Performance traits of pigs fed sweet potato (Ipomoea batatas L.) foliage ad libitum and graded levels of protein

C González, Ivonne Díaz, H Vecchionacce 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
jlyca@yahoo.com

Abstract

A growth trial was conducted with a total of 40 crossbred castrate males and female pigs (1:1) of 29.3 kg mean initial live weight distributed at random into five treatments to study the effect of feeding ad libitum fresh foliage from sweet potato (Ipomoea batatas L.) and graded levels of protein. From 30 to 60 kg the animals received 1.6 kg/day of a feed mix (20.7 MJ/kg) containing 25.1, 23.7, 17.0 or 13.2% protein. From 60 to 90 kg the pigs were fed with 1.8 kg/day of a feed mix (22.0 MJ/g) containing 23.0, 20.6, 14.5 and 9.9% protein. In both periods the animals were fed fresh sweet potato foliage (SPF) ad libitum.

In both periods feed intake decreased (P<0.05) with less protein in the feed. Intake of SPF showed a non linear response (P>0.10) with lower values for intermediate levels of protein in the feed. There was no treatment effect on carcass traits of the animals. For the overall growth and finishing periods, the mean daily gain (721 g) and feed conversion (2.40 kg DM/kg gain) were the best with a combination of 23.7/20.6% protein in the feed supplement (1.6/1.8 kg per day).

It is suggested that it is possible to obtain good performance traits in pigs fed fresh sweet potato foliage ad libitum, provided a feed supplement is given which contains either 23.7and 20.6% or 17.0 and 14.5% protein during the growing and finishing periods, respectively.

Key words: Carcass,  Ipomoea batatas (L.), performance, pigs,sweet potato foliage

Introduction

A trend has been observed in the majority of tropical countries to search for alternative feed resources for animal feeding. This should allow the total or partial substitution of cereals and soybean traditionally employed for feeding pigs. Roots and tubers are amongst those feeds that could potentially substitute the conventional animal feeds, due to their agro-ecological advantages in tropical areas, such as high yields in roots and foliage (Machin 1992). In the particular case of sweet potatoes, the use of foliage as animal feed has received less attention than roots  (Nwokolo 1990; Scott 1992). Even less attention has been paid to the potential advantage of the use of an integrated sweet potato-pig production system (González et al 1994), where the use of roots and foliage in an integral form should decrease the feeding costs in pig production (González and Díaz 1997).

One of the main constraints for the use of tropical foliages could be the high content of the  fibre fractions, therefore determining a decrease in voluntary feed intake and a deleterious effect on performance traits of economic interest (García 1998). In this connection, the use of fibrous feeds for pigs precludes a search for an optimum energy: protein ratio in order to warrant an adequate feed intake (Chiba et al 1991).

The aim of the present experiment was the evaluation of voluntary feed intake of fresh foliage from sweet potato and performance and carcass traits when growing-finishing pigs are fed graded levels of protein in the ration in a tropical environment.

Materials and methods

General

Sweet potato foliage (SPF) was harvested daily from the Faculty of Agronomy farm, at Maracay. A representative sample of this foliage was obtained from the entire period of harvesting, and its characteristics are set out in Table 1. Analyses of the foliage and feeds were conducted at the University following procedures described by the AOAC (1990) and Van Soest et al (1991) for detergent fractions of fibre. Gross energy was determined by bomb calorimetry. All analyses were conducted in duplicate.

A relatively high protein and low NDF content were outstanding characteristics of the foliage employed in the current study.

Animals and treatments

Forty hybrid pigs (Yorkshire-Hampshire-Landrace-Duroc) of 29.3 kg initial live weight were used in the experiment, which lasted 90 days. The animals were distributed at random according to sex and weight into five treatments. Each treatment had the same number of replications of two pigs (one castrate male and one female). The pigs were housed in 1.5x1.4 m pens in an open stable. The pigs had free access to the dry feed supplement and the sweet potato forage in two feeders and to the nipple water drinkers in every pen. During the trial the live weight of the pigs and feed consumption were recorded every two weeks. Feed refusals were recorded daily.

Five treatments were evaluated during the experiment: a control, conventional diet given ad libitum with no SPF, and another four treatments consisting of  chopped, fresh SPF given ad libitum, and a fixed amount of supplement containing graded levels of protein, which varied in characteristics during the respective growing and finishing periods (Tables 2 and 3). All the supplements had a similar gross energy content.

When the animals reached 90 kg live weight they were fasted during 24 hours, then slaughtered for carcass analysis. Carcass yield was calculated prior and after refrigeration at 4^oC during 24 hours. Then the different carcass traits were determined in the cold material (Gonzalez et al 2002). In addition all the organs from the digestive system were weighed after being thoroughly washed. The length of the duodenum, caecum and small intestine was established with the aid of a graduated ruler.

The data were analyzed according to a one-way classification and means comparison was made by the Duncan's new multiple range and multiple F test (Duncan1955) as described by Steel and Torrie (1980). The pen with two animals was considered the experimental unit.

Results and Discussion

Performance traits

It was observed that protein intake was similar among pigs fed the control diets and those from treatments with approximately 25 and 23% protein in the supplement (Table 4). Daily protein intake was less (P<0.05) with lower protein content in the supplement. Total DM consumption was reduced when SPF was fed as compared with the control (P<0.05). On the SPF diets, intake of SPF was highest when the protein content of the supplement was lowest. Live weight gain was lower on the SPF diet containing the supplement with the lowest protein content, as compared with all other diets.

The SPF diet in which the supplement had the lowest concentration of protein, and intake of SPF was highest,  resulted in the worst feed conversion, but all other SPF diets were better than the control for this parameter. These results are in agreement with those of Malynicz and Nail (1973) with pigs fed SPF in Papua. It is possible there was a reduced availability of nutrients with increasing levels of SPF consumed by the pigs (Domínguez and Ly 1997) due to an increase in the rate of passage of digesta through the alimentary canal (Díaz et al 1997; Díaz 1998). Poorer availability of nutrients may result in a poor efficiency of feed utilization by the animals.

Results for the finishing period (Table 5) were similar to those for the growing period, with lowest DM and protein intake, lowest live weight gain and poorest feed conversion for the SPF diet with the lowest protein content in the supplement.Intake of SPF was not apparently high enough to provide more protein to the animals.