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|Workshop-seminar "Making better use of local feed resources" SAREC-UAF, January , 2000.|
College of Agriculture and Forestry, National University of Ho Chi Minh City, VietNam (email@example.com)
1 Swedish University of Agricultural Sciences, 750 07, Uppsala, Sweden.
An experiment was conducted in a 4*4 Latin square design with four dairy cows with an average live weight of 460 kg, an initial average milk yield of 13.8 kg/day, and 96 days of lactation. The objective was to evaluate the effect of substituting cotton seed meal by cassava leaf meal at levels of 0, 20, 40, and 60% in the concentrates on milk yield and milk composition. The composition of the concentrates was: (CLM0) cereals with 40% cotton seed meal, (CLM8) cereals with 32% cotton seed meal and 8% cassava leaf meal, (CLM16) cereals with 24% cotton seed meal and 16% cassava leaf meal, and (CLM24) cereals with 16% cotton seed meal and 24% cassava leaf meal. The basic diet was Napier grass (Pennisetum purpureum) offered ad libitum. There were no differences in dry matter intake and milk production among treatments. The milk production for treatment CLM24 was 12.3 kg/cow/day, followed by the treatments CLM16, CLM8 and CLM0, with 11.9, 11.7, and 12.1 kg/cow/day, respectively. The average milk fat contents in the treatments CLM24, CLM16, CLM8 and CLM0 differed (P<0.05) with values of 3.74, 3.75, 3.84, and 3.98%, respectively. The average milk protein contents in the treatments CLM24, CLM16, CLM8 and CLM0 were 2.75, 2.73, 2.73, and 2.81%, respectively. It is concluded that cassava leaf meal can substitute for cottonseed meal as protein supplement in dairy cow rations based on fresh grass forage and cereals at least up to 9% of the total ration (maximum studied level) without effects on milk yield.
Key words: Milk production, cassava leaf meal, cottonseed meal.
Cassava or tapioca (Manihot esculenta, Crantz) is an annual tuber crop grown widely in VietNam. It thrives in sandy-loam soils with low organic matter, in areas receiving low rainfall and at high temperatures. It is therefore a cash crop second in rank after rice cultivated by smallholder farmers within the existing farming systems in VietNam. Beside the root, each hectare of cassava produces a large amount of leaf. The potential yield of cassava leaves varies considerably, depending on cultivar, age of plant, plant density, soil fertility, harvesting frequency and climate (Gomez and Valdivieso 1984; Wanapat et al 1997). If cassava is grown as foliage in the dry season, it can give 41,000 kg/ha of fresh leaf, equivalent to about 12,000 kg/ha of cassava hay. The protein content in cassava leaf is about 22 %. Therefore from one hectare of cassava, it is possible to obtain 3,000 kg of protein (Wanapat et al 1997). If cassava leaves are obtained as a by-product at root harvest, the leaf dry matter yields will be lower, from 1,200 (Gomez and Valdivieso 1984) to 4,640 kg/ha (Ravindran et al 1988). Generally, the amount of forage available at root harvest is equivalent to about 30 % of the root yields (Ravindran 1993). Cassava leaves are therefore a potential protein supplement for ruminants in the tropics.
The low nutritive value of tropical grasses and roughage, commonly available for use in ruminant production systems in the tropics, highlights the need for low-cost supplementation to improve animal production (Preston 1995). Considerable progress has been made in the use of tree legumes such as Leucaena (Arrivillaga and Preston 1978; Wanapat et al 1998) and Gliricidia (Preston and Leng 1997). Surprisingly, despite its availability and high protein content, there was little interest until recently to utilize fresh cassava forage in ruminant feeding. This reluctance is probably related to possibilities of cyanide toxicity. Wilting reduced cyanide toxicity in fresh cassava foliage. Wilting not only lowers potential cyanide toxicity, but also reduces the free tannin levels and improves its acceptability to ruminants. Cassava foliage or hay made from cassava foliage has been fed to ruminants with good results (Fernandez et al 1977; Ffoulkes and Preston 1978; Teeluck et al 1981; Devendra 1977; Wanapat et al 1997; Wanapat et al 1998).
The hypothesis to be tested was that dried cassava leaf meal is a protein source equivalent in nutritive value to cottonseed meal when fed to dairy cows. Thus, the specific aim of this experiment was to determine the degree to which cassava leaf meal could replace cottonseed meal in the diet of dairy cows fed Napier grassad libitum.
The experiment was carried out between August and October at the ‘HungViet’ farm, BaRia-VungTau province in the South of VietNam. The farm lies on the coast of the Pacific Ocean, with annual averages of 73.5 % relative humidity and 26.2 °C air temperature.
Four Holstein-Friesian cows (460±67 kg live weight and average milk yield of 13.8 kg/cow/day) were used for the experiment. Three of them were pure Holstein-Friesian and one of them was a crossbred Holstein-Friesian (75%). These cows were in their 2nd lactation period. They were on average in their 13th week of lactation at the onset of the experiment.
The cows were tethered in individual stalls in a barn with open walls. Clean and fresh water was available ad libitum during the whole experiment.
The treatments were arranged in a 4x4 Latin square. Each of the experimental periods lasted 24 days. Fourteen days of each period were for adaptation to the new diets. Samples of feedstuffs in the diets were taken to determine their chemical composition. Feed intake was registered during the last 10 days of each period. Samples of the diets were also taken during the last 3 days of each period for chemical analysis. Milk yield was registered by weighing every milking throughout the entire experiment of 96 days.
