Effect of level of cottonseed meal and protein in diets containing cassava chips and rice straw for lactating dairy cows

C Promkot and M Wanapat*

Sakon Nakhon Agricultural Research and Training Center, Rajamangala Institute of Technology, Sakon Nakhon, Thailand
^* Department of Animal Science, Faculty of Agriculture, Khon Kaen University, Khon Kaen ,

Abstract

The effects of different levels of crude protein (CP) and cottonseed meal replacing for soybean meal in cassava chips and rice straw-based diets for mid-lactating cows (100 -150 d in milk [DIM], were studied using 32 multiparous Holstein Fresian crossbred dairy cows. Diets containing 10.5, 12.5, 13.7, 14.4 % CP of the rations and 0 , 12.1, 14.9, 17.8 % cottonseed meal were fed to cows for 60 days. Thirty two cows were randomly divided into four dietary treatments using a Randomized complete block design. Four dietary treatments were offered in the form of total mixed ration (TMR) with concentrate to roughage (chopped rice straw ) at 60:40 and offered ad libitum.

Dry matter (DM) and neutral detergent fiber (NDF) intakes tended to linearly increase with increasing dietary CP levels. Intakes and digestibility of crude protein increased linearly with increasing dietary CP level (P<0.01) .CP digestibility of 10.5 %CP was lower (P<0.05) than that in higher level of CP,while there were no significant differences among the three levels of CP(12.5, 13.7 and 14.4 % CP). Daily milk yield tended to increase with increased CP from 10.5 to 14.4 %. Income over feed in terms of US$/kg of milk increased with increased CP from 10.5 to 13.7% and decreased when the CP level was higher than 13.7% (quadratic effect P < 0.09). Milk composition was not significantly affected by increasing level of CP, however there were relatively high contents of protein and fat among treatments.The proportion of milk-urea N (MUN), ammonia-N (NH₃-N) and blood-urea N (BUN) were closely correlated and increased linearly with increasing CP levels (P<0.01). Balanced diet was found in diet containing 12.5 and 13.7 % CP of the rations when BUN and MUN were used asindicators of the protein to energy ratio in the diet.

Conclusions can be made that increasing dietary CP levels from 10.5 to 13.7 % using cottonseed meal as the main source to completely replace soybean meal was beneficial to cows consuming rice straw and cassava chips based-diets. Increasing the CP level above 13.7% of total ration did not additionally improve milk yield and composition or net income.

Key Words: Protein ,Cottonseed meal, Lactating dairy cow, MUN, BUN, Ammonia- N, Dry matter intake, Milk yield and composition, Rice straw, Urea-treated rice straw.

Introduction

Although dairy farming in Thailand started in 1960 Thai farmers still can not produce enough raw milk to meet the demand of the whole country. As reported in the year 2000, Thailand produced 494,692 tons of raw milk and imported 161,423 tons of milk and milk products.(Deparment of Livestock Development, 2002).The Thai Government's plan for the development of dairying is aimed at a reduction of foreign exchange for the purchase of imported milk powder and dairy products, and also to provide the farmers the opportunity to earn increased and more regular incomes and generate employment opportunities in the farming, milk processing and manufacturing industries. One major constraint on raw milk production is the high cost of feed in the production. Feeding of dairy cattle in the tropics is often difficult because of deficiencies in feed supply, in both quality and quantity (Wanapat and Devendra, 1992). The use of rice straw as a feed in the dry season, in spite of its low nutritive value, has been a common feeding system, generally practiced by dairy farmers in the tropics when green forages are often scarce(Leng and Preston 1983 ; Wanapat , 1994).

