Rabbit nest construction and its relationship with litter development

Applied Animal Behaviour Science, 31 ( 1991 ) 2 5 9 - 2 6 6

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Elsevier Science Publishers B.V., A m s t e r d a m

Rabbit nest construction and its relationship with litter development E. Canali a, V. Ferrante b, R. Todeschini c, M. Verga b a n d C. C a r e n z i b alstituto per la Difesa e la Valorizzazione del Germoplasma Animale, C.N.R., Via Celoriu I0, Milan 20133, Italy blstituto di Zootecnica Veterinaria, Via Celoria 10, Milan 20133, Italy CDipartimento di Chimica Fisica ed Elettrochimica, Via Golgi 19, Milan 20133, Italy (Accepted 14 February 1991 )

ABSTRACT Canali, E., Ferrante, V., Todeschini, R., Verga, M. and Carenzi, C., 1991. Rabbit nest construction and its relationship with litter development. AppL Anim. Behav. Sci., 31: 259-266. The influence of maternal prenatal behaviour and of the micro-climate on the development of young rabbits was evaluated for three successive litters of female New Zealand White rabbits. The quality of the straw and hair nests produced for each litter and several characteristics of the litter up to weaning at 30 days of age were recorded. The quality of the straw nest improved from the first to the third parturition, whereas the hair nest seemed to be influenced by climatic conditions alone, especially temperature. The importance of nest building on growth and survival of young until the thirtieth day of life was confirmed and the straw shell was identified as the more plastic component of the nest.

INTRODUCTION

The neonatal habitat, which has a large effect on the vitality and growth of young rabbits (Delaveau, 1982; Verga et al., 1987), is moulded by the doe through the construction of the nest (Ross et al., 1956; Zarrow et al., 1961; Denenberg et al., 1969; Berovides and Fernandez, 1982 ). In particular, Canali et al. ( 1988 ) have shown that nest quality improves from the first to the third delivery. In order to expand our knowledge of this particular aspect of maternal behaviour, a progress check was undertaken of the two phases of nest construction in the first three litters. The effects of nest building on the growth and survival of the pups were then studied using multivariate analysis, which permits evaluation of the data as a whole. 0168-1591/91/$03.50

© 1991 - - Elsevier Science Publishers B.V.

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ANIMALS, MATERIALS AND METHODS

Rabbits and their rearing system For this experiment 32 primiparous New Zealand White does were mated with four bucks of the same breed so that each buck was used for a specific group of eight does over the three successive litters. The does and their young were housed in galvanized steel hutches (61 X 45 × 35 cm 3) each with a double bottom and a closed external nesting box (24 X 35 X 45 cm3). Three days before birth the nesting boxes were open and the does were given barley straw for nest construction. The rabbits were fed pelletized feed containing 18% crude protein ad libitum, through a feed hopper, and fresh water was supplied through nipple troughs. The lighting regime was 16 h of light out of 24 h. The young rabbits were weaned at 30 days by removal from the does.

Data collection and analysis On the day after parturition the quality of each of the two construction phases of the nest, straw and hair, was evaluated using a points system (Verga et al., 1983 ) from 1 for very poor to 5 for very good. The following data were recorded for all litters during the first m o n t h of life: total number of young born, total number of deaths litter weight at, and deaths after 5, 15 and 30 days and number weaned. Weekly averages for daily recordings of ambient temperature and humidity were calculated. Several variables, including litter order, quality of the straw and hair nest, total number of young born, total number of deaths, ambient temperature and humidity were analysed by multivariate analysis (Wold et al., 1987) in order to establish their role with respect to the total variability. The distribution of the data into clusters was also analyzed (MacQueen, 1967; Massart and Kaufman, 1983). To characterize the relationship between the number of weaned pups and each of the independent variables two regression methods were used: the classic ordinary least squares (OLS) and partial least squares (PLS) (Hoskuldsson, 1988 ). The new algorithm described by Merengo and Todeschini ( 1991 ) has been used, with the SCAN software package (Todeschini et al., 1990) to obtain the PLS regression coefficients in a closed form to compare them with OLS coefficients. After a preliminary refinement of the models, only five independent variables (parity, temperature, straw nest score, hair nest score and litter weight at 5 days) were retained to predict the number of weaned rabbits. (As a discriminant analysis showed that the male had no effect on growth and survival of the pups until 30 days of life, this variable was not considered. )

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RESULTS

Our results show that the quality of the straw nest improved from the first to the third litter while that of the hair nest declined (Fig. 1 ). The analysis of the principal components undertaken on 14 variables revealed that the first three principal components explained approximately 64% of the total variance. This analysis showed the close correlation that exists between the weight of the young at 5, 15 and 30 days and, by analogy, the 5-

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Fig. 1. T r e n d o f straw and hair nest scores according to litter order.

TABLE 1 Principal component (PC) analysis undertaken on 10 variables

PC1 PC2 PC3

Eigenvalue

Explained variance (%)

Cumulative explained variance (%)

3.680 2.101 1.205

36.8 21.0 12.0

36.8 57.8 69.8

Variables

PC 1

PC2

PC3

Parity Temp. ( ° C ) Relative humidity Straw nest score Hair nest score Pups dead at 5 days Pups dead at 30 days Weaned pups Litter weight (g) at 5 days Litter weight (g) at 30 days

0.232 0.119 - 0.002 0.441 0.138 -0.357 -0.009 0.490 0.430 0.408

0.527' 0.533 0.181 - 0.010 - 0.566 0.133 -0.239 - 0.087 -0.044 0.012

0.128 0.086 0.576 0.165 0.061 -0.279 0.636 0.087 -0.072 0.343

~The most significant variables for each component are in bold.

