Composition of Growth of Holstein Calves Fed Milk Replacer from Birth to 105-Kilogram Body Weight1

J. Dairy Sci. 84:830–842  American Dairy Science Association, 2001.

Composition of Growth of Holstein Calves Fed Milk Replacer from Birth to 105-Kilogram Body Weight1 M. C. Diaz,2 M. E. Van Amburgh, J. M. Smith, J. M. Kelsey, and E. L. Hutten Department of Animal Science, Cornell University Ithaca, NY 14853

ABSTRACT Sixty calves were assigned to a comparative slaughter study to determine the changes in composition of milk replacer-fed Holstein bull calves from birth to 105kg body weight (BW). Six calves were slaughtered on day of birth and served as a baseline for comparison of compositional changes. Fifty-four calves were assigned to one of three treatments (18 calves per treatment). Calves were fed milk replacer containing 30% crude protein (CP) and 20% fat. Target growth rates for treatments 1, 2, and 3 were 500, 950, and 1400 g/d, respectively. Six calves from each treatment were slaughtered and analyzed for energy, nitrogen, ether extract, and ash when they reached 65, 85 and 105 kg of BW. Actual daily gains from birth to slaughter were 560, 973, and 1100 g, and net deposition of CP and fat were 140 and 44, 204 and 154, and 247 and 161 g/d for treatments 1, 2, and 3, respectively. Results were used to develop equations to predict retained energy [retained energy = (empty BW0.223) × (empty BW gain1.32)], and retained protein, [retained protein = (184 × empty BW gain (kilograms/d)) + (17.2 × (retained energy)/empty BW gain] where retained energy is in Mcal/d, retained protein is in g/d, and empty BW and gain are in kilograms. The composition of gain observed was compared to predictions from the 1989 Dairy NRC and 1996 Beef NRC equations and demonstrated the equations do not represent the composition of gain in calves of this weight. (KEY WORDS: calves, energy, protein, growth) Abbreviation key: BV = biological value, EB = empty body, EBG = empty body gain, EBW = empty BW, FIG = fat in gain, GE = gross energy, G:F = gain to feed,

Received June 12, 2000. Accepted November 27, 2000. Corresponding author: M. E. Van Amburgh; e-mail: mev1@ cornell.edu. 1 Research supported in part by the Cornell University Agricultural Experiment Station. 2 M. C. Diaz was partially supported by the Fulbright Scholars Program. Present address: Facultad de Ciencias Agrarias—U.C.A, LEAA (Lab. Evaluacio´n de Alimentos para Uso Animal), Cap. Gral. Ramo´n Freire 183, (1426) Capital Federal, Buenos Aires—Argentina.

HHFT = head, hide, feet, tail, LW = live weight, LWG = live weight gain, ME = metabolizable energy, MR = milk replacer, PIG = protein in gain, PUN = plasma urea nitrogen, RE = retained energy, RP = retained protein. INTRODUCTION A recent evaluation of the National Research Council Nutrient Requirements of Dairy Cattle (NRC, 1989) (1989 Dairy NRC) and the Cornell Net Carbohydrate and Protein System (Fox et al., 1992) for growing Holstein heifers indicated that neither system adequately accounted for the energy requirements of lightweight growing Holstein heifers (Van Amburgh et al., 1998). The Cornell Net Carbohydrate and Protein System utilizes the growth equations of the National Research Council Nutrient Requirements of Beef Cattle (NRC, 1996) (1996 Beef NRC). The equations used in the 1989 Dairy NRC and 1996 Beef NRC to predict energy and protein requirements for growth were based on equations developed by Garrett (1980, 1987) and the 1984 Beef NRC committee (NRC, 1984). The equations were derived primarily from beef breeds of cattle, and slaughter weights were rarely less than 250 kg of BW. Therefore, use of these equations to predict energy and protein requirements for cattle of lighter BW involves extrapolation beyond the range of data used to derive them (Garrett, 1980, 1987; Lofgreen and Garrett, 1968). Waldo et al. (1997) published data describing the energy and protein content of pubertal Holstein heifers fed either alfalfa- or corn silage-based diets to achieve two average daily BW gains. The energy and protein content of the heifers did not match that predicted by the 1989 Dairy NRC equations for growth. The heifers in the Waldo et al. (1997) data set contained approximately 30% less fat and 14% more protein than heifers from a comparable but older data set (Anrique, 1976; Simpfendorfer, 1974). The authors concluded that the causes of the differences in composition were unknown but may be due to phenotypic differences in mature body size; our current US Holsteins have a mature BW larger than previously estimated (Waldo et al., 1997).

830

COMPOSITION OF GROWTH IN CALVES

Other systems developed for predicting nutrient requirements for growth (Commonwealth Scientific and Industrial Research Organization, 1990; Institut National de la Recherche Agronomique, 1989) have recognized that mature size will influence the composition of gain at a particular BW and have instituted a size scaling procedure to more accurately account for that variation. Accordingly, to adjust nutrient requirements for variation in mature BW, Tylutki et al. (1994) published a procedure for size scaling that used a standard reference animal of known BW and chemical composition (478 kg and 28% whole body fat content) to account for variation in the fat and protein content of gain relative to any input mature size. Fox et al. (1999) incorporated this size scaling approach into a growth and reserves model designed to predict requirements for dairy replacement heifers. This model (Fox et al., 1999) accounted for 96% of the variation in energy retained with a 4% overprediction bias, and accounted for 71% of the protein retained with an underprediction bias of 10% using available slaughter data for Holstein heifers. To predict the energy content of gain in the heifers described by Waldo et al. (1997), Fox et al., (1999) adjusted the mature BW of the Waldo heifers to 540 and 580 kg for the two treatment groups, respectively. Those adjusted mature BW are significantly lighter than what was described in the 1989 dairy NRC (800 kg), but are consistent with the observations of Waldo et al. (1997) that the composition of the heifers was leaner and contained less energy at a particular stage of maturity and suggests our current nutrient requirement systems do not adequately describe tissue requirements for growth. These studies indicate a need to reevaluate the nutrient requirements of growing Holstein cattle, particularly at early stages of growth. Our comparative slaughter study was designed to determine net tissue requirements for energy and protein for growing preruminant Holstein calves from birth to 105 kg of BW. We hypothesized, based on the available data, that the energy required for growth in this class of growing cattle is higher than currently predicted and that this difference in energy required confounds the prediction of protein required. MATERIALS AND METHODS Animals The experimental protocol was reviewed and approved by the Cornell University Institutional Animal Care and Use Committee. Sixty male Holstein calves were used to evaluate the changes in carcass composition of preruminant calves from birth to 105 kg of BW. Calves weighing 45 ± 4 kg were obtained from four