Cottonseed meal (CSM) is a by-product from oil extraction and is a source of rumen by-pass protein supplement in dairy cattle feeding (Grings et al.,1991;Wanapat et al., 1996). Several studies have been devoted to study the potential value of CSM in ruminants (Erdman et al., 1987; Coto et al., 1990; Kandylis and Nikokyris,1990; Cunha et al.,1998 ; Sampaio et al., 2000).According to NRC (1989), the degradability of CSM is 57 % and for crude protein (CP) ,and total digestible nutrients (TDN) 44.3 % and 78%, respectively (Kearl, 1982). Cottonseed meal has been used at 8.6 % of a total mixed ration in dairy cattle diets, could increase feed intake,economical benefits and milk yield (Grings et al.,1991). Paengkoum (1998) reported that voluntary roughage intake of a ration containing cottonseed meal, cassava chips and urea-treated rice straw in lactating cows ration was higher than of the ration without cottonseed meal. A large scale project in China demonstrated that intensive beef production could be achieved with rice straw diets provided these were adequately supplemented with a source of rumen by-pass protein such as cottonseed meal(Weixian et al., 1994). Wanapat et al. (1996) reported that milk production of crossbred Holstein-Zebu cows fed a low protein basal diet of rice straw and cassava chips was markedly improved when the CSM supplement was increased from 2 to 4 kg/day, while Blackwelder et al. (1998) suggested that cottonseed meal in the diet can be substituted for soybean meal, resulting in similar milk production and composition. This feeding system is an economicaly attractive alternative to farmers who traditionally use commercial concentrates. Therefore, CSM is typically a very useful, and locally available by product in many tropical countries. Cassava chip is locally available in Thailand,and the price is relatively low. Cassava chip is known to be a good energy source, with 80% TDN (Kearl, 1982), and is highly degraded in the rumen (94% DM)(Sathapanasiri et al., 1990). Cassava chip contains 88.3 % DM, 2.1 % CP, 1.5 %CF (Kearl, 1982). Several studies have been carried out on the effects of cassava chips replacing from 30 to 50 % of corn meal (Pimpa et al.,2000 ; Sommart et al., 2000). Recent a study by Wanapat and Petlum (2001) reported that a concentrate based on a high proportion of cassava chips (85% of concentrate) and a high urea level could support good milk production. However, limited data on levels of cottonseed meal in concentrate cassava chip-based diets is rather limited. Therefore, the objectives of the experiments were:

• To study the effects of different level of levels of CP and CSM in rations containing cassava chips and rice straw on milk production milk composition.
• To study the relationships between CP in rations, protein, ruminal NH3-N, blood urea nitrogen (BUN) and milk urea nitrogen (MUN) in mid-lactating dairy cows .
• To determine the most economical levels of cottonseed meal and CP in concentrate mixtures for lactating dairy cattle.

Materials and methods

Location

These studies were conducted on-station at the Skon-Nakhon Agricultural Research and Training Center, Rajamangala Institute of Technology, Skon-Nakhon,Thailand. The area lies at 190 m above sea level with an annual rianfall of 1450-1500 mm, an average maximum temperature of 31.6 ^oc (16 - 39 ^oc ) and humidity of 92.92 ±6.68. The average of maximum, minimum temperature and rainfall during the experimental period (May - September 2002.) were 32.25 ^oc (25-38 ^oc), 24.93 ^oc (21-28 ^oc) and more than 2000 mm, respectively. Some of the laboratory analyses were done at the Department of Animal Science, Faculty of Agriculture, Khon Kaen University ,Thailand.

Experimental feeds

Ingredient composition and cost of concentrate feeds are shown in Table 1. Concentrate and roughage (chopped rice straw) feeds were provided every day in the form of total mixed ration (TMR) with concentrate to roughage at 60:40 by using a mixing machine, and offered ad libitum.The composition of the TMR diets were shown in Table 2 and were formulated to contain chopped rice straw, cassava chips, rice bran ,soybean meal(for dietary treatment 1.), broken rice, urea and other minor ingredients to balance vitamins and minerals for varying levels of CP and CSM, and made iso-caloric (TDN).

Animals and management

Thirty two, multiparous Holstein Fresian crossbred dairy cows, ranging from 100 - 150 day in milk (DIM) and yielding between 10 - 15 kg/day were used in a Randomized complete block design (RCBD) to determine the effect of four levels of CP (16, 18, 20 and 22 % of concentrate) by varying the levels of cottonseed meal in the diet on milk yeild and milk compositions for two months. The experiment was arranged in two periods using 16 cows for each period. Cows were housed individually for each treatment and had ad libitum access to a TMR, fresh water and a mineral block. The cows were adjusted for the first two weeks, and actual intake and measurements were taken during two months.

