Comparison of In Sacco Rumen Dry Matter Degradability and Feeds intake and Digestion of Crossbred Dairy Cows (Holestian Friesian X Horro) Supplemented with Concentrate Diet

A study was conducted at Bako Agricultural Research Centre to evaluate the feeding value of Pennisetum purpureum Silage (PPS) as basal diet when offered sole or in mixture with Natural Grass Hay (NGH) on voluntary feed intake, digestibility, degradability, milk yield and composition of crossbred dairy cattle. Ten dairy cows (Horro X Friesian) with similar milk yield (6.2-8.5 kg d -1 ), initial body weight of 307.99±8.53 kg (mean ± SEM), early stage of lactation, but differing in parities were used in a switch over 5X5 double Latin square design. There were five periods each composed of 30 days, 15 days for adaptation and the remaining 15 days for data collection. Treatments were NGH and PPS at a ratio of 100:0 (T1), 75:25 (T2), 50:50 (T3), 25:75 (T4) and 0:100% (T5), respectively. The basal diets were fed ad libitum. All animals were fed concentrate mix (49.5% maize grain + 49.5% noug seed cake + 1% salt) at a level of 0.5 kg/l of milk and additional 100 gram mineral mixtures was added for each cows daily into feed trough. Results of chemical analysis and degradability studies of experimental feeds indicated that PPS (CP=13.85%, ME=10.22 (MJKg-1DM) had better nutritive value than NGH (CP=11.72% and ME=7.98 (MJKg-1 DM). Ruminal in Sacco degradation characteristics observed for PPS were good indicative of being better basal feed than NGH. The daily DM, CP, and ME intake were highly significant (P<0.001) among the treatments with the highest intake observed when cows were fed sole PPS (T5). Apparent DM digestibility of T5 (66.1) were higher (P<0.001) than T1 (63.4), T2 (63.6), T3 (64.1) and T4 (64.9%). Crude protein and neutral detergent fiber digestibility coefficient were not affected by the different dietary treatments (P>0.05). Daily milk yield was higher (P<0.01) for T4 (6.60) and T5 (6.89) as compared to T1 (6.28 l/d). Composition of all milk constituents were not significantly (P>0.05) different among dietary treatments. Mean daily live weight loss was not significantly (P>0.05) different among treatments. Therefore, the result demonstrated that PPS had better feeding value as compared to the NGH for crossbred lactating dairy cows and can be conserved and used especially in the dry season when conventional roughages are in short supply and low in CP content.


Introduction
The inadequacy and fluctuations in feed supply is the major stumbling block affecting livestock production in Ethiopia [1]. In the mixed crop-livestock production systems of the Ethiopian highlands, feed resources for livestock mainly come from marginal pasturelands, crop residues, and aftermath grazing [2]. Nevertheless, forages from marginal pasturelands and crop residues are generally low quality. Thus, the nutritional requirements of dry pregnant and lactating cattle for milk production are not sufficiently met. Under such circumstances, cows in early lactation and high Tesfaye Mediksa: Comparison of In Sacco Rumen Dry Matter Degradability and Feeds intake and Digestion of Crossbred Dairy Cows (Holestian Friesian X Horro) Supplemented with Concentrate Diet producing cows are typically in a negative energy balance. Factors associated with a negative energy balance have been suggested to have adverse implication on reproductive efficiency and milk production and body weight loss of animals [3,4]. This is further aggravated by the fact that yield and nutritive value of tropical grasses decline sharply as dry season approaches [5]; leading to reduced feed intake, greater weight loss, and poor milk production from cattle raised in extensive production systems [6]. The situation may be reversed during the wet season when there is more forage than being used [7] and opportunity to cultivate forage is high. Thus, surplus and cultivated quality forages should be conserved during the wet season for use during the dry season. To this effect, silage-making is a common means of preserving surplus forage which could be fed to livestock during periods of scarcity [8]. By conserving excess forage produced during the wet season to silage [8], the low production and productivity of dairy animals during the dry season due to scarcity of forage can be ameliorated. For such purpose, Napier grass (Pennesitum purpureum) is a high yielding tropical grass with great potentials for making silage. Napier grass (Pennisetum purpureum) is recommended as basal forage for intensive cattle production because of its high biomass fresh dry matter yield of 40 t/ha compared to other grasses [9]. Napier grass is tall growing perennial grass which is indigenous to tropical and subtropical climates. Since Pennesitum purpureum, yields high biomass, it can be used for silage production which will ensure sufficient availability of feed on farm throughout the year. However, the potential of this forage as a quality roughage feed for dairy when made to silage is not well studied in Ethiopia. Its' supplementation with commercial protein supplements was not fully explored, although generally supplementing Napier grass with concentrate or leguminous forage plants was reported to improve animal performance [10]. Moreover, the potential of Napier grass in improving the utilization of other grasses such as natural hay is not also well documented. To fill the existing information gap, evaluation of Pennesitum purpureum through animal feeding trials is important [11]. Therefore, the objective of this study was to study the effects of feeding Napier grass silage with natural grass hay in varying proportions on voluntary feed intake, digestibility, and milk yield and composition of crossbred dairy cattle and its degradability of feed.

