Growth, nutrient utilization and amino acid digestibility of dairy calves fed milk replacers containing different amounts of protein in the preruminant period.
ABSTRACT : This study was designed to examine the effects of different dietary protein levels on growth performance, nutrient utilization, amino acid amino acid (əmē`nō), any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. (AA) digestibility digestibility
the proportion of a feed or diet which can be digested by the normal animal of the subject species.
see digestibility coefficient. and serum biochemical parameters of preruminant dairy calves. Fifteen healthy new-born calves were randomly allotted to three experimental groups and fed with different milk replacer that contained 18% (LP), 22% (MP) or 26% (HP) of protein. The results showed that final BW, net gain and ADG ADG
average daily gain.
ADG Ambulatory diagnostic group were significantly higher in the MP group than in LP and HP groups (p<0.05). In addition, the apparent digestibility of CP in the MP group was significantly higher than in the other two groups (p<0.05). The values of N intake and fecal fecal /fe·cal/ (fe´k'l) pertaining to or of the nature of feces.
Relating to or composed of feces.
pertaining to or of the nature of feces. N excretion were significantly increased following the increase of dietary protein content (p<0.05). However, in all three groups of animals, dietary protein content had no significant effect on urinary N concentration (p>0.05). BUN concentration, on the other hand, decreased as calves grew but increased following the increase of dietary CP content. Furthermore, no significant differences in digestibility of amino acids were observed among these three groups of animals (p>0.05). We concluded that calves fed with milk replacer containing 22% of protein had better growth performance and nutrient utilization as compared to animals treated with milk replacer containing either 18% or 26% of protein. (Key Words : Calves, Dietary Protein Level, Amino Acid, Digestibility, Growth)
One of the major challenges of rearing preruminant calves on the dairy farm is to reduce feed costs (Babu ba·bu also ba·boo
n. pl. ba·bus also ba·boos
1. Used as a Hindi courtesy title for a man, equivalent to Mr.
a. A Hindu clerk who is literate in English.
b. et al., 2003). One effective strategy is using milk replacer (MR) instead of whole milk for young calves. Protein is the most expensive and key component in formulating rations for animals. However, the optimum level of protein in the diet remains to be determined. The level of protein in the diet of calves is critical, because excessively low or high protein content can cause animal production, welfare and environmental problems. Indeed, several researchers have stated the absolute need to accurately define the protein requirement for dairy calves as well as the optimal protein level in milk replacer (Blome et al., 2003; Lohakare et al., 2006).
The Nutrient Requirements of Dairy Cattle, established by NRC NRC
1. National Research Council
2. Nuclear Regulatory Commission
Noun 1. NRC - an independent federal agency created in 1974 to license and regulate nuclear power plants (2001), is the widely accepted feeding standard. However, this system was established based upon limited earlier body composition data of young calves that may not reflect the composition of current Holstein calves (Bartlett et al., 2006). Because of the differences between dairy farms (e.g., environment, management, feedstuff feedstuff
see feed. conditions, etc), this system may not be suitable to all countries. Most importantly Adv. 1. most importantly - above and beyond all other consideration; "above all, you must be independent"
above all, most especially , those previous studies were based upon a supplement of animal proteins but not vegetable proteins; therefore, it does not reflect the function of current milk replacers supplied with vegetable proteins.
Previous studies on calves fed with different levels of dietary protein mainly emphasized growth performance (Donnelly and Hutton, 1976a; Blome et al., 2003), body composition (Donnelly and Hutton, 1976b; Jagusch et al., 1970; Bartlett et al., 2006) and health (Nyachoti et al., 2006; Quigley et al., 2006). These studies lack unanimity UNANIMITY. The agreement of all the persons concerned in a thing in design and opinion.
2. Generally a simple majority (q.v.) of any number of persons is sufficient to do such acts as the whole number can do; for example, a majority of the legislature can pass on optimum dietary CP content (Lohakare et al., 2006). In the current study, we performed a complete panel of experiments to determine the influence of different protein contents of milk replacers on growth performance, nutrient utilization, amino acid (AA) digestibility and blood metabolism in preruminant calves.
