- Email: [email protected]
A comparison of digestible and net energy models to predict rates of gain of hereford steers
Agricultural
PII:
SO308-521X(96)00103-5
Systems, Vol. 54, No. 4. pp. 429431, 1997 0 1997 Published by Elsevier Science Ltd All rights reserved. P&ted in Great Britain 0308-521X/97 $17.00+0.00
ELSEVIER
A Comparison of Digestible and Net Energy Models to Predict Rates of Gain of Hereford Steers R. Hironaka,
B. Freeze & G. C. Kozub
Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada, Tl J 4Bl (Received 23 May 1996; accepted 26 November
1996)
ABSTRACT Equations to predict rates of gain and eficiency of feed utilization are widely used by feedlot operators to make decisions on what and how much to feed to maximize rates of gain and/or feed utilization. Two widely used systems to predict these parameters are the net energy (NE) and the digestible energy (DE) systems. A comparison of the two systems over a wide range of diets would be useful to select the system that is the more useful to the feedlot operator. The objective of this study was to compare the observed and predicted rates of gain of steers fed eight diets ranging from 100% silage to 100% concentrate. Data from an experiment in which 80 Hereford steers were fed diets containing barley-silage and concentrate in ratios of lOO:O, 75.1:24.9, 58.3:41.7, 34.4.656, 18.9:81.1, 8.0:92.0, 3.7:96.3 and 0:lOO on a dry matter (DM) basis were used to compare the accuracy of prediction of average daily gain (ADG) from equations using the NE and DE systems. For steers fed 100 or 75% silage, the NE system more closely predicted the observed rate of gain, but when the concentrate was greater than 40% of the diet, ADG was more closely predicted using the DE than the NE system. For steers fed the all-silage diet for one year then fed an all-concentrate diet, predictions from the NE system over-estimated ADG but were closer than those from the DE system. 0 1997 Published by Elsevier Science Ltd
INTRODUCTION
Feedlot operators use models to predict rates of gain and feed efficiency based on energy intake and utilization. Protein, minerals and vitamins are 429
430
R. Hironaka, B. Freeze, G. C. Kozub
assumed to be present in sufficient concentration not to limit rate and efficiency of gain. Accurate estimates of rates of gain and energy requirements allow feedlot operators to develop economically sound diets and feeding programs and maximize their returns. Kozub & Hironaka (1992) derived empirical equations based on daily digestible energy (DE) intake per day and body weight to predict rates of gain for steers fed an all-concentrate diet to appetite (C-A), an all-concentrate diet restricted to limit average daily gain (ADG) to about 0.5 kg between six and 12 months (C-R) and a 50% hay diet fed to appetite (H-A). These equations consider several factors such as age of the cattle, composition of the diet (and, by implication, the associative effect of roughage and concentrate in the diet), level of DE intake, type of animal and the previous level of feed intake; these are the basis for a feedlot model (Hironaka & Freeze, 1992). This DE-based method for predicting gain is referred to as the ‘DE system’ in this study. The DE system provides several equations for different situations. However, which equation to use for a particular diet is not clear. The data used to derive the equations did not have a wide range of roughage to concentrate ratios and did not include high hay or silage diets. Therefore, predictions for very high roughage diets may lack precision. The NE system, widely used to express energy requirements and predict rates of gain (National Academy of Sciences-National Research Council, 1984) assigns efficiencies of utilization of feed energy for maintenance and gain (NE, and NE,) to different feeds. As with the DE-based equations, rates of gain, or NE, and NE,, can be calculated for animals of different weights and a given feed intake. The NE system assumes a constant efficiency of utilization of the NE for maintenance and gain for a given feedstuff and does not allow for associative effects between feeds or animals gaining at different rates. Both systems (the DE and NE) are used to predict rate of gain from a given feed intake or, conversely, to calculate the feed intakes required to obtain a desired rate of gain. However, the prediction of rate and efficiencies of gain over a wide range of diets of the two systems have not been compared. The purpose of this study was to compare the predicted rates of gain using DE and NE equations with the actual rates of gain observed in a feeding trial with Hereford steers fed eight diets differing in silage:concentrate ratios.