Data collection ,analysis and sampling procedures

Feeds were randomly collected and fecal samples were collected from rectum of individual cow of each treatment during the last 5 days of each month. All feed samples were kept in a refrigerator until analyzed in the laboratory. Feed intake and feed composition were analyzed in order to calculate nutrient supply. Feed and fecal samples were analyzed for DM, ash, CP (AOAC, 1990), NDF, ADF (Goering and Van Soest, 1970). Acid insoluble ash (AIA) (Van Keulen and Young, 1977) was used as internal indicator to calculate digestibility.On the last day of each month , 60-80 ml whole rumen fluid were collected from individual cows of each treatment at 0 and 4 h-post feeding. The pH of rumen contents was determined immediately after collection using a glass electrode pH meter. Ruminal NH₃-N was determined by the hypochlorite-phenol procedure(Beecher and Whitton, 1978) on the supernatant of centrifuged (3000 ´g, 15min) rumen fluid.

Milk yields of each cow were recorded daily .Milk samples were collected twice daily during milking (05.00 and 17.00 h) on the last five days of each month. Milk composition of milk samples collected during the last five days of each month were analyzed for fat, protein, lactose and solids-not-fat using infared apparatus (Milko-scan 104, Foss Electric, Denmark) and a sub-sample of the composite was analyzed for MUN according the method of Roseler et al. (1993) using a Sigma diagnostics kit #535 reading at 540 nm.

Bood samples were collected from the coccygeal vein of each cow twice daily at 0 and 4 h-after the morning feeding on the last day of each month. Samples were refrigerated for 1 h and then centrifuged at 3500 x g for 20 min. The serum was removed and analyzed for BUN composition according to the method of Croker. ( 1967) using automated clinical chemistry analyzers.

Statistical analyses

Data were analyzed using Proc. GLM (SAS,1987). The following models were used to determine treatment mean differences using Duncan's New Multiple Range Test. The model was:

Y_ij = m+a_i +b_j + e _{i j}

where

Y_ij = the criteria under study, response of cow in treatment j of  block i
m = over all sample mean,
a_i = effect of block i ,
b_j = effect of treatment j,and
e _{i j} = error

Multiple regression procedures of SAS (1987) were used to separate effects of dietary component (CP), NH3-N, BUN and MUN when overall treatment effects were significant at P< .05. Trend analysis for increasing dietary CP level was used using orthogonal polynomials analysis.

Results

Nutrient intake and body weight

Mean daily intake of dry matter and nutrients per cow by ration group are presented in Table 3. Daily DM intake did not differ significantly among treatments but there was a trend to a linearly increase with increasing dietary CP concentrations (P<0.05). NDF and ADF intakes were not different among treatments and increased linearly with increasing dietary CP concentration(P> 0.05). The daily CP intake differed significantly (P<0.01) among treatments while CP intake increased from dietary Treatment 1 to Treatment 4. The body weights were not changed during the experimental period and did not differ significantly among treatments.

Ruminal fermentation, BUN and MUN

Rumen pH (Table 4) was found to be similar between 0 and 4 h-post feeding and was similar among treatments. Ammonia nitrogen concentration (NH3-N, mg %) in ruminal fluid (Table 4) increased with increasing dietary CP level, the differences being significant for Treatment 1 and 2 as compared with Treatment 3 and 4 (P<0.01).The highest level of ruminal ammonia nitrogen was found for the treatment containing the highest level of CPt. (14.4%CP) .Ammonia nitrogen was found to be positively related (P<0.05) with increasing CP content in the diet. Increasing ammonia nitrogen within treatments was found at 4 h-post feeding. There was a positive linear association between milk and blood urea nitrogen both at 0 and 4 h-post feeding (Table 4) with dietary CP level (P<0.01). Both milk urea nitrogen and BUN at 4 h-post feeding for 14.4 %CP were higher than the other treatments (P<0.01) and were similar between Treatment 1 and 2 (10.5 and 12.5 %CP).

