The aims of this study were to determine the effect of the quality of sugar cane juice (sugar concentration), as influenced by season of harvesting, on the performance of fattening pigs given this feed as the basis of their diet. The hypothesis to be verified was that the feeding value of the juice for pigs would be lower for sugar cane harvested in the rainy season compared with cane harvested in the dry season.

The sugar cane used in the experiment had been planted at monthly intervals between July 1994 and 1995 in plots measuring 800 m². There were two treatments applied in each of two trials which were carried out consecutively in the wet and dry seasons. The treatments were: SCJ: Sugar cane juice and protein supplement; Control: Broken rice and protein supplement. The trials were done with different lots of pigs from July 1995 to November 1995 (Trial 1; wet season) and from December 1995 to May 1996 (Trial 2: dry season). Four groups each of 3 crossbred pigs (Large White x Mong Cai) were allocated to each of the two treatments in each of the trials. The initial weight at the start of each trial was 20 kg on average and the trial continued until the pigs reached an average of 70 kg liveweight (trial 1) and 65 kg liveweight (trial 2).

There were marked differences in the sugar content of the juice which was 40% higher in the cane stalk harvested in the dry season (°Brix of 22) than in the wet season (°Brix 16). Intake of juice was higher in the wet season but not enough to compensate for the lower brix content as intake of sugars was 1.05 kg/d in the wet season compared with 1.22 kg/d in the dry season. The growth rate of pigs fed cane juice in the wet season was 28% lower than for those fed the control diet and 20% lower than for pigs fed cane juice in the dry season. In both seasons the feed conversion rate was worse for sugar cane juice than for the broken rice. Pigs fed cane juice in the wet season had fatter carcasses than the control animals but there were no differences between diets in the dry season.

The lower content of sugars (°Brix) in the juice appeared to be the reason for the lower growth rates and fatter carcasses of pigs fed juice from wet season cane.

Sugar cane is a crop with very high potential for biomass production. It can be envisaged as a multipurpose crop with an important role in animal production. Much of the research into sugar cane feeding has been conducted and has largely been confined to studies with cattle and pigs (Preston 1995). It was confirmed that sugar cane juice can completely replace cereals as the major energy source in diets for pigs (Mena 1981, Mena et al 1982; Figueroa 1989; Sarria et al 1990; Speedy et al 1991; Bui Huy Nhu Phuc et al 1994; Le Thi Men et al 1996).

The decision to use sugar cane to make sugar or to feed animals will depend on the relative prices of sugar and animal product, which in turn will be influenced by the locality where sugar cane is grown. In the areas where sugar cane is traditionally grown and processed into sugar the alternative use for livestock feed will be attractive in situations where local processing is difficult and the nearest sugar factory is some distance away (Nguyen Thi Loc et al 1992; Oanh 19..; Le Viet Ly and Luu Trong Hieu 1994). This has been confirmed in the provinces of Tuyen Quang, Bac Thai and Cao Bang in North Vietnam where it has been shown clearly that there is strong incentive to use sugar cane juice in livestock feeding systems (Nguyen Thi Oanh 1994; Hoang Thi Tham - Hoang Thi Tao 1996; Mai van Sanh et al 1996).

It is important to do more research on the use of sugar cane as livestock feed since the requirements are different from those which apply when the end purpose is production of sucrose. In the latter case a high concentration of sucrose in the juice is essential in order to reduce the cost of processing since there will be less water to evaporate and a higher yield in the factory of sucrose as percent of cane. To achieve these conditions the harvesting of sugar cane for sucrose production is restricted to the period of the year when the climatic conditions favour accumulation of sucrose; for example when there is little rain (dry season) or a low temperature. Usually the actual harvest period lasts only for some 4-6 months. In contrast, for livestock production, a year-round supply of feed is required.

Most of the research with sugar cane for livestock feeding has been based on its use during the traditional harvest season when sugar content (°Brix) of the cane is highest. This has been based on the belief that feeding value would be directly related to sugar content. On the other hand, some reduction in animal performance might be acceptable when weighed against the advantages of having access to sugar cane throughout the year.

The principal objective of the research to be reported here was to determine the effect of the quality of sugar cane juice (sugar concentration), as influenced by season of harvesting, on the performance of fattening pigs given this feed as the basis of their diet. The hypothesis to be verified was that the feeding value of the juice for pigs would be lower for sugar cane harvested in the rainy season compared with cane harvested in the dry season. The eftects of month of planting and of harvesting on biomass yield and °Brix of the juice are reported in a companion paper (Nguyen Thi Mui et al 1996).

