Livestock Research for Rural Development 14 (6) 2002

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Growth performance and carcass traits in pigs fed sweet potato (Ipomoea batatas [Lam.] L) root meal

C González, Ivonne Díaz, Milagro León, H Vecchionacce, Alexia Blanco and J Ly* 

Faculty of Agronomy, Central University of Venezuela,
PO 2101 El Limón, Maracay, Venezuela
caraujo2@telcel.net.ve
* Swine Research Institute, PO Box 1, Punta Brava, La Habana, Cuba
julioly@utafoundation.org

Abstract 

A growth trial was conducted with a total of 40 crossbred castrate males and female pigs (1:1) of approximately 35 kg initial live weight distributed at random into five treatments to study the effect of feeding ad libitum diets, in which maize and sorghum were substituted by graded levels of sweet potato (Ipomoea batatas L.) root meal (SPRM, 0, 25, 50, 75 and 100% respectively). 

Animals receiving the diet with no cereals had the poorer performance traits as compared with those from the control diet (SPRM, 0%) whereas those fed graded levels of SPRM showed an intermediate response, during growing (35-60 kg) and finishing (60-90 kg) phases. Overall, SPRM had no influence on feed intake and very little effect on daily gain, but  feed conversion ratio was negatively affected by the presence of SPRM (R² = 0.81). Results from pigs with 75% of substitution of cereals in the diet were similar to the others with lower levels of sweet potato in the feed. There was no effect of treatment on carcass traits. An increase in pancreas weight found in pigs fed graded levels of SPRM suggests that some anti-nutritional factor could have negatively affected performance traits of animals through some disturbance of digestive processes.  

It is suggested that sweet potato root meal can provide 54and 58% of the diet during the growing and the finishing phase, respectively, making it possible to replace 75% of the cereal components.

Key words: Carcass,  conversion, growth, Ipomoea batatas (Lam.) L., pigs,  sweet potato roots

Introduction 

Sweet potato (Ipomoea batatas (Lam.) L.) is a tropical convulvalacea which has received some attention as a possible animal feed (Machin 1992; Scott 1992), due to its relatively abundance in the tropical area of the World. Some literature reviews have been published concerning the use of the roots for growing pigs (Nwokolo 1990; Pérez 1997). 

Although sweet potato roots possess several advantages to be used as a common animal feedstuff, such as its high rate of growth year round with a minimum of culturing manipulation (González 1994; González and Díaz 1997), there are some constraints concerning its use, and its main limitation could be that sweet potato is a human staple food too (Wolfe 1992). However, in Venezuela, there is no marked human preference for sweet potato root products, and perhaps this is one reason which could explain why sweet potato is not commonly produced in this country in relatively high amounts. 

The aim of the present experiment was the evaluation of performance and carcass traits of pigs fed sweet potato root meal as a replacement of conventional cereal ingredients during the growing-finishing period.

Materials and Methods 

A growth trial was conducted with a total of 40 crossbred castrate male and female pigs (1:1), of approximately 35 kg initial live weight distributed at random into five treatments, to study the effect of feeds in which maize and sorghum were substituted by graded levels of sweet potato (Ipomoea batatas L.) root meal (SPRM, 0, 25, 50, 75 and 100% respectively). The sweet potato tubers were harvested from a plantation of the Faculty of Agronomy at Maracay, and were from an improved cultivar. The roots were chopped after harvest, sun-dried and ground prior to mixing with the other ingredients of the diets. The growth trial was divided into a growing and a finishing period of 49 and 46 days on average, respectively. Increasing proportions of soya bean meal were added to the diets containing increasing amounts of sweet potato root meal, to compensate for the lower protein content of the sweet potato compared with maize and sorghum.

The protein content of the diets was determined by a Kjeldahl procedure following AOAC (1990) recommendations. Gross energy was measured by combusting the samples in an adiabatic bomb calorimeter. 

Table 2 lists the composition of the diets used during the finishing period. The characteristics of the control diet were similar to that of the growing period, and again, a decrease in protein and gross energy content was apparent with increasing levels of SPRM in the diet.

The animals were housed in an open stable with cement floor provided with an individual trough and drinking nipple. Two animals, one castrate male and one female, were housed per pen of 1.5x2.5 m. 

When the animals reached 90 kg liveweight they were fasted during 24 hours, then slaughtered for carcass analysis. Carcass yield was calculated and after refrigeration at 4oC during 24 hours, different carcass traits were determined in the left half of the cold material. In addition, fresh liver and pancreas weight were determined at sacrifice of the animals. 

The data were analyzed according to a one-way classification and mean comparison was made by the Duncan’s new multiple range and multiple F test (Duncan 1955) as described by Steel and Torrie (1980). The pen with two animals was considered the experimental unit.

Results 

A slight difference in initial live weight was obtained in this trial (Table 3), but this effect was not significant, and therefore, no adjustment of data was made in any performance trait, during the conduction of the analysis of variance. Significant differences (P<0.05) among treatments were found for final weight of the animals. In this connection, it was found that treatments containing SPRM from 0 to 50% of cereal substitution did not have difference in growth rate. However, 75 and 100% of replacement of maize and sorghum determined a significantly (P<0.05) low daily gain in the pigs as compared to that of the animals from the other treatments. There was no treatment effect in feed consumption, and feed conversion was the lowest (P<0.05) in pigs fed SPRM with no cereals in the diet. 