MATERIALS AND METHODS
Animals, diets, and management
Fifteen healthy new born Holstein calves were used to evaluate growth performance, nutrient utilization and AA digestibility of preruminant calves less than 8 weeks age. All the animals received 3 kg of colostrum colostrum /co·los·trum/ (kol-os´trum) the thin, yellow, milky fluid secreted by the mammary gland a few days before or after parturition.
n. within 12 h after birth, and were fed whole milk with nipple nipple - Trackpoint buckets at a rate of 8% body weight (BW) during the first week. The calves were stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers.
Arranged in the form of layers or strata. on bodweight and then randomly divided into three groups of five animals In the Chinese martial arts, imagery of the Five Animals (Chinese: 五形; Pinyin: wǔ xíng . All the groups had an adaptation period over days 8-14 when they were fed mixed milk (milk replacer and whole milk), with the ratio of milk replacer to whole milk increased from 1:3 to 3:1 gradually during this period. From day 15 to 56, each group was fed one of the three milk replacers with different protein levels.
The milk replacers contained 18% (low protein, LP), 22% (medium protein, MP), and 26% (high protein, HP) of crude protein (CP), and were reconstituted to 12.5% solid content and fed at 10% of BW daily; feeding was allocated across three times at 8:30, 14:00, and 20:30 and the amount fed to each calf was adjusted with growth. Milk replacers were formulated to be isocaloric and were based on soy protein Soy protein is generally regarded as the storage protein held in discrete particles called protein bodies which are estimated to contain at least 60–70% of the total soybean protein. concentrate, whey whey
liquid residue from milk after the removal of cheese curds in the manufacture of cheese. An excellent protein supplement but difficult to handle in the liquid form, except to pigs maintained close to the cheese factory. Dried whey is easy to handle but processing costs are high. powder, skim milk skim milk
The milk from which the cream has been removed.
the residue from whole milk after the cream has been skimmed off. In today's usage it is the residue after the butterfat is removed. , fat and compound premix premix
a finite mixture of nutritional supplements such as minerals and vitamins, usually combined with a carrier and ready for mixing with a total ration. , but did not contain antibiotics. Nutrient composition of the milk replacers is shown in Table 1. Milk replacers were sampled weekly and pooled by group of calves. The calves were weighed twice weekly in the morning before feeding in order to assess changes in BW and average daily gain (ADG).
Concentrate feed was offered when calves were 3 weeks of age, and 300 g, 500 g, or 1,000 g concentrate feed was offered for each calf per day during weeks 3-4, 5-6 or 7-8, respectively, and any residue was recorded daily. Hay was offered ad libitum ad libitum
ad libitum feeding
food available at all times with the quantity and frequency of consumption being the free choice of the animal. and intake was recorded daily. Fresh water was provided to all the calves once each morning and afternoon throughout the study.
[FIGURE 1 OMITTED]
Each group of calves was housed individually in a well ventilated ven·ti·late
tr.v. ven·ti·lat·ed, ven·ti·lat·ing, ven·ti·lates
1. To admit fresh air into (a mine, for example) to replace stale or noxious air.
2. , dry-floored shed (5 x 5 [m.sup.2] large) before the metabolism test. The sheds were cleaned regularly and disinfected Disinfected
Decreased the number of microorganisms on or in an object.
Mentioned in: Isolation fortnightly fort·night·ly
Happening or appearing once in or every two weeks.
Once in a fortnight.
n. pl. fort·night·lies
A publication issued once every two weeks. . Calf health was monitored daily, fecal score was recorded using the following system: 0 = dry, hard; 1 = soft, formed; 2 = pudding-like; 3 = runny run·ny
adj. run·ni·er, run·ni·est
Inclined to run or flow: runny icing; a runny nose.
[-nier, -niest ; and 4 = liquid, splatters.
To obtain an accurate measure of the utilization of the diets throughout the study period, a metabolism trial of 10 d duration was conducted on all the experimental calves from day 46 to 56. During this period, all the calves were held individually in special metabolism stalls. Samples were not collected in the first 5-d to ensure the calves adapted to the environment. Collections of feces and urine of each calf were conducted during the last 5-d.
