Livestock Research for Rural Development 14 (6) 2002

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Protein level and amino acid supplementation in pigs fed sugar cane molasses. Growth performance and carcass traits

Carmen María Mederos, J M Pérez Valdivia, J L Piloto, E Alemán and Rosa María Martínez 

Swine Research Institute, PO Box 1, Punta Brava, La Habana, Cuba
iip00@ceniai.inf.cu 
 

Abstract 

Growth performance was compared in growing-finishing pigs fed ad libitum enriched sugar cane molasses and graded levels of full-fat soybeans. Forty-eight  Yorkshire male pigs (mean  13.2 kg live weight) were allocated to a randomized complete block design in a 2x2 factorial arrangement. Factors were protein supply according to conventional requirement or 25% less than this; and lysine/methionine supplementation. 

Reducing the protein level resulted in 10% slower growth and 13% poorer DM feed conversion, but with no effect on carcass lean meat content and backfat thickness.  There was no effect of amino acid supplementation on these traits.  

It is suggested that a pig feeding system based on enriched sugar cane molasses and full-fat soybean supports similar performance and carcass traits to those obtained with a conventional cereal based diet. Supplementation with synthetic lysine and methionine is unnecessary.  

Keywords: Amino acids, carcass, conversion, full-fat soybeans, growth, pigs, protein, sugar cane molasses

Introduction 

It is well known that feeds account for 70 to 80% of the cost of pig production throughout the World, including Cuba. Protein represents the most expensive component of the diet, and suitable sources are not always readily available, which makes this ingredient an important element in the competitiveness of non-conventional feeding systems for pigs (Figueroa 1996). Several reports suggest that the protein supply for growing-finishing pigs can be reduced by 25 to 30% below recommended conventional levels (NRC 1988, 1998) when the basal diet is either sugar cane juice (Estrella et al 1986; Sarría et al 1990; Bui Huy Nhu Phuc 1994) or molasses type "B" (Maylin et al 1989; Figueroa et al 1991; Mederos et al 1996).

A decrease in protein requirements for optimal pig growth could be related to the fact that sugar cane products are practically devoid of protein. Therefore, protein supplementation of diets formulated to contain high amounts of sugar cane products has been based on the use of torula yeast, soybean meal or full-fat soybeans. These protein sources have a good balance of essential amino acids, such that the overall diet is superior in this respect compared with conventional diets in which cereals such as maize provide from 30 to 70% of the protein (see Figueroa 1996). The amino acids lysine and methionine + cystine are the first limiting amino acids when vegetable protein sources such as soybeans provide most of the protein as can be the case in diets based on sugar cane juice or sugar-enriched  molasses.  Nevertheless, several attempts to define methionine supplementation in these types of feeds for growing-finishing pigs have not been conclusive (Maylin 1985; 1988; Lezcano 1989). On the other hand, the role of lysine supplementation in sugar cane molasses diets has not been studied up to the present. 

The aim of the present experiment was the study of the influence of graded levels of protein and of lysine and methionine supplementation on growth performance and carcass traits of growing-finishing pigs fed enriched, sugar cane molasses and full-fat soybeans.   

Materials and Methods 

Forty-eight Yorkshire male pigs (mean live weight 13.2 kg) were used to evaluate performance and carcass traits according to a randomized complete block design in a 2x2 factorial arrangement. Factors were low (LP) or high (HP) levels of protein intake, and lysine/methionine supplementation in sugar cane molasses based diets. Protein intake was from full-fat soybeans treated in a cooker designed at the Institute (thermo-mechanical reactor, RMT-1.5) during 30 min at 115^oC and 0.7 bar of pressure, in order to neutralise the anti-nutritional factors present in the raw beans. The urease index (RMACE 1976) as measured in representative samples from the cooked full-fat soybeans was on average 0.03 UA, which was similar to that reported by Delgado et al (1998) for imported soybean meal samples (0.04 UA). The cooked full-fat soybean had on average 30% dry matter (DM) and 38% crude protein (Nx6.25) in dry basis. The feeding scale for low and high protein intake and levels of vitamins and minerals given throughout the trial are shown in Table 1.  

The supplement used in treatments without amino acid supplementation (NVM1) contained: vitamin and mineral premix 2.32, common salt 3.64, dicalcium phosphate 11.59, zeolite 32.54, maize 50.0% in air dry basis. In the case of treatments with amino acid supplementation, the supplement (NVM2) contained:  vitamin and mineral premix 2.28, common salt 3.58, dicalcium phosphate 11.38, zeolite 31.89, methionine 0.31, lysine 0.56, maize 50.0% in air dry basis. The basal diet consisted of enriched sugar cane molasses prepared in a ratio 55:45 (fresh basis) with sugar cane final molasses and raw sugar, considered unsuitable for human consumption. 