The basal diet consisted of Napier grass offered ad libitum at 7:00, 11:00, 15:00, and 18:00 h and a locally compounded concentrate feed for dairy cows with about 15% crude protein on a dry matter basis. Napier grass was harvested at 42 days of growth, two times per day in the morning (9 h) and afternoon (15 h) for the whole experimental period. The basic ingredients of cassava root meal (20%), rice bran (25%) and maize meal (15%), were constant in all the four mixtures, while the cotton seed meal (40%) was replaced by cassava leaf meal at the rate of 0, 20, 40, and 60% levels in the four treatments, respectively. In addition, a mineral premix and salt (0.2%) were included in the mixtures. During lactation, the amount of concentrate fed was adjusted each week (0.4 kg concentrate/kg milk) according to the milk production during the adaptation period, and the predicted production for the following week.
Feed intake was recorded by weighing the feed offered and refused each morning during the last 10 days of each period. The dry matter of Napier grass was also measured daily during the experiment. The samples of the cotton seed meal, cassava leaf meal, cassava root meal, rice bran and maize meal in the concentrates were also analyzed for dry matter, crude protein, ether extract, ADF, NDF and ash for each period. In addition, samples of the Napier grass and concentrates were taken weekly at intervals of approximately 3 days for each period for analysis of crude protein, ash and ether extract (AOAC 1990) and ADF and NDF (Van Soest et al 1991).
Milking and milk recording
The cows were hand-milked twice a day, in the early morning at about 05.30 h and in the afternoon at about 16:00 h. Milk production was recorded daily by weighing. Milk samples were also collected daily during the last ten days of each period. Milk samples were stored at -15 ºC until analysis. All calves were bucket-fed during the experiment. This was a pre-requisite for the experiment in order to obtain a precise measurement of milk production.
Data were analyzed by ANOVA using the General Linear Model and Pair-wise comparison by Minitab Statistical Software version 12.21. The following statistical model was used:
Y ijk = m + A i + B j + Ck + E ijk
Y ijk: Dependent variable
m : General mean
A i: Effect of diet
B j: Effect of animal
C k: Effect of period
E ijk: Random error
The cassava leaf meal and the cottonseed meal contained similar levels of crude protein, at about 22 % of DM (Table 2). However, NDF and ADF contents of cassava leaf meal were lower in the leaf meal. These data are in agreement with previous reports by Maaruf et al (1995) and Wanapat et al (1997). The ether extract content of cottonseed meal was slightly higher than in cassava leaf meal.
Table 1. Chemical composition of feed ingredients in the concentrate mixtures and of the Napier grass (# in air dry feed; other values as % of DM)
DM# OM CP EE ADF NDF
Cottonseed meal 91.2 95.4 22.8 5.14 27.4 38.8
Cassava leaf meal 92.7 91.2 22.1 4.36 19.1 27.3
Cassava root meal 93.8 92.3 1.08 2.24 2.24 3.42
Rice bran 93.5 87.2 14.2 10.4 17.8 33.0
Maize meal 92.6 98.4 8.14 3.78 3.14 9.12
Napier grass 15.7 91.8 11.7 0.58 36.0 64.3
Total dry matter intake was the same on all diets (Table 2). The amounts of protein from cassava leaf meal were 0, 83, 177 and 278 g/day, corresponding to 0, 3, 6 and 9 % of the total crude protein supply.
Feed intake, milk yield and milk composition of cows fed different
amount of cottonseed meal and cassava leaf meal
CLM0 CLM8 CLM16
Napier grass, kg DM/day
Concentrate, kg DM/day
Total DMI, kg/day
Total CP, kg/day
CLM as % of total DMI, %
CSM as % of total DMI, %
CLM= cassava leaf meal, CSM= cotton
seed meal, DMI= dry matter intake
DM= dry matter, FCM= fat corrected
Values in the same rows with
different letters are significantly different (P<0.05).
There were no significant differences in milk yield between the treatments (Table 3). The fat content of the milk was highest on the high cottonseed meal diet and decreased with increasing proportions of cassava leaf meal in the diet (P<0.05). The milk protein content did not differ among diets.
Cottonseed meal is considered to be one of the best sources of bypass protein for ruminants (Preston and Leng 1987). The fact that milk yields were similar at all levels of substitution of cottonseed meal by cassava leaf meal can be interpreted as a strong indication that the protein in the latter has good bypass characteristics. The research of Garcia and Hernandez (1996), who substituted up to 35 % of the cereals in the concentrates by the integral cassava plant, of Garcia and Herrera (1998) who used cassava as a supplement for dairy cows on pasture, and of Ffoulkes and Preston (1978) who successfully used cassava foliage as the only protein source in a molasses-urea fattening diet, provides further support for the hypothesis that by-pass nutrients, especially protein, are the principal limitations to ruminant production on tropical forages (Preston and Leng 1987; Ravindran 1993).
The results of this experiment show that milk yields are equal when cottonseed meal, representing 9 % of the total dry matter intake, was substituted by equivalent amounts of cassava leaf meal. It can be concluded that cassava is a potential source of bypass protein for dairy cows.
The authors are grateful to the Swedish International Development Authority (SIDA/SAREC) for funding this study. We are also grateful to the Hung Viet farm, Ba Ria Vung Tau Province and the Department of Animal Nutrition, College of Agriculture and Forestry Ho Chi Minh City for assisting in providing materials and equipment for the study; and the technical assistants, Tuan, Quoc, Thuc for their help.
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