The same trend observed during the growing period for daily gain and feed conversion ratio was found during the finishing period (Table 4), with significantly poorest values (P<0.05) for animals fed the highest substitution of maize and sorghum by SPRM in the diet. No treatment effect was observed on voluntary feed intake.

Overall performance traits for the growing and finishing periods are listed in Table 5. Obviously, these indices reflected the dietary influence found in both periods, and therefore, although differences in the increase in daily weight was only evident (P<0.05) for the pigs fed no cereals in the diet as compared with the other treatments, a decrease in daily gain was more evident with the increase of graded levels of SPRM in the diet (P<0.05). Nevertheless, treatments with SPRM substituting up to 50% of the maize and sorghum were similar to the control diet. Since the trial was finished when the animals reached approximately 90 kg of live weight, days in test were significantly higher in pigs fed diets with 100% of substitution of cereals by SPRM (P<0.05).

Table 5. Performance traits of growing-finishing pigs fed sweet potato root meal (35-90 kg)
	Cereal substitution by sweet potato root, meal, %
	0	25	50	75	100	SE ±
Initial weight, kg	36.6	37.2	35.1	35.9	34.6	1.1
Final weight, kg	89.6a	87.3ab	86.9ab	83.6b	74.3c	2.6*
Weight increase, kg	53.0a	50.1ab	51.8ab	47.7b	39.7c	4.5*
DM intake, kg/day	1.78	1.89	1.95	1.86	1.73	0.09
Gain, g/day1	632a	596ab	617ab	567b	473c	27*
Conversion, kg/kg2	2.82a	3.17ab	3.16ab	3.28bc	3.65c	0.20*
Days in test	84.0a	89.0a	89.4a	95.5a	118.5b	6.2*
1  Linear effect (R2 0.281; P<0.115) 2  Linear effect (R2 0.806; P<0.001) * P<0.05 abc Means without letter in common in the same row differ significantly  (P<0.05)

The analysis of regression revealed that treatment influence was not evident in feed intake and very little effect was found of SPRM on mean daily gain (P<0.115). However, feed conversion ratio showed a strong, negative response to the introduction of SPRM in the diets of the pigs, with poorer values for animals fed diets with 75 and 100% of substitution of cereals by SPRM with a straight relationship (R2 = 0.806; P<0.001) between both variables  (Figure 1).

Figure 1. Effect of sweet potato root meal on feed

Data corresponding to carcass traits are set out in Table 6. Not significant differences were encountered in any of the measurement made in the animal's carcass as influenced by the level of dietary SPRM. On the other hand, SPRM in the diet did not influence the weight of the liver, but the pancreas showed a significant dietary influence, with significantly (P<0.05) heaviest organs in pigs fed least cereals in the diet.  

Discussion

Results from the current investigation concerning feed consumption are not in agreement with those from other studies (Alvarado et al 1977; Acurero et al 1981; Moita et al 1991) where it has been observed that growing pigs decreased its voluntary feed intake with increasing levels of SPRM in the diet.  

Other investigations have obtained a similar response in growth rate to that found in this investigation, since several results have indicated a depression in daily gain when pigs are allowed to eat diets with sweet potato roots as the only source of energy (Koo and Kim 1974; Lee and Lee 1979; Soares 1989; Moita et al 1991). In this connection, previous data from our laboratory indicated that when roots and foliage from sweet potato were given mixed to the pigs, only a depression in growth rate was observed when no cereals were used in the diet (González et al 1997; García 1998). 

Data from the present trial are in accordance with other showing the same trend for feed conversion ratio (Alvarado et al 1977; Moita et al 1991). However, there are several reports suggesting that the efficiency of feed conversion is not deteriorated when sweet potato roots are the only source of energy in the diet (Tai and Lei 1970; Lee 1975; Lee and Lee 1979; Lee 1980; Lee and Yang 1982). 

Little is known concerning the influence of the inclusion of sweet potato roots in the diet on several carcass traits of pigs. However, some data refer no influence (Lee 1975) or even an improvement effect (Lee and Lee 1979) of sweet potato roots on carcass traits of pigs. The current study did not provide a comprehensive explanation for the increase of pancreas weight as affected by increased levels of sweet potato roots in the diet. However, since sweet potato roots do contain some anti-nutritional factors with anti-trypsin activity (see Pérez 1997), and this compounds could be influencing digestive processes where the pancreas is decisive. Ly et al (1999) found that in vitro pepsin/pancreatin digestibility of nutrients from sweet potato tubers is rather low, thus supporting results from pancreas enlargement observed in the present investigation. A deficiency in pre-caecal digestibility of nutrients in pigs fed sweet potato roots must be directly related with a deterioration in performance traits such as that found in the current study.

Conclusions 

It is suggested that with 54.2 and 57.7% of sweet potato root meal in the diet during the growing and the finishing phase, it is possible the substitution of 75% of the cereal components of the diets for pigs. More investigation is needed to improve the use of high level of sweet potato roots in diets for pigs.

Acknowledgments 

The authors thank the assistance of the librarian from the Swine Research Institute at Havana for his assistance in literature search, and to the staff from the Pig's Unit at the Faculty of Agronomy at Maracay for his support during the conduction of the present experiment.

References 

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