Effect of dietary protein supply on the reproductive performance of crossbred rabbits

Nguyen Thi Kim Dong, Nguyen Van Thu and T R Preston*

Cantho University, Cantho City, Vietnam
ntkdong@ctu.edu.vn
*UTA, TOSOLY, AA #48, Socorro, Santander, Columbia

Abstract

An experiment was conducted in the experimental farm of Cantho University to evaluate the effects of different dietary protein levels on the reproductive performance of crossbred rabbits in three parities. The experiment had a complete randomized design, with four treatments, three replicates and one female rabbit per experimental unit. The diets included para grass, supplemented with different amounts of water spinach (Ipomoea aquatica) leaves and concentrate in order to provide 28 (28CP), 31 (31CP), 34 (34CP) and 37 (37CP) g crude protein (CP) per rabbit per day, respectively.

In three litters the results indicate that intakes of dry matter (DM) and CP significantly increased (p<0.03) with increasing the levels of CP in the diet, with the highest values for the 37CP diet. Higher litter sizes at birth were found for rabbits fed higher CP levels, with the highest on the 37CP diet (P<0.05), and litter size at weaning had a similar tendency. Mean weights at birth were only slightly different among treatments, and mean weights at weaning in litters 1 and 2 were highest on the 34CP and 37CP diets. Weight gains in pregnancy were highest on 37CP (P<0.05) and milk yields increased (P<0.01) with increasing CP level in the diet, with the highest values on 37CP. A comparison between the three parities showed that litter size at birth and weaning and milk yield were better in the second litter, and significantly higher weight gains in pregnancy were found in the first litter.

It was concluded that a daily intake of 37g CP per day resulted in optimum reproductive performance of female crossbred rabbits.

Key words: Crossbred rabbits, birth weight, dietary protein, milk yield, litter size, para grass, water spinach, weaning weight.

Introduction

Rabbit meat production has increased considerably in Vietnam recent years in order to meet the increasing demand for human food from animal products, and to replace poultry meat, which has declined in importance as a result of Avian Influenza. Rabbit meat is also increasingly popular due to the fact that it is very nutritious, lean and low in fat and cholesterol. However, breeding rabbit stocks are still limited, so it is not possible for farmers to buy weaned rabbits for their production systems. Moreover, most studies have focused on feeding and diet digestibility of growing rabbits rather than of reproductive does. Improving the nutrition of breeding females is of primary importance for increasing the productivity of domestic rabbit farming. In particular determining the optimal level of protein supply for breeding rabbits is the key to making the best of the rabbit's production potential and has a direct relationship to the income of the rabbit keeper (Ren et al. 2003). According to Lebas (1986) does require diets with levels of protein ranging from 17 to 18% in pregnancy and lactation.

Several kinds of locally available protein-rich forages are found in the Mekong Delta, and water spinach (Ipomoea aquatica) leaves (WSL) have been shown to be a very good source of plant protein for rabbits (Dong 2006), and provides adequate levels of protein and other nutrients essential for rabbits. Para grass is a good fibre source for rabbits and contains around 30% crude fibre (CF) (Trang 2006). The hypothesis of this study is that reproductive performance of crossbred does fed basal diets of para grass will be improved as the level of protein supplied is increased through supplementation with WSL and concentrate pellets. The objectives of the study are therefore to evaluate the effect of different levels of protein on the reproductive performance of crossbred rabbit does.

Materials and methods

Animals and experimental design

The trial was carried out at the Experimental farm of Cantho University in Cantho City. Twelve crossbred rabbit does at five months of age were arranged in a complete randomized design, with 4 treatments and 3 replications. One animal was housed individually per wire mesh and wood cage, as an experimental unit. The dietary treatments included para grass ad libitum supplemented with 300g fresh WSL and with concentrate levels of 29, 46, 63 and 80g to give in total 28, 31, 34 and 37g CP per doe per day, corresponding with the 29CP, 31CP, 34CP and 37CP treatments, respectively.

Feeds, feeding and management

Para grass was collected daily in the areas surrounding Cantho University. Water spinach leaves were bought from farmers who plant and sell WS stems for human consumption, with the WSL available as a by-product. Concentrate was bought at a local feed store on one occasion during the experiment. The animals were fed three times a day, at 8:00, 15:00 and 19:00h. Para grass was offered ad libitum, while 300g WSL per day was given to all does. Concentrate pellets were offered at levels of 29, 46, 63 and 80g/ doe/ day to give a total of crude protein supply of 28, 31, 34 and 37g per female per day. The WSL and pellets were adjusted weekly by increasing allowances by 5, 10 and 15% in the second, third and fourth week of pregnancy, respectively. During the lactation period allowances were increased by 10% in the first week, 30% in the second and third week, and 40% in the fourth week. All animals had access to fresh water at all times.