Nutrient digestion coefficients

Digestion coefficients of nutrients are shown in Table 5. Digestion coefficients of DM, NDF, ADF were not affected by increasing dietary CP levels. Digestion coefficient of CP was found to be higher (P<0.01) in dietary treatments which contained cottonseed meal (12.5, 13.7 and 14.4 %CP ) than without cottonseed meal. Digestion coefficient of CP increase with increasing of CP content in the diet (P<0.01). NDF and ADF digestibility coeficients tended to increase with increasing CP content of the diet (P =0.1 for both NDF and ADF).

  6.0

  6.2

6.6

7.2

Milk production and composition

Milk yield and composition (Table 6) were not affected by level of CP in the diet but there were relatively high fat and protein contents among treatments.Milk yeild tended to increase (P = 0.22) with increasing CP content in the diet.

Cost and net pofit

Feed cost (Table 7) decreased when the CP level of the diet increased from 10.5 to 12.5 % by completely replacing soybean meal with cottonseed meal at 12.1 % of DM and increased with the level of cottonseed meal in the diet (Quadratic effect, P<0.05). Income over feed (US$/kg of milk ) tened to affected by level of CP (Q, P=0.09) which, increase when CP level of diets increased from 10.5 to 13.7 % and decrease at CP level above 13.7 %, while there was no significant differences among treatments.

Correlations among dietary CP content, NH₃ -N, BUN and MUN

NH₃-N, BUN and MUN were linearly and positively correlated with dietary CP content (P<0.5). Coefficients of determination (R²) were 0.86, 0.81 and 0.89 for NH₃-N, BUN and MUN, respectively (Figure 1,2 and 3). Simple regression for BUN and NH₃-N was found strongly correlated ( R² =0.97 )(Figure 4). There was also a high correlation between BUN and MUN (R²= 0.90) (Figure 5).

Discussion

CP and TDN requirements of dairy cattle

CP and TDN intakes of dietary treatment 1 to 4 were 1.1, 6.9; 1.4,6.9; 1.6,7.3 and 1.8,7.8, respectively. DailyCP and TDN requirements of dairy cattle given by NRC(1989) in dairy cattle with 450 kg of body weight, daily milk yield and fat composition at 12.5 kg and 3.5 %, respectively were 1.4 and 7.2 kg/h/d, respectively. CP and TDN intakes in dietary treatment 1 were slightly lower than those given by NRC (1989) which could be due to lower dry matter intake (DMI) than those in recommended by NRC(1989), while those in other treatments were similar.

NDF and ADF and Dry matter intake (DMI)

Daily DMI of treatments1 to 4 were 10.89, 10.91, 11.71, 12.42kg/cow/dayand expressed as apercent of body weight were 2.44, 2.45, 2.49,and 2.73,respectively. There were no significant differences among treatments,this results beingsimilar to a report of Christensenet al. (1993, 1994) who showed that intakes of DMwere not altered by level (14.2to19.6%)of dietary CP. However, daily DM intake in the present study were slightly lower than typical intake levels for lactating dairy cows of varying body weights as given by NRC (1989) due to the influence of NDF concentration. Many studies (Briceno et al., 1987; NRC, 1988; Ruiz TM et al., 1995; Mertens, 1997)demonstrated thatincreased dietary NDF concentration linearly decreased DMI because of physical fill. It was thought that generally, cows would consume about 1.2% of their body weight /day as NDF ( Merck,1991). Average NDF intake as a percentage of BW in this study was 1.22 %,which is similar to the NDF intake capacity suggested by Merck (1991).

