Preliminary studies on the use of chopped sugar cane stalk as the basal diet for fattening pigs

Fifty-six crossbred pigs were used in two experiments to evaluate chopped whole sugar cane stalk as the basal diet. In Experiment 1 the treatments were different combinations of fish meal, soya bean meal and meat meal with chopped cane at 17% (fresh basis) of liveweight; in Experiment 2 different offer levels of chopped cane were compared (17, 14, 10 and 6% of liveweight) with the same protein supplement. Estimates were made of sugar extraction rate by applying coefficients for ?Brix (total sugars) and the dry matter content of the stalk residue, after it had been chewed, determined by Sarria (1996) (Sarria Patricia, personal communication).

In Experiment 1 growth rates from 420 to 580 g/day were obtained on the chopped cane stalk when soya bean or fish meal were the protein sources; the control pigs (on maize-soya bean meal) grew at 650 g/day. The extraction rate of sugar by the pigs was estimated to be 67% resulting in a daily sugar intake of about 1 kg.

In Experiment 2, growth rate decreased linearly as the offer level of cane stalk was reduced (from 441 to 237 g/day) but sugar extraction rate increased from 67% at the 17% offer level to 84% on the lowest level (6% of liveweight).

Traditionally. small scale farmers in sugar cane growing regions have fed whole or chopped sugar cane to their pigs. Observations show clearly that the pigs chew the cane stalk to extract the juice and then "spit-out" most or all of the fibre; and that they grow slower than on cane juice or cereal grain based diets (Bon-Aimé et al 1989). However, there is little documented information about the efficiency with which this feed resource is used by pigs at different stages of the productive cycle; nor the degree to which the pigs extract the sugars which presumably is influenced by the offer level.

The following experiments were carried out at CATIE (Centro para la Agricultura Tropical, Investigación y Ensañanza) in Costa Rica in the early ‘80s and are discussed in the light of more recent developments with sugar cane as feed for pigs (Mena et al 1986; Sarria et al 1990).

Thirty-six crossbred pigs (Large White x Duroc) with an initial weight of 31 kg and approximately 3.5 months of age were allocated by sex and weight to six dietary treatments with two replications (pens of 3 pigs). The diets were:

The concentrate used for the control group was a mixture (%) of maize 53, rice bran 34, meat meal 6, soya bean cake 6, salt 0.5 and 0.5 of mineral and vitamin supplement. On the experimental treatments, the sugar cane stalk was fed chopped in small pieces using a chopping machine for forages; the chopped pieces were put on the floor twice a day. The offer level was enough to let the pigs extract the juice and to leave a residue every day. There was no basis on which to adjust the amount to offer so the method used was to offer three times the estimated intake for all the treatments. The protein supplement was fed according to the requirements of NRC (1979). Additionally the pigs received a mixture of mineral and vitamins.

Data for live weight gain, final weight and feed intake were recorded. The experiment ended when the pigs on the control treatment reached a mean liveweight of 90 kg.

Twenty crossbred pigs (Duroc x Yorkshire) with an initial weight of 26 kg and approximately 3 months of age were allocated by sex and weight to fourth groups of three pigs and 4 groups of two pigs. There were four treatments representing offer levels of cane stalk of 100, 75, 50 and 25% of that used in Experiment 1. There were two replications (one pen of 3 pigs and one pen of pigs) of each treatment. The diets were:

A protein supplement was used based on 50% fish meal and 50% soya meal; it was fed in amounts calculated to supply the protein requirements recommended by NRC (1979). The sugar cane stalk was chopped and offered on the floor twice daily. Amounts offered and refused were recorded. Liveweights were taken at the beginning and end of the trial.

The mean values for liveweights and feed intake are in Tables 1 and 2 for experiments 1 and 2, respectively. The residues are composed of fibre, sugar and saliva, representing cane stalk which has been chewed and then discarded, after part of the juice has been extracted. It has been diluted with saliva and is of much lower dry matter content than the original stalk. Thus simple estimates of intake by subtracting residues from amounts offered have no meaning. Similarly, estimates of dry matter intake are also confounded, in this case by the fact that the sugar in the dry matter is obviously less in the residue than in the material offered. In order to arrive at an approximation of intake of sugars and conversion rates, calculations were made using data derived by Sarria (1996, personal communication) from pigs fed similarly with chopped cane stalk and protein supplement. Sarria measured brix of the juice and the dry matter in both the cane offered and in the residue. The values were:

Using these figures the amounts of sugar in the cane offered (cane offered C=kg/day) can be calculated in the following steps as:

Sugars in cane = [C x (100-A)/100/(100-B) x B] (for every 80 kg of water there are 20 kg sugars)

