Luận án A study of dietary protein for growing californian rabbits in the Mekong delta of Vietnam

ormally used diets containing high proportion of roughage and low 
proportion of high-protein feeds for feeding rabbits. Thus, it was necessary to 
supply feedstuffs that contained high protein and energy in the diets for 
growing and reproduction rabbits. Soybean, fish meal, feather meal and blood 
meal were used to supply protein, while maize, broken rice and sweet potato 
tuber for energy supplementation. All feedstuffs including soybean, fish meal, 
feather meal, blood meal, maize and broken rice had high concentration of 
DM being 894, 830, 842, 905, 884 and 894 g/kg, respectively. A high CP 
content was found for the protein supplemental feeds with the highest values 
for feather meal and blood meal (801 and 829 g/kgDM, respectively). The ME 
content of these feedstuffs was not considerably variable from 10.8 to 12.1 
MJ/kgDM. The CP, CF, NDF and ADF values of soybean in this investigation 
were slightly higher than those of soybean reported by Maertens et al. (2002) 
being 410, 62.2, 130 and 81.1 g/kgDM, respectively. However, CF value (105 
g/kgDM) was in an agreement with result stated by NIAS (2001) ranged from 
72.2 to 140 g/kgDM. The nutrient composition including DM and CP of fish 
meal in this investigation were slightly lower those of fish meal reported by 
NIAS (2001) (875 g/kg and 650 g/kgDM, respectively). The feather meal in 
this investigation containing DM, CP and EE was similar to findings of 
Ayanwale (2006) being 900 g/kg, 820 and 61.0 g/kgDM, respectively. The 
DM, CP, EE and CF of blood meal (905 g/kg, 829, 6.50 and 15.2 g/kgDM) 
were consistent with results of Balogun (1982) being 895 g/kg, 865, 5.90 and 
16.3 g/kgDM, respectively. The DM, CP and ME concentration of soybean, 
fish meal, feather meal and blood meal were shown in Figure 4.5. 
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Figure 4.5 DM, CP and ME concentration of soybean, fish meal, feather meal 
and blood meal 
 Soybean contained low value of essential amino acid and non-essential 
amino acid as compared to those of fish meal, feather meal and blood meal, 
with the exception of methionine, glutamic and arginine concentrations. The 
lysine and threonine of soybean in a previous study of Maertens et al. (2002) 
were 25.9 and 16.0 g/kgDM being higher than those of the results in a present 
investigation, however, methionine concentration (5.80 g/kgDM) was lower 
(11.0 g/kgDM). NIAS (2001) found that lysine, methionine and threonine of 
soybean were 27.1, 6.14 and 14.4 g/kgDM, respectively. Those findings were 
higher than our results. Similarly, NIAS (2001) reported that lysine, 
methionine and threonine of fishmeal (65% CP) were 52.5, 21.8 and 27.9 
g/kgDM. The difference could be explained that the composition of the final 
fish meal product depended on both the kind of raw material and the type of 
processing procedure. The lysine value of feather meal in this investigation 
was lower than that of NIAS (2001) (33.3 g/kgDM), but methionine and 
threonine values were higher (8.97 vs 6.98 g/kgDM, 16.5 vs 13.2 g/kgDM, 
respectively). Balogun (1982) reported that lysine, methionine and threonine 
values of blood meal were 90.8, 23.5 and 43.1 g/kgDM. Those values were 
slightly higher than results of this investigation. Besides, fish meal, feather 
meal and blood meal had strong smell that could effect on feed intake amount 
of rabbits. Moritz and Latshaw (2001) concluded that feather meal and blood 
meal were generally unpalatable with a high indigestible protein proportion. 
Feather meal had low nitrogen retention and amino acid digestibility (Bielorai 
et al., 1982; Knabe et al., 1989). Therefore, it was necessary to think over for 
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using fish meal, feather meal and blood meal in rabbit diets. The Lysine, 
Threonine and Methionine concentration of soybean, fish meal, feather meal 
and blood meal were shown in Figure 4.6. 
Figure 4.6 Lysine, Threonine and Methionine concentration of soybean, fish 
meal, feather meal and blood meal 
 Energy supplement feeds, maize and broken rice had similar CP and 
ME values with 84.0 and 86.5 g/kgDM; 14.8 and 14.2 MJ/kgDM, 
respectively. The sweet potato tuber had the highest ME value (15.3 
MJ/kgDM), but the lowest CP value (39.6 g/kgDM) among energy supplement 
feeds. The CP value of maize in this investigation was lower than results of 
maize reported by NIAS (2001) (102 g/kgDM) and Rana et al. (1985) (11.4 
g/kgDM). The EE and CF values (42.0 and 26.7 g/kgDM) were resembled to 
findings of Enyisi et al. (2014) (21.7-44.3 and 21.0-268 g/kgDM, respectively) 
and NIAS (2001) ranged 34.4-50.4 and 15.1-33.0 g/kgDM, respectively. 
