Effect of level of cane molasses in fattening diets on performance of beef steers and heifers.

S Sibanda, C Chakanyuka and N Mlilo
Grasslands Research Station, Private Bag 3701, Marondera, Zimbabwe.

Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
Acknowledgements
References

Abstract

The performance in feedlot of 100 each 18 month-old steers and heifers, one half of which comprised Sussex x Africaner and the other half Hereford x Mashona x Sussex breeds, was determined in a 2 x 5 factorial trial. Five groups of 18 animals (mean starved body weight 280 kg) for each sex were balanced for breed and body weight and randomly allocated to one of five dietary treatments containing 0, 10, 20, 30 or 40 per cent. molasses respectively. The animals were fed ad libitum for 90 days and slaughtered. The results show that molasses can be included in fattening diets up to a maximum level of 30 per cent. without any adverse effects on body and carcass weight gains, efficiency of feed-use and carcass grades. There was little difference in feedlot performance between steers and heifers.

Introduction

The practice of fattening cattle on maize-based high energy diets has become uneconomical due mainly to the high cost of maize grain relative to beef producer prices in Zimbabwe. In an earlier trial a less expensive diet than the conventional maize-based fattening diet was achieved by using cane molasses, a by-product of the sugar industry (Chakanyuka, Sibanda, Grant and Mlilo, 1987). Molasses was incorporated into this diet at the rate of about 20 per cent, equivalent to replacing 23 per cent of the maize, with no adverse effect on the performance of cattle in feedlot.

Molasses cannot fully replace maize due to handling problems and possible toxic effects if it is fed at very high levels (Van Niekerk 1981). However, since it is cheaper than maize grain, as much of it as possible should be included in fattening diets. It was therefore necessary to determine the maximum level of molasses which could be used in cattle fattening diets without adversely affecting performance. This study was carried out to investigate the relationship between the level of molasses in the diet and the performance in feedlot of both steers and heifers over a 90 day feeding period.

Materials and methods

A total of 100 eighteen month old steers and heifers, 50% Sussex x Africaner and the other 50% Hereford x Mashona x Sussex crossbreds, with an average starved body weight of about 280 kg were used. Animals of each sex were divided into 5 equal groups of 18 animals each balanced for breed and body weight. A 6th group of 10 animals for each sex was slaughtered at the start to estimate the initial carcass weight of the remaining 5 groups for each sex, which were randomly allocated to one of five dietary treatments, the first a conventional high energy diet containing no molasses, and the other four containing increasing proportions of molasses; their formulations are shown in Table 1.

Table 1. Formulation and chemical composition (% air fresh) of cattle fattening diets.

	Level of molasses (%)
	0	10	20	30	40
Snap corn	92.6	75.2	54.3	33.4	20.0
Molasses	0	10.0	20.0	29.4	40.1
Cottonseed hulls	2.2	8.0	17.2	25.1	24.0
Cottonseed meal	2.4	4.0	6.2	8.0	10.0
Urea	1.70	1.70	1.70	1.70	1.70
Limestone flour	0.80	0.70	0.60	0.40	1.80
Monocalcium phosphate	-	-	-	2.00	2.40
Coarse salt	0.30	0.20	-	-	-
Chemical composition (as fed)
Crude protein	12.5	12.5	12.5	12.5	12.5
Crude fibre	11.0	11.8	13.6	15.2	13.3
Fat	2.90	2.54	2.12	1.70	1.34
Ash	3.77	4.11	4.36	4.89	8.87
Sulphur	0.26	0.24	0.21	0.17	0.14
TDN	74	70	65	60	55
ME (MJ/kg)	11.1	10.5	9.7	9.0	8.2

Each group was divided into 3 sub-groups of 6 animals comprising the heaviest, medium and lightest animals balanced for breed. The 6 animals in each sub-group were housed in one pen and group-fed ad libitum for a period of 90 days. The animals were weighed fortnightly and food intake was calculated weekly. At the end of the feeding period the animals were slaughtered and carcass measurements taken.

