It is suggested that the difference in body size between domestic-type rabbits and small pet-type rabbits results in different nutrient requirements. The nutritional requirements of pet rabbits have been assessed, although such assessments require evaluation throughout the rabbit life span. The present study was conducted under a cecotrophy prevention program with young and adult rabbits. Six male Dutch rabbits were housed individually in a dormitory-type cage, and they were randomly fed graded levels of dietary methionine and threonine, at ratios of 4:0, 3:1, 2:2, 1:3, and 0:4 mixed with two types of feed, 4:0 and 0:4. Four days after switching diets and 4 hr s after starting morning feeding, approximately one milliliter of blood was collected from the vein of the ear. Free amino acid concentrations in the plasma were determined with a high-speed amino acid analyzer. Plasma concentrations of methionine and threonine compared to dietary methionine and threonine levels are shown in young rabbits. The plasma concentration of methionine remained constant at a low level and then increased linearly. The intersection was estimated as 0.16 g/d. In the same manner, the intersection of the plasma threonine value was estimated as 0.27 g/d. These values were calculated as 0.27% and 0.47% of the diets, respectively. In the case of adult rabbits, the baseline was not obtained for dietary methionine and threonine levels. The methionine requirement was estimated as 0.11 g/d. The threonine requirement was estimated as 0.22 g/d. These values were calculated as 0.15% and 0.30% of the diets, respectively. In comparison with young and adult rabbits, both methionine and threonine showed a low baseline level in young rabbits, while their variations in plasma levels of adult rabbits w ere not determined. The requirement of both amino acids in young rabbits is higher than that in adult rabbits. The dietary values of both amino acids in young rabbits were also higher than those in adult rabbits. Small pet-type adult rabbits required lower amino acid levels than domestic-type rabbits.
Detailed information on the nutritional requirements of rabbits has been derived from studies with strains that produce meat and/or fur. Currently, there are more than 50 breeds of rabbits in the world, and feeding objectives do not consider rabbits for production of meat and fur and/or for research. Rabbits, as a pet animal have a very important status in the life of humans. It has been suggested that the difference in body size between the domestic-type rabbits and the small pet-type rabbits causes different nutrient requirements for maintenance [
The present study was conducted with consideration for animal welfare established in the guidelines for animal experiments at Tokyo University of Agriculture.
Six male Dutch rabbits weighing 0.71 ± 0.1 kg at 5 weeks of age were purchased from Kitayama Rabes Co., Ltd. in Nagano. In this study we could not prepare the female rabbits. They were housed individually in a dormitory-type cage (32 × 47 × 35 cm) in a room, in which temperature and relative humidity were controlled at 24˚C ± 1˚C and 60%, respectively.
After the preliminary feeding of the rabbits with cecotrophy prevention methods utilizing color, the first study with the young stage was conducted at 7 weeks of age for 20 days to observe the amino acid requirements.
The experimental diets contained 14% of CP (
1 | 2 | |
---|---|---|
Wheat flour | 10.0 | |
Soybean meal | 11.9 | |
Alfalfa meal | 8.0 | |
Millet meal | 36.0 | |
Corn starch | 28.0 | |
Soybean oil | 0.5 | |
Beer yeast | 2.0 | |
NaCl | 0.5 | |
CaCO3 | 0.5 | |
Ca3(PO4)2 | 0.1 | |
Pre mix1) | 0.2 | |
Amino acid mix.2) | 2.0 | |
L-Met | 0.3 | - |
L-Thr | - | 0.3 |
Chemical analysis | ||
Moisture | 9.6 | |
CP | 13.6 | |
Ether extracts | 1.65 | |
Crude fiber | 56.6 | |
NFE | 13.0 | |
Crude ash | 5.56 | |
GE (kcal/g) | 3.94 |
1)Contains vitamin A, D, E, B1, B2, B6, B12, C, niacin, pantothenic acid, biotin, folic acid, choline chloride, inositol, FeSO4, MnSO4, CoSO4, and KIO3. 2)Contains essential amino acids (leucine, lysine, arginine, phenylalanine, isoleucine, histidine, tryptophan and valine) and glutamic acid.
