 92 91
Neutral detergent fibre 310 373 350
Acid detergent fibre 172 206 184
Acid detergent lignin 42 51 45
Gross energy (MJ) 16.5 16.0 16.2 Days
litters, separated from their mothers by putting them in a Figure 1. Milk yield (g/d).
closed cage, suckled one time a day for 15 minutes. Daily
milk production was measured by weighing the does procedure (GLM, statistical analysis System Institute, SAS,
immediately before and after suckling; body weight of kits 1989). The weights at weaning were covariated for live
was measured on a weekly basis. From day 18 until weight at birth (SAS, 1989). When treatments differed,
weaning (day 35) a weaning commercial diet (Diet W, Table comparisons of the means were tested using the Ryan-
1) was distributed ad libitum to kits. Solid feed intake was Einot-Gabriel-Welsch procedure (SAS, 1989). Mortality
recorded from the 18th day of life to weaning. and the sanitary risk index were analysed with the Chi-
At weaning 60 rabbits per group were raised for six square method.
weeks to ascertain post-weaning performance and health.
Hence the rabbits were housed in individual cages on two RESULTS AND DISCUSSION
semi-superposed levels, kept in an experimental room with
artificial ventilation and a 12 h light-12 h dark schedule. Pre-weaning performance
The rabbits were given ad libitum the same feed used before Table 2 reports the variables observed in the pre-
weaning for 3 weeks; then a finisher feed was administered weaning period. The birth weight of kits was on average
(Diet F, Table 1). Body weight and feed intake were 45.2, 45.5 and 70.3 g, respectively for groups KT6, KT8
determined once a week. Mortality and the sanitary risk and KN8. During the first few weeks of life, a period in
index were recorded daily; the risk index is defined as the which kit intake is almost exclusively milk, the daily gain
sum of mortality and morbility. The criteria used to identify was 14.2, 13.0 and 14.2 g respectively for groups KT6, KT8
a morbid animal were detection of digestive troubles (signs and KN8. These results are due both to doe milk yield
of diarrhoea) and/or severe disturbance of feed intake, (Figure 1) and to litter size.
associated with a negative or very low daily weight gain Confirming the findings of other authors (De Blas and
(mean-2 X standard deviation) during one week. Chemical Galvez, 1973; Torres et al., 1979; McNitt and Lukefahr,
analysis of diets (Table 1) followed the AOAC method 1989; Sabater et al., 1993; Ayyat et al., 1995) the females
(1990) for dry matter (DM), ash, ether extract (EE), crude with 6 kits per litter (KT6) produced less milk than the
protein (CP) and crude fibre (CF), and van Soest et al. others with 8 kits (5,082, 6,072 and 6,440 g respectively for
(1991) procedures for acid detergent fibre (ADF) with a groups KT6, KT8 and KN8). The 18-21% reduction in milk
thermostable amylase pre-treatment. Gross energy was produced by KT6 does was higher than that (16%) reported
determined by adiabatic bomb calorimeters (Parr). by Ayyat et al. (1995) in the same comparison of litter size
Data were analysed by ANOVA using the general linear (6 vs. 8). However, the above authors obtained these results

Table 2. Pre-weaning performance (means) of the three rabbit groups

Groups
SEM
KT6 KT8 KN8
Litters n. 21 17 20
Live weight at 1 day g 45.2B 45.5B 70.3A 2.23
Live weight at 35 days 894B 888B 966A 41.39
Daily weight gain (1st-3rd wk) g/d 14.2a 13.0b 14.2a 0.86
Daily weight gain (4th-5th wk) 40.0b 40.7b 42.8a 1.49
Milk intake (1st-3rd wk ) g 544.3A 497.7B 520.0 26.34
Milk intake (4th-5th wk) 302.7Aa 261.3B 285.0Ab 14.81
Solid feed intake (4th-5th wk ) g/d 23.1b 26.8a 26.2a 1.66
Mortality (1-35 d) % 11.9 14.7 10.6 1.05*
A, B
p<0.01; a, b p<0.05. * chi square value.
1160 MEO ET AL.