The following measurements were taken: initial and final starved body weight (no food and water for 24 and 15 hours, respectively), initial and final cold dressed carcass weight, total food intake, efficiency of food conversion and carcass grades.

Differences between treatments were determined by analysis of variance with initial starved body weight as a covariate for all the variables, except carcass grades where only means are presented.

Results

Body weight changes

The body weight changes are shown in Table 2. There was no significant difference between the steers and heifers, although the heifers had marginally smaller body weight changes than the steers. There was a significant (P<0.05) quadratic effect of level of molasses on body weight changes with the rate of increase falling with increasing level of molasses. Body weight changes for the animals on 10, 20, and 30 per cent molasses were similar and higher (P<0.05) than the zero and 40 per cent molasses groups. The 40 per cent molasses diet gave the lowest body weight change but this was not significantly lower than that of the conventional zero molasses diet. Initial body weight as a covariate of body weight change and the interaction between sex and diet were not important.

Carcass weight changes

The initial carcass weights of the feedlot cattle were estimated from equations based on data derived from 10 each of steers and heifers slaughtered at the start of the experiment. Regression equations (1) and (2) were used for steers and heifers, respectively:

CW = 133.2 ln BW - 613.6 (r = 0.823) ... (1)

CW = 305.8 - 1.723 BW + 0.004 BW² (r = 0.978) ... (2)

where CW is cold dressed carcass weight (kg), BW is the initial starved body weight (kg) and ln is the natural logarithm. The carcass weight changes of heifers and steers were similar (Table 3). There was a significant (P<0.05) quadratic effect of level of molasses on carcass weight change, as the rate of increase decreased with the higher levels of molasses. The mean carcass weight change of the conventional zero molasses animals was lower (P<0.05) than those of all the other dietary treatments. The diets containing 10, 20, and 30 per cent molasses produced similar gains which were higher (P<0.05) than those of the zero and 40 per cent molasses diets. The highest mean carcass weight changes were achieved by the animals on the 20 per cent molasses diet for both sexes. As with body weight gains, initial body weight as a covariate of carcass weight change and interaction between sex and level of molasses was not important.

Food intake and efficiency of food conversion

There was little difference between the two sexes in total food intake (Table 4), but intake increased as the level of molasses increased, reaching a peak at 30 per cent molasses. The efficiency of food conversion for body and carcass weight gain was the same for steers and heifers (Table 4). The efficiency of conversion for body weight gain exhibited a linear relationship with the level of molasses in the diet as the rate of decrease continued to increase with higher levels of molasses, but the decline became very marked (P<0.05) at 40 per cent molasses. The rate of decrease in efficiency of food-conversion decreased as the level of molasses increased. However, there was no significant difference between the efficiency of food-conversion for carcass weight gains of the zero, 10, 20 and 30 per cent molasses animals. The 40 per cent molasses diet produced a significantly (P<0.05) lower efficiency of food-conversion for carcass weight gain than all the other diets. There was no interaction between sex and diets and similarly initial body weight as a covariate of efficiency of food-conversion for carcass and body weight gain was not important.

Table 2. Body weight changes (kg) of cattle fattened on diets with different levels of molasses.

		Level of molasses (%)
		0	10	20	30	40	Mean
Initial starved body weight
	Steers	279.4	278.9	279.2	278.6	279.2	279.1
	Heifers	280.3	281.8	280.6	278.8	280.3	280.4
	Mean	279.8	280.4	279.9	278.7	279.8
Final starved body weight
	Steers	402.2	419.9	414.4	417.1	396.7	410.1
	Heifers	400.1	417.3	425.4	404.3	396.2	407.8
	Mean	401.2	418.6	419.9	410.7	396.4
Body weight change
	Steers	122.8	141.0	135.2	138.5	117.5	131.0
	Heifers	119.8	135.5	144.8	125.5	115.9	128.2	3.46
	Mean	121.3 ab	138.3c	139.9c	132.2 bc	116.7a
				5.45

Means in the same row or column in the same part of the table with different superscripts are significantly different (P<0.05).

Table 3. Carcass weight changes (kg) of cattle fattened on diets with different levels of molasses.