Study Area
Bako Agricultural Research Centre is located in Oromia Regional State West Shoa Zone at about 257 Km from the capital city Addis Ababa on the way to Nekemte town. The center is located at 8 km from Bako town. The altitude of the research center is 1650 masl and lies at about 09°6'N latitude and 37°09'E longitude. The area has a warm sub-humid climate with annual mean minimum and maximum temperature of 13°C and 29.9°C, respectively. Mean monthly minimum and maximum temperatures are about 10.4°C and 33.6°C, respectively, with an average monthly temperature of 21°C. The daily mean minimum and maximum temperatures are 9.4°C and 31.3°C, respectively. The relative humidity of the study area was 48.8% for the year 2013/14 cropping calendar during which the study was conducted. The area is known by Unimodal types of rainfall and receives annual rainfall of 1431 mm mainly from May to September with maximum precipitation in the month of June to August. Sixty percent of the soil is reddish brown in color, and clay-loam in texture [12].

Experimental Animals and Management
A total of ten crossbred cows (Horro x Holstein Fresian) were used for this experiment. Experimental cows with similar lactation performance, same early stage of lactation, similar body weight, but with different parities were selected. All cows were weighed and drenched with broad-spectrum anti-helminthics (Albendazole 500 mg) prior the commencement of the experiment. The calves were separated from their dams five days after parturition and reared according to the standard calf rearing procedures of the research center. The cows were placed in an individual pen in a well-ventilated barn with concrete floor and appropriate drainage slope and gutters and stall-fed. The cows were hand-milked twice daily at approximately 12-hour intervals in milking room.

Feed Preparation and Feeding
Napier grass was harvested, chopped, ensiled and Natural pasture hay was harvested before it is matured, and sun dried, chopped and stored under a hay shade and used as basal diet throughout the experimental period. The basal feed offer was adjusted daily by allowing 20% of refusal from previous day's intake. The quantity of concentrate mix offered daily was at the rate of 0.5 kg/l of milk produced by each cow and offered with equal portions at 5:00 am and 5:00 pm during the morning and evening milking time, respectively. Representative and composite samples of all experimental feeds were taken for laboratory analysis.