MATERIALS
AND METHODS
Data from an experiment (Hironaka et al., 1994) in which 80 Hereford steers were fed diets containing barley-silage and concentrate in ratios of lOO:O,
Comparison of digestible and net energy models
431
751:24.9, 58.3:41.7, 34.465.6, 18.9:81-l, 8.0:92.0, 3.7:96.3 and 0:lOO on a dry matter (DM) basis were used to compare predicted and actual rates of gain using the DE and NE systems. For 24 weeks (Period l), the rations provided about equal DE per unit live weight with a target ADG of 0.6 kg. Data from the period of feed restriction were used to compare the rates of gain among groups to avoid the confounding effects of variation in level of DE intake. After week 24, the steers were fed their respective diets to appetite until they reached a market weight of about 515 kg (Period 2), except the all-silage group (group 1). Steers in group 1 were fed the all-silage diet until week 52, then the all-concentrate diet from week 52 until they reached market weight. Data from steers in group 1 fed the all-concentrate diet to appetite after 52 weeks on the all-silage diet were used to examine ADG of steers in a period of compensatory gain after 1 y of feed restriction. Rates of gain were predicted using all three DE equations for Hereford steers (Kozub & Hironaka, 1992) (Table 1) and the NE, and NE, for barley silage and barley (National Academy of Sciences-National Research Council, 1984). Root mean squared forecast error (RMSFE) (Mood et al., 1974; Epplin et al., 1980) of the difference between the predicted and the observed rates of gain for each diet was calculated and used to evaluate the precision of prediction of the two systems. In each period (period 1 = 24 weeks; period 2 = variable length), until the steers reached about 5 15 kg live weight, the equation: RMSFE = J[X(Gi - Gi)2], where Gi and G’i are the observed and predicted mean daily gains, respectively, for steer i(i= 1,2...8) in a diet group, was used to calculate RMSFE.
RESULTS Observed rates of gain of steers fed diets with 100 and 75% silage in the restricted feeding period were more closely predicted with the NE equations than with the DE equations (Table 2). For groups fed 42% or greater concentrate, the DE equation predictions for C-A and H-A in period 1 were closer to the observed ADG than those from NE equations. At high levels of concentrate, rates of gain predicted from the NE system were lower than those observed. The average RMSFE during the period of feed restriction was O-129 for the NE predictions compared to O-103 and O-118 for the DE predictions using the H-A and C-A equations, respectively. However, when
432
R. Hironaka, B. Freeze, G. C. Kozub
groups fed 100 or 75% silage were not considered, the corresponding RMSFE values were 0.135, 0.071 and 0.08 1 for the NE, H-A and C-A equations. For period 2 (feeding to appetite), a faster rate of gain (O-95 kg d-l predicted vs 0.63 kg d-l observed) was predicted using the DE equation derived from the 50% hay diet (H-A equation) than was observed in steers fed the 100% silage diet (Table 3). At 75% silage, predictions from the DE equations derived from the 50% hay diet (H-A equation) (predicted 0.98 kg d-l) and from the NE equations (predicted 0.96 kg d-l) were close to the observed ADG (0.98 kg d-l) and their RMSFEs were similar. For cattle fed diets with 42% or higher concentrate, the DE equations derived from the restricted (C-R equation) or fed to appetite all-concentrate diets (C-A equation) were more effective in predicting the observed ADG. The ADG predicted with the NE equation (0.82 kg d-l) was higher than observed for the 100% silage diet (0.63 kg d-l) but this prediction was closer than that predicted using the DE equations. For diets with 42% and higher concentrate, the NE-predicted ADG were lower than observed. During the period of feeding to appetite, the average RMSFE for the NE predictions was 0.215 when all-silage and 90% silage diets were omitted, compared to 0.158 and 0.159 for the C-R and C-A predictions, respectively. For steers fed the all-silage diet for 52 weeks and then fed the all-concentrate diet, the observed rate of gain was 1.35 kg d-l on the all-concentrate diet compared to DE-predicted rates of 0.57, 1.06 and 0.97 kg d-’ for the HA, C-R and C-A equations, respectively. The rate of gain predicted using the NE system was 1.49 kg d-l. The rate of gain predicted using the NE system was higher than the observed but closer than that from any of the DE equations. TABLE 1 Digestible Energy (DE) Equations Used to Predict Rates of Gain (Kozub & Hironaka,
1992)
Breed and feeding typs’
Daily gain (kg) prediction equationb
C-A
G=-1.526+0.02145 DEI+0.007719 W +0.0004388 DEI*W -0~000120 DE12-O~OOO02001W2 G=-0.3631+0~01574 DEI+OXlO2302 W+O.O0001897 DEI*W-O.00005257 DE12-0~0000082341 W2 G=-1~700+0~001048 DEI+0.01452 W+O.O00139 DEI*W -0.000195 DE12-O~OO04396W2
C-R H-A
“Feeding type: C-R, all concentrate diet with feed restriction in periods 1 and 2 and ad Zibitum feeding in period 3; C-A, all-concentrate diet fed ad libitum in periods l-3; and H-A, hay (50%) and concentrate mixture fed ad libitum in periods 1-3. bVariables in regression equations: DEI, mean daily digestible energy intake (MJ); G, mean daily gain (kg); and W, mean weight (kg).