Mix ratio of Met:Thr | 4:0 | 3:1 | 2:2 | 1:3 | 0:4 |
---|---|---|---|---|---|
Met | 0.44 | 0.36 | 0.29 | 0.22 | 0.14 |
Thr | 0.38 | 0.46 | 0.53 | 0.60 | 0.68 |
threonine, the two prepared diets were mixed at ratios of 4:0, 3:1, 2:2, 1:3, and 0:4. The diet was administered using a time-controlled feeding method for 1 hr (9:00 - 10:00) and 3 hrs (16:00 - 19:00) in a day. The rabbits were fed ad libitum. Each experimental diet was provided for 4 days in the following order: 1, 4, 2, 5, 3. It was recognized that the plasma free amino acid concentration responded to the new amino acid dietary levels by 3 days after the dietary changes. In addition, the changes in dietary amino acid levels were reflected in the plasma amino acid levels within 2 hr after eating began. Therefore, in the fourth day after switching diets and 4 hr after starting morning feeding, approximately one mL of blood was collected from the vein of the ear. Body weight was determined before switching diets, and diet intake was recorded everyday.
Collected blood was centrifuged at 6.93 g for 5 min, and plasma was obtained. This plasma was thoroughly mixed with the same volume of 8% sulfosalicylic acid solution. After 10 min of decantation, the mixture was centrifuged at 6.93 g for 5 min under 5˚C. Supernatant fluid was filtered with a 0.45 μm filter (Advantec, Dismic-25) as reported previously [
After the first study, the rabbits were fed a commercial diet until they grew up to the adult stage at 35 weeks of age. The second study was conducted with 35-weeks-old rabbits in the same manner as the first study.
Free amino acid concentrations in the plasma kept at −40˚C were determined with a high-speed amino acid analyzer (Hitachi L-8500).
Statistical treatment was carried out by one-way analysis of variance. When a significant difference (P < 0.05) was recognized, the means were analyzed by Tukey’s multiple range test. The requirements of methionine and threonine were estimated by the broken line model.
Body weight gain and feed efficiency decreased in proportion to a decrease in methionine intake, and there was no change induced by a decrease in threonine intake, as shown in both stages in
Diet group | 4:0 | 3:1 | 2:2 | 1:3 | 0:4 | |
---|---|---|---|---|---|---|
Young rabbit | ||||||
Body weight gain (g/day) | 10.7 ± 1.9b | 18.1 ± 2.6a | 17.3 ± 2.4a | 8.3 ± 2.2b | 8.5 ± 1.4b | |
Diet intake (g/day) | 47.3 ± 1.8c | 59.3 ± 2.3b | 66.1 ± 2.7a | 48.1 ± 3.1c | 55.1 ± 0.9b | |
Feed efficiency (%) | 22.4 ± 3.6ab | 30.5 ± 4.3a | 25.7 ± 3.2a | 16.2 ± 3.4b | 15.4 ± 2.4b | |
Adult rabbit | ||||||
Body weight gain (g/day) | 1.5 ± 6.0ab | 4.0 ± 2.1ab | 7.1 ± 1.4a | −1.6 ± 4.3ab | −6.0 ± 2.5b | |
Diet intake (g/day) | 69.6 ± 2.3 | 70.9 ± 1.9 | 74.0 ± 2.7 | 71.2 ± 2.3 | 69.3 ± 4.9 | |
Feed efficiency (%) | 2.8 ± 9.5ab | 5.5 ± 2.8ab | 9.5 ± 1.8a | −2.6 ± 6.3ab | −10.1 ± 5.2b |
Each value is means for 6 rabbits. a-cmeans with different superscripts in the same row are significantly different (P < 0.05).
(P = 0.047 - 0.032) with a quadratic effect among the tested threonine levels; the present data showed the same trend.