Experimental Design, Treatments, and Measurements
At the beginning of the experiment, ten cows were randomly assigned in a switch over 5X5 double Latin square design. There were five periods each consisting 30 days. During the first 15 days of each period, animals were acclimated to the experimental diet and the remaining 15 days were used to collect data. Hence, the experiments took 150 days; being started in November 2013 and finished in March 2014. The experimental animals were initially randomly allotted to one of the five dietary treatments given below. The concentrate mix is 49.5% maize grain + 49.5% noug seed cake + 1% salt). Treatments were: T1 = Natural grass hay ad libitum + Concentrate mix (0.5 kg/l of milk) T2 = 75% Natural grass hay + 25% Napier grass silage + Concentrate mix (0.5 kg/l of milk) T3 = 50% Natural grass hay + 50% Napier grass silage + Concentrate mix (0.5 kg/l of milk) T4 = 25% Natural grass hay + 75% Napier grass silage + Concentrate mix (0.5 kg/l of milk) T5 = Napier grass silage ad libitum + Concentrate mix (0.5 kg/l of milk) The basal feed was offered ad libitum at a 20% refusal rate and the offer was adjusted every four days. Treatment one and treatment five were fed ad libitum natural grass hay and Pennisetum Purpureum silage at a 20% refusal rate, respectively. For other treatments (T2, T3 and T4) that were offered the mixture of the two basal diets (natural grass hay and Pennisetum Purpureum silage), the proportion was determined from the measurements of the individual basal diets intake determined before the beginning of the actual experiment. This was done by feeding each cow with each basal diet for five days and determining the mean intake of each basal diet, which was then used to determine the amount of each basal diet in the mixture. The 20% refusal rate was also calculated based on the average intake. The amount of the roughages calculated for the day was measured and placed in front of the animal and was offered three times at 08:00, 14:00 and 20:00 hours each day. The quantity of concentrate mix offered daily was at the rate of 0.5 kg/l of milk produced by each cow and it was offered with equal portions at 05:00 and 17:00 hours during the morning and evening milking. Adjustments for concentrate offer was made at the end of each period and for each treatment based on the actual milk produced. Feed offered and refused was measured and recorded for each cow to determine daily feed and nutrient intake and feed conversion ratio was calculated from total dry matter intake in kg divided by milk yield in kg and times by hundred. Water was available to the animal all the time throughout the experiment and 100 gram mineral mixtures composed of (Ca 280g, P 170g, Mg 120g, K 200g, Na 105g, Cl 124g, Cu 95mg, Zn 278mg, Mn 277mg, Fe 350mg) was added for each cow daily into feed trough.

Diet Apparent Digestibility
Apparent digestibility of the diet used in each treatment was determined using total feacal collection methods for a period of 5 consecutive days. Farm personnel were assigned around the clock to scoop faeces into plastic buckets as soon as the animals defecated. Urine contamination was minimized by frequent washing of the concrete floor with high pressure running water using a plastic water tube. Individual cow's faeces were weighed every morning before 08:00 hours and before fresh feeds were given to the animals. After weighing, the faeces from each cow were thoroughly mixed and a sample taken and placed in polyethylene bag. Composite samples of about 1% of the daily collected fecal samples were mixed and stored as one sample in a deep freezer (-20°C) until the end of the collection period. At the end of the collection period, the 5 days pooled samples were subsequently thawed and mixed thoroughly and two subsamples taken. One sample for estimating DM was oven dried at 105°C for 24 hours, while the other sample was oven dried at 65°C for 72 hours, ground to pass a 1mm sieve and stored in sample bottles at room temperature. Composite samples of the hay, Napier grass silage, concentrate mixture and faecal DM output were analyzed to determine DM, OM, N, NDF, and ADF digestibility.

Invitro Organic Matter Digestibility
The two stage rumen inoculums-pepsin method of [13] was used to determine IVOMD. Rumen liquor was collected from ruminally festulated steers and transported to the laboratory using thermos flasks that had been pre-warmed to 39°C Rumen liquor was taken in the morning before animals are offered feed. A duplicate sample of 0.5 g of each were incubated with 30 ml of rumen liquor and a buffer in 100 ml test tube in water bath at 39°C for a period of 48 hour for microbial digestion followed by another 48 hour for enzyme digestion with acid pepsin solution. Blank samples containing buffered rumen fluid were incubated in duplicates for adjustment.

In vitro OM/DOMD = OM in the feed − (OM in residue -blank) x 100 OM in the feed
Where OM = 100 -Ash (measured after incineration of feed or residue) Metabolisable energy contents of the feeds were estimated from in vitro organic matter digestibility (IVOMD) as described by [14] as: ME (MJ/kg)=0.016IVOMD.

Nylon Bag Degradability
The kinetics of feed digestion for both the basal diet and supplementary feeds in the rumen was studied in three festulated steers fed standard diet (ad libitum natural pasture hay + 2 kg concentrate mix (74% wheat bran, 25% noug seed cake and 1% salt). Dry matter degradability of the experimental feeds was determined using nylon bag technique developed by [15]. Feed samples grounded to pass 2 mm screen and weighing 3g on air-dry basis were transferred into each nylon bag. The bags were then incubated in duplicates for 6, 12, 24, 48, 72, and 96 hours in the rumen of each cow. On the removal of the bags at the end of each incubation period, the bags were washed manually under a running tap water until clear water appeared. The zero hour bags (two bags per sample) were not incubated, but allowed to stay in bucket containing clean water for about half an hour. After washing, the bags were dried in a forceddraught oven at 65°C for 72 h, cooled and weighed. The residues were then pooled for each animal by incubation time and analyzed for determination of DM degradability. Data from nylon bag disappearance were fitted to the model given below [15] using the neway excel programme: Y = a + b (1e -ct ); where; Y = the potential disappearance of DM at time t; a = the rapidly soluble fraction; b = the potentially but slowly degradable fraction; c = the rate of degradation of b; t = time (hr). Effective degradability (ED) was calculated using the exponential model [15] as ED = a + bc/ (k + c); where; k= passage rate estimated at 3%/h. Potential degradability (PD) = a+b.