		Level of molasses (%)
		0	10	20	30	40	Mean
Initial carcass weight
	Steers	136.4	136.2	136.3	136.0	136.2	136.2
	Heifers	133.4	134.2	133.7	132.8	133.8	133.6
	Mean	134.9	135.2	135.0	134.4	135.0
Final carcass weight
	Steers	212.5	233.0	233.9	233.5	221.4	226.8
	Heifers	212.1	227.9	236.0	223.8	218.8	223.6
	Mean	212.3	230.4	234.9	228.6	220.1
Carcass weight change
	Steers	76.1	96.8	97.6	97.5	85.2	90.6
	Heifers	78.7	93.7	102.3	91.0	85.0	90.0	2.00
	Mean	77.4a	95.2c	100.0c	94.2c	85.1b
				3.15

Means in the same row or column in the same part of the table with different superscripts are significantly different (P<0.05).

Table 4. Total food intake (kg/head, air-fresh) and efficiency of food-conversion for body weight gain (kg food/kg body weight gain) and carcass weight gain (kg of food/kg carcass weight gain) of cattle fattened on diets with different levels of molasses.

		Level of molasses (%)
		0	10	20	30	40	Mean
Total food intake
	Steers	933.7	1147.7	1212.8	1259.5	1288.6	1168.5
	Heifers	965.4	1215.9	1316.3	1297.5	1267.5	1212.5
	Mean	946.6	1181.8	1264.6	1278.5	1278.0
	ME intake (MJ)	10540.6	12408.9	12266.6	11506.5	10479.6
Efficiency of food-conversion for body weight gain
	Steers	7.86	8.60	9.05	9.26	11.23	9.20p
	Heifers	8.78	9.50	9.29	10.67	11.13	9.86q	0.310
	Mean	8.31a	9.04 ab	9.17 ab	9.95b	11.18c
				0.487
Efficiency of food-use for carcass weight gain
	Steers	12.7	12.4	12.5	13.1	15.6	13.3r
	Heifers	12.8	13.3	13.0	14.6	15.2	13.8r	0.363
	Mean	12.7m	12.8m	12.8m	13.8m	15.4n
				0.570

Means in the same row or column in the same part of the table with different superscripts are significantly different (P<0.05).

Carcass grades

The fleshing and fat grades awarded at slaughter are shown in Table 5. The fleshing index is based on the ratio of carcass weight to length. Classes 1 and 2 depict animals with adequate fat cover, class 3 would be underfat and class 9 overfat. The last two classes carry some form of penalty. Overall the highest fleshing grades were obtained with the 20 per cent molasses diet, whilst the conventional zero molasses diet produced the lowest grades. The fleshing grades for heifers fell more markedly than those for steers at molasses levels higher than 20 per cent. There was little difference between the treatments in fat grades, although heifers tended to be fatter than steers.

Discussion

The results of this study agree with earlier trials carried out in this laboratory (Chakanyuka et al. 1987) and elsewhere (Lishman 1967; Elliot and O'Donovan 1973; Van Niekerk 1981). They indicated that molasses can make up to 30 per cent of fattening diets without adversely affecting animal performance.

The diets containing molasses up to and including 30 per cent, produced higher body and carcass weight gains than the conventional maize-based diet with no molasses. This confirms the results of the earlier work in which a diet containing 20 per cent molasses produced marginally higher carcass weight gains than the conventional high maize diet (Chakanyuka et al. 1987).

The reason for the better performance of cattle on molasses diets compared to the conventional high maize diets is thought to be the creation of a more suitable rumen environment for the microbial population (Hatch and Beeson 1972). This would mean that animals on molasses diets would have fewer digestive problems and would take a shorter time to adapt to the diets. In the present trial in took up to three weeks before the animals on the conventional zero molasses diet stopped scouring, while those on the molasses diets did not scour at all.