831

dairy farms within 24 h of birth and received 3.7 L of colostrum on the farm as soon as possible after birth. Six randomly selected calves were assigned to slaughter within 24 h of birth to serve as a baseline for analyzing changes in body composition. The remaining 54 calves were housed individually in adjacent pens in a greenhouse calf barn and were bedded on straw and sawdust. Upon arrival at the calf barn, calves received a single dose of colostrum supplement (Lifeline, American Protein Corp., Ames, IA). Calves also were given a physical examination and received 2 ml of vitamin B complex subcutaneously (The Butler Co., Dublin, OH), 2.5 ml of BoSe intramuscular (1 mg of selenium, 50 mg (68 IU) of vitamin E/ml; Schering-Plough Animal Health Corp., Union, NJ), and 2 ml of iron dextran intramuscular (100 mg of elemental iron/ml; The Butler Company). Calves were vaccinated against infectious bovine rhinotracheitis virus and PI-3 intranasally, (2 ml of TSV-2, Pfizer Animal Health, Exton, PA) at approximately 3 d of age, against Pasteurella multocida and P. hemolytica (2 ml of Once PMH, Bayer Corp., Shawnee Mission, KS) at approximately 7 and 28 d of age, against bovine viral diarrhea, bovine respiratory syncytial virus, infectious bovine rhinotracheitis virus, PI-3 i.m. (2 ml of BRSV Vac 4, Bayer Corp.) at 7 and 28 d of age, and against five clostridial diseases with a toxoid (2 ml of Vision Seven, Bayer Corp.) at d 14 and 35. Calf health was monitored daily. Body temperatures were recorded daily for the first 2 wk, then only if calves were ill. Scour and respiratory scores were also recorded daily. Scours were treated primarily with oral electrolytes (Entrolyte H.E., Pfizer Animal Health, Exton, PA) and milk replacer (MR) was never withheld. Intravenous fluids were administered to severely dehydrated calves. Indices of calf health were monitored and recorded several times per day, under the following guidelines: Fecal scores: 1 = firm, well-formed (not hard), 2 = soft, pudding-like, 3 = runny, pancake batter, and 4 = liquid, splatters; Respiratory scores: 1 = normal, 2 = runny nose, 3 = heavy breathing, 4 = cough–moist, 5 = cough–dry, and 6 = fever. Other health disorders were diagnosed and treated according to veterinary instructions. Fifty-four calves were assigned randomly among three treatments (TRT) after a 3- to 5-d period of adjustment. The DMI of the calves during the adjustment period (MR at 1% BW reconstituted to 15% DM as fed) was included in the calculation of tissue retention and the generation of the prediction equations. The adjustment period was used to ensure that calves were acclimated and healthy before starting TRT diets. Treatments were designed to achieve three targeted daily rates of gain (TRT 1 = 500, TRT 2 = 950, and TRT 3 = 1400 g) in live weight (LW). Journal of Dairy Science Vol. 84, No. 4, 2001

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Table 1. Chemical composition of milk replacer fed to calves at three levels of intake1. Component

Treatment 1

Treatment 2

Treatment 3

DM, % Protein, % of DM Fat, % of DM Lactose, % of DM Ash, % of DM Calcium, % of DM Phosphorus, % of DM Gross energy, kcal/g Vitamin A2, KIU/kg Vitamin D32, KIU/kg Vitamin E2, IU/kg

96.20 31.20 19.97 42.90 5.90 1.10 0.71 4.97 60.00 20.00 200.00

95.80 29.48 20.96 43.40 6.10 1.03 0.70 5.19 30.00 15.00 150.00

96.00 30.56 20.18 42.96 6.30 1.24 0.77 4.92 15.00 10.00 100.00

1

Each treatment represents a separate batch of milk replacer. Vitamin levels were the formulated levels and were based on the expected level of DMI (1, 3, and 4% of BW per day for treatment 1, 2 and 3, respectively) necessary to achieve the target growth rates. 2

Feeding and Management The MR (Milk Specialties Co., Dundee, IL) was formulated to contain 30% CP and 20% fat (DM basis; Table 1). The MR was an all-milk protein formulation. This dietary CP content was selected based on previous studies (Donnelly and Hutton, 1976a, 1976b; Gerrits et al., 1996) that indicated a plateau in daily protein accretion might be achieved at near maximal DMI with a CP concentration of 30%. The goal of the diet formulation was to ensure that protein would not be the most limiting nutrient. The initial feeding protocol for each TRT was based on providing DM from MR at 1, 3, and 4% of BW to meet the energy requirements for the target growth rates for each TRT, respectively. The initial estimated energy requirements were derived from the available data (Donnelly and Hutton, 1976a, 1976b; Gerrits et al., 1996; NRC, 1989, 1996). The vitamin contents of the MR were formulated based on the expected amount of DMI, thus the concentrations were decreased in TRT 2 and 3 to prevent excessive intake. The calves assigned to TRT 1 and 2 were fed their respective MR reconstituted to 15% DM; TRT 3 calves received MR reconstituted to 18% DM. Calves were fed individually in buckets three times per day (0700, 1400, and 2100 h) and water was offered ad libitum throughout the study. No dry feed was offered. All amounts of feed and water offered and refused were recorded at each feeding. The calves were weighed twice weekly before feeding, and if the live weight gain (LWG) of a calf exceeded the target growth rate, then the animal’s calculated DMI was reduced. Calves were allowed 30 min to consume the meal. If the MR was not consumed within 30 min, the refusal was quantified and recorded. No attempt was made to force feed calves that did not consume the amount offered. Blood (10 ml) was colJournal of Dairy Science Vol. 84, No. 4, 2001

lected weekly 4 to 6 h after the morning feeding from all calves via jugular venipuncture, and plasma was harvested within 1 h of sampling. Plasma was frozen at −20°C until subsequent analysis. Slaughter Procedure A total of six calves per TRT were slaughtered at each predetermined BW (65, 85, and 105 kg) as each calf selected reached the target weight. Immediately before slaughter, BW was measured. Calves were slaughtered by captive bolt and exsanguination in the abattoir of the Department of Animal Science. Blood was collected into a tared plastic bag and included in the organ fraction for composition analyses. Immediately postmortem, the gastrointestinal tract was removed and weighed before and after removal of contents. Body components were separated into four fractions: 1) carcass; 2) head, hide, feet, and tail (HHFT); 3) organs (including blood, emptied gastrointestinal tract, and all other organs except the liver) and 4) liver. Component fractions were weighed and kept in plastic bags to avoid moisture losses until processing. Processing occurred within 4 h of slaughter. The carcass was split into left and right halves, reweighed, and the right half was further processed. Each fraction was ground separately seven times through an Autio grinder (10-mm aperture plate, Autio 801 B, Paul Autio, Astoria, OR), to assure thorough mixing and complete grinding. Subsamples of each fraction (approximately 1 kg) were placed in aluminum pans, weighed, frozen and freeze-dried. The freeze-dried body components were weighed again to determine loss of moisture and stored at +4°C. Additional subsamples were taken at the time of initial grinding in case of spoilage or other loss of the freezedried samples. Grinding and Sampling for Chemical Analysis The freeze-dried samples were broken into pieces and mixed with crushed dry ice in approximately equal proportions. The mixture was ground in a Wiley Mill (Arthur H. Thomas, Philadelphia, PA) through a 2-mm screen. The ground material was again subsampled and kept at +4°C pending analysis. The MR was sampled weekly and composited monthly. Proximate Analysis of Body Tissues and Milk Replacer Feeds and tissues were analyzed for gross energy with an adiabatic bomb calorimeter (Model 1241, Parr Instrument Co., Moline, IL). Nitrogen content was measured by a macro-Kjeldahl digestion procedure ac-