Total feces of each calf was collected and weighed twice daily (9:00 and 16:00), and after thorough and uniform mixing in a clean plastic basin, representative samples were taken and mixed with a few ml of 10% hydrochloric acid hydrochloric acid: see hydrogen chloride.
or muriatic acid
Solution in water of hydrogen chloride (HCl), a gaseous inorganic compound. solution, then stored at -20[degrees]C immediately. The feces samples from each calf were pooled over the 5-d collection period and dried at 65[degrees]C for 48 h. The pooled sample was sub-sampled for analysis of dry matter (DM), nitrogen (N), ether extract (EE), ash, calcium (Ca) and phosphorus (P) (AOAC, 1990), and AA.
Total urine was collected in a plastic bucket placed under the metabolism stall and measured twice a day at the same time as feces. 1% of total urine was collected and filtered through two-double pledgets into plastic bottles containing a few ml of 10% hydrochloric acid solution to maintain pH below 3. Samples were pooled for each calf after the collection period and stored at -20[degrees]C until analysis for N, Ca and P.
Samples of milk replacer, dry feed and hay were collected daily in the morning during the collection period, pooled over the 5 d of collection, then ground to pass through a 2 mm sieve and stored in plastic bags at -20[degrees]C. All the diet samples were assayed for DM, N, EE, ash, Ca, P and AA.
Blood sample collection
Blood was sampled fortnightly before the morning feeding from each calf by jugular jugular /jug·u·lar/ (jug´u-lar)
2. pertaining to a jugular vein.
3. a jugular vein.
adj. venipuncture venipuncture /veni·punc·ture/ (ven?i-pungk´chur) surgical puncture of a vein.
ve·ni·punc·ture or ve·ne·punc·ture
n. into separate evacuated tubes and centrifuged within 1 h at 3,000 rpm for 20 min at room temperature to obtain the serum. Serum was frozen at -20[degrees]C and used to determine concentrations of urea N (BUN), total protein (TP), albumin (ALB) and globulin globulin, any of a large family of proteins of a spherical or globular shape that are widely distributed throughout the plant and animal kingdoms. Many of them have been prepared in pure crystalline form. (GLOB).
The growth (Initial BW, Final BW, Net Gain and ADG), digestion (Nutrients and AA digestibility) and utilization (N, Ca and P retention) data were analyzed using the one-way ANOVA anova
see analysis of variance.
ANOVA Analysis of variance, see there procedure of SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance. 13.0. The fortnightly body weight and the blood variables (BUN, TP, ALB, GLOB concentrations and A/G ratios) were analyzed using the general linear models procedure (GLM GLM Global Language Monitor
GLM Global Marine (stock symbol)
GLM Graduated Length Method (ski instruction)
GLM Good Looking Mom (used in pediatric practices)
GLM God Loves Me ) of SPSS 13.0. Differences were identified using the Duncan's multiple range test (Duncan, 1955). Significance was declared at p<0.05 for all comparisons and the results were presented as mean values and standard deviation (SD).
RESULTS AND DISCUSSION
Initial BW did not differ among the three groups. Fortnightly BW gain of all calves increased from 2 to 8 wk (Figure 1). The highest values of final BW, gain and ADG were observed in the MP group (p<0.05) with average values of BW gain and ADG which reached 34.8 kg and 829 g/d, respectively, throughout the study. From the 2nd to the 4th wk, the changes in body weight gain were similar between the HP and the LP groups. However, by the 6th wk of age, calves of the HP group were heavier than the LP group. A growth response in calves by increasing dietary protein has been reported previously. Blome et al. (2003) reported that the final BW of calves increased linearly as dietary CP increased from 16% to 26%; similar results were obtained in calves fed skim milk-based replacers (Donnelly and Hutton (1976a). Furthermore, Brosh et al. (2000) reported higher BW gain in Holstein-Friesian calves fed a high CP diet as compared to those fed medium or low CP diets. In addition, the elevation of BW gain could be induced by increased availability in protein and energy levels in diets containing normal or high level of protein but not in diets with low level of protein (Singh et al., 1994; Verma, 1998). In contrast, it has been noted that there was no significant difference in BW gain of growing calves fed diets containing varied levels of protein (Sengar et al., 1985; Gonzalez et al., 1990; Lohakare et al., 2006). In the current study, we fed the calves according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. their body weight, and the diet supply was adjusted as calves grew. We found that the calves in the LP group gained less weight than the other groups during the whole experiment period. This might have been due to the reduced MR intake, and the lower level of dietary protein content that could not meet the requirement of their growth. The calves fed with the MP milk replacer had the best growth performance among the three groups.