However, DMI tended to linearly increase with increasing dietary CP,and the mean of increased DMI was 0.38 kg/d per percent unit increase in diet CP. This result agrees with the work of Allen (2000)who summarizedthat increasing CP content of the diets can increase DMI of lactating cows, particularly when the CP content of diets was low. When significant effects of CP content on DMI were detected, the range for increased DMI was 0.18 to 0.84 kg DMI/d with a mean of 0.63 kg DMI/d per percentage unit increase in diet CP content. Oldham (1984)and Roffler et al. (1986)showed that the CP content of diets was often related positively to DMI of lactating cows. Theseworkers noted thatthe mechanism involved was presumably a reduction in distension as fiber and DM digestibility increase.For this study DM digestibility was highest in Treatment 4with the highest DMI.

Intakes of ADF, and NDF were not different among treatments. Christensen (1993) stated that the amount of CP did not alter intakes of ADF, NDF and N when the TMR contained 25% alfalfa haylage, 25% corn silage, and 50% concentrate and provided either 16.4 or 19.6% CP, when offered to Holstein cows.

There was a tendency (P = 0.10 for NDF and p = 0.15 for ADF ) for intake of NDFand ADF to increase with intake of DM as CP level increased.

Cottonseed meal intake

CSM intakes were 0, 1.32, 1.74, 2.21 kg/cow/day of dietary treatment 1, 2, 3 and 4, respectively. This shows that supplementation of CSM at 2 kg/head/day did not depress feed intake of the ration containing rice straw and cassava chips. This is in agreement with results from previous work in which cottonseed meal was supplemented at 2 to 4 kg/day in diets based on rice straw and 5 kg/head/day of cassava chips in mid-lactating Holstein-Zebu crossbred cows with no effect on rice straw intake (Wanapat et al., 1996). On the other hand, intake of cottonseed meal plus whole cottonseed increased from 2.5 to 9.1 kg/head/day and resulted in increased DM intake of a ration containing alfalfa-based diets in early lactation (Grings et al.,1991).

Nutrient digestibility

The concentration of protein in rations for dairy cows had no effect on nutrient digestion coefficient(P>0.05), except for CP.(Table 4.). This result agrees with the data of Klusmeyer et al. (1990) who stated that the amount (14.5 or 11.0%) of CP in the diet did not affect digestion in the rumen of ADF and NDFin Holstein cows.The results from Christensen et al. (1993) were also similar, where apparent total tract digestibilities for ADF, and NDF of Holsteincows were similar among levels (16.4 or 19.6%)of CP.

Increasing ration CP content from 10.8 to 15 % in DM had no effect on digestibility of energy of dry cows but there was an effect for lactating cows (digestibilty of energy increased by 0.04 to 0.08 digestibility units) (review by Oldham, 1984). It seems that levels of CP in diet of more than 4 % unit of DM can affect DM digestibility.

For this study the lowest and highest levels of CP were 10.5 and 14.4 %. However,increasing trends ofDM ,NDF, and ADF digestion coefficients were found with increasing dietary CP.(P=0.10, 0.10 and 0.14 respectively). While OM digestion coefficients was increased with increasing of dietary CP. CP digestibility was higher(P<0.05) for cows fed diets containing higher levels of cottonseed meal (treatments 2, 3, and 4)and linearlyincreasedwith level of CP.Christensen(1994)stated that apparent digestibilities of CPin the total tract were greater for cows fed a 17.5% CP dietthan a 14.2 %CP diet.

The mechanism underlying this effect has been suggested that higher protein increased microbial fermentation in the rumen, which would improve digestion of DM and OM (Mehrez et al., 1977).

Milk yield and composition

Daily milk yield tended (P=0.22) to linearly increase as level of CP in the in diet increased(Table 6). The largest change in milk yield (0.82 kg/d) was due to increasing CP level from 10.5 to 12.5 %,while increasing CP level above 12.5 % of the ration milk yield was increase very small. However, there were no significant differences among the four levels of CP. Kalscheur et al. (1999) reported that milk yield in mid-lactation cows was not effected by increasing dietary CP from 13.3 to 15.3 % of DM. DailyCP and TDN requirements of dairy cattle given by NRC(1989) in dairy cattle with 450 kg of body weight, daily milk yield and fat composition at 12.5 kg and 3.5 % were 1.4 and 7.2 kg/h/d, respectively.