The sugar cane used in the experiment had been planted at monthly intervals between July 1994 and 1995 in plots measuring 800 m². It was estimated that approximately 300 kg of cane stalks were available daily for harvesting throughout the year and that this could provide enough juice (150 litres/day) to cover the needs of 12 pigs (about 8 litres/pig/day).

There were two treatments applied in eachof two trials which were carried out consecutively in the wet and dry seasons. The treatments were:

• SCJ: Sugar cane juice and protein supplement
• Control: Broken rice and protein supplement

The trials were done with different lots of pigs from July 1995 to November 1995 (Trial 1; wet season) and from December 1995 to May 1996 (Trial 2: dry season).

Four groups each of 3 crossbred pigs (Large White x Mong Cai) were were allocated to each of the two treatments in each of the trials. The initial weight at the start of each trial was 20 kg on average and the trial continued until the pigs reached an average of 70 kg liveweight (trial 1) and 65 kg liveweight (trial 2).

Feeding with sugar cane juice and broken rice began on 25 June 1995 with an adaptation period of 1 month to accustom the pigs to the new feeds and give them time to reach the starting weight of 20 kg. Sugar cane stalks were harvested every third day from the trial area beginning with the plots established in July 1994 and ending with the plots planted in November 1994. Harvesting was arranged to ensure that the sugar cane juice that was fed came from cane stalks planted 12 months earlier.

The juice was extracted twice daily (8:00-10:00 am and 3:00-5:00 pm) by passing the stalks three times through a 2-roll crusher driven by a buffalo. It was offered ad libitum three times daily at 10:00 am, 1:30 pm and 6:00 pm, in approximately equal amounts at each feed.

The protein supplement contained (%w/w): fish meal 25, groundnut cake 75 and was fed at the rate of 500 g/pig/day (approximately 200 g/day of protein) according to the recommendations of Sarria et al (1991). The control diet consisted of broken rice grains fed ad libitum and the same protein supplement. Sweet potato vines were given at the rate of 1 kg (fresh basis) per pig per day on both treatments.

The concentration of sugars in juice (°Brix) was determined daily with a hand refractometer. The pigs were weighed at the start of the trial and every 20 days. Feed offered and refused was recorded daily. Samples were taken to determine dry matter and nitrogen by conventional methods. The quality of the carcass was assessed in terms of yield of the dressed carcass as a percentage of the liveweight at slaughter, the eye muscle area and thickness of the back fat at the 3rd, 10th and 13th rib.

Data on the composition of the feeds are given in Table 1. There were marked differences in the sugar content of the juice which was 40% higher in the cane stalk harvested in the dry than in the wet season. Protein content of the sweet potato vines was higher in the wet season and the dry matter content was lower.

Table 1: Mean values for dry matter in fresh material and N x 6.25 in dry matter in the feed ingredients
Item	---DM---		---N x 6.25---
Season	Wet	Dry	Wet	Dry
Juice	16	22	0.7	0.5
Rice	88	89	7.2	8.4
SPV	12.5	14	20	17
Suppl.*	87	89.5	42	42

* 75% of ground nut cake and 25% of fish meal

Overall treatment effects are shown in Table 2. The pigs readily consumed the sugar cane juice and there was no problem of digestive upsets except for a few cases of diarrhoea in the first days of the experiment.

Table 2: Effect of sugar cane juice from cane harvested in the wet and dry season on growth performance of the pigs (12 pigs per treatment)
	Wet season			Dry season
	Juice	Rice	SE/P	Juice	Rice	SE/Prob
Days of expt.	105	105		89	89
Live weight, kg
Initial	22.7	22.6		22	21.5
Final	67	80.3		66.3	65.2
Gain, g/day	405	560	±20/0.001	503	501	±15/0.1
Feed intake, kg/day
Juice	7.5	-		5.54	-
(sugars)	1.05			1.22
Broken rice	-	1.47		-	1.03
DM	1.78	1.81	±0.012/0.06	1.61	1.30	±0.03/0.001
N x 6.25	0.191	0.275	±0.001/0.001	0.176	0.230	±0.003/0.001
Feed conversion, kg DM/
kg gain	4.2	3.25	±0.17/0.007	3.16	2.54	±0.15/0.042

Intake of juice was higher in the wet season but not enough to compensate for the lower °Brix content as intake of sugars was 1.05 kg/d in the wet season compared with 1.22 kg/d in the dry season.