In the statistical treatment of plasma amino acid concentration (
Diet group (Met:Thr) | Pooled | P < 0.05 | |||||
---|---|---|---|---|---|---|---|
Amino acid | 4:0 | 3:1 | 2:2 | 1:3 | 0:4 | SD | |
Tau | 68 | 48 | 45 | 41 | 67 | 19 | NS |
Asp* | 7 | - | 10 | 7 | 13 | ||
Thr | 37d | 71cd | 91bc | 125b | 191a | 55 | |
Ser | 189b | 218ab | 187b | 208ab | 278a | 52 | |
Glu | 47 | 57 | 36 | 46 | 53 | 13 | NS |
Gly | 692 | 695 | 759 | 772 | 896 | 165 | NS |
Ala | 704b | 1116a | 1106a | 821ab | 975ab | 213 | |
Cys | 21ab | 24a | 23ab | 15ab | 13b | 7 | |
Val | 115 | 149 | 146 | 129 | 174 | 41 | NS |
Met | 113a | 107a | 69b | 11c | 13c | 45 | |
Ile | 101 | 133 | 130 | 118 | 115 | 38 | NS |
Leu | 67 | 97 | 86 | 72 | 110 | 29 | NS |
Tyr | 45b | 65ab | 61b | 41b | 92a | 23 | |
Phe | 35 | 47 | 38 | 27 | 45 | 13 | NS |
Lys | 157 | 197 | 210 | 173 | 222 | 69 | NS |
His | 77 | 84 | 85 | 61 | 107 | 27 | NS |
3-Mehis* | - | 2 | - | 5 | - | ||
Arg | 159 | 180 | 175 | 108 | 176 | 45 | NS |
Pro | 277 | 371 | 356 | 309 | 388 | 78 | NS |
*: Statistical analysis could not be conducted because of value deletions.
Diet group | Pooled | P < 0.05 | |||||
---|---|---|---|---|---|---|---|
Amino acid | 4:0 | 3:1 | 2:2 | 1:3 | 0:4 | SD | |
Tau | 50 | 51 | 47 | 39 | 49 | 12 | NS |
Asp* | - | - | - | - | - | ||
Thr | 85c | 123bc | 135ab | 177a | 173a | 38 | |
Ser | 217b | 218b | 229ab | 265a | 245ab | 25 | |
Glu | 51ab | 41b | 48ab | 58a | 47ab | 8 | |
Gly | 624c | 638c | 783bc | 806a | 794a | 111 | |
Ala | 607 | 674 | 606 | 663 | 607 | 82 | NS |
Cys | 54 | 53 | 46 | 55 | 51 | 19 | NS |
Val | 150b | 164ab | 158ab | 179a | 159ab | 14 | |
Met | 100a | 76b | 66b | 43c | 21d | 27 | |
Ile | 78 | 84 | 96 | 101 | 88 | 16 | NS |
Leu | 116 | 116 | 112 | 126 | 116 | 20 | NS |
Tyr | 97 | 87 | 89 | 98 | 96 | 17 | NS |
---|---|---|---|---|---|---|---|
Phe | 57 | 54 | 52 | 59 | 55 | 8 | NS |
Lys | 157 | 158 | 165 | 178 | 165 | 13 | NS |
His | 89 | 82 | 83 | 86 | 89 | 8 | NS |
3-Mehis | 9 | 7 | 9 | 9 | 9 | 2 | NS |
Arg | 141 | 121 | 154 | 144 | 133 | 30 | NS |
Pro | 226 | 245 | 258 | 272 | 245 | 27 | NS |
*: Aspartic acid was not detected in the serum from adult rabbits.
the dietary level of it exceeds the requirement, the level of it increases linearly with increasing dietary levels. Therefore, the intersection level means a requirement level. The current intersection of methionine was estimated as 0.16 g/d. In the same manner, the intersection of plasma threonine value was estimated as 0.27 g/d. These values were calculated as 0.27% and 0.47% of the diets.
In
In a previous study [
our data suggesting a methionine requirement of 0.28% of the diet [
The present data of both amino acids from adult Dutch rabbits are half the values of previous data [
In comparison with young and adult rabbits in the present study, both methionine and threonine showed a low baseline level in young rabbits, while their variations in plasma levels of adult rabbits was not determined. Furthermore, the requirement of both amino acids in young rabbits is higher than that in adult rabbits. The dietary values of both amino acids in young rabbits were also higher than those in adult rabbits. Maertens et al. [
The authors wish to thank Mr. T. Sakoda, and Mr. H. Goto, for the determination of amino acids and Ms. S. Hashimoto and Ms. Y. Umehara for their help in the maintenance of rabbits, preparation of samples, and statistical analysis of data in this study.
The authors declare no conflicts of interest regarding the publication of this paper.
Abe, Y., Muramatsu, H. and Sukemori, S. (2019) Methionine and Threonine Requirements of Dutch Rabbits Fed under a Cecotrophy Prevention Program. Open Journal of Animal Sciences, 9, 163-172. https://doi.org/10.4236/ojas.2019.92014