This increase in milk yield was less than that observed in previous work in which milk production increased by 1.4 kg / d as dietary CP increased from 13.8 to 17.5 % by the addition of cottonseed meal(Grings et al.,1991). In the earlier trial, however, with in early lactating cows DM intake was increased by 1.6 % by feeding higher CP, whereas, in the present study, DM intake increased by only 0.92 as dietary CP increased from 10.5 to 12.5 %. When calculated in terms of increasing milk production per percent unit increasing of dietary CP by the addition of cottonseed meal, in previous work milk production increased by 0.37 kg/unit increased of dietary CP. This level was similar to this experiment, where milk production increased by 0.41 kg/unit of dietary CP, increased by addition of cottonseed meal.

Although the total amount of milk produced increased with increasing CP, the amount of milk produced per unit of CP fed decreased. The kilograms of milk produced per kilogram CP consumed were 8.92, 8.21, 7.25, and 6.11 for the 10.5, 12.5, 13.7, and 14.4% dietary CP diets, respectively. This value is less than observed in previous work (Grings et al.,1991), The kilograms of milk produced per kilogram CP consumed were 11.03, 8.82, 7.45, and 6.10 for the 13.8, 17.5, 20.4, and 23.9% CP diets respectively. However, in earlier work, on early lactating cows ( 3rd week of lactation) they were producing a minimum of 27 kg/d of milk, while in this experiment was cows had average milk yields 10-15 kg/d during mid-lactation (14 -21 wk of lactation).

The increasing dietary CP could have altered other chemical components (nonstructural carbohydrates ) of the diet due to the decreased proportion of grain in the diet (Grings et al.,1991). For the dietary treatments of this study the proportion of grain (rice bran, broken rice ) was decreased when CP increased in order to make the TDN of the different dietary treatments equal. This change could result in an increase of ratio CP to total non-structural carbohydrates that may effect rate and extent of digestion and microbial protein production that could result in changes in milk yield (Oldham, 1984).

Percentages of fat, protein, lactose, solids- not- fat and total solids in milk were not affected by dietary CP concentration by addition of cottonseed meal. Grings et al.(1991) observed no differences in milk composition as dietary CP was increased from 13.8 to 17.8%.Meanwhile Wanapat et al. (1996) found that supplementation of cottonseed meal up to 5 kg/head/day did not affected milk composition in crossbred dairy cows fed rice straw in the tropics.

Ruminal fermentation BUN and MUN

Ruminal NH₃-N, BUN and MUN were linearly and positively correlated with dietary CP content (P<0.001),which is in agreement with previous studies (Gustafsson, 1993; Roseler et al., 1993; Baker et al., 1995;) when dietary CP was increased. Preston et al.(1965) stated that the quantity of ammonia absorbed from the rumen was reflected in circulating BUN, and the results of the present study showed that simple regression for BUN on NH₃-N (Figure 4) and correlation between BUN and MUN were strongly correlated ( R² =0.97, R²= 0.90 respectively). This is supported by the study of Hammond (1983), where BUN was found to be highly correlated with ruminal ammonia. Several studies (Roseler et al., 1993; Baker et al., 1995; Butler et al., 1996) had shown that MUN was highly correlated with BUN. Recently, Abeni et al.(2000) reported that BUN concentrations more relate to dietary CP to energy ratio of diets. Therefore, in healthy ruminants, BUN and MUN concentrations are indicative of the protein to energy ratio in the diet (crude protein :digestible organic matter, CP: DOM ratio). This situation was explained by Hammond ( 1983) who stated that when energy intake was held constant, increasing dietary protein would increase BUN concentrations. Also, in lactating dairy cows, an increase in BUN and MUN was caused by excess CP (Grings et al.,1991; Baker et al., 1995). However, MUN may prove to be a better indicator of excess CP because concentrations are a result of equilibration overtime. The reason was explained by Gustafsson and Palmquist (1993) who have observed diural variations in BUN, ruminal NH₃-Nand MUN for the whole day, and typically BUN concentrations peak about 4 to 6 h-post feeding.

