Research Article

Effects of Varied Levels of Amino Acid-Rich Sweet Potato Composite on the Reproductive Performance of Rabbit Does Reared in the Tropics

I.F. Olaleru and O.A. Abu
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Objective: The primary objective of this study was to investigate how varied levels of Amino Acid-rich Composite Sweet potato affected lactating performance and overall Reproductive Cycle Outcomes in does. Materials and Methods: The crude protein content and amino acid profile of leaf, roots and composite meal produced from 65% root and 35% leaves for two varieties of sweet potato (Ipomoea batatas Lam.) namely, TIS 87/0087 white flesh sweet potato (WFSP) and CIP 440293 orange flesh sweet potato (OFSP), were analyzed. Twenty-five rabbit does of mixed breeds (New Zealand White×California×Chinchilla) aged 6-7 months were assigned randomly to one of five experimental diets: T1 (control), T2 and T3 contained 25 and 50% orange-fleshed CSPM and T4 and T5 contained 25 and 50% white-fleshed CSPM. The diets comprised 10.6-12.6% crude fibre, 16.4-17.6% crude protein and metabolizable energy of 2610-2788 kcal kg–1. Results: The crude protein content in roots of 87/0087 (WFSP) and CIP 440293 (OFSP) were 3.32 and 8.04%, respectively. There was an appreciable higher value of crude protein in the leaf of TIS 87/0087 (11.18%) and CIP 440293 (11.26%), respectively. The crude protein content was least in composite WFSP (6.13%) and higher in composite OFSP (14.8 %). Total amino acid content ranged from 7.704 to 18.35 and 23.717 to 23.863 g/100 g protein for root and leaf samples, respectively. The overall feed intake of does in all the treatments was not significantly different (p>0.05). Does fed on diets T4 and T5 had the largest litter size at birth (5.00) compared to the other treatments. In different treatments, there was no significant difference in initial average body weight, gestation duration, or litter weight of does at birth. Conclusion: The high content of crude protein and its quality amino acids in the two varieties of the sweet potato composite meals placed it on a commensurate level for consideration as a potential replacement for expensive conventional protein source in livestock diet.

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  How to cite this article:

I.F. Olaleru and O.A. Abu, 2022. Effects of Varied Levels of Amino Acid-Rich Sweet Potato Composite on the Reproductive Performance of Rabbit Does Reared in the Tropics. Pakistan Journal of Nutrition, 21: 12-22.

DOI: 10.3923/pjn.2022.12.22

Copyright: © 2022. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.


Nutrition is one of the factors that could influence reproductive performance by limiting productivity especially during pregnancy and lactation1. An understanding of nitrogen nutrition, especially protein and amino acid needs, is therefore critical for developing productive and cost-effective domestic animal diets.

The evaluation of the protein value of a feedstuff in terms of nitrogen and amino acid availability is the first step in formulating balanced meals with a lower crude protein content.

Growing rabbits require diets that contain certain proportions of 10 of the 21 amino acids that make up proteins2. With two extra amino acids that can partially replace two of the necessary amino acids, they are known as the basic or essential amino acids. The list include: Arginine, histidine, leucine, isoleucine, lysine, phenylalanine plus tyrosine, methionine plus cystine, threonine, tryptophan and valine arginine, histidine, leucine, isoleucine, lysine2. The nutrition of rabbit in Nigeria is primarily based on forage whose growth and availability in the dry season cannot sustain all-year rabbit production3 and had mitigated the potential increase in rabbit production.

More importantly the reproductive phase of rabbits is around 45 percent of the entire life. As a result, factors impacting doe performance during lactation will affect kit development and survival before and after weaning, as well as meat yield and profit on commercial farms. Aside from environmental variables like high temperatures, poor feed component quality can affect rabbit and other species' productivity and reproduction. Maertens et al.4 found that rabbit kits primarily rely on mothers' milk up to 21 days for survival and growth.

The conflicting requirements of gestation and lactation have a deleterious impact on milk output and composition, as well as body condition, reproductive traits and milk supply5. Dietary needs of the reproductive doe on the other hand, are diametrically opposite, since they require a lot of energy to stimulate lactation and a lot of fibre for digestive health6.

Olaleru et al.7 reported that composite sweet potato can support the growth performance of kids of rabbit doe without adverse effect on the reproductive performance of rabbits.

Read et al.8 reported that from a few days before kindling until 25 days postpartum, a diet high in quality protein and energy is required to meet the high nutritional needs during this time, followed by a diet high in fibre until weaning to protect kits from digestive problems after weaning. However, in terms of litter health, this strategy is ineffective in meeting the demands of pregnant and lactating does at the same time9, leading the does to lose body condition. As a result, introducing a feed component that may provide high fibre and protein without compromising the energy level required to fulfil the rabbit's physiological condition could improve doe and kit performance.