Chemical Analysis
All samples of feed offered and refusals and faeces were analyzed for DM, ash, N (Kjeldahl-N) according to [16]. Organic matter (OM) was determined as 100-ash. Neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were determined by the methods of [17]. Invitro organic matter digestibility of feed offered and refusal was determined using the procedures outlined by [13). The milk samples were used to determine percentage fat, protein and solid not fat (SNF) by Ultrasonic Ekomilk Analyzer (30 w Bulteh 2000, Bulgaria), which have the capacity to measure 20 -25 samples per hour. Total milk solids (TS) were calculated as TS = SNF+Fat. Calcium and phosphorous content of the offered feeds were analyzed by atomic absorption spectrophotometry and colorimetry [18] respectively.

Statistical Analysis
Voluntary DM and nutrient in takes, live weight change, milk yield and compositions, and digestibility were subjected to GLM procedure for double Latin Square Design using Statistical Analysis System [19]. Treatment means were separated using Least Significant Difference (LSD). The models used for the analysis of data were: Yijk=µ +Ci+Pj+Tk+Eijk, Where; µ=Overall mean; Ci=Cow effect (parity); Pj=Period effect; Tk=Treatment effect; Eijk= Experimental error

Chemical Composition of Experimental Feeds
The NDF, ADF, and ADL contents of natural grass hay used in this study were higher than that of Pennisetum Purpureum Silage. The CP contents were high in Pennisetum Purpureum Silage than natural grass hay, but OM was almost similar. The CP content of concentrate was higher than that of Pennisetum Purpureum Silage and their combination with natural grass hay. The natural grass hay contained 7.49% and 32.30% more NDF than Pennisetum Purpureum Silage and concentrate mix, respectively. The same trend was observed for ADF and ADL contents of the feeds. The level of ADL concentration observed for natural grass hay and Pennisetum Purpureum Silage was much higher and almost 3.1 and 2.67 times greater than that observed for the concentrate mix. The CP content of maize grain was 9.9%. These indicates that crushed maize grain is a good source of protein, which could be used as a supplement when animals feed is based on native grass hay, pasture grazing or crop residues.

Degradability Characteristics of Feeds Used in the Study
Rumen degradability characteristics of the feedstuffs are presented in Table 2. Effective degradability, potential degradability, rate of degradation, lag phase and insoluble but fermentable fractions were highly different (P<0.001) among feed types. In all these parameters except lag phase values were highest for concentrate followed by PPS and were lowest for NGH, while the reverse was true for lag phase. Washing loss was not significant (P>0.05) among feed types. According to [20] the lag time in the degradation of fibrous feeds is caused by the substrate and a long lag time is one of the factors limiting intake and utilization of fibrous feeds. The relatively long lag time of NGH could be a reflection of its probable higher lignin and cellulose contents compared with PPS and concentrate feeds. The degradation characteristics are generally comparable to those reported earlier [21,22].