The does were kept individually in separate cages, and only one buck was used for mating. The breeding service was done at two weeks after birth. The new-born animals were weaned at the 30th day. Refusals and spillage were collected and weighed daily in the morning to calculate feed intake. Weights of rabbits at birth and weaning, and daily milk yields were measured. The does were weighed weekly from mating to parturition and their weight gains calculated during pregnancy. Before entering experiment all does were vaccinated to prevent some diseases, especially rabbit Hemorrhagic diarrhea and also parasite diseases.

Measurements

Reproduction criteria were recorded in 3 litters. Feeds and refusals were taken for analyses of DM, OM, CP, NDF and ADF following the procedure of AOAC (1990) and Van Soest et al (1991). The measurement taken included: daily feed and nutrient intakes for each litter, litter size at birth and weaning, weight gain of does in pregnant period and daily milk yield recorded by weighing the kits before and after suckling.

Statistical analysis

The data were analyzed by analysis of variance using the ANOVA of General linear model of Minitab Reference Manual Release 13.20 (Minitab, 2000). For the comparison of the reproduction criteria between the litters the paired T test of Minitab Reference Manual was also used.

Results and discussion

Feed characteristics

Characteristics of feeds used in the trial are presented in Table 1.

Table 1. Chemical composition of feeds (% DM basis except for DM which is on fresh basis)
Feed	DM	OM	CP	EE	CF	NFE	NDF	Ash
Para grass	18.7	88.7	13.7	6.00	23.1	45.9	59.2	11.3
Water spinach leaves	12.0	89.0	31.8	7.61	8.90	40.7	40.2	11.0
Concentrate	87.0	91.1	20.0	5.20	5.00	50.9	-	8.06
DM: dry matter, OM: organic matter, CP: crude protein, EE: ether extract, CF: crude fiber, NDF: neutral detergent fiber,

The para grass (PG) contained higher DM, but lower CP concentrations as compared to water spinach leaves (WSL). The concentrate pellets had higher DM and moderate CP contents compared to other feeds. Supplementation of both WSL and pellets to para grass diets increased the protein content in the diets. The CP content of the WSL used in our experiment was similar to values reported by Hongthong Phimmmasan et al (2004) and Pok Samkol et al (2006).

Feed and nutrient utilization and reproduction

Daily DM intakes of the does increased with daily CP intakes, with the significantly highest value (P< 0.01) recorded for animals given the highest amount of CP (37CP) (Table 2, 3 and 4). These results are similar to those reported by Nicodemus (1999), which ranged from 134 to 174g per day. For all three litters, litter size at birth significantly improved with increasing CP intake (P=0.02), while the mean rabbit weight at birth was not significantly different among treatments, probably because of the negative relationship between mean litter size and mean birth weight. The number of live rabbits at birth and at weaning in all three litters significantly increased with increasing amounts of CP supplied, with the highest number on the 37CP diet. The mean litter size at birth was similar to the values cited by Arrington and Kelly (1976) (6-8 kits/litter), Mai (2005) (3-8 kits/litter) and Lebas et al (1986) (7-9 kits/litter). However, the results reported by Ren et al (2003), working with Rex rabbits, showed lower litter size at weaning and survival rate (3.0-6.1 and from 63.3 to 76.1%, respectively) than values obtained in the present study.

Table 2. Effect of protein supply on feed and nutrient intakes and reproductive performance of does, first litter
	g CP/ rabbit /day*
	28CP	31CP	34CP	37CP	SE/P
DM intake (g/rabbit/day)	138a	153a	167ab	189b	7.15/0.01
CP intake (g/rabbit/day)	28.0a	31.2ab	34.2bc	38.3c	0.92/0.01
Litter size at birth (rabbit)	6.00a	6.67ab	7.00b	9.00c	0.16/0.01
Weight of litter at birth (g)	345	358	315	400	20.3/0.11
Mean weight at birth (g / rabbit)	49.9	53.9	48.6	44.4	2.05/0.08
Number of live rabbits at birth	6.00a	6.67a	7.00a	8.67b	0.23/0.01
Number of live rabbits at weaning	5.33a	6.00ab	6.67ab	7.67b	0.41/0.02
Weight of litter at weaning (g)	1,933a	2,352ab	2,795ab	3,135b	232/0.04
Mean weight at weaning (g/rabbit)	368	392	416	408	25.5/0.59
* Amounts of 28, 31, 34 and 37g CP / day, respectively. Means with different letters within the same row are significantly different at the 5% level.