Intake and digestibility of nutrients
The digestibility of DM, EE and ash were not affected by dietary CP concentration (Table 2) although the digestibility of CP declined as the CP content of the diet increased. The DM intake tended to be lower in the LP group than the other groups, however no significant differences between the three groups existed (p>0.05). The average value of DM digestibility was 74.6, 73.0 and 73.9% in the LP, the MP and the HP groups, respectively, which was similar to previous observations (Krishna Mohan et al., 1987; Babu et al., 2003). Compared to the MP or the HP groups, the LP group had the lowest level of digested EE (p<0.05); however, digestibility of EE did not differ significantly between the three groups (p>0.05). The apparent digestibility of ash did not differ significantly among the three groups (p>0.05). As expected, CP intake of calves increased with elevated diet protein level. The highest level of digested CP was found in the MP and HP groups, and the digestibility of CP was highest in the LP and MP groups (p<0.05). This might have been due to calves in the LP group not receiving adequate amounts of protein in their diet; while the calves fed with higher protein were unable to utilize dietary N as efficiently as the calves fed with medium CP content.
Balances of nutrients
Nitrogen balance nitrogen balance
The difference between the amount of nitrogen taken into the body and the amount excreted or lost.
n : Gross efficiency of dietary CP usage (retained N as a proportion of dietary CP intake) for calves in the MP group was higher than in the other groups (Table 3). The average daily N intake varied significantly (p<0.05) in calves under different dietary regimes that matched the CP levels applied in the experiments. Following increased CP level in the diet, N intake increased linearly according to the experimental design. Fecal N increased with the increase of dietary CP (p<0.05), and similarly with protein intake. Pattanaik et al. (2003) reported that there was a positive relationship between N intake and excretion in feces. In contrast, Blome et al. (2003) reported that fecal N for calves showed a significant quadratic quadratic, mathematical expression of the second degree in one or more unknowns (see polynomial). The general quadratic in one unknown has the form ax2+bx+c, where a, b, and c are constants and x is the variable. relationship from 16.1 to 25.8% CP when animals were fed with whey protein-based milk replacers at 1.5% of BW daily. In the present study, the absorbed N value was used as an index for the percentage of intake N (i.e., N apparent digestibility); surprisingly, this value was significantly lower in the HP group than the MP or LP groups (p<0.05).
Moreover, contrary to the values of fecal N, there were no significant differences in urine N among the three groups of animals (p>0.05). Some authors reported that urine N apparently showed a positive relationship with intake (Dabiri and Thonney, 2004; Lohaare et al., 2006). Retained N expressed either as a percentage of intake N or as a percentage of absorbed N which increased linearly as the dietary CP increased probably induced the greater growth rates Growth Rates
The compounded annualized rate of growth of a company's revenues, earnings, dividends, or other figures.
Remember, historically high growth rates don't always mean a high rate of growth looking into the future. associated with feeding higher amounts of dietary CP (Blome et al., 2003). However, in the current study, retained N as a proportion of absorbed N or of N intake was significantly higher in the MP group than the other groups (p<0.05). On the other hand, the significantly lower value of the ratio between the retention of N and the absorbed N in the HP group indicated a higher N excretion through urine; hence, it further suggests that the N intake was in excess of the animals' capacity of energy availability (Lohaare et al., 2006). This data demonstrated that the calves in the MP group had more effective dietary protein utilization and, therefore, more rapid growth. Indeed, the average gross efficiency of N usage in the MP group achieved the highest value (54.66%) of the three groups. This was similar to the average value reported by Bartlett et al. (57.6%) (2006) even through the latter was obtained from calves fed with 22% CP at 1.75% of BW daily, which were much higher than the levels of these parameters used in the current study.