Chumpawadee et al. (2007) found that DM, CP and ADF of broken rice were 
910g/kg, 71.9 and 7.40 g/kgDM, respectively. Those findings consisted with 
our results obtained. NIAS (2001) stated that DM, CP, EE and CF of sweet 
potato tuber cultivated in different regions of Vietnam were 215-316g/kg, 
28.0-46.0, 8.00-23.1 and 18.9-51.2 g/kgDM, respectively. Those findings were 
consistent with the results of our study. The DM, CP and ME concentration of 
maize, broken rice and sweet potato tuber were shown in Figure 4.7. 
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Figure 4.7 DM, CP and ME concentration of maize, broken rice and sweet 
potato tuber 
 The amino acid concentration of energy supplement feedstuffs was 
lower than that of protein supplement group. The lysine content of maize in 
the present study was consistent with the results of NIAS (2001) and Rana et 
al. (1985) being 3.14 and 2.30 g/kgDM, respectively. However, threonine 
value was lower than the findings of these authors (1.57 g/kgDM vs 3.94 and 
3.20 g/kgDM). The lysine and methionine values (3.65 and 3.38 g/kgDM, 
respectively) of broken rice in this investigation were slightly higher than the 
findings of Paraksa (2002) being 2.50 and 1.70 g/kgDM, respectively, while 
threonine value was similar (2.22 vs 2.70 g/kgDM). The lysine, methionine 
and threonine values (0.95, 0.21 and 0.53 g/kgDM, respectively) of sweet 
potato tuber were slightly lower than the results of NIAS (2001) being 1.49, 
0.53 and 1.49 g/kgDM, respectively. 
 Locally available forages could be provided a major part of protein and 
fiber requirement of rabbits. However, feeding unique forages would not meet 
adequate nutrient for growth and reproductive performance, thus 
supplementation of protein and energy feed sources was needed. Soybean, fish 
meal, feather meal and blood meal could provide protein, while maize, broken 
rice and sweet potato tuber supplied energy for rabbits. Utilizing local 
feedstuffs for rabbits should be considered for nutrient content, digestibility, 
palatability and economic efficiency. The Lysine, Threonine and Methionine 
concentration of maize, broken rice and sweet potato tuber were shown in 
Figure 4.8. 
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Figure 4.8 Lysine, Threonine and Methionine concentration of maize, broken 
rice and sweet potato tuber 
 4.1.4 Summary 
 It was concluded that para grass, water spinach vines, Psophocarpus 
scandens, Operculina turpethum and sweet potato vines should be used as 
basal feeds in rabbit diets because of their adequately essential amino acid, 
high crude protein and fiber compositions. These feeds were naturally 
available almost all the year round in the Mekong Delta. In term of using by-
products for rabbit, rabbit producers should utilize water spinach leaves and 
soya waste due to its high protein and amino acid concentration and low price. 
Besides, soya waste is a watery feed that could be used as a substrate for 
mixing protein and energy supplemental feeds to avoid flour dust for rabbits. 
Soybean extraction meal contained high amino acid concentration and crude 
protein; good smell; palatability and low cost that should be used as a protein 
supplement feed for rabbits. Sweet potato tuber had a high metabolizable 
energy with low price that could be used in rabbit diets as an energy 
supplement feed. The combination among feedstuffs created balanced nutrient 
diets for rabbits in terms of crude protein, amino acids, fiber and 
metabolizable energy. 