833

COMPOSITION OF GROWTH IN CALVES

cording to the procedure (AOAC, 1990) that was modified to include the use of boric acid and steam distillation (Pierce and Haenisch, 1940). Crude protein was calculated as N × 6.25 for tissue and N × 6.38 for MR. Fat content was measured by petroleum-ether extraction (AOAC, 1981). Ash content was determined by ashing the samples in a muffle furnace for 48 h at 600°C. All analyses were conducted in duplicate. Empty BW (EBW) was calculated as the sum of the weight of the whole body components: HHFT, carcass, blood, and organs (minus the liver) and liver. The organs include all internal organs (e.g., heart, lungs, kidneys, and gastrointestinal system). The chemical composition of the animal was calculated as the sum of the amount of energy, protein, fat, or ash in the four fractions of each animal on an empty body (EB) basis. The composition of gain for each animal was calculated as the amount of energy, protein, fat, and ash in EB of the animals at slaughter weight minus the average chemical composition of the EB of the baseline calves. Weekly samples of plasma were assayed for plasma urea nitrogen (PUN) by automated procedures (method no. SE40001FD4, Technicon Auto Analyzer, Tarrytown, NJ) which measures the colored product formed when urea reacts with diacetyl monoxime in the presence of thiosemicarbazide and ferric ion (Marsh et al., 1965). The PUN values were used as an indicator of protein status. Digestibility Study To obtain an accurate measure of the utilization of the diets throughout the slaughter experiment, apparent digestibility and metabolizability of the ingested energy and nitrogen were determined in a separate study. Twelve Holstein bull calves weighing 45 ± 4 kg were assigned randomly to each of the three TRT groups previously described (four calves per TRT). Calves assigned to each TRT were fed the same diet throughout the study and when the animals achieved the BW representing the slaughter weights 65, 85, and 105 kg of BW, collections of urine and feces were conducted for 5 d. Subsequently, four calves were collected 3 times while being fed each respective TRT diet. During the 5-d collection, the calves were housed individually in metabolism stalls (Cornell University Large Animal Research and Teaching Unit). Calves were maintained in an environment with an ambient temperature of 25°C throughout the study period. We assumed that digestibility was not affected by differences in the environments between the slaughter study and the collection study, and thus the data generated from the collection study were applicable to the slaughter study (Schrama et al., 1993). Because methane production is negligible in prerumi-

nant calves (Roy, 1980b), the potential gas losses were not considered in calculating energy losses. Feeding and management of the calves was conducted as described for the slaughter experiment. Plastic bags were harnessed to the calves to allow quantitative collection of the feces. Bags were emptied twice a day, pooled per calf over the 5-d collection period, and stored at −20°C pending analysis. Samples were weighed and freeze-dried. The dry samples for a given animal were weighed for DM analysis then ground together, and the composite sample was subsampled for analysis of energy and N as previously described. Total collection of urine was conducted over the same 5-d period. Urine was collected in pans placed under the metabolism stall. Each day, 2 g of K2Cr2O7 was added to the collection pan to inhibit growth of bacteria and enzymatic processes that cause loss of nitrogen. Ten percent of total urine collected was filtered through glass wool and pooled per calf per collection period. Samples were assayed for DM, N, and gross energy as previously described. The apparent biological value (BV) was calculated as the percentage of apparently absorbed nitrogen that was retained in the body (N retained/N apparently absorbed × 100). Apparent digestibilities of DM, N, and energy were calculated as: (((nutrient consumed – nutrient in feces)/nutrient consumed) × 100). Metabolizable energy (ME) intake and digestible protein intake during the slaughter experiment were computed by multiplying the gross energy (GE) and CP intakes during the slaughter trial by the ME/GE ratio and feed protein digestibility, respectively, measured in the balance experiment. Statistical Analysis All calculations were made from birth (baseline) to slaughter. The growth, composition and digestion data were analyzed using the general linear models procedure (Proc GLM) in SAS (1990). The main effects included TRT, slaughter weight, and TRT × slaughter weight interactions. Differences were identified using the least significant difference mean comparison test when the F-value for a main effect was significant (P < 0.05). Correlations among components of the empty body gain (EBG) (e.g., fat and protein) and the relationship between rate of gain and deposition of fat and protein were conducted using correlation procedures (Proc Corr) in SAS (1990). The energy and protein equations were derived in a manner consistent with the form of the equations currently in use in the NRC publications (1989, 1996). Protein and energy equations were derived by multiple regression (Proc Reg), SAS (1990) for the selected variJournal of Dairy Science Vol. 84, No. 4, 2001

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DIAZ ET AL.

Table 2. Body weights, feed intake, and growth performance of calves fed three levels of milk replacer and slaughtered at three different BW. P Treatment 1 n Target slaughter weight, kg Birth weight, kg Actual slaughter weight, kg Days on treatment Total DMI, kg Daily DMI, kg DMI, % of BW Gain to feed ADG, g/d

Treatment 2

1

Treatment 3

SE

TRT

2

SL3

TRT*SL4

6

6

6

6

6

6

6

6

6

65

85

105

65

85

105

65

85

105

44.7

44.8

47.8

44.4

45.2

44.5

45.8

44.0

44.0

1.27

0.9

0.9

0.9

65.5a

85.0b

105.5c

68.0a

86.0b

102.5c

68.0a

84.0b

104.0c

1.26

0.9

0.001

0.15

a

b

c

a

b

c

a

b

c

40.0

32.0a

67.0

98.5

25.0

39.0

62.0

24.0

34.0

50.0

1.94

0.02

0.01

0.001

59.6b

88.9c

30.0a

57.8b

95.0c

27.0a

50.3b

84.5c

3.54

0.04

0.03

0.4

0.80a 1.62a

0.89b 1.44b

0.90b 1.23c

1.20a 2.46a

1.48b 2.45a

1.53b 2.15b

1.13a 2.39a

1.48b 2.67b

1.69c 2.48c

0.01 0.05

0.04 0.001

0.02 0.05

0.4 0.05

0.65a 0.52a

0.65a 0.60a

0.42b 0.59a

0.57a 0.94ab

0.60b 1.04b

0.62b 0.94a

0.78a 0.93a

0.76a 1.17b

0.70b 1.21b

0.03 0.04

0.001 0.003

0.02 0.08

0.03 0.03

Values with different superscripts differ (P < 0.05) by slaughter weight within treatment. SE = Standard error of the mean. 2 Treatment. 3 Slaughter weight. 4 Interaction. a,b,c 1