245 254 257 254 251 256 254 254
loo:o 75.11249 58.3:41.7 34.4~65.6 18.9:18.1 8.0:92.0 3.7:96.3 0:lOO Average Adjusted averaged
0.39 0.52 0.56 0.51 0.51 0.54 0.51 0.51
Observed ADG (kg a’) 0.68 0.68 0.64 0.56 0.52 0.53 0.47 0.49
Predicted ADG (kg a’) 0.293 0.167 0.105 0.084 0.063 0.065 0.089 0.077 O-1 18 0.08 1
(kg d-l)
RMSFE
-
0.76 0.74 0.71 0.66 0.63 0.63 0.59 0.60
Predicted ADG (kg a’)
C-Rb
0.367 0.235 0.167 0.161 0.134 0.114 0.110 0.105 0.174 0.132
(kg d-l)
RMSFE
0.64 0.64 0.62 0.56 0.53 0.54 0.48 0.50
Predicted ADG (kg a’)
H-A”
0.53 0.53 0.48 044 0.41 0.42 0.34 0.38
of age.
0.118 0.100 0,110 0.118 0.122 0.134 0.192 0.134 0.129 0.135
(kg ii’)
RMSFE
about six and 12 months
0.253 0.141 0.089 0.084 0.063 0.045 0.084 0.063 0.103 0.071
(kg a’)
Predicted ADG (kg d-l)
Net Energy (NE)
system
of Steers Fed Diets
error ( RMSFE)e
RMSFE
“C-A prediction equation based on all-concentrate diet fed to appetite. bC-R prediction equation based on all-concentrate diet restricted to obtain an ADG of about 0.5 kg between ‘H-A prediction equation based on 50% hay dietfed to appetite. dAdjusted average eliminating 100% silage and 75.1:24.9 diets. ‘RMSFE = root mean square forecast error.
DM basis
Animal weight (kg)
C-A”
system
rates of gain and root mean squared forecast
Digestible energy (DE)
Predicted
TABLE 2 Daily Gains (ADG) (kg d-t) Observed and Predicted by Digestible Energy (DE) and Net Energy (NE) Systems with Different Silage to Concentrate Rations During the Restricted Feed Period (168 days)
Ratio silage:conc
Average
d 3 & $
r$ F 3 Q. g : g
$
Q 2 a E. 8 q
TABLE 3
344 426 425 425 421 423 420 418
100:o 75.1:24.9 58.3:41.7 34.4656 l&9:81.1 8*0:92.0 3.7:96.3 0:lOO Average Adjusted averaged
0.486 0.257
1.11 1.22 1.22 1.33 1.29 1.24 1.25 1.24
0.98
0.63
1.15 1.31 1.30 1.23 1.25 1.24
0.158 0.138 0.176 0.105 0.232 0.145 0.212 0.159
(kg a’)
RMSFE
Predicted ADG (kg d-‘)
Observed ADG (kg a’)
0.167 0.126 0.176 0.110 0.221 0.148 0.206 0.158
0446 0.255
1.07 1.22 1.23 1.35 1.32 1.24 1.26 1.25
(kg a’)
RMSFE
Predicted ADG (kg a’)
C-Rb
0.97 1.09 l-04 0.99 1.oo 1.00
0.95 0.98
Predicted ADG (kg a’)
0.224 0.259 0.319 0.263 0440 0.352 0.287 0.310
0.336 0.100
(kg a’)
RMSFE
H-AC
0.99 1.22 1.20 1.11 1.11 1.15
0.82 0.96
Predicted ADG (kg a’)
0.212 0.155 0.212 0.158 0.332 0.221 0.199 0.215
0.214 0.089
(kg a’)
FiUSFE
Net energy (NE) system
“C-A prediction equation based on all-concentrate diet fed to appetite. bC-R prediction equation based on all-concentrate diet restricted to obtain an ADG of about 0.5 kg between about six and 12 months of age. ‘H-A Prediction equation based on 50% hay diet fed to appetite. dAdjusted average eliminating 100% silage and 75.1:24.9 diets. ‘RMSFE = root mean square forecast error.