Expressed as digestible organic matter: crude protein (DOM:CP) the optimum ratio was about 1/7 (Moore et al., 1995). Balanced diets for lactating dairy cows were associated with average BUN concentrations of 15 mg% (Roseler et al., 1993) and average MUN concentrations of 15 to 16 mg% (Baker et al., 1995) or 11 - 17 mg/% (Hwang, et al., 2000). High levels of BUN and MUN indicated NH₃-N losses from the rumen with loss of protein. Hwang (2000)summarizedthat cattle producing milk that contains a level of MUN and milk protein within the ranges of the standard reference values of 11-17 mg% and 3.0% milk protein was regarded as indicating a balanced protein and energy intake. BUN, MUN and CP:DOM ratio lower than this reference could be due to the insufficiency in CP perunit of energy, in other hand higher than this reference could be due to excess in CP perunit of energy.

The results of this study showed that digestible intake of crude protein :organic matter were 1/8.3, 1/ 7.3, 1/ 6.4, 1/5.7 for the 10.5, 12.5, 13.7, and 14.4% CP diets, respectively, and average BUN concentrations at 4 h-post feeding 11.6, 13.6, 16.12, 19.87 mg/dL and average MUN concentrations of 10.63, 12.8, 15.0, 18.5 mg/dL for the 10.5, 12.5, 13.7, and 14.4% CP diets respectively.According to previous studies, the most balanced diets in present study were dietary CP 12.5 and 13.7 % which save optimum levels of BUN, MUN and crude protein to organic matter ratio . The most imbalanced diet in terms of excess energy content was CP 10.5 diet %, with lower levels of MUN , BUN and crude protein to organic matte ratio. The diet withan excess of was the CP 14.4 diet % ,with surplus levels of BUN, MUN and crude protein to organic matter ratio.Both imbalanced diets could affect milk yeild. From this experiment it was shown that increasing CP level above 13.7% of the ration did not improve milk yield, it could be due to excess the CP in the diet.

Income over feed, expressed as US$/kg of milk was high in the 12.5 and 13.7 diets CP %.

The high level of dietary CP was reflected by with high feed costs. Although high levels of dietary CP were offered to ruminants, the response of animals to protein may not occur if protein and energy imbalance from those resulting in loss of profit. Godden et al.( 2000) noted that herds with mean milk urea nitrogen had a positive relationship with feed costs per cow per day. Therefore,excessive feeding of dietary CP can be costly and economically, through increased feeding cost and the results of the present study showed loss of income with dietary CP level above 13.7 %.

Conclusions and recomendations

From the results of the current study, it can be concluded that:

• DMI tended to linearly increase with increasing dietary CP by the use of cottonseed meal.
• OM digestion coefficient was increased with increased dietary CP level.
• Daily milk yield tended to linearly increase as level of CP in the diet increased.
• Daily milk yield tended to increase with increased CP from 10.5 to 13.7 % with normal levels of BUN and MUN.
• Income over feed in terms of US$/kg of milk increased with increased CP from 10.5 to 13.7% and decreased when the CP level was higher than 13.7% (quadratic effect P < 0.09).
• Increasing dietary CP levels from 10.5 to 13.7 % using cottonseed meal as the main source to completely replace soybean meal was beneficial to cows consuming rice straw and cassava chips based-diets. Increasing CP level above 13.7% of total ration did not result in additional improved milk yield and composition or net income.
• The use of cottonseed meal should be highly recommended as a protein source in concentrate supplement especially for small-holder dairy farmers.

However, further researches relating to the balance of energy to protein should also be considered in protein supplementation for dairy cows.

Acknowledgements

Acknowledgements are extended to the Swedish Agency for Research Co-operation with Developing Countries (SAREC) for providing schorship and research support for the senior author. Dr. Manit Thungtagun director of Skon-Nakhon Agricultural Research and Training center, Rajamangala Institute of Technology, Skon-Nakhon Thailand for animals and laboratory supported. Assistant Professor Narong Ponvong , Dr Sunton Wittayakun and Mr. Chaweng Sankong , DVM. for facilitation in this experiment, Onanong Poungchompoo for laboratory suggestions.
 

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