ables (using the mean values for TRT among slaughter points). To derive the retained energy (RE) equation, the LW and LWG were transformed to a log basis and regressed, as described by Lofgreen and Garrett (1968). The resulting equation was determined by computing the antilogs of the regression. The protein equations were derived by regressing the daily EBG and the EB energy content per unit of EBG on the protein deposition, without an intercept. Effects were considered significant when P < 0.05 for all comparisons. RESULTS Intakes, Weight Gains, and Feed Efficiencies The average birth weights and weights at the start of the treatment were not different among TRT groups and averaged 45 ± 4 kg and 47 ± 4 kg of LW, respectively (Table 2). One calf died prior to assignment to TRT and was replaced. There was no observed difference in health problems (diarrhea, respiratory, or other) among calves assigned to the three TRT. The calves assigned to TRT 2 and 3 exhibited higher mean fecal scores (2.06 and 2.14, respectively) compared with calves assigned to TRT 1 (1.65). The calves on TRT 2 and 3 exhibited softer feces compared with calves on TRT 1, reflecting the difference in the total volume of feed and water consumed. Journal of Dairy Science Vol. 84, No. 4, 2001

The actual DMI, as a percentage of BW, was 1.43 ± 0.2, 2.35 ± 0.2, and 2.51 ± 0.3%, for TRT 1, 2, and 3, respectively (Table 2). There were no differences in total DMI between calves assigned to TRT 1 and 2. Calves assigned to TRT 3 had the lowest cumulative DMI (P < 0.05) to reach the target slaughter weights. Dry matter intake by age is found in Figure 1. Intake was significantly different for TRT 1 calves compared with TRT 2 and 3. By the third week of life, calves assigned to TRT 3 were consuming significantly greater quantities of MR than calves assigned to TRT 2. For calves assigned to TRT 3 the dilution of MR (18%) might have been too low for the calves at the lighter BW (< 65 kg) to allow adequate DMI to meet the target growth rate regardless of the availability of free choice water. When calculated over the treatment period, calves on TRT 1 and 2 exceeded target growth rates of 500 and 950 g/d by 14.0 and 2.5%, respectively (Table 2). Because of the inability to achieve adequate DMI during the period from birth to 65 kg, calves assigned TRT 3 were 28.5% below their target growth rates. Days to first and second slaughter weights were not different between calves on TRT 2 and 3. Calves on TRT 3 achieved the final slaughter weight (105 kg) 50 d earlier than calves on TRT 1 and 14 d earlier than TRT 2 calves (Table 2). Overall, the gain to feed (G:F) was greater (P < 0.05) for calves assigned to TRT 3 and decreased with de-

835

COMPOSITION OF GROWTH IN CALVES

creasing DMI (e.g., TRT 1 < TRT 2). However, the G:F decreased by the last slaughter period for calves assigned to TRT 1 and 3 (Table 2). The significant decrease in G:F for the TRT 1 calves slaughtered at 105 kg might have been due to the difficulty encountered in controlling daily LWG due to TRT 1 calves increasing bedding consumption leading to a confounding gut fill effect; however, these ratios are similar to those reported in another study (Everitt and Jury, 1977). The increase in bedding consumption in calves assigned to TRT 1 and slaughtered at 105 kg of BW was reflected in the organ fraction having the highest percentage of EBW compared with calves of similar slaughter weight on the other two TRT (Table 3). All calves consumed some bedding, which was found in the rumen upon slaughter. The rumens were inspected for indications of development and fermentation. Visual inspection of the calves’ rumens suggested no rumen development had occurred in any of the three TRT. Relationships Between LW and EBW and LWG and EBG Slaughter weight was similar among TRT (Table 2). Overall, the EBW was 95.0% of live BW (data not shown). This value was not different when compared among slaughter weights, except for the 85 and 105 kg slaughter weights of calves receiving TRT 1 diet. As a percentage of EBW, carcass and HHFT were not different, whereas organs and liver were significantly differ-

ent among TRT (Table 3). As a percentage of EBW organs were larger for calves assigned to TRT 1 and reflect increased bedding intake. Liver weight, as a percentage of EBW, increased with increasing DMI. Liver weight for calves assigned to TRT 1 was less (P < 0.05) than liver weight for calves on TRT 2 and 3 for the same slaughter weight. The effect of slaughter weight was significant (P < 0.05) for all components among TRT except for the carcass fraction (Table 3). For all fractions except HHFT, the interaction between TRT and slaughter weight was significant (P < 0.05). The EBG was determined to be 99.0% LWG (data not shown). Chemical Composition Calves assigned to TRT 1 had a higher water content (P < 0.05) than calves on TRT 2 and 3 (Table 4). At any EBW, TRT 1 calves contained less fat (P < 0.05) and more protein (P < 0.05) as a percentage of EBW than calves on TRT 2 and 3 (Table 4). The EB ash content of TRT two calves was less than that of calves on TRT 1 or 3 (Table 4). The protein content of the calves was not different at 65 and 85 kg (Table 4), but was lower (P < 0.05) in calves slaughtered at 105 kg. The concentration of fat in the EB of calves on TRT 1 remained constant throughout the experimental period and was unaffected by BW. Fat content of the EB increased (P < 0.05) between 65 and 105 kg for calves assigned to TRT 2 and 3. The higher fat content of calves on TRT 2 and 3 compared with TRT 1 demonstrated that as rate of gain increased, fat deposition increased. However, fat content did not increase linearly as BW increased and did not follow a consistent pattern among TRT, which was reflected in the significant interaction among TRT and slaughter weight for fat percentage (Table 4). Composition of the Gain

Figure 1. Weekly DMI of calves fed milk replacer at three different levels from birth to slaughter weight. Intakes were initially developed to achieve target rates of liveweight gain of 500 g/d for treatment 1 (▲), 950 g/d for treatment 2 (䊏) and 1400 g/d for treatment 3 (●). The asterisk (*) at wk 2 denotes a difference (P < 0.001) in DMI between treatment 1, and the remaining treatments and the double asterisk (**) at wk 3 denote a difference (P < 0.001) in DMI between calves assigned to treatment 3 versus treatment 2. Treatment differences were significant from the initial difference to the end of the treatments.

Empty body gain reflects the LWG and was significantly different among TRT (Table 5). Variation in EBG among slaughter weights within TRT was minimal but reflected some of the difficulty in feeding for a particular rate of LWG. Energy content of tissue gain (Mcal/kg) increased (P < 0.05) with heavier slaughter weights in all calves, especially from 65 to 85 kg of BW. The protein content of the EBG was highest (P < 0.05) for calves assigned to TRT 1. The mean protein content of the EBG in calves assigned to TRT 1 was 251 g/kg. The content of fat in the EBG was lower in TRT 1 than TRT 2 and 3 (P < 0.05). However, the fat content of the EBG for TRT 2 and 3 were not different (Table 5). The fat content of the gain generally increased with Journal of Dairy Science Vol. 84, No. 4, 2001

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DIAZ ET AL.