Table 3. Post-weaning performance of the three rabbit groups during the period 35-77 d
Groups
SEM
KT6 KT8 KN8
Rabbits n 60 60 60
Initial weight g 895 886 962 37.59
Daily weight gain g/d 36.3 36.1 36.4 1.39
Feed intake g/d 111.2 110.0 111.9 3.30
Feed conversion ratio 3.063 3.047 3.074 0.54
Final weight (77 d) g 2,432 2,402 2,491 48.24
Mortality % 5.0 6.7 3.3 0.70*
Health risk index % 18.3 20.0 15.0 0.53*
* chi square value.

in New Zealand White does which yielded less milk than Fernandez Carmona et al., 1998; Heinzl et al., 2000; Nizza
the does used in our research. Although the milk yield of et al., 2001).
KT6 does proved lower, their kits were able to ingest more The high weight reached by individuals of groups KT6
milk as there were fewer of them (6) per litter: in fact and KT8 suggested that they are able to ingest all the milk
individual milk intake of kits in the first three weeks of yield from the mother and hence achieve sufficient daily
suckling amounted to 544.3, 497.7 and 520.0 g respectively gains. The intake capacity of kits is known to be much
for groups KT6, KT8 and KN8, significant different higher than the mothers milk availability. In this regard,
between KT6 and KT8 (p<0.01). The greater increase McNitt and Moody (1988) and Gyarmati et al. (2000)
(about 9.2%) obtained by reducing litter size from 8 to 6 is showed that kits can suckle twice a day from two does and
borne out by the findings of Szendr et al. (1996) and achieve almost double the intake of rabbits that are suckled
Rommers et al. (2000). However, these authors report only by their mothers. Mortality rates observed until
higher differences (18 and 30% respectively). Moreover, weaning did not differ significantly among groups (11.9 vs.
neither of the above works reports milk yield. A similar 14.7 vs. 10.6%, respectively, for groups KT6, KT8 and
increase (9.2%) was recorded by birth weight while KN8). These results indicate that neither individual birth
maintaining the litter size constant. Also in this case, the weight nor litter size affects the mortality rate. Similar
differences observed by Szendr et al. (1996) appear about results are reported by Szendr et al. (1996) only for litter
20% higher. In particular, for kits weighing 40-49, 50-59 size. This authors report in the first three weeks of life
and 60-69 g at birth daily weight gains of 12.7, 13.7 and mortality rates equal to 6.8 and 10.2% respectively for a
15.2 g are reported respectively. Also in the last two weeks litter of 6 to 8 kits and in the first six weeks 13.6 and 13.9%
of suckling, milk intake was significantly (p<0.01) higher in respectively per litters of 6 to 8 kits. Depending on birth
group KT6 (302.7 vs. 261.3 vs. 285.0, respectively for weight, the same authors report significantly different
groups KT6, KT8 and KN8), although KT6 kits recorded a mortality rates in the first three weeks (20.0 vs. 12.7 vs.
lower (p<0.05) solid feed intake (23.1 vs. 26.8 vs. 26.2 7.4% respectively for kits of 40-49, 50-59 and 60-69 g). It
respectively for groups KT6, KT8 and KN8). is concluded that birth weight proved to be significant only
These results suggested that lower milk intake during the suckling period, particularly during the first
stimulates a higher intake of solid feed. Similar results are week of life and in the case when low-weight rabbits at
also reported in other research (Scapinello et al., 1999; birth are reared in large litters, a common situation under
Pascual et al., 2001; Nizza et al., 2002). In this period, the natural circumstances.
kits whose birth weight was about 70 g (KN8) supplied a
higher (p<0.05) daily gain than the two other groups (42.8 Post weaning performance
vs. 40.0 vs. 40.7 respectively for groups KN8, KT6 and The variables measured in the post-weaning period are
KT8). The daily weight gain recorded in the two periods reported in Table 3. The daily weight gain was on average
affected weight at weaning which was higher in kits from 36.3 g, with no significant differences between the groups.
group KN8 than those of the two other groups (966 vs. 894 Similar results are reported by Szendr et al. (1996) in the
vs. 888 g respectively for groups KN8, KT6 and KT8). The 6-10 week period. Rommers et al. (2000) also report similar
difference between the groups was statistically significant daily gains from weaning until first mating in does of
even after covariated weights at weaning for live weight at different litter size before weaning (6 and 9 kits/litter). Also
birth. The weaning weight of rabbits that had a birth weight the feed intake (average 111 g) and hence the feed
of about 45 g (groups KT6 and KT8) appears fairly high conversion ratio (average 3.06) showed no statistically
and definitely falls within the averages reported by other significant differences and fall within the range of values
authors for the same weaning age (Nizza et al., 1995; reported in the literature (Fernandez-Carmona et al., 1998;
 BIRTH WEIGHT AND LITTER SIZE ON PERFORMANCE OF RABBITS 1161