The sweet potato plant has a high energy content and can potentially replace the conventional maize in rabbit diet10. The sweet potato roots have a higher protein content when compared to the root crops11. Sweet potato leaves are high in critical amino acids like lysine and tryptophan, which are constantly short in grains. As a result, sweet potato may easily substitute grain-based animal diets12. There are lots of information on the usage of sweet potato plant but there is limited information on the use of the composite sweet potato meal on the reproductive performance of rabbits. Therefore, this study was conducted to evaluate the amino acid profiles and protein quality of composite sweet potato meal from two varieties as well as the reproductive performance of does raise on diets containing the composite sweet potato.


Animals and experimental design: The experiment was conducted at the University of Ibadan's Rabbitry Unit, Teaching and Research Farm, in Ibadan, Oyo State, Nigeria. A total of twenty-five does comprising of mixed breeds (New Zealand White×California×Chinchilla) were used for this experiment.

The does aged 6-7 months were allocated randomly into five treatments each treatment having five does. The animals were caged individually. Throughout the duration of the experiment water and feed were offered ad libitum. Each doe was housed in an individual standard sized galvanized battery cage equipped with drinkers and feeders. Rabbit does were fed a pellet diet containing the test ingredients, The diets were formulated (18.32% crude protein and 10.76 MJ kg–1 digestible energy) to meet the National Research Council recommendation for daily nutritional requirements for does. Five proven bucks were used to mate the does across the treatments. The twenty-five does were weighed prior to mating and at parturition for the litters and final weight at the end of the experiment. Kits were weaned at 6 weeks of age. The kits were weighed at birth and weekly till weaning. Feeds intake and refusals were weighed daily and samples were analysed for proximate components using the methods of AOAC13. Milk yield was estimated according to Lebas et al.14:

Milk production of does = (Live weight of new born at 21 days of age-Live weight of new born)×1.18

Ethical approval: The study received the ethical approval of the Institutional Animal Care and Use Committee, through the Agricultural Biochemistry and Nutrition Unit of the Department of Animal Science, University of Ibadan, Nigeria.

Varieties of sweet potato studied: Two varieties of sweet potato plants CIP 440293 (Orange flesh) and TIS 87/0087 (White flesh) were harvested from the National Roots Crops Research Institute, Umudike, Abia State, Nigeria from May 2017 to September 2017. The harvested whole sweet potato roots were cleaned, chipped to about 2 mm thickness slices manually using a sharp knife and shade dried for 3-5 days with an average temperature of 32.9°C during the dry season. The leaves and vines were also shade dried for 3-5 days with an average temperature of 32.9°C during the dry season and they were thereafter milled to a fine powder and their chemical composition was determined.

The composite sweet potato meal contains 65% whole root and 35% of the leaves and vines15 and fed at the graded levels. The diets were labelled as T1-control, 25 and 50% of orange flesh sweet potato composite meal were T2 and T3, respectively, 25 and 50% of white flesh sweet potato composite meal were T4 and T5, respectively. Other ingredients used include: -soybeans, maize offal, maize, rice offal, premix, bone meal and salt. The diets were formulated to meet 16% crude protein15 (Table 1).

Sample preparation and extraction: Selected healthy roots from each variety were washed and cut into tiny parts using a knife afterwards thoroughly mixed for uniformity to attain samples weighing 400 g hence placed in a paper bag and dried to a constant weight in a hot air oven (DHG-9055A, Memmert Germany) set at around 105°C. For leaf samples, freshly developed leaf tips weighing about 200 g were washed, chopped into small pieces and oven dried at 70°C to achieve constant weight. The oven dried leaf and tuber samples were ground into a fine powder using an electronic mill (FW 100, Yusung Industrial Ltd, China). The powder was sieved using a 0.425 mm mesh size. The dry powder samples were then packed in airtight polyethylene bags and stored at 4°C for further analysis.

Crude protein determination: The Kjeldahl method was used to determine the Crude protein content16. A carefully weighed 0.5 g sample was digested with a known quantity of concentrated H2SO4 (Sigma-Aldrich, USA) in the Kjeltec digestion apparatus (Gerhardt vapodest, Germany). The digested material was distilled after being treated with alkali. The ammonia emissions were collected in a Kjeltec Automatic Distilling Unit with 4% boric acid. The ammonia generated by the digestion was retained in the boric acid, which was then titrated with 0.1N hydrochloric acid (HCl) (Sigma-Aldrich, USA). The protein content was calculated by multiplying the nitrogen concentration by a factor of 6.25.

Determination of amino acid profile of sweet potato varieties: In this study, Amino acid profile was determined as described by Ayalew et al.17 with modification. Amino acid analysis was carried out at the Evonik Nutrition and Care GmbH laboratory in Germany. Ninhydrin-Derivatized analysis using an amino acid analyser (Hitachi L-8800 Amino Acid Analyzer, Tokyo, Japan) was used to perform the test, which included performic acid oxidation and acid hydrolysis of amino acids.