Table 3. Body components as percentage of empty BW of calves fed three levels of milk replacer and slaughtered at three different BW. P BL1 EBW,6 kg Carcass, % of EBW Organs,7 % of EBW Liver, % of EBW HHFT,8 % of EBW

Treatment 1

Treatment 2

Treatment 3

SE2

TRT3

SL4

TRT*SL5

40.4

63.6a

77.6b

95.7c

64.9a

82.0b

97.2c

64.8a

81.7b

98.7c

1.16

0.001

0.001

0.7

64.2

64.4a

61.7a

60.4b

62.4a

63.1a

63.2a

61.7a

65.1b

63.1ab

1.00

0.12

0.14

0.001

11.2

13.4a

19.1b

20.1c

15.6a

16.4b

16.6b

15.8a

14.3b

16.1a

0.46

0.001

0.001

0.001

2.3

2.2a

2.1a

2.0b

3.1a

2.8b

2.6c

3.1a

3.5b

3.0a

0.12

0.001

0.03

0.007

22.3

a

b

b

a

b

b

a

b

b

0.32

0.11

0.001

0.9

18.8

17.4

17.6

18.5

17.5

17.5

18.6

17.1

17.1

Values with different superscripts differ (P < 0.05) by slaughter weight within treatment. BL = Baseline slaughter group. 2 Standard error of the mean. 3 Treatment. 4 Slaughter weight. 5 Interaction. 6 Empty BW. 7 Organs (heart, lungs, empty gastrointestinal tract, kidneys, spleen, and blood) without liver. 8 Head, hide, feet, and tail. a,b,c 1

slaughter weight for calves on TRT 2 and 3 and was related to the increased rate of EBG compared with TRT 1. From TRT 1 to 2 and 3, as rate of gain increased, fat gain (g/d) also increased (P < 0.05); (Table 5). The correlation between EBG (g/d) and fat content (g/kg) was 0.76 (P < 0.001) among all calves on TRT. In addition, the correlation between fat gain (g/d) and energy content (Mcal/kg) was 0.93 (P < 0.001). There was no effect of slaughter weight on fat gain within TRT. Energy gain (Mcal/d) was significantly affected by TRT, but was similar among slaughter weights within TRT. The correlation between EBG (g/d) and energy content (Mcal/kg) was 0.89 (P < 0.001) among TRT. Protein gain (g/d) was also significantly affected by TRT and was different (P < 0.05) among slaughter weights. Protein gain (g/d) decreased with increasing BW in TRT

1 and 2 but not 3 (P < 0.05). The correlation between EBG (g/d) and protein content in the gain (g/kg) was – 0.246 (P < 0.07), whereas the correlation between protein content (g/kg) and energy content (Mcal/kg) was 0.89 (P < 0.001). The correlation between protein and fat gain in g/d was 0.83 (P < 0.001), whereas the correlation between the concentration of protein and fat in the gain (g/kg) was –0.38 (P < 0.005). Digestibility and Metabolizability of the Dietary Components Diet DM and N digestibility were not different among TRT or slaughter weights (Table 6). Overall, apparent digestibility of DM and energy were equal to or greater than 95% and N digestibility was 93.5%.

Table 4. Empty body composition of calves fed three levels of milk replacer and slaughtered at three different BW. P 1

BL Empty BW, kg Water, % of EB6 CP, % of EB Crude fat, % of EB Crude ash, % of EB

40.4 70.2 20.9 4.7 4.2

Treatment 1 63.6a 68.6a 21.7a 5.8a 3.9a

77.6b 68.7ab 21.3a 5.7a 3.9a

95.7c 69.6c 21.1b 5.4b 3.8a

Treatment 2 64.9a 67.3a 21.0a 7.8a 3.7a

82.0b 65.4b 20.5b 9.8b 3.8a

97.2c 66.2a 19.8c 9.8b 3.5b

Treatment 3 64.8a 67.7a 21.0a 7.0a 3.9a

81.7b 65.1b 21.1a 9.1b 3.9a

Values with different superscripts differ (P < 0.05) by slaughter weight within treatment. BL = Baseline slaughter group. 2 Standard error of the mean. 3 Treatment. 4 Slaughter weight. 5 Interaction. 6 EB = Empty body. a,b,c 1

Journal of Dairy Science Vol. 84, No. 4, 2001

98.7c 65.1b 19.9b 10.0c 4.0a

2

3

SE

TRT

1.16 0.78 0.02 0.01 0.23

0.001 0.001 0.004 0.001 0.03

SL4

TRT*SL5

0.001 0.001 0.001 0.001 0.8

0.7 0.3 0.9 0.01 0.6

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COMPOSITION OF GROWTH IN CALVES

Table 5. Composition of gain, calculated from birth, of calves fed three levels of milk replacer and slaughtered at three different BW. P Treatment 1 EBW,5 kg EBW gain, kg EBW gain, kg/d Energy content of gain, mcal/kg Protein content of gain, g/kg Fat content of gain, g/kg Energy gain, mcal/d Protein gain, g/d Fat gain, g/d

63.6a 23.6a

77.6b 37.5b

Treatment 2 95.7c 55.7c

64.9a 24.9a

Treatment 3

82.0b 42.0b

97.2c 57.2c

64.8a 24.8a

81.7b 40.8b

98.7c 58.7c

SE1

TRT2

SL3

TRT*SL4

1.16 1.16

0.001 0.001

0.001 0.001

0.7 0.9

0.58a

0.55a

0.56a

0.98ab

1.06b

0.91a

1.01a

1.21b

1.16b

0.33

0.0001

0.08

0.03

2.15a

2.16a

1.91b

2.38a

2.62b

2.51c

2.36a

2.49b

2.56b

0.08

0.001

0.003

0.8

244.3a

256.0a

228.7b

200.9a

211.9a

a

a

a

a

b

82.0

77.0

1.25a a

141.7 47.6a

70.0

1.18b a

141.0 42.4a

144.7

1.08c b

128.1 39.2b

196.9 141.8a

ab

162.5

2.34a a

194.0b 151.5

2.81b

231.0a

218.1b

203.4c

0.08

0.007

0.08

0.8

a

b

b

0.90

0.002

0.45

0.26

0.14

0.002

0.001

0.14

1.19 1.22

0.002 0.005

0.05 0.04

0.5 0.03

123.7

2.29a

b

2.40a

c

224.7 172.3b

140.4

3.06b

a

176.5 137.9a

152.0

3.00b

b

233.3 124.9a

a

263.9 169.0b

235.9 176.3b

Values with different superscripts differ (P < 0.05) by slaughter weight within treatment. Standard error of the mean. 2 Treatment. 3 Slaughter weight. 4 Interaction. 5 Empty BW. a,b,c 1

Table 6. Dry matter intake of milk replacer, apparent digestibilities, digestible, and metabolizable energy content of milk replacer and retained protein determined from total collection study.1 P Treatment 1 BW, kg DMI, kg/d Apparent digestibility of DM, % Apparent digestibility of nitrogen, % Digestible energy, mcal/kg Metabolizable energy, mcal/kg Apparently retained protein,6 g/d Biological value of absorbed protein7 Plasma urea nitrogen,8 mg/dl