Dry Matter and Nutrients Intakes
There was no significant difference (P>0.001) between T1 and T2 in daily DM intake, but values were lower than T4 and T3. The difference could be attributed to the high rumen degradable protein content of the Pennisetum Purpureum Silage compared to natural grass hay, which might have enhanced the efficiency of rumen microorganisms that increase fiber degradability and digestibility thereby improving feed intake [23]. The low CP and high fiber contents of the natural grass hay likely depressed both feed intake and digestibility since NDF is negatively correlated with feed intake and its content above 55% can limit DM intake [24,25]. Animals consuming feeds containing better protein will eat more than those given less protein containg diets [26].
In this study, cows fed with sole Pennisetum Purpureum Silage (T5) as a basal diet consumed 0.56, 0.86, 1.43, and 1.62 kg/d more basal diet than T4, T3, T2, and T1, respectively. The intake of DM (% BW) was highly significant (P<0. 01) among the treatments. This result was comparable with the 3.1% BW intake reported by [27] and higher than the values (2.2 -2.3%) reported by [28]. Daily DM intake of 3.32 kg/d for urea treated rice straw supplemented with Veranostylo [29] and 2.46 kg/100 kg BW for treated rice straw were reported by [29]. The total DM intake (g/kg W 0.75 ) was highly significant (P<0.001) among the treatments and this result was comparable with that reported by [30] who noted 147 g/kg W 0.75 for lactating crossbred cows fed rations containing calcium salts of palm oil fatty acids (bypass fat). As well 113.2 and 122.1 of DM intake (g/kg W 0.75 ) was reported by [31]. The observed variations among the studies emanated from the differences in the quality of the feed used, animal factors (age, physiological status of the animals and breed), rumen fill, rate of passage of particulate matter and rates of degradation of experimental feeds used. Increased organic matter intake (P<0.001) when cows were fed with basal diet consisting Pennisetum Purpureum Silage might be due to the increased total DM and CP intake. means within rows having different superscript are significantly different at *** = P<0.001; ** = P<0.01; * = P<0.05; SL = Significance level; SEM = Standard error of mean; DMI = Dry matter intake; CP = Crude protein; ME = Metabolisable energy; NDF= Nutral detergent fiber; ADF=Acid detergent fiber intake; ADL= Acid detergent lignin; BW=Body weight; W 0.75 =Metabolic body weight; T1= ad libitum Hay + Concentrate mix (0.5 kg/l of milk); T2= 75% Hay + 25% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T3=50% Hay + 50% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T4=25% Hay + 75% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T5= ad libitum Napier Grass Silage + Concentrate mix (0.5 kg/l of milk), Concentrate =49.5% maize grain + 49.5% noug seed cake + 1% salt Intake of feed by ruminant can be improved through concentrate supplementation [32]. Addition of CP supplement may stimulate efficient rumen fermentation, more passage rate and intake [33]. This implies the presence of direct relationship between CP content of feeds and feed intake [34]. Earlier report [35] showed improvement in the Crossbred Dairy Cows (Holestian Friesian X Horro) Supplemented with Concentrate Diet daily total DM intake due to supplementation. This may be attributed to the ability of the supplements to provide nitrogen and energy for the cellulolytic microbes upon degradation in the rumen [36] and increases the nitrogen content of the total diet, which in turn is likely to increase feed intake and the rate of degradation of the basal diet in the rumen [37]. When the rate of breakdown of digesta increases, feed intake is accordingly increased [38]. [39] Reported that if the ingested feed is retained longer in the rumen, it is expected that the animal would consume less feed, because of the occupied space or 'gut fill'. The highest (p<0.001) DM intake obtained for T5 might have arisen from the more balanced intakes of both CP and ME that have led to a more efficient utilization of the fiber in the total diet, which is in agreement with other studies [40,41].
The CP intake was 17.1, 17.2, 17.3, 17.6 and 17.7% of the total DM intake for T1, T2, T3, T4 and T5, respectively and its intake has shown an increase (P<0.001) with increasing level of Pennisetum Purpureum Silage in the mixtures due to the relatively higher CP content of Pennisetum Purpureum Silage than NHG and their mixture. As far as protein requirements concerned, the CP intake in all treatments of the present study was higher than the estimated daily CP (866.5 g/d) requirement of lactating cows producing 8-10 kg of milk per day with 4.5% butter fat [42]. This was due to almost similar milk production, hence amount of concentrate supplement offered to the experimental animals in all treatment groups during the entire feeding period. Moreover, protein supplementation brings about increase in the protein content of the feeds and this eventually leads to increase in protein intake [43].
The intake of NDF and ADF tend to increase as the proportion of Pennisetum Purpureum Silage in the basal diet increases and it was higher (p<0.001) in T5 than T1, T2, and T3. The ADL intake also showed a similar trend and was higher (P<0.05) in T5 than other treatments. Higher fibre intake when cows consumed higher proportion of Pennisetum Purpureum Silage was obviously attributed to the high total DM intake. Metabolisable energy intake among the treatments was highly significant (P<0.001). Higher ME intake was observed in T5 compared to T1, T2, and T3; and T4 has similar ME with T5 and higher as compared to T1. The positive association observed between Pennisetum Purpureum Silage and the concentrate mix was typically higher for T5 which can be explained by higher total DM intakes (Table 3). According to [44], feeds that have < 9, 9 -12 and >12 MJ ME/kg DM are classified as low, medium and high energy sources, respectively. The highest ME intake (101.5 MJ/head/day) obtained for 100% of Pennisetum Purpureum Silage and concentrate mix (T5) is above the estimated daily ME (97.6 MJ/head/day) requirement of lactating cows weighing 400 kg and producing 8-10 kg milk of 4.5% butter fat [43]. According to the [43], estimation of energy balance from this study showed a deficit of -14.54, -11.66. -5.63 and -2.11 MJ/d for T1, T2, T3 and T4, respectively, while a positive energy balances of +3.9 MJ/d was obtained for T5. The finding from this study was supported by [45] who noted that molasses or alkali treated straw based diets are more digestible, but they support little improvement in animal productivity unless they are supplemented with by-pass nutrients.