 4.2 Experiment 2: Effects of dietary crude protein levels on 
growth rate, meat production, digestible nutrients and economic return of 
Californian rabbits in Mekong Delta of Vietnam 
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 4.2.1 Feed and nutrient intakes 
 The feed and nutrient intakes of rabbits fed different CP levels were 
stated in table 4.4 
 The feed intakes of rabbits were significantly different (P<0.05) among 
treatments. The DM intakes of soybean extraction meal increased significantly 
(P<0.05) while sweet potato tuber decreased significantly (P<0.05) with the 
increasing of dietary CP levels. The intakes of DM and OM were not 
significantly different (P<0.05) among treatments with 71.2-71.9 g/rabbit/day 
and 66.3-67.0 g/rabbit/day, respectively. The DM intake in this experiment 
was similar to the findings on growing Californian rabbits fed different 
soybean extraction meal in the diets of Luan (2012) from 71.0 to 71.6 
g/rabbit/day. However, the DM intake in present experiment was higher than 
the results of Hoang (2009) by using different diets (9 gCP/kg live weight and 
12 gCP/kg live weight) on the New Zealand White rabbit with 57.5-59.3 g 
DM/rabbit/day. In our experiment, the values of g CP intake/kg live weight 
were from 8.86 to 11.3 g/kg, thus rabbits had to more consume of DM to 
satisfy nutrient requirements. The CP intake increased (P<0.05) while the 
NDF, ADF and EE intakes decreased (P<0.05) when increasing of soybean 
extraction meal in the diets because the soybean extraction meal contained a 
high CP and low NDF, ADF and EE. The CP intake values were similar to the 
results of Hang (2012) by using diets containing 9, 10, 11 gCP/kg live weight 
Table 4.4 The feed, nutrient and metabolizable energy (ME) intakes of rabbits 
 Treatment 
 CP15 CP17 CP19 CP21 CP23 SEM/P 
Feed intakes, g/rabbit/day (DM) 
O.turpethum vine 15.1a 14.3b 12.1c 9.98d 7.14e 0.06/0.001 
Para grass 15.1a 15.0a 15.7b 16.4c 17.9d 0.08/0.001 
Soybean extraction meal 8.63a 12.2b 16.4c 20.7d 25.0e 0.03/0.001 
Soya waste 7.19a 7.16a 6.41b 5.71c 5.00d 0.03/0.001 
Sweet potato tuber 25.9a 22.9b 20.6c 18.5d 16.4e 0.09/0.001 
Nutrient intake, g/rabbit/day 
Dry matter 71.9 71.6 71.2 71.3 71.4 0.29/0.498 
Organic matter 67.0 66.7 66.3 66.5 66.6 0.25/0.489 
Crude protein 10.8a 12.1b 13.5c 15.0d 16.4e 0.06/0.001 
Ether extract 2.95a 2.95a 2.84b 2.76c 2.66d 0.01/0.001 
Neutral detergent fiber 23.2a 23.1ab 22.8b 22.6b 22.7b 0.09/0.007 
Acid detergent fiber 16.7a 16.6a 16.3a
b 
16.2b 16.2b 0.06/0.002 
Crude fiber 10.2a 10.0a 9.67b 9.39c 9.15d 0.04/0.001 
ME, MJ/day 0.835 0.827 0.824 0.827 0.829 0.003/0.269 
 DP/DE ratio 8.71a 10.1b 11.6c 13.3d 14.5e 0.06/0.001 
DP/DE ratio (gDP/MJDE). The numbers with different superscript letters in the same row were 
significantly different (P < 0.05) 
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on Californian, Hyla, New Zealand White and local rabbits from 13.6 to 15.4 
g/rabbit/day. 
 The ME intake was similar (P>0.05) among treatments from 0.824 to 
0.835 MJ/rabbit/day. The ME intake results were higher than the findings of 
Hang (2012) (0.65-0.74 MJ/rabbit/day). The DP/DE ratio was significantly 
different (P<0.05) among treatments being from 8.71 to 14.5 g/MJ for the 
CP15 to CP23 treatments, respectively. According to Carabano et al. (2008), 
the optimal level for CP in a diet depends on its digestibility and the DE 
content. In present experiment, the DP/DE ratio was from 13.3-14.5 for better 
growth rate, digestible nutrient and nitrogen retention. It was similar to the 
findings of Amber (2000) being 13.1 for the optimum growth rate, final live 
weight and nutrient digestibility. 