Calcium and phosphorus balance : The mean values of daily intake of dietary calcium and phosphorus remained unaffected by different dietary treatments (Table 3). However, the excretion of Ca and P in the feces or urine in the MP group were significantly lower than the other groups (p<0.05). Consequently, the values of retained Ca and P were significantly higher in the MP group than the LP or the HP groups (p<0.05). Although several previous reports suggested that the diet protein levels had no effect on Ca or P utilization (Sengar et al., 1985; Lohaare et al., 2006), we found in the current study that, as a percentage of intake, the retained Ca or P were significantly higher in the MP group than in the LP or the HP groups (p<0.05). These results suggested that medium protein content may favor transporting of dietary calcium and phosphorus.
Digestibility of dietary amino acids
Although research on amino acid digestibility in the young calf is deficient compared to studies with swine and poultry, a few studies have indicated that lysine lysine (lī`sēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. and methionine methionine (mĕthī`ənēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the L-stereoisomer appears in mammalian protein. plus cysteine cysteine (sĭs`tēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of mammalian protein. are the first and second limiting factor A factor or condition that, either temporarily or permanently, impedes mission accomplishment. Illustrative examples are transportation network deficiencies, lack of in-place facilities, malpositioned forces or materiel, extreme climatic conditions, distance, transit or overflight rights, for growth (Williams and Hewitt, 1979; Tzeng and Davis, 1980). Several researchers have estimated the amino acid profile required for the growth of calves (Williams and Hewitt, 1979) and pigs (Chung and Baker, 1992; Hansen et al., 1993). However, we argued that the requirements for young calves fed with restricted amounts of milk replacer would differ from those of rapidly growing young pigs and veal veal, flesh of a calf from two to three months old weighing usually less than 300 lb (135 kg). The locomotion of the veal calves is often restricted, and they are fed a real or synthetic milk that is high in protein and low in iron; this produces the desired calves that were fed at high intakes (Davis and Drackley, 1998). In the current study, we found that, among the indispensable amino acids, histidine histidine (hĭs`tĭdēn), organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. had the lowest apparent digestibility and tryptophan tryptophan (trĭp`təfăn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. had the highest digestibility within all three groups, whereas, among the dispensable dis·pen·sa·ble
Capable of being dispensed, administered, or distributed. Used of a drug. amino acids, the digestibilities of alanine alanine (ăl`ənēn'), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of proteins (see stereochemistry). and cystine cystine: see cysteine. were the lowest (Table 4). Except for alanine, there were no differences in the fecal digestibility of amino acids among the three groups (p>0.05). The average digestibility of the total AA was 82.7%, 83.4% and 79.4% in the LP, MP and HP groups, respectively. However, these values were a little lower than those reported previously by Wang et al. (2006).
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
One of the important objectives of the current study was to determine the impact of different dietary CP levels on blood metabolites. We found that the value of BUN was affected by both age and dietary protein levels (Figure 2). The BUN concentration decreased as calves grew in the current study, which was similar to a previous report in lambs (Holcombe, 1994). Similarly, we found that BUN increased following the increased dietary CP content, which agrees with several previous reports (Blome et al., 2003; Bartlett et al., 2006).
Previous investigations lacked unanimity in the influence of dietary CP content on serum protein metabolism Protein metabolism
The transformation and fate of food proteins from their ingestion to the elimination of their excretion products. Proteins are of exceptional importance to organisms because they are the chief constituents, aside from water, of all the soft . Several researchers have suggested that serum concentrations of total protein, albumin, globulin, and albumin: globulin ratios were unaffected by dietary CP content (Sahoo et al., 2002; Blome et al., 2003). However, Sykes and Field (1973) reported that higher protein intake could increase serum albumin serum albumin
See seralbumin. concentration. In the current study, we found that total protein and globulin concentrations in the LP group were lower than other groups (p<0.05) (Figure 3); however, albumin concentration was unaffected statistically (p>0.05). On the other hand, the total protein and globulin concentrations increased with age, but the albumin concentrations remained constant during the whole test. These results suggested serum albumin may have better adaptation tolerance in the face of protein deficiency than total protein or globulin.
Received September 29, 2007; Accepted January 21, 2008
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That can be chemically degraded: degradable plastic wastes.
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* This work has been carried out with financial support of the Key Technologies R&D Programme, China.