DM basis
Animal weight (kg)
Ratio silage:conc
C-A”
Digestible energy (DE) system
Predicted rates of gain and root mean squared forecast error (RMSFE)’
Daily Gains Observed and Predicted by Digestible Energy (DE) and Net Energy (NE) Systems of Steers Fed Different Ratios of Silage and Concentrate Fed to Appetite
g &
a 2 a m a 9
-;
3 8 %
P
Comparison of digestible and net energy models
435
DISCUSSION We attribute the smaller RMSFE from the DE- than the NE-system for diets with more than 40% concentrate in the feed restricted period to allowance in the DE system for variation in efficiency of DE utilization of different mixes of roughage and concentrate and to different efficiencies of DE utilization at different rates of gain. The equations used were derived using diets with about 50% concentrate, and the efficiency of DE utilization for gain increases between 21 and 41% concentrate in the diet and levels off at higher levels of concentrate (Hironaka et al., 1986). This is likely to be why the 50% hay equation over-estimated the efficiency of DE utilization for gain on the all-silage diet. When the diets contained more than 40% concentrate, the RMSFE using the DE equation remained constant and smaller than RMSFE for the NE system. Over this range of concentrates in the diet, the DE system was a better predictor of ADG than the NE system. Within the DE system, the lower than predicted ADG observed for the allsilage and the 75.1% silage diets supports observations of other workers that rates of gain of steers on all-roughage diets are lower than those on isocaloric high concentrate diets (Bailey, 1989). We attribute the larger difference between observed and predicted ADG on the 100% silage diet than on diets with concentrate to the development of prediction equations using data from diets with a maximum of 50% roughage. The equation based on data from a 50% roughage diet over-estimated the efficiency of DE utilization for gain on a 100% silage diet. This suggests that the efficiency of DE utilization declines between 60 and 100% silage DM in the diet. Rates of gain for the restricted feed period were most closely predicted using the H-A and C-A equations. In the period of feeding to appetite, for the 100 and 75% silage diets, RMSFE was lowest using the equation derived from the 50% hay diet. At 42% or higher levels of concentrate, predictions made using C-R and C-A equations produced the smallest RMSFE. Thus, the point at which the products of digestion change resulting in a change in efficiency of DE utilization is between 25 and 42% concentrate in the diet. Using the NE equation, the ADG was over-estimated on high silage diets. As the concentrate in the diet increased, the predicted ADG increased. At about 25% concentrate the observed and predicted rates of gain were similar. However, as the level of concentrate was increased above about 25%, the predicted ADG was less than observed, apparently due to a non-linear substitution between DE of barley-silage and barley for maintenance and gain. This view agrees with that of Epplin et al. (1980) and Freeze and Hironaka (1990) that the gain to roughage-concentrate ratio isoquant is not convex to the origin.
R. Hironaka, B. Freeze, G. C. Kozub
436
Steers on restricted feed for 52 weeks had greater ADG than predicted using the DE equation for steers on restricted feed for 24 weeks, suggesting the efficiency of feed utilization during realimentation increases with the length of moderate feed restriction. The wide discrepancy between the predicted and observed rates of gain is attributed to the high efficiency of energy utilization due to compensatory gain in steers that have been restricted in feed for an extended period of time. The smaller RMSFE using the NE system than any of the DE equations is attributed to an increase in the efficiency of feed utilization due to compensatory gain. The DE system predicted rate of gain better than the NE system under most feeding conditions encountered in practical feedlot feeding conditions. The prediction of rate of gain in the restricted period of feeding was similar and best using the C-A and the H-A derived equations. During the period of feeding to appetite, the prediction of rate of gain was similar and best using the C-A and C-R derived equations. Since the C-A derived equation was common to both feeding situations, it appears that the C-A equation may be used in practical situations when the diet contains at least 40% concentrate, a condition that is common to practical feedlot practice. With very high silage diets (100 or 90% on