The amino acids alanine, arginine, aspartic acid, cysteine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline and serine were determined using this approach. Norvaline was used as an internal benchmark to uniformly recover each amino acid from injection to injection. The method was calibrated across a range of 0.08-22.7% for each amino acid. Since acid hydrolysis entirely destroys tryptophan, a separate hydrolysis procedure is required for accurate measurement, hence tryptophan (Trp) was not studied18.

Evaluation of protein quality: Based on the measured amino acid profiles, the nutritional value of the protein in the composite sweet potato meal was determined. The approach taken by Ayalew et al.17 was used. The ratio of total essential amino acids (TEAA) to total amino acids (TAA) in the protein was estimated using the Chavan et al.19 technique. The essential amino acid composition's amino acid score was computed using the method described by Chavan, et al.19:

Essential amino acid index (EAAI) was calculated according to Ijarotimi and Keshinro20.

EAAI = √[n&(100a×100b×…100j)/(av×bv…jv)]


n is the number of essential amino acids, a, b …. j represent the concentration of essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine and valine) in the tested sample and av, bv…. jv is the content of the same amino acids in standard protein (%) (egg or casein), respectively.

Predicted biological value (P-BV) was calculated according to Mune-Mune et al.21:

P-BV = 1.09×EAAI-11.7

The predicted protein efficiency ratio (P-PER) was calculated by the regression equations as cited by Mune-Mune et al.21:

P-PER = −0.468+0.454(LEU)−0.105(TYR)

The nutritional index was calculated as cited by Ijarotimi and Keshinro22:

Nutritional index (%) = EAAI×% protein/100.

Statistical analysis: Data were analyzed using one-way analysis of variance (one-way ANOVA), followed by Duncan's multiple range tests using SAS 9.1 statistical package23 (SAS, 2004). Differences among treatments were detected at a 5% level of significance.


Crude protein content and amino acid composition: The dry matter of the root and leaves of the two varieties of sweet potato ranged from 91.77 to 92.53% and were not significantly different from each other but were comparable to maize.

The amino acid profile of the two varieties of sweet potato is presented in Table 2. The methionine value was the highest (p<0.05) in maize (0.21g/100 g protein) followed by white flesh sweet potato (WFSP) leaves and vine, orange flesh sweet potato (OFSP) leaves and vine and OFSP root with 0.140, 0.135 and 0.107 g/100 g protein respectively with the WFSP root having the least value of 0.053 g/100 g protein. The value of cysteine and methionine followed a similar trend, with the maize having the highest value (0.230) and white flesh sweet potato having the least value (0.044). Combination of methionine and cysteine was absent in maize.

The amino acids profile of sweet potato leaf and vine showed that lysine (0.438-0.414 g/100 g protein) was the highest for WFSP and OFSP, respectively. Threonine value also followed a similar trend with the orange and white flesh sweet potato leave and vine having the highest value of 0.429 and 0.426 g/100 g protein respectively, values which were very close. Threonine value for maize was higher than the values of both varieties of the roots. The Arginine value in the white flesh, orange flesh sweet potato leaves and vine and that of maize were really close with values of 0.524, 0.500 and 0.485 g/100 g, respectively. Isoleucine value in maize is 0.385 and it is lower than that of WFSP and OFSP leaves and vine with values 0.418 and 0.418 g/100 g, respectively.

Valine and leucine value showed a similar trend, maize has the highest valine value (0.535), which is closely followed by the WFSP leave and vine, OFSP leave and vine and OFSP root with values of 0.528, 0.526 and 0.332, respectively with the WFSP root having the least value (0.145). Maize has the highest value (0.330) for histidine. The two varieties of sweet potato has a value ranging from 0.148-0.053. There was a similar trend for Phenylalanine, Glycine, Proline, Alanine and Glutamic acid with maize having the highest values followed by the leaves and vines of the two varieties and the root having the least.

The amino acid profile of the composite meal of two selected sweet potato varieties based on their protein content is presented in Table 3. The OFSP has the highest while the WFSP has the lowest amino acid profile. Methionine value observed in OFSP meal was 0.192 while WFSP meal has a value of 0.097. The Cysteine value in the OFSP meal was 0.164 while WFSP meal has a value of 0.092, actually follow a similar trend with that of the Methionine. The OFSP meal and WFSP meal has a value of 0.356 and 0.189, respectively. For Lysine, the composite OFSP meal has the highest value (0.462) while the composite WFSP has the lowest value (0.225). Threonine value was the highest (0.508) in the composite OFSP meal and composite WFSP meal has a value of 0.258 which were far apart. The Arginine value in the composite OFSP meal is 0.59 while the composite WFSP meal has the least value of 0.249. Isoleucine value in the composite OFSP meal is 0.488 which is relatively far apart from the value of composite WFSP meal (0.237). The composite OFSP meal has the highest Leucine value (0.834) while the composite WFSP meal has a value of 0.398. Valine and leucine followed a similar trend, composite OFSP meal has the highest valine value (0.664) while the composite WFSP meal has the lowest value (0.315). For histidine, composite OFSP meal has a value of 0.23 while the composite WFSP meal has a value of 0.102.