Since the level of metabolisable energy (ME) decreased with the increase in the level of molasses it would seem that total food intake was controlled by the level of ME. On as fed basis all molasses diets produced lower efficiency of food-conversion, a finding which confirms earlier studies in this country (Elliot and O'Donovan 1973; Chakanyuka et al. 1987) and elsewhere (Van Niekerk and Voges 1976; Van Niekerk 1981).

Table 5. Carcass grades (%) of cattle fattened on diets with different levels of molasses.

	Level of molasses (%)
	0			10			20			30			40
Fleshing grades	A	B	C	A	B	C	A	B	C	A	B	C	A	B	C
Steers	16.7	72.2	11.1	72.2	22.2	5.6	88.9	11.1	-	88.9	11.1	-	44.4	50.0	5.6
Heifers	22.2	66.7	11.1	76.5	17.6	5.9	88.2	11.8	-	64.7	29.4	5.9	29.4	70.6	-
Mean	19.4	69.4	11.1	74.4	19.9	5.8	88.6	11.4	-	76.8	20.2	3.0	36.9	60.3	2.8
Fat grades	1	2	9	1	2	9	1	2	9	1	2	9	1	2	9
Steers	77.8	22.2	-	88.9	11.1	-	77.8	22.2	-	100	-	-	77.8	22.2	-
Heifers	94.4	5.6	-	100	-	-	94.1	-	5.9	94.1	5.9	-	100	-	-
Mean	86.1	13.9	-	94.4	5.6	-	86.0	11.1	3.0	97.0	3.0	-	88.9	11.1	-

However, the diets containing 10, 20, 30 and 40 per cent molasses had 5.4, 12.2, 18.9 and 25.7 per cent, respectively less ME than the conventional diet. Therefore the ME in the diets containing 10, 20, 30 and 40 per cent molasses was utilised more efficiently than that of the conventional diet by 4.4, 11.2, 7.1 and 4.5 per cent, respectively. These results are in agreement with the last trials when the ME in the diet containing 20 per cent molasses was utilised with 5.5 per cent higher efficiency than the conventional diet (Chakanyuka et al. 1987).

The results of the carcass grades are also in favour of molasses-based diets. While the conventional diet may exhibit a higher efficiency of food-conversion the returns from it are likely to be lower due to the resultant smaller carcass and lower grades.

It has been customary to assume that heifers were less efficient than steers in feedlot. The results of the present trial show that there was no difference between steers and heifers in efficiency of food-conversion for carcass weight gain. However, the fat grades indicate that heifers may tend to get fatter. It may be advisable to slaughter heifers earlier than steers of similar size.

Conclusion

Molasses can be included in fattening diets by up to 30 per cent without any marked detrimental effects on performance. This would result in relatively cheaper diets, provided the molasses was available and continued to be cheaper than maize grain. These results apply to both steers and heifers, although heifers may need to be slaughtered earlier to prevent them from getting overly fat.

Acknowledgements

We are grateful to Agrifoods Division, Farmers' Co-op Ltd., for mixing and supplying the diets. We would also like to thank Mr. L. Svisvah for taking care of the animals.

References

Chakanyuka C., Sibanda S., Grant J.L. and Mlilo N. 1987. Effects of salinomycin, potassium chloride, synovex and the re placement of maize with molasses on feedlot performance of cattle. In press.

Elliot R.C. and O'Donovan W.M. 1973. Comparative feeding trial T32 and high energy maize diets for feed conversion and laminitis observations. Annual Report 1972/73. Henderson Research Station, Department of Research and Specialist Services, Ministry of Agriculture, Rhodesia.

Hatch C.F. and Beeson W.M. 1972. Effect of different levels of cane molasses on nitrogen and energy utilisation in urea rations for steers. Journal of Animal Science. 35: 854-858.

Lishman A.W. 1967. Cane molasses as a substitute for maize in beef finishing rations. South African Journal of Agricultural Science. 10: 51-59

Van Niekerk B.D.H. 1981. By-products of the sugar industry as animal feeds. South African Journal of Animal Science. 11: 119-137

Van Niekerk B.D.H. and Voges D.H. 1976. Cane molasses as a replacement for maize in beef fattening rations. South African Journal of Animal Science. 6: 67-72