64.0 0.98a

85.0 0.91b

95.7

95.1

93.8 4.67

4.57a a

181.4

66.0 12.0

4.73

162.1

65.0 a

92.3 b

4.52a b

9.3

b

104.5 0.71c 93.8

92.5 ab

Treatment 2 86.0 1.99b

95.7

96.1

92.5

4.61

a

4.42b 114.4

c

58.0 10.2

68.0 1.72a

c

5.00

4.83a 308.5

a

65.0 12.5

a

93.9

4.96

a

4.83a 318.6

a

62.0 13.1

102.0 1.64c 95.6

92.5 a

Treatment 3

b

b

4.73b b

58.0 9.4

84.0 2.13b

96.0

95.8

92.8

4.91

270.4

65.0 1.72a

94.2

4.74

4.62a 320.8

a

70.0 c

a

10.1

a

b

4.53b b

69.0 12.4

b

3

TRT

SL4

TRT*SL5

104.0 2.52c

1.38 0.17

0.001

0.02

0.04

96.0

0.28

0.6

0.7

0.8

93.5

4.69

384.0

SE

2

0.58

0.7

0.6

0.6

b

0.10

0.04

0.03

0.03

4.53b

0.10

0.05

0.03

0.03

98.90

0.001

0.04

0.4

0.02

0.3

0.4

0.4

1.29

0.4

0.02

0.06

4.69

341.3

a

57.0 10.2

a

Values with different superscripts differ (P < 0.05) by slaughter weight within treatment. Complete collections were conducted on four calves per treatment (total of 12 calves) when the average BW represented the weight closest to the slaughter weight from the slaughter study. 2 Standard error of the mean. 3 Treatment. 4 Mean weight during total collection. 5 Interaction. 6 Calculated protein retained based on the nitrogen balance, total collection data. 7 Biological value was calculated as (nutrient retained/nutrient apparently absorbed) × 100). Data from collection study was applied to slaughter data. 8 Plasma urea nitrogen values from slaughter study calves (n = 54) from weekly samples over treatment period. a,b,c 1

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Calves on TRT 1 and 3 had the lowest measured digestible energy and ME content (P < 0.05) compared with TRT 2, consistent with the measured GE content of the MR. Nitrogen retention as measured in the collection study was greater (P < 0.05) for calves on TRT 2 and TRT 3 compared with TRT 1, but was similar between TRT 2 and 3. Biological values were similar among TRT, but decreased (P < 0.05) with increasing BW, especially from 85 to 105 kg of BW (Table 6). There were no differences in PUN among TRT and slaughter weights (Table 6). DISCUSSION Composition Few studies have analyzed body composition changes in cattle under 100 kg (Donnelly and Hutton, 1976ab; Gerrits et al., 1996). Reid et al. (1955) reported that the water, protein, and ash content of ruminant tissues is relatively constant on a fat-free basis and is not greatly influenced by such factors as diet, rate of gain, stage of maturity, or breed. This was supported by subsequent studies (Maiga, 1975; Simpfendorfer, 1974). Conversely, the energy content of the gain is highly influenced by the fat content, and it is well established that the fat content is influenced by these factors (Anrique, 1976; Garrett, 1980, 1987; Simpfendorfer, 1974). As expected, based on energy intake, the changes in composition among TRT were significant. With increased energy intake, fat, and protein deposition increased. However, as EBG increased, the fat content of the gain increased, and the protein content decreased in a manner similar to previous studies (Anrique, 1976; Garrett, 1980, 1987; Simpfendorfer, 1974). Due to an inability to consume the targeted DMI at less than 65 kg of BW, the calves assigned to TRT 3 did not vary in composition compared with the TRT 2 calves up to 65 kg. For calves assigned to TRT 3 up to 65 kg of BW, the inability to consume adequate MR to achieve the target growth rate was most likely due to the lower dilution of MR used in that TRT compared with TRT 1 and 2. The data are consistent with the findings of Donnelly and Hutton (1976b) for calves fed higher levels of protein, although subtle differences were observed in protein and energy retained. In their study (Donnelly and Hutton, 1976b), calves slaughtered at 69 kg of EBW and fed MR that averaged 30.5% CP deposited an average of 19.6% protein in their tissue gain. This was 12.9% lower than the average protein content (22.5%) of the gain achieved by the slightly lighter (64.4 kg of EBW) calves on this study. The energy retained in the tissue gain averaged 2.25 Mcal/kg for the Donnelly and Hutton (1976b) calves, while the energy content (2.07 Mcal/ Journal of Dairy Science Vol. 84, No. 4, 2001

kg) of the gain for calves on this study was approximately 8% less. The fat content of the gain was nearly identical for the calves on the two studies [11.7 vs. 11.1%, for Donnelly and Hutton (1976b) and this study, respectively]. Current industry standard MR contains between 18 and 22% CP. Comparison of our data with that from calves fed a 21.8% CP MR (Donnelly and Hutton, 1976b) demonstrates dramatic changes in composition of gain. The protein content of the gain in calves fed the 21.8% CP MR (Donnelly and Hutton, 1976b) was 17.3%, which was 23% less than that of the calves in our study (22.5%). The fat content of gain was 18.4% (Donnelly and Hutton, 1976b), which was 166% of the fat content of gain of the calves on our study. For the calves (Donnelly and Hutton, 1976b) fed 21.8% CP MR, 64% of the energy was retained as fat; whereas, for calves fed the 31.5% CP MR, 51% of the energy was stored as fat. On average, the 65-kg calves on our study stored 48% of retained energy as fat. We conclude that alteration of diet composition significantly alters composition of growth in milk fed calves, and that this should be accounted for when calculating requirements for growth. Predictive Equations A goal of our study was to evaluate published requirement equations with our data, and to propose new equations where appropriate. The RE predicted by the 1989 Dairy NRC equation was equal to the observed RE for calves assigned to TRT 1 and approximately 12.5 to 14% lower than the observed RE for calves assigned to TRT 2 and 3 (Table 7). The 1996 NRC underpredicted the RE in the empty body by 21, 28, and 30% for calves assigned to TRT 1, 2, and 3, respectively. The apparent inability of the 1989 Dairy and 1996 Beef NRC equations to accurately predict the RE in calves on this study, especially at the higher growth rates, is due to differences between the fat and protein content of the EBG of calves in this study and the cattle used to derive the prediction equations. The cattle used to derive the original equation (Garrett, 1980) were generally heavier than 250 kg of BW and of beef origin. Thus, per unit of energy deposited, a greater proportion of the RE was fat. Use of the current 1996 Beef NRC equation to predict the energy content of lightweight cattle results in an under prediction because a greater proportion of the RE will be in the form of tissue protein and less will be in fat. The 1989 Dairy NRC will also underpredict RE because of adjustments (described in the publication) made to the energy content of the gain as stated in the publication.