H. Li, Q. Y. Diao **, N. F. Zhang and Z. Y. Fan
Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, 100081, China
** Corresponding Author: Q. Y. Diao. Tel: +86-010-68975843, Fax: +86-010-62169105, E-mail: email@example.com
Table 1. Ingredient and chemical composition of diets Milk replacer Nutrients LP MP HP Ingredient composition (% as fed basis) Soy protein concentrate 33.0 43.5 55.5 Whey powder 40.0 30.0 21.8 Skim milk 6.5 8.3 7.0 Fat 10.5 8.2 5.7 Compound-premix 10.0 10.0 10.0 Calculated composition ME (MJ/kg) 17.8 17.8 17.8 CP (%) 18.1 22.1 26.0 Analyzed composition (%) DM 97.4 97.2 96.8 CP 17.2 21.4 25.8 EE 15.0 16.1 17.0 Ash 8.2 7.7 7.5 Ca 1.5 1.5 1.5 P 0.7 0.7 0.7 AA composition (% as DM basis) Asp 1.8 2.2 2.7 Thr 0.7 0.8 1.0 Ser 0.8 1.0 1.2 Glu 3.0 3.7 4.5 Gly 0.6 0.7 0.9 Ala 0.7 0.8 1.0 Val 0.8 1.0 1.2 Ile 0.8 0.9 1.1 Leu 1.3 1.5 1.9 Tyr 0.6 0.7 0.9 Phe 0.8 0.9 1.2 His 0.6 0.7 0.8 Lys 1.5 1.5 2.1 Arg 0.3 0.4 0.4 Pro 1.2 1.5 1.8 Cys 0.3 0.4 0.5 Met 0.5 0.7 1.0 Trp 0.9 1.0 1.3 Total 16.9 20.3 25.3 Nutrients Concentrate Hay feed Ingredient composition (% as fed basis) Soy protein concentrate - - Whey powder - - Skim milk - - Fat - - Compound-premix - - Calculated composition ME (MJ/kg) - - CP (%) - - Analyzed composition (%) DM 87.4 91.6 CP 21.8 6.6 EE 1.7 3.6 Ash 6.8 4.6 Ca 0.6 0.4 P 0.7 0.2 AA composition (% as DM basis) Asp 2.2 0.6 Thr 0.8 0.3 Ser 1.1 0.3 Glu 4.2 0.7 Gly 0.9 0.3 Ala 1.1 0.4 Val 1.0 0.4 Ile 0.9 0.3 Leu 1.8 0.5 Tyr 0.7 0.2 Phe 1.0 0.3 His 0.7 0.3 Lys 1.2 0.3 Arg 1.5 0.3 Pro 1.2 0.4 Cys 0.4 0.1 Met 0.3 0.1 Trp 0.2 0.2 Total 21.2 5.7 Table 2. Effects of different CP levels on nutrient digestibility of calves CP content Variable LP Dry matter Intake (g/d) 1,874.5 [+ or -] 199.1 Digested (g/d) 1,397.9 [+ or -] 132.5 Digestibility (%) 74.6 [+ or -] 0.9 Crude protein Intake (g/d) [307.0 [+ or -] 40.7.sup.b] Digested (g/d) [235.9 [+ or -] 29.9.sup.b] Digestibility (%) [76.7 [+ or -] 1.0.sup.a] Ether extract Intake (g/d) [134.7 [+ or -] 3.7.sup.b] Digested (g/d) [121.8 [+ or -] 7.0.sup.b] Digestibility (%) 90.4 [+ or -] 2.8 Ash Intake (g/d) 129.3 [+ or -] 13.5 Digested (g/d) [71.4 [+ or -] 4.6.sup.b] Digestibility (%) 55.5 [+ or -] 3.9 CP content Variable MP Dry matter Intake (g/d) 2,114.9 [+ or -] 128.8 Digested (g/d) 1,542.7 [+ or -] 91.3 Digestibility (%) 72.96 [+ or -] 0.9 Crude protein Intake (g/d) [374.35 [+ or -] 9.0.sup.a] Digested (g/d) [291.7 [+ or -] 11.6.sup.a] Digestibility (%) [77.9 [+ or -] 1.2.sup.a] Ether extract Intake (g/d) [157.5 [+ or -] 4.6.sup.a] Digested (g/d) [142.3 [+ or -] 5.5.sup.a] Digestibility (%) 90.3 [+ or -] 1.1 Ash Intake (g/d) 140.6 [+ or -] 6.0 Digested (g/d) [84.7 [+ or -] 4.3.sup.a] Digestibility (%) 60.3 [+ or -] 2.4 CP content Variable HP Dry matter Intake (g/d) 2,019.1 [+ or -] 148.5 Digested (g/d) 1,490.8 [+ or -] 107.6 Digestibility (%) 73.87 [+ or -] 2.8 Crude protein Intake (g/d) [397.2 [+ or -] 23.5.sup.a] Digested (g/d) [280.3 [+ or -] 23.5.sup.ab] Digestibility (%) [70.5 [+ or -] 2.9.sup.b] Ether extract Intake (g/d) [161.2 [+ or -] 3.7.sup.a] Digested (g/d) [143.3 [+ or -] 7.9.sup.a] Digestibility (%) 88.8 [+ or -] 2.8 Ash Intake (g/d) 133.2 [+ or -] 8.9 Digested (g/d) [77.0 [+ or -] 7.0.sup.ab] Digestibility (%) 57.8 [+ or -] 1.8 Table 3. Effects of different CP levels on N, Ca and P utilization of calves CP content Variable LP N Intake N (g/d) 49.1 [+ or -] 6.5 (b) Fecal N (g/d) 11.4 [+ or -] 1.8 (b) Urine N (g/d) 16.5 [+ or -] 1.0 Absorbed N (g/d) 37.7 [+ or -] 4.8 (b) Absorbed N (% of intake N) 76.9 [+ or -] 1.0 (a) Retained N (g/d) 21.3 [+ or -] 5.2 (b) Retained N (% of absorbed N) 55.8 [+ or -] 7.3 (b) Retained N (% of intake N) 42.9 [+ or -] 5.6 (b) Ca Intake Ca (g/d) 16.7 [+ or -] 1.2 Fecal Ca (g/d) 8.0 [+ or -] 0.5 (a) Urine Ca (g/d) 2.3 [+ or -] 0.4 (a) Retained Ca (g/d) 6.4 [+ or -] 0.3 (c) Retained Ca (% of intake Ca) 38.5 [+ or -] 1.2 (c) P Intake P (g/d) 10.5 [+ or -] 1.3 Fecal P (g/d) 3.1 [+ or -] 0.2 (a) Urine P (g/d) 4.0 [+ or -] 0.5 (a) Retained P (g/d) 3.4 [+ or -] 0.7 (c) Retained P (% of intake P) 32.3 [+ or -] 3.5 (c) CP content Variable MP N Intake N (g/d) 59.9 [+ or -] 1.4 (a) Fecal N (g/d) 13.2 [+ or -] 0.4 (b) Urine N (g/d) 13.9 [+ or -] 2.1 Absorbed N (g/d) 46.7 [+ or -] 1.9 (a) Absorbed N (% of intake N) 77.9 [+ or -] 1.2 (a) Retained N (g/d) 32.8 [+ or -] 3.0 (a) Retained N (% of absorbed N) 70.2 [+ or -] 4.7 (a) Retained N (% of intake N) 54.7 [+ or -] 4.2 (a) Ca Intake Ca (g/d) 18.4 [+ or -] 0.5 Fecal Ca (g/d) 5.8 [+ or -] 0.7 (b) Urine Ca (g/d) 2.0 [+ or -] 0.4 (ab) Retained Ca (g/d) 10.6 [+ or -] 0.3 (a) Retained Ca (% of intake Ca) 57.5 [+ or -] 1.0 (a) P Intake P (g/d) 11.7 [+ or -] 0.3 Fecal P (g/d) 2.8 [+ or -] 0.4 (b) Urine P (g/d) 0.7 [+ or -] 0.0 (c) Retained P (g/d) 8.2 [+ or -] 0.2 (a) Retained P (% of intake P) 69.7 [+ or -] 3.0 (a) CP content Variable HP N Intake N (g/d) 63.6 [+ or -] 3.8 (a) Fecal N (g/d) 18.7 [+ or -] 1.9 (a) Urine N (g/d) 18.9 [+ or -] 3.9 Absorbed N (g/d) 44.8 [+ or -] 3.8 (ab) Absorbed N (% of intake N) 70.5 [+ or -] 2.9 (b) Retained N (g/d) 26.0 [+ or -] 0.7 (ab) Retained N (% of absorbed N) 58.2 [+ or -] 5.3 (b) Retained N (% of intake N) 41.0 [+ or -] 3.3 (b) Ca Intake Ca (g/d) 17.7 [+ or -] 0.8 Fecal Ca (g/d) 7.7 [+ or -] 1.0 (a) Urine Ca (g/d) 1.4 [+ or -] 0.5 (b) Retained Ca (g/d) 8.7 [+ or -] 1.2 (b) Retained Ca (% of intake Ca) 48.7 [+ or -] 4.6 (b) P Intake P (g/d) 11.5 [+ or -] 0.8 Fecal P (g/d) 3.8 [+ or -] 0.5 (a) Urine P (g/d) 2.4 [+ or -] 0.2 (b) Retained P (g/d) 5.4 [+ or -] 0.9 (b) Retained P (% of intake P) 46.6 [+ or -] 6.1 (b) Data are expressed as mean [+ or -] SD. (a, b, c) Values with different letter in the same row are different (p<0.05). Table 4. Effects of different CP levels on AA digestibility of calves CP content Variable LP MP Indispensable amino acids MET 84.2 [+ or -] 1.0 86.9 [+ or -] 2.0 ARG 86.6 [+ or -] 0.2 86.5 [+ or -] 2.2 LYS 84.5 [+ or -] 1.3 84.3 [+ or -] 1.6 HIS 66.3 [+ or -] 2.9 63.8 [+ or -] 2.1 PHE 82.6 [+ or -] 0.6 84.3 [+ or -] 2.6 VAL 78.7 [+ or -] 1.1 78.9 [+ or -] 2.8 ILE 80.1 [+ or -] 0.9 81.1 [+ or -] 2.8 LEU 82.3 [+ or -] 1.1 82.9 [+ or -] 2.5 THR 78.1 [+ or -] 1.6 78.1 [+ or -] 2.3 Trp 94.2 [+ or -] 1.2 95.8 [+ or -] 0.7 Dispensable amino acids ASP 82.8 [+ or -] 0.9 83.5 [+ or -] 2.6 SER 83.8 [+ or -] 1.1 84.1 [+ or -] 2.1 GLU 87.7 [+ or -] 0.9 88.1 [+ or -] 1.9 GLY 77.3 [+ or -] 0.9 77.4 [+ or -] 3.0 ALA 72.4 [+ or -] 1.4 (ab) 73.9 [+ or -] 2.9 (a) TYR 81.8 [+ or -] 0.5 84.3 [+ or -] 2.7 CYS 72.4 [+ or -] 1.9 76.1 [+ or -] 6.7 PRO 88.6 [+ or -] 1.6 89.4 [+ or -] 1.9 Total 82.7 [+ or -] 1.0 83.4 [+ or -] 2.2 CP content Variable HP Indispensable amino acids MET 85.1 [+ or -] 1.9 ARG 81.6 [+ or -] 4.1 LYS 82.7 [+ or -] 2.4 HIS 63.1 [+ or -] 4.4 PHE 78.7 [+ or -] 4.3 VAL 74.8 [+ or -] 3.5 ILE 76.4 [+ or -] 3.7 LEU 78.1 [+ or -] 4.1 THR 73.0 [+ or -] 3.3 Trp 93.1 [+ or -] 1.9 Dispensable amino acids ASP 79.7 [+ or -] 3.4 SER 79.3 [+ or -] 3.3 GLU 84.1 [+ or -] 3.4 GLY 73.4 [+ or -] 3.1 ALA 67.8 [+ or -] 3.6 (b) TYR 78.7 [+ or -] 4.0 CYS 74.1 [+ or -] 5.3 PRO 85.8 [+ or -] 2.9 Total 79.5 [+ or -] 3.2 Data are expressed as mean [+ or -] SD. (a, b, c) Values with different letter in the same row are different (p<0.05).