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E. CANALI ET AL. Av-Envlrons Temper ot Jre

(a) Parity

AvRH N pups deod at 5doys

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N, pups deod ot 30 doys

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Fig. 2. Projections for the loadings of the 10 variables considered on the principal components: (a) PC1 vs. PC2; (b) PCI vs. PC3. mortality. Thus the same analysis was undertaken, reducing the number of variables by eliminating those carrying the same information (live births, stillborn, mortality at 15 days and weight at 15 days),

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RABBIT NESTCONSTRUCTION TABLE 2

Cluster analysis on all the litters (n =68 ) undertaken on 10 variables

Parity Temp. ( ° C ) Relative humidity Straw nest score Hair nest score Pups dead at 5 days Pups dead at 30 days Litter weight (g) at 5 days Litter weight (g) at 30 days Pups weaned

Mean n=68

Cluster 1 n=12

CLuster 2 n=25

Cluster 3 n=31

1.7 19.3 64.8 4.2 2.4 0.9 0.2 695 3251 5.2

1.5 19.9 63.8 2.7 1.8 3.6 0.2 480 2244 1.1

1.0 14.7 64.4 4.1 2.8 0.4 0.3 655 2937 5.1

2.3 22.8 65.6 4.8 2.3 0.2 0.2 810 3894 6.9

TABLE 3

Results obtained from regression analysis, response variable: weaned rabbits Variables

Parity Temp. ( ° C ) Straw nest score Hair nest score Litter weight (g) at 5 days

OLS

PLS (2 PC)

Coefficient

Standard coefficient

Coefficient

Modelling power PC 1

Modelling power PC2

0.363 0.043 0.882 0.970 0.007

0.098 0.093 0.302 0.226 0.527

0.440 0.018 1.083 0.935 0.006

0.139 0.035 0.575 0.038 0.445

0.606 0.471 0.573 0.413 0.485

Table 1 highlights the variance explained by the first three principal components, and their significance. In Figs. 2 ( a ) and 2 ( b ) projections for the loadings of the variables considered on the principal components are shown. It can be seen that the quality of the nest and the number of weaned young are closely related, both contrasting with mortality, and the quantity of hair present in the nest is inversely correlated to the ambient temperature (Fig. 2 ( a ) ). Mortality at 30 days seems to be linked to ambient humidity levels (Fig. 2 ( b ) ). The results of the cluster analysis, which allowed the litters to be placed into three groups on the basis of ten different variables, are shown in Table 2. In particular it can be noted that the group which had a high number of births and good points for hair and straw nests showed the best development of the young, in terms of the number of weaned rabbits and weights at Day 5 and Day 30. In contrast, the group which demonstrated the worst points for nest

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quality had the highest mortality at Day 5 and the lowest number of weaned rabbits, even though the group contained does which were not primiparous. The percentages of the explained variance R used to fit the data are 76% (OLS) and 75% (PLS). The values of R calculated to check the prediction capability of the models are good enough at 71% (OLS) and 74% (PLS). Both the regression models confirm the significant role of the related independent variables to predict the number of weaned pups, giving comparable results (Table 3). However, the PLS model stresses the relative importance of each component and is of more use in prediction than the OLS model. DISCUSSION

The present research supports earlier observations on the influence of litter order on the weight of the young, on the number of weaned rabbits (Coudert, 1982; Battaglini et al., 1986 ) and on straw nest quality, which improves (Ross et al., 1956). The decrease in hair nest quality with each litter can be attributed to the increase in ambient temperatures more than to litter order. Small changes in the external environment probably do not have much direct effect on the climate within the nest (Borka and Adam, 1988 ), but rather influence the construction of the nest. Of the two factors considered, temperature seems to be the more important as it produces a variation in the amount of fur used in the nest lining, although Szendro' et al. ( 1988 ) assumed that this variation was simply due to the doe's state of moulting. The most important factors seem therefore to be linked to maternal prenatal behaviour which, however, is subdivided into the preparation of the straw nest and the preparation of its fur lining. The different factors involved in the two phases of nest construction allow us to formulate a few hypotheses: variations in the construction of the hair nest are not due to experience, but to precise stimuli, such as temperature and endocrine changes (Zarrow et al., 1961, 1963). The construction of the straw nest can be understood as a behavioural pattern which is more plastic, as it improves over time as a function of experience, and not as a function of external stimuli. These characteristics of maternal behaviour have a marked impact on the development of the young as well. In particular, we found that a good straw nest led to a greater number of weaned young following a lower mortality in the first 5 days of life in agreement with the results obtained by other authors (Delaveau, 1979, 1982; Szendro' et al., 1988 ). Improved nest qualities also allow for increased growth of the litter. CONCLUSION

The results of this study have indicated the importance of prenatal behavior, particularly the construction of a straw nest, on the growth and survival

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o f t h e y o u n g . I t m a y b e p o s s i b l e t o i m p r o v e c o m m e r c i a l r a b b i t s t o c k s b y selecting for breeding those rabbits that construct good straw nests.

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Zarrow, M.X., Farooq, A., Denenberg, V.H., Sawin, P.B. and Ross, S., 1963. Maternal behav. iour in the rabbit: endocrine control of maternal-nest building. J. Reprod. Fertil., 6: 375383.