Apparent Dry Matter and Nutrient Digestibility
When cows fed T5 diet, the DM digestibility was higher by 2.72, 2.54, 2.05, and 1.23% as compared to T1, T2, T3, and T4, respectively. The diet that consist higher Pennisetum Purpureum Silage compared to 25% Hay + 75% Napier grass silage (T4) has also higher DM digestibility than T1 and T2 demonstrating that increased Pennisetum Purpureum Silage proportion in the basal diet improved DM digestibility. The improved DM digestibility at high level of Pennisetum Purpureum Silage in the basal diet might be associated with the nutrient contents of Pennisetum Purpureum Silage. Therefore, sole Pennisetum Purpureum Silage as basal diet can fairly be a better basal diet for crossbred dairy cows for good milk production when it is supplemented by concentrate diet at the rate of 0.5 kg/l of milk yield. The DM digestibility coefficient of treatment feeds in the current study was higher than 55.3% and 48.6% reported by [46,47], respectively. However, similar level of digestibility as in the present study was obtained by [48,49,50] who reported a value of 61.4, 60.7, and 63.3%, respectively.
The apparent OM digestibility (P<0.01) was significantly different among treatments. There were no significance difference (P>0.01) among T1, T2 and T3; and among T2, T3 and T4 in OM digestibility. Cows in T5 had shown higher OM digestibility compared to Cows in T1, T2, T3 and T4, which might be due to the higher CP intake in T5 ( Table 3) that have created a better environment by providing more N for rumen microorganisms. In support of the present finding, [51] noted that supplementation of Mubende goats fed Napier grass with different protein and energy sources increased DM and OM digestibility. Likewise, supplementation of sheep fed maize stover with Desmodium intortum hay resulted in improved digestibility of the diet as a result of increased microbial N supply and rumen fermentation [52].
Apparent ADF digestibility differed among treatments (P<0.05). Neverthles, NDF and CP digestibility were similar (P>0.05) among treatments. Apparent ADF digestibility was higher (P<0.05) in T4 and T5 as compared to T1. Absence of significant difference among treatments for NDF digestibility in the present study is also supported by previous research results [53,54,55] who reported that supplementation with dietary protein had no significant effect on NDF digestibility. The value of NDF digestibility in the present study is comparable with that reported (63.3%) earlier by [48] for low quality native hay supplemented with graded levels of tagasaste replacing a concentrate mix in the daily ration of lactating crossbred cows. [56] Reported high content of NDF and lignin fractions to be responsible for lower fiber degradation. The lack of response to fiber apparent digestibility was in agreement with that reported by [57]. The reason may be due to the higher NDF and ADF content in the basal diet as a result their intakes, which might have detrimental effect on the digestion of fiber. The observed disparity in the digestibility of feeds and nutrients between different experiments might be related with the differences in the nature of CP found in the treatment diets [58], breed and condition of the animals [59]. means within rows having different superscript are significantly different at *** = P<0.001; ** = P<0.01; * = P<0.05; ns = non-significant; T1= ad libitum Hay + Concentrate mix (0.5 kg/l of milk); T2 = 75%Hay + 25% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T3=50%Hay + 50% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T4=25% Hay + 75% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T5= ad libitum Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); Concentrate mix = 49.5% maize grain + 49.5% noug seed cake + 1% salt; DM = dry matter; CP = crude protein; OM = organic matter; NDF = neutral detergent fiber; ADF = Acid detergent fiber.
The CP digestibility was expected to follow the differences in CP intake observed among treatments. It has been reported that increasing CP in the diet increased the digestibility of CP [60]. The CP digestibility observed in the present study could safely be compared to the mean CP digestibility of 71.5% reported by [41] for crossbred cows fed low quality basal diets and supplemented with graded levels of lablab hay and wheat bran. Likewise, [49,50] reported CP digestibility of 67.9% and 72.7%, respectively in crossbred dairy cows, which is similar to the present value. In contrast to the present study 48.6% digestibility have also been reported by [47] for 3% urea treated wheat straw supplemented with a concentrates plus some green forage legume for local cows.