The animals were housed in individual metallic pens of the flat deck style, each provided with a trough and a drinking nipple, in an open stable during the first five weeks of the trial. Thereafter the animals were housed individually in pens with cement floor in another open stable.

There was no previous adaptation of the animals to the experimental diets. Every day at 8:00 am the pigs were offered the cooked full-fat soybean mixed with the vitamin and mineral supplement. This feed was consumed completely in about two hours. Thereafter, the enriched sugar cane molasses was given ad libitum.  The residues of sugar cane molasses were recorded daily before the distribution of the protein supplement. Water was always available. 

The pigs were weighed every two weeks, and were slaughtered on reaching approximately 98 kg of live weight. Carcass yield and backfat thickness were determined on the hot carcass. After 24 hours of refrigeration the dissection of the right half carcass  was made according to the procedure outlined by Kielanowski and Osinska (1954). The commercial cuts were separated and the amounts of lean meat, fat and bone were determined. All carcass data were adjusted according to the cold carcass weight.  The commercial yield included the head as part of the carcass. 

The chemical composition of the cooked full-fat soybean, including the analysis of amino acids, was determined in three representative samples obtained from batches of the soybean utilized in the experiment. Methods used in the characterization of the samples were described elsewhere (Mederos et al 1995). 

Data were subjected to analysis of variance according to Steel and Torrie (1980) recommendations.  

Results  

Table 3 lists the chemical composition of the samples of cooked full-fat soybean utilized in the trial, and the data corresponding to soybean meal composition as described elsewhere (NRC 1998). The most relevant contrast between both sources of protein could be the ether extract and gross energy content. As it is well known, soybean meal is the residue after the extraction of the oil from the beans by industrial processes.

 There were no significant interaction between levels of protein and amino acid supplementation in any of the measured traits, and the results are reported showing the main effects (Tables 3 and 4). Increasing the protein level resulted in 10% improved growth rate and 13% better DM feed conversion. However, protein conversion (g dietary protein/g live weight gain) favoured the diet with the low protein level.

Amino acid supplementation appeared to reduce slightly the growth rate but had no effect on intake or feed conversion (Table 4).

The carcasses of pigs fed the lower level of protein contained more bone, but had similar proportions of lean meat and fat (Table 5). Backfat thickness did not differ between protein levels.   Amino acid supplementation had no effect on carcass traits (Table 6). 

 
Discussion 

It is considered that the performance traits on the one hand, and the carcass indices on the other, are indicative of a high level of efficiency in the feeding system, comparable with what could be expected on a conventional diet of cereal grain and extracted soyabean meal. The lack of response to supplementary lysine and methionine confirms the nutritional adequacy of both the low and high protein diets, in terms of the balance of amino acids. These results are broadly in agreement with those reported by other researchers for growing pigs given diets based on sugar cane juice (Estrella 1986; Motta et al 1994; Bui Huy Nho Phuc1994), high test molasses (concentrated, partially inverted sugar cane juice) or "B" type molasses (Maylin et al 1989; Figueroa et al 1991).

The choice of protein level is a question of economics. Reducing the protein supply by approximately 25% led to a 10% reduction in growth rate and 13% poorer feed conversion. The carcass quality in terms of the content of lean meat was not affected by the protein level, thus the economics in favour of the high or low protein diet will be determined by the relative market prices of full-fat soybeans and enriched molasses, and the additional labour cost of keeping the low protein pigs an additional 6 days to reach slaughter weight.  It is estimated that the pigs fed the low protein diet consumed on average 168 kg enriched molasses and 80.0 kg of full-fat soybeans (both on DM basis), compared with 124 and 94.4 kg of these feeds, respectively for the high protein diet. For the low protein diet, the saving of 14.4 kg of soybeans has to be offset against the extra expense of 64 kg of enriched molasses.

Conclusions 

It is considered that the use of enriched sugar cane molasses and cooked full-fat soy beans as the basal diet for growing-finishing pigs supports equivalent performance and carcass traits as conventional diets based on cereals. There was no advantage for using methionine and lysine supplementation in this feeding system. 

There was a moderate reduction in average daily gain and a poorer feed conversion with a daily protein allowance of 75% of NRC (1998)  recommended standards, but no change in carcass quality. Nevertheless, the saving in protein supplementation  could be an attractive alternative from the point of view of economy, in situations in the tropics where energy feeds are cheap and readily available and protein sources are expensive.
 

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 Received 7 June 2002

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