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COMPOSITION OF GROWTH IN CALVES

Table 7. Comparison of observed energy and protein retained, and composition of gain in calves in this study with prediction equations used in the 1989 Dairy (NRC, 1989) and 1996 Beef NRC (NRC, 1996) publications and the energy equation of Toullec (1989)1. Retained energy, (Mcal/d)

Treatment 1 Treatment 2 Treatment 3

Retained protein, (g/d)

Observed

Predicted dairy2

Predicted beef3

Predicted Toullec4

1.17 2.48 2.82

1.17 2.12 2.45

0.92 1.72 2.01

1.54 2.99 3.52

Observed

Predicted dairy5

Predicted beef6

136.9 199.4 244.4

98.8 160.6 183.3

130.0 213.1 244.0

Fat in gain, %

Protein in gain, %

Observed

Predicted beef7

Observed

Predicted beef8

7.6 15.2 13.8

0.0 15.5 19.6

24.3 20.2 21.8

21.7 18.3 17.4

1 The weight and weight gain units for the equations are kg. The prediction of retained protein utilized the actual energy value of the gain of the calves on study as determined by bomb calorimetry. 2 Calculated using the equation: NEg (Mcal/d) = (0.035 × LW0.75) × (LWG1.119) + LWG. 3 Calculated using the equation: RE (Mcal/d) = 0.0635 × EBW0.75 × EBG1.0973. 4 Calculated using the equation: RE (Mcal/d) = (0.84 × LW0.355 × LWG1.2) × 0.69. 5 Calculated using the equation: RPN (g/d) = (211−(26.2 × NE (mcal/d)/LWG) × (LWG). 6 Calculated using the equation: Net protein (g/d) = SWG × (268 − (29.4 × (RE (mcal/d)/SWG))). 7 Calculated using the equation: Proportion of fat (g/100/g) = 0.122 × RE (Mcal/d) − 0.146. 8 Calculated using the equation: Proportion of protein (g/100/g) = 0.248 − 0.0264 × RE (Mcal/d).

The Toullec equation (Toullec, 1989) for predicting RE overpredicted the RE content by approximately 21 to 32% (Table 7). The overprediction of RE might be due to heavier calves used to develop the equation (Toullec, 1989), and calves that were fed a lower protein MR and, consequently, had increased fat deposition and increased RE per unit of weight gain compared with calves on this study. Both NRC (1989, 1996) equations to predict retained protein (RP) are based on RE per unit of weight gain. For this comparison, the actual RE (Mcal/d) values determined from calves on this study were used to compute RP. This allows evaluation of the RP equation independent of the prediction of RE. Among the three TRT, the equation used in the 1989 Dairy NRC underpredicted the RP by 23 to 31% (Table 7). This RP prediction equation was modified from the 1984 Beef NRC equation on the assumption that gut fill was 15% of LWG and that the EBG was 85% of LWG. This reduced the original value of 249 to 211 g of protein/kg of EBG at zero fat in the gain. The 1996 Beef NRC assumes shrunk weight gain is 96% of LWG and EBG is 89.1% of LWG (NRC, 1996). Although gut fill will dilute the grams of protein deposited per kilogram of live BW, the composition of the gain will not change (i.e., the protein concentration at zero fat in the EB). The prediction of RP by the 1996 Beef NRC equation was much more accurate than the 1989 Dairy NRC equation as predicted and observed values differed by less than 7%. The protein equation used in the Beef NRC (1984, 1996) was developed in a manner that represents the amount of protein in the gain (PIG) (268 g) at zero fat in the gain (FIG) when the energy content of gain was represented by the energy in 1 kg of EB protein deposition. Thus, if the energy content of the gain can be predicted with greater accuracy, the 1996

Beef NRC protein equation should work for all classes of growing cattle. The 1996 Beef NRC FIG equation predicted that calves assigned to TRT 1 should have a fat content of gain of 0% compared with the 7.6% observed (Table 7). The equation accurately predicted the FIG for calves assigned to TRT 2 but overpredicted the FIG for calves assigned to TRT 3. Retained energy is the only variable in the equation that makes the equation insensitive to stage of growth. The predictive behavior of the equation suggests that the proportion of FIG in the cattle used to derive the NRC equations (1989, 1996) does not necessarily represent the FIG found in these lighter weight animals and suggests that the equation is overly sensitive to RE in calves less than 105 kg. Predicted values from the 1996 Beef NRC PIG equation were 10 to 20% less than observed values and demonstrated a greater underprediction for calves at the higher EBG. This underprediction of PIG does indicate that the cattle used to derive the equation do not adequately represent the lightweight Holstein. Energy and Protein Predictive Equations New equations were developed from our data to predict the energy and protein content of gain. The RE required by an animal is equal to the total energy in the tissue gain and is a function of the proportion of fat and protein in the gain (Garrett, 1980). These proportions are influenced by EBG and EBW. The RE content of the EBG of preruminant calves ranging in LW from 45 to 105 kg and gaining in BW from 500 to 1400 g/d resulted in the following equation: RE (Mcal/d) = (EBW0.223) × (EBG1.32) where EBW and EBG are in kilograms. Journal of Dairy Science Vol. 84, No. 4, 2001

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DIAZ ET AL.

To check the potential variation in the prediction of RE from the equation, the predicted values were plotted against the actual RE and the residuals were also plotted (Figure 2). The new equation accounted for 91% of the variation in actual RE with no bias. The use of this RE equation assumes that protein is not limiting growth. To ensure protein is not limiting growth, the 1996 Beef NRC RP equation or the following equation for RP can be used. The RP was calculated as a function of the energy concentration of the gain consistent with the 1996 Beef NRC equation, except without an intercept. The following equation for predicting the RP content of the EBG was developed from the current data: RP (g/d) = (184 × EBW gain, kg/d) + (17.2 × (RE, mcal/d /EBW gain, kg/d)) where EBW and EBG are in kilograms. Again, to check the variation associated with the prediction of RP from the new equation, the predicted RP was plotted against the actual RP, and the residuals were plotted (Figure 3). The new RP prediction equation accounted for 85% of the variation in actual RP, with an 8% underprediction bias. At lower growth rates, the equation will tend to underpredict the actual protein retained. However, as previously stated, the 1996 NRC equation is appropriate for this class of animal as long as the energy content of the gain is predicted more accurately. Digestibility, Protein Utilization, and Feed Efficiency Deposition of N in the balance trial was 27.5% higher (on average among TRT) than deposition measured in

Figure 2. Predicted retained energy (●) from the equation generated from the slaughter study data plotted against the observed retained energy. The regression equation is Y = 1.015x − 0.0187, R2 = 0.91. The residuals (䊏), calculated as predicted minus observed are plotted on the X-axis. The dashed line represents unity. Journal of Dairy Science Vol. 84, No. 4, 2001

Figure 3. Predicted retained protein (●) from the equation generated from the slaughter study data plotted against the observed retained protein. The regression equation is Y = 0.9203x + 26.26, R2 = 0.85. The residuals (䊏), calculated as predicted minus observed are plotted on the X-axis. The dashed line represents unity.