The growth rate of pigs fed cane juice in the wet season was 28% lower than for those fed the control diet and 20% lower than for pigs fed cane juice in the dry season. In both seasons the feed conversion rate was worse for sugar cane juice than for the broken rice. Similar findings were reported by Figueroa (1989) in comparisons of maize versus high test molasses (cane juice clarified, partially inverted and concentrated) fed to growing pigs. Ly (1996) attributed this difference to higher losses of energy in the metabolism of fructose which accounts for 50% of the digestible energy in molasses; in contrast, the digestion of starch as in rice and maize yields only glucose. The higher intake of protein on the rice diet compared with the juice diet, in both seasons, could also have contributed to the better feed conversion on the former diet.

Carcass evaluation

The data on carcass quality are shown in Table 3. There were no differences between the two treatments in carcass yield, carcass length or backfat thickness. There was an indication of greater eye muscle area in favour of the pigs fed broken rice.

Table 3: Mean values for carcass yield, length, back fat and loin area (LA) adjusted by covariance for live weight at slaughter
	Wet season			Dry season
	Juice	Rice	SE/Prob	Juice	Rice	SE/Prob
Yield, %	83.4	83.8	±1.2/0.86	72.5	74.4	±1.1/0.31
Length, cm	65.1	64.8	±0.86/0.84	59.3	59.8	±0.61/0.59
Backfat, mm	3.47	3.19	±0.41/0.35	3.91	3.94	±0.14/0.93
LA, cm2	27.7	31.8	±1.5/0.20	29.6	31.7	±0.65/0.11

In the wet season, the pigs fed cane juice tended to have a lower percentage of lean meat and had a higher percentage of fat than those fed broken rice (Table 4). There were no differences between treatments for the trial done in the dry season. The proportion of skin was not influenced by diet. The data for organ weights (Table 5) show few differences due to diet, other than the weights of the small intestine which were less in pigs fed cane juice than in those fed broken rice (P=0.001 and 0.34 for wet and dry seasons respectively).

Table 4: Mean values for lean, fat, bone and skin in valuable cuts as percentage of carcass weight, adjusted by covariance for liveweight at slaughter
	Wet season			Dry season
	Juice	Rice	SE/Prob	Juice	Rice	SE/Prob
Total lean	27.6	33.7	±1.6/0.10	37.4	35.8	±0.86/0.31
Total fat	34.5	26.5	±1.2/0.03	35.6	37.8	±1.33/0.59
Bone	5.91	8.19	±0.94/0.23	7.36	6.94	±0.34/0.456
Skin	7.13	8.31	±0.47/0.22	5.92	6.71	±1.0/0.64

Table 5: Mean value for weights (g) of internal organs adjusted by covariance for liveweight at slaughter
	Wet season			Dry season
	Juice	Rice	SE/Prob	Juice	Rice	SE/Prob
Liver	1482	1528	28/0.39	1400	1366	55/0.70
Kidney	272	271	6.0/0.88	217	227	9/0.51
Stomach	759	778	30/0.33	613	580	19/0.33
Intestine
Small	2535	1455	54/0.001	2085	2208	75/0.34
Large	3049	2845	222/0.61	2512	2372	53/0.17

Data on chemical composition of the loin eye muscle and the iodine index of side fat are given in Table 6. There were no differences due to dietary treatment apart from the ether extract in the eye muscle which, in the wet season, was higher for pigs fed juice compared with rice.

Table 6: Mean values for chemical composition of loin eye muscle and iodine index of side fat adjusted by covariance for carcass weight
	Wet season			Dry season
	Juice	Rice	SE/Prob	Juice	Rice	SE/Prob
Composition of loin eye muscle, %
DM	29.1	25.6	1.1/0.14	26.6	26.5	0.35/0.33
Protein	19.0	19.3	1.5/0.80	18.6	19.2	0.51/0.52
EE	6.84	8.68	0.087/0.001	5.41	4.96	0.33/0.42
Ash	1.13	1.20	0.092/0.67	1.03	1.03	0.013/0.9
pH	5.29	5.37	0.042/0.33	5.48	5.29	0.14/0.43
Side fat
Iod. index	55.1	59.5	1.1/0.09	50.3	49.9	1.05/0.83

Sugar cane juice derived from cane stalks harvested in the wet season supported 20% lower growth rates in pigs than juice from cane harvested in the dry season. Pigs fed the control diet of broken rice grew at similar rates in both seasons. In the dry season pig growth rate on cane juice was the same as on broken rice.

In the wet season the carcasses of pigs fed sugar cane juice were fatter than those fed broken rice. In the dry season, carcass quality did not differ between diets. The content of sugars (°Brix) was 40% higher in the juice from cane stalks harvested in the dry season than in juice from wet season cane. This appeared to be the reason for the lower growth rates and fatter carcasses of pigs fed juice from wet season cane.

This researched was supported by the International Foundation for Science through a grant (B/2291-1) to the senior author.

Received 26 November 1996