Sugars in residue (D= fresh weight of residue) = [D x (100-A1)/100/(100-B1) x B1]

Table 1: Mean values for changes in liveweight and feed intake in pigs fed chopped sugar cane stalk with different protein supplements with estimates of sugar intake#

		--------Sugar cane stalk and--------------
	Control	FM	SBM	75MM	50FM	50MM

Liveweight, kg
Initial	30.8	31.1	33.5	28.2	30.9	27.7
Final	90	74	69.9	50.8	77.3	58.7
Daily gain	0.651	0.484	0.42	0.251	0.534	0.359
Feed intake, kg/day
Concentrate	2.59	-	-	-	-	-
Cane offered	-	9.23	9.23	9.23	9.23	9.23
Cane residue	-	6.25	6.18	6.61	6.24	6.52
Supplement	-	0.537	0.576	0.638	0.573	0.602
Sugar in:
Offered cane		1.62	1.62	1.62	1.62	1.62
Residue		0.525	0.520	0.556	0.525	0.548
Intake		1.09	1.10	1.06	1.09	1.07
Extraction rate, %##		67.0	67.8	0.656	67.5	66.1
Total DM	2.33	1.57	1.61	1.63	1.61	1.61
Conv. (DM)	3.58	3.25	3.84	6.51	3.01	4.48

#derived from coefficients calculated by Sarria (1996); see text
##100 x (sugar intake/sugar offer)

Table 2: Mean values of liveweight change and feed intake with estimates of sugar intake# for pigs fed different amounts of chopped sugar cane and protein supplement

	SC100	SC75	SC50	SC25

Liveweight, kg
Initial	26.5	26.1	26.5	26
Final	91.3	80.7	79.2	60.8
Daily gain	0.441	0.371	0.358	0.237
Feed intake, kg/d
Supplement	0.545	0.54	0.545	0.495
Sugar cane
Offered	10.1	7.4	5.3	2.5
Residue	6.56	4.54	2.76	0.76
Sugar in cane
Offer	1.77	1.30	0.93	0.44
Residue	0.55	0.38	0.23	0.06
Intake	1.22	0.91	0.70	0.37
Extraction, %	68.8	70.5	75.0	85.4
Total DM	1.71	1.40	1.19	0.82
DM convers.	3.87	3.77	3.31	3.46

It is assumed that the pigs in these experiments extracted the juice with the same efficiency as those studied by Sarria (1996), that the efficiency would not be affected by offer level and that the fibre in the sugar cane stalk did not contribute any nutrients. These assumptions are unlikely to hold in exact terms, however, they provide an oportunity to get some idea of the approximate amounts of sugars consumed and the overall feed conversion.

The observations in Experiment 1 show that reasonable growth rates can be obtained (450-500 g/day compared with 650 g/day on the cereal-based control) when sugar cane stalk is fed at the rate of 17kg (fresh basis) for every 100 kg liveweight and the protein supplement is provided by fish meal, soya bean or a mixture of the two. Results with meat meal were much poorer. It was estimated that actual intakes of sugars were of the order of 1 kg/day giving feed conversion ratios (DM basis) slightly poorer than on the control diet.

The average amount of cane fed (9.5 kg/day) would have yielded slightly less than 5 litres of juice if it had been passed through a 3-roll mill. This would not have been enough to support the recorded liveweight gains of 450-550 g/day on the basis of the recommendations of Sarria et al (1991). This implies that the pigs were extracting more juice by chewing than a 3-roll mill.

Thus the efficiency of the pig in extracting the sugars appears to be higher than that of a typical 3-roll mill used for artisan sugar production. Extraction rates in such mills are of the order of 50% (50 kg juice from 100 kg cane stalk) which is equivalent to about 56% of the total sugar in the cane. From the data in tables 1 and 2, it can be calculated that the pigs extracted about 67% in Experiment 1 when offer rate was high (17% of liveweight) while an extraction rate of 84% was reached in Experiment 2 when the amount offered was restricted to 10% of liveweight.

Lower offer level of cane and, as a result, higher extraction rate of sugars, reduces cost of inputs (the sugar cane) but causes a reduction in gross return (rate of liveweight gain). Research is needed to establish the relationship between these contrasting criteria for different stages of the growth and reproductive cycles of the pigs.

Pigs grew satisfactorily (450-550 g/day) when given free access to fresh chopped sugar cane stalk (17% of liveweight) supplemented with soya bean meal or fish meal. Extraction rate of sugars was about 67% which is higher than what is achieved with a 3-roll mill used for artisan juice extraction.

As offer level was reduced, rate of gain in liveweight decreased linearly but extraction rate appeared to increase, reaching 84% at the 6% of liveweight offer level.