Milk Yield and Composition
Daily milk yield was significantly different among treatments (P<0.01) and was higher in T4 and T5 as compared to T1. Cows fed with sole Pennisetum Purpureum Silage (T5) produced more milk than those in T2 and T3 basal diets. The difference in milk yield among treatment groups is attributed to the differences in crude protein and energy contents in the diets [26]. [61] Indicated that supplemented cows produced significantly more milk than those grazed on natural pasture alone. Milk protein, milk fat, solid not fat (SNF) and total solid (TS) contents were not significantly (P>0.05) different among treatments. Results of the present study of milk composition agreed with [62] who reported that feeding lactating Holstein cows with either ammonium sulphateneutralised rice straw or non-neutralized rice straw for increased CP intakes did not change milk composition. However, [61,63] noted differences in milk composition under different concentrate supplementation regimes. The observed lack of differences in milk composition is due to the similar type and same amount per kg milk of concentrate supplementation across the treatments. means within rows having different superscript are significantly different at; (**)= P<0.01; (*)= P<0.05; SL = significance level; SEM = standard error of mean; ns = not significant; T1= ad libitum Hay + Concentrate mix (0.5 kg/l of milk); T2=75%Hay + 25% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T3=50%Hay + 50% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T4=25% Hay + 75% Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); T5= ad libitum Napier Grass Silage + Concentrate mix (0.5 kg/l of milk); Concentrate mix = 49.5% maize grain + 49.5% noug seed cake + 1% salt; SNF=solid not fat; TS = total solid; FCR = feed conversion ratio; TDMI=total dry matter intake; MY =milk yield.
Generally, both the CP and ME intake were sufficient to meet requirement for the observed milk yield (6.5 kg/d). The mean daily milk yield obtained from the present trial was almost comparable to the values of 6.5, 6.7 and 5.6 kg d -1 reported by [49,54,65] for crossbred lactating cows fed urea treated teff straw basal diet and supplemented with oats-vetch hay with a concentrate at the rate of 2.5 kg/day and barely straws supplemented with concentrate mix, respectively. The feed conversion ratio was significantly (P <0.05) different and increased from T1 to T5, but it is lower than the value reported by [28] who noted that the DM intake, milk yield and feed conversion ratio of Sokoto Gudali cows fed Napier Crossbred Dairy Cows (Holestian Friesian X Horro) Supplemented with Concentrate Diet grass-cassava peel silage were 13.93 kg/d, 6.7 kg/d and 2.08 DMI/ kg milk yield, respectively. The variation between different reports might be due to the differences in metabolizable energy intake and intrinsic factors like level of production, parity, stage of lactation, external factors like environmental stress, and unequal intervals between milking and changes in feeding.

Conclusion
If farmers establish and use Napier grass silage, milk yield from crossbred dairy cows can be improved, because Napier grass silage has better degradability (in sacco) and digestibility (in vivo). Therefore, considering milk yield in this study, it can be concluded that cows fed basal diet of sole Napier grass silage with recommended concentrate mix (0.5 kg/l of milk yield) optimize biological benefits as compared to cows consumed other basal diets. There is a need for further study to determine effect of such dietary treatments over the entire lactation period for conclusive economic decision. In order to verify the importance of the present study at farmer's level, undertaking on-farm trials using the treatments used in the current study is worthwhile