 

Table 3. Effect of protein supply on feed and nutrient intakes and reproductive performance of does, second litter
	g CP/ rabbit/day*
	28CP	31CP	34CP	37CP	SE/P
DM intake (g/rabbit/day)	140a	156ab	163ab	183b	8.16/0.03
CP intake (g/rabbit/day)	27.7a	31.1ab	33.4bc	37.0c	0.95/0.01
Litter size at birth	6.33a	6.67a	7.33ab	9.33b	0.53/0.02
Weight of litter at birth (g)	328a	328a	315a	413b	19.1/0.03
Mean weight at birth (g / rabbit)	53.9	49.5	42.9	44.2	4.09/0.28
Number of live rabbits at birth	6.33	6.67	7.33	8.67	0.53/0.06
Number of live rabbits at weaning	5.67	6.33	7.00	7.67	0.50/0.09
Weight of litter at weaning (g)	2,137	2,278	2,619	2,917	215/0.14
Mean weight at weaning (g/rabbit)	378	376	384	390	12.3/0.86
* Amounts of 28, 31, 34 and 37g CP / day, respectively. Means with different letters within the same row are significantly different at the 5% level.

 

 

Duration of pregnancy was similar between treatments for all three litters (table 5). Daily weight gain of the does during pregnancy was influenced by the supply of CP, and was lowest on the 28CP diet and highest on the 37CP diet, the difference being significant in the first and the third litters (P=0.02 and P=0.04, respectively). Daily milk production was strongly affected by protein intake (Figure 1), and was lowest for the animals fed 28g CP (mean for 3 litters of 67.7 g /day), then significantly improved with increasing CP amount in the diet, and the highest milk yield (P<0.01) was for the 37CP diet (mean for 3 litters of 101 g /day). Daily milk yield recorded in our study is considerably higher than the values of 45.2-53.5g reported by Ren et al. (2003).

Figure 1: Effect of protein supply on milk yield of the does during three successive lactations

A comparison of the reproductive criteria of the does among the three litters is presented in Table 6. There was no significant difference in litter size at birth between the three litters, while number of weaned rabbits was significantly higher in the second litter than in the third. Mean weight at birth and at weaning was not statistically different among litters (P>0.05). Does had the highest daily weight gain during pregnancy in the first litter as they were immature, and would not have attained mature body size and weight. Daily milk yield was significantly higher in the second litter than in the other litters (P<0.05).

Table 6. Comparison of  reproductive performance among the three litters
	Litter number
	1st	2nd	3rd
Litter size at birth  (rabbits)	7.27	7.54	7.00
Litter size at weaning (rabbits)	6.42ab	6.67b	6.01a
Mean weight at birth (g / rabbit)	48.2	46.2	49.6
Mean weight at weaning (g / rabbit)	396	382	362
Daily weight gain of does in pregnancy (g)	15.0a	12.3b	12.6b
Daily milk yield (g)	79.1a	96.7b	83.8a
abMeans with different letters within the same row are significantly different at the 5% level.

Figures 1 and 2 illustrate that in the three litters the increasing protein supply had positive linear effects on the litter size at birth (R²=0.95) and daily milk yield of does (R²=0.93). There was also a close relationship between milk production and litter weight of the kits at weaning (Figure 4) (R²= 0.92). Thu (2004) reported that the CP requirement for breeding does was from 35-40g per day for the improved breeds, which is in agreement with the findings of the present study for crossbreed does.

Figure 2: Effect of protein supply on litter size at birth		Figure 3: Effect of protein supply on milk yield

Figure 4. Relationship between daily milk yield of does and weight of litter at weaning

 

Conclusions and implications

• Water spinach leaf is a good source of protein, with high acceptability and palatability for breeding rabbit does

• Does given a diet that supplied 37g crude protein per day had better reproductive performance and economic returns than those given 28-34 g CP per day.

• Studies of a wider range of crude protein supply for crossbred breeding does than in the present study should be carried out.

Acknowledgements

Financial support of this work from the MEKARN project, financed by SIDA-SAREC, is gratefully acknowledged. The authors would like to thank the Department of Animal Science, Faculty of Agriculture and  Applied Biology of Cantho University, and also acknowledge the valuable help of Professor Brian Ogle.

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