the slaughter trial (Table 6). This difference is similar to previously reported values (MacRae et al., 1993). Compared with slaughter experiments, balance trials overestimate N deposition (Just et al., 1982; MacRae et al., 1993) primarily because balance trials overestimate N intake and underestimate N excretion. Fuller et al. (1983) demonstrated in pigs that at zero N gain, determined by slaughter trial, the animals were still retaining 2 g of N per day by the balance technique. The high digestibility values for DM, N, and energy are in agreement with values reported by others for preruminant calves fed liquid diets (Donnelly and Hutton, 1976a; Gerrits et al., 1996; Toullec, 1989). There was no difference in either DM or N digestibility among all TRT groups and BW. Many studies have found reduced digestibility of milk and diarrhea with high levels of feeding (Radostits and Bell, 1970; Williams et al., 1986). In our study, high levels of liquid feeding rates did not result in diarrhea, and DM digestibilities were high. This supports other studies (Khouri and Pickering, 1968; Roy, 1980a) that found high levels of intake did not affect DM digestibility in preruminant calves. The concentration of protein in the MR fed to the calves in our study was high compared with current industry practice. However, the comparison should be made to whole milk. Whole milk, on a DM basis can range in protein content from 23 to 27%, and fat can range from 26 to 32% or higher. Therefore, the protein content of the MR used in our study was approximately 20% higher on average than that of whole milk and 50% higher than most MR. The level of protein we used in the MR should have resulted in a lower BV. The BV is a function of the amount and AA profile of protein

841

COMPOSITION OF GROWTH IN CALVES

available to the animal. In studies by Lodge and Lister (1973), milk proteins exhibited a BV of 73 to 78% when fed to calves at reasonably high intakes. The BV calculated in our study, based on digestibility and efficiency of use, averaged 65% among TRT, which was 16% higher than values reported by Donnelly and Hutton (1976b) for similar milk-based diets. The BV observed in our study might be lower than that of Lodge and Lister (1973) due to the high level of protein in our MR and indicates that the objective of formulating diets to ensure protein was not limiting was met. The PUN values (Table 6) grossly represent protein status and the efficiency of use of absorbed protein. Collectively, the BV and PUN data suggest that the absorbed protein was used with reasonable efficiency at each level of intake up to the heaviest weights in our study, then decreased significantly. Lowering the CP level to what is required and adjusting the AA profile of the MR might offer the potential to increase the BV of the protein for similar levels of protein deposition and LWG. Altering the carbohydrate and fat content of MR might also offer the opportunity to increase the BV of the absorbed protein. Restricted rates of liquid feeding result in considerably lower feed conversion efficiencies for young dairy calves compared with feeding practices for the young of other domestic species such as lambs and pigs (Greenwood et al., 1998; Harrell, 1998; Hodge, 1974). Lower feed intakes lead to lower rates of gain and a smaller dilution of maintenance costs, resulting in lower feed efficiencies in calves. The feeding patterns currently used by most dairy producers (once or twice daily) contrast with the feeding strategies used for pigs, lambs, or beef calves (milk intake close to ad libitum). Roy (1980b) determined that ad libitum DMI for milk fed calves was approximately 2.2% BW. Khouri and Pickering (1968) reported ad libitum consumption at 2.25% BW for the first 6 wk of life. After they reached 65 kg of BW, calves on TRT 3 in our study were consuming DM at 2.5% BW, and we did not attempt to feed for ad libitum consumption. These results demonstrate growing calves have the capacity for greater DMI than provided by most dairy management programs. The G:F ratio for calves up to 85 kg of BW on TRT 1 was 0.64, whereas the calves on TRT 3 had a gain to feed ratio of 0.74, a 16% improvement. This compares favorably with the efficiencies reported for pigs of 0.66 to 0.73 (Harrell, 1998) and lambs 0.69 to 0.73 (Hodge, 1974) at similar stages of maturity. Khouri and Pickering (1968) observed efficiencies of 0.75 to 0.80 for preruminant calves fed for ad libitum consumption, which are similar to those found in our study for calves assigned to TRT 3. This study clearly demonstrated that when nutrient supplies are not limiting, feed efficiencies can

be comparable to those of lambs and pigs. The higher efficiencies observed in TRT 1 calves in our study compared with other calf growth data may be due to diet composition and slightly higher rates of gain compared with other data (Everitt and Jury, 1977). CONCLUSIONS This study demonstrated current recommendations for nutrient requirements of the young calf are inadequate and that the energy content of deposited tissue in these animals is not adequately represented by the current prediction equations. The 1989 Dairy NRC equations for predicting the tissue requirements for growth as well as the energy equation in the 1996 Beef NRC need to be revised for this weight animal. This study provides a basis for refining the energy predictions of calves up to 105 kg of BW. New equations for net energy and protein were developed based on calves fed an all milk diet that was not limiting in protein. Results of this study indicate that nutrient supply can alter the body composition of neonatal calves. Further research is needed to investigate effects of rapid early growth rate on body composition and subsequent productivity. ACKNOWLEDGMENTS The authors thank Milk Specialties, Co. (Dundee, IL) for their donation of milk replacer and financial support of this research, with special thanks to Douglas Waterman and Troy Scott. We also thank Cargill, Inc., (Minneapolis, MN) for financial support. Special thanks to Denny Shaw, Jimmy Robertson, Tom Kuntz, Bill Harrower, and Bill English for technical support. REFERENCES Anrique, R. 1976. Body composition and efficiency of cattle as related to body type, size, and sex. Ph.D. Diss. Department of Animal Science. Cornell University, Ithaca, NY. Association of Official Analytical Chemists International. 1981. Official Methods of Analysis. 13th ed. AOAC, Washington, DC. Association of Official Analytical Chemists International. 1990. Official Methods of Analysis. 15th ed. AOAC, Arlington, VA. Commonwealth Scientific and Industrial Research Organization. 1990. Feeding Standards for Australian livestock. CSIRO Publ., East Melbourne, Victoria, Australia. Donnelly, P. E., and J. B. Hutton. 1976a. Effects of dietary protein and energy on the growth of Friesian bull calves. I. Food uptake, growth and protein requirements. N.Z. J. Agric. Res. 19:289–297. Donnelly, P. E., and J. B. Hutton. 1976b. Effects of dietary protein and energy on the growth of Friesian bull calves. II. Effect of level of feed intake and dietary protein content on body composition. N.Z. J. Agric. Res. 19:409–414. Everitt, G. C., and K. E. Jury. 1977. Growth of cattle in relation to nutrition in early life. N.Z. J. Agric. Res. 20:129–137. Fox, D. G., C. J. Sniffen, J. D. O’Connor, P. J. Van Soest, and J. B. Russell. A net carbohydrate and protein system for evaluating cattle diets. III. Cattle requirements and diet adequacy. J. Anim. Sci. 70:3578–3596. Journal of Dairy Science Vol. 84, No. 4, 2001

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