Muriu et al., 2002; Taranto et al., 2003). Final live weight, 7th World Rabbit Congress, Valencia. Vol. C. 291-297.
which was higher in kits of group KN8 as they were heavier McNitt, J. I. and S. D. Lukefahr. 1990. Effects of breed, parity, day
at weaning, showed no significant differences when it was of lactation and number of kits on milk production of rabbits. J.
Anim. Sci. 68:1505-15012.
covariated for the post-weaning weight.
McNitt, J. I. and J. Moody. 1988. Milk intake and growth rates of
Mortality observed in this period was low (average 5%) suckling rabbits. J. Appl. Rabbit Res. 11:117-119.
and not affected by the experimental design. Moreover, Muriu, J. I., E. N. Njoka-Njiru, J. K. Tuitoek and J. N. Nanua.
Szendr et al. (1996) report no significant effects of litter 2002. Evaluation of sorghum (sorghum bicolor) as
size and birth weight on mortality for the same period. replacement for maize in the diet of growing rabbits
Indeed, after weaning there are many factors that may affect (Oryctolagus cuniculus). Asian-Aust. J. Anim. Sci. 15:565-569.
mortality: of these a prime role is played by the buildings Nizza, A., G. Moniello and T. Di Lella. 1995. Prestazioni
environmental and sanitary conditions. The sanitary risk produttive e metabolismo energetico di conigli in
accrescimento in funzione della stagione e della fonte proteica
index also remained at acceptable levels (average 17.8%)
alimentare. Zoot. Nutr. Anim. 21:173-183.
and there were no significant differences between groups.
Nizza, A., C. Di Meo, G. Stanco and M. I. Cutrignelli. 2001.
Influence of solid feed intake and age at weaning on caecal
CONCLUSIONS content characteristics and post-weaning performance. World
Rabbit Sci. 9:149-153.
The results obtained in our study suggest that birth Nizza, A., G. Stanco, C. Di Meo, M. L. Marongiu, S. Taranto, M. I.
weight, despite affecting weaning weight, does not result in Cutrignelli and L. Juliano. 2002. Effect of pre-weaning solid
very great differences in this parameter. Differences are feed and milk intake on caecal content characteristics and
limited to 100 g, a range normally found between winter performanceof rabbits around weaning. Ital. J. Anim. Sci.
2:95-101.
and summer, between kits of primiparous and multiparous
Pascual, J. J., C. Cervera and J. Fernandez-Carmona. 2001. Effect
does, etc. of solid feed intake before weaning on the performance of
Secondly, reduction in the size of lighter litters from 8 growing rabbits. In: Proceedings of the 2nd Meeting of
to 6 kits does not improve productive performance as rabbit workgroup 3 and 4 COST Action 848. Godollo, Hungary.
does reduce their milk yield. Finally, after weaning, birth Poigner, J., Zs. Szendr, A. Lvai, I. Radnai and E. Bir-Nemeth.
weight and litter size do not affect either livestock variables 2000. Effect of birth weight and litter size at suckling age on
or mortality. reproductive performance in does as adults. World Rabbit Sci.
8:103-109.
Rommers, J. M., B. Kemp, R. Meijerhof and J. P. T. M.
ACKNOWLEDGEMENTS
Noordhuizen. 2000. Rearing conditions in rabbit : effect of
litter size before weaning on feed intake and body
Thanks are due to Giuseppe Rizzo at the Pinuccio farm development and composition of young rabbit does. In:
for having consented to the trial. Proceedings of the 7th World Rabbit Congress, Valencia. Vol.
C. 415-422.
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