 4.2.2 Daily weight gain and economic returns 
Daily weight gain, feed conversion ratio and economic returns of 
experimental rabbits were showed in table 4.5 
Table 4.5 Daily weight gain, feed conversion ratio and economic returns of 
experimental rabbits 
 Treatments 
 Item CP15 CP17 CP19 CP21 CP20 SEM/P 
IW, g/rabbit 463 469 463 477 475 6.96/0.475 
FW, g/rabbit 1,975a 2,168b 2,341c 2,435c 2,421c 27.0/0.001 
DWG, g/rabbit 18.0a 20.2b 22.4c 23.3c 23.2c 0.30/0.001 
Feed conversion ratio 3.99a 3.54b 3.19c 3.06c 3.08c 0.04/0.001 
Feed cost, USD/rabbit 1.04 1.11 1.19 1.26 1.34 - 
Total cost, USD /rabbit 5.18 5.27 5.38 5.47 5.58 - 
Income, USD /rabbit 7.05 7.74 8.36 8.70 8.65 - 
Profit, USD /rabbit 1.88 2.47 2.98 3.22 3.06 - 
IW: initial live weight, FW: final live weight, DWG: daily weight gain. The numbers with different 
superscript letters in the same row were significantly different (P<0.05). 1kg rabbit live 
weight=80,000VND; 22400VND=1USD 
 Growth and economic returns of rabbits fed different dietary CP levels 
were shown in Table 4.5. Daily weight gain was significantly different among 
the treatments (P<0.05) with the highest value for the CP21 treatment. It was 
similar to the results of the New Zealand White rabbits reported by Wang 
(2012) being from 21.5 to 28.1 g/day. Rabbit fed CP21 diet had the best FCR 
(3.06) (P<0.05). The obtained values for FCR were acceptable and consistent 
with the results being from 3.37 to 3.63 indicated by El-Tahan et al. (2012). 
The economic analysis showed that profit got from the CP21 diets were higher 
than the other diets due to better final body weight. There was a close linear 
relationship (R2= 0.95) between CP intake and daily gain of experimental 
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rabbits (Figure 4.9). Daily gain of rabbit increased when increasing CP intakes 
from 10.8 to 15.0 gCP/rabbit/day and decreased slightly at 16.4 g 
CP/rabbit/day. De Blas and Wiseman (2010) stated that if CP intakes and 
DP/DE ratio increased and they were higher than the requirements, then 
growth rate was not modified, nitrogen retention remained constant and 
nitrogen excretion increased. 
Figure 4.9 Effect of CP intake on daily gain of rabbits in the experiment 
 4.2.3 Carcass and meat nutrients 
 The carcass and meat quality of rabbits fed different dietary CP levels 
were presented in table 4.6 
 Table 4.6 Carcass and meat quality of rabbits in the experiment 
 Treatments 
Item CP15 CP17 CP19 CP21 CP23 SEM/P 
Live weight, g (LW) 1,990a 2,183b 2,353c 2,466c 2,437c 24.4/0.001 
Carcass weight, g 1,047a 1,143b 1,238c 1,289c 1,286c 16.8/0.001 
Carcass percentage, %LW 52.6 52.3 52.6 52.3 52.8 0.25/0.621 
Lean meat weight, g 789a 863ab 940bc 978c 980c 21.5/0.001 
Lean meat percentage, % 75.4 75.5 75.9 75.9 76.2 0.97/0.970 
Thigh meat weight, g 272a 310b 346c 383d 372d 4.98/0.001 
Thigh meat percentage, % 
carcass 
26.0a 27.1ab 27.9bd 29.8c 28.9cd 0.34/0.001 
Caecum length, cm 56.0 54.4 57.9 56.5 56.0 0.84/0.142 
Chemical compositions of meat, % in fresh 
 Dry matter 26.7 26.1 26.3 26.0 26.1 0.32/0.606 
 Crude protein 21.0 20.9 20.8 21.0 20.8 0.29/0.956 
 Ether extract 4.15 4.34 4.45 4.38 4.40 0.07/0.092 
 Ash 2.49 2.51 1.74 2.48 2.71 0.55/0.767 
CP15, CP17, CP19, CP21 and CP23 were the treatments contained different crude protein levels of 15, 
17, 19, 21 and 23% in DM, respectively. Means with different letters within the same rows are 
significantly different at the 5% level. 
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 The carcass and thigh meat weights were significantly different 
(P<0.05) by increasing CP levels in the diets with the highest values at the 
CP21 diet (1,289 and 383g, respectively). However, carcass percentage was 
not significantly different (P>0.05) among the treatments and it was 52.6, 
52.3, 52.6, 52.3 and 52.8% for the CP15, CP17, CP19, CP21 and CP23, 
respectively. The carcass percentage in this experiment was lower than that 
reported by Abedo et al. (2012) from 58.1 to 59.3%. The chemical 
compositions of meat were not significantly different (P>0.05) among 
treatments. This indicated that the dietary CP levels did not effect on chemical 
composition of rabbit meat. De Blas and Wiseman (2010) stated that there was 
no variation of meat quality when studying dietary protein content on the 
rabbit meat. 
 4.2.4 Nutrient digestibility and nitrogen retention 
 Nutrient intakes, digestible nutrients and nitrogen retention of 
experimental rabbits fed different dietary CP levels were presented in table 
4.7. 
Table 4.7 Nutrient intakes, digestible nutrients, and nitrogen retention of experimental 
rabbits 
 Treatment 
Items CP15 CP17 CP19 CP21 CP23 SEM/P 
Nutrient intake (g/rabbit/day) and metabolizable energy (MJ) intake 
Dry matter 53.4 53.3 52.7 52.7 52.6 0.28/0.265 
Organic matter 49.7 49.6 49.1 49.2 49.1 0.27/0.290 
Crude protein 8.00a 9.02b 9.98c 11.1d 12.1e 0.04/0.001 
Ether extract 2.19a 2.19a 2.10b 2.04c 1.96d 0.01/0.001 
Neutral detergent fiber 17.2a 17.1ab 16.8ab 16.7b 16.7b 0.09/0.009 
Acid detergent fiber 12.4a 12.4a 12.1ab 12.0b 11.9b 0.06/0.003 
ME, MJ/day 0.620 0.616 0.610 0.611 0.610 0.003/0.237 
 Digestible nutrient, g/rabbit/day 
Dry matter 37.0a 37.7ab 38.1ab 39.0b 38.5b 0.28/0.008 
Organic matter 35.0a 35.5ab 35.9ab 36.7b 36.2ab 0.29/0.027 
Crude protein 5.68a 6.57b 7.44c 8.54d 9.33e 0.06/0.001 
Ether extract 1.61ab 1.64ab 1.64ab 1.65b 1.57a 0.01/0.018 
Neutral detergent fiber 9.29a 9.79ab 10.1ab 10.6b 10.5b 0.17/0.004 
Acid detergent fiber 4.44b 4.84ab 4.86ab 5.13a 4.80ab 0.12/0.039 
Nitrogen balance 
N intake, g/rabbit/day 1.28a 1.44b 1.60c 1.77d 1.94e 0.007/0.001 
N retention, g/rabbit/day 0.77a 0.89b 1.02c 1.18d 1.21d 0.01/0.001 
N intake, g/kgW0.75 1.10a 1.17b 1.24c 1.34d 1.47e 0.01/0.001 
N retention, g/kgW0.75 0.66a 0.72b 0.79c 0.89d 0.91d 0.01/0.001 
N retention/N intake, % 59.8a 61.4ab 63.9c 66.5d 62.3bc 0.41/0.001 
CP15, CP17, CP19, CP21 and CP23 were the treatments contained different crude protein levels of 15, 17, 
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19, 21 and 23% in DM, respectively; N: nitrogen. The numbers with different superscript letters in the 
same row were significantly different (P<0.05) 
 Nutrient intakes of growing Californian rabbits at 12 weeks of age had 
the similar pattern of the whole experiment. The digestible nutrients were 
significantly different (P<0.05) among treatments. The digestible DM and OM 
for CP21 and CP23 treatments were significantly higher than others, although 
DM and OM intakes were similar (P>0.05) among treatments. It could be 
explained that the apparent digestibility of DM and OM was significantly 
improved (P<0.05) by increasing soybean extraction meal in the diets being 
69.4-73.9% and 70.5-74.7%, respectively. The findings in this experiment 
consisted with the results of Amber (2000) in which the growth rate and 
nutrient digestibility increased significantly (P<0.05) when increasing soybean 
meal levels in the New Zealand White rabbit diets. The digestible CP values 
(g) was proportionally increased by increasing levels of soybean extraction 
meal in the diets. It was 5.68, 6.57, 7.44, 8.54 and 9.33 g for the CP15, CP17, 
CP19, CP21 and CP23 treatments, respectively. The results of digestible CP 
(g) in the present experiment was consistent with those reported by Dong and 
Thu (2012) being from 7.96 to 9.40 g/rabbit/day. The nitrogen retention was 
significantly different (P<0.05) among the treatments with the significant 
higher values of the CP21 and CP23 treatments. This resulted in the rabbits of 
CP21 and CP23 treatments having higher values of daily weight gain, final 
live weight, carcass quality and economic returns. However, the economic 
analysis showed that profit for the CP21 diets was higher than CP23 diets 
because of low feed cost and high income. 
 4.2.5 Summary 
 The conclusion of the study was that growth performance, nutrient 
digestibility, carcass quality and economic returns were improved for 
Californian rabbits fed the diets containing 19% and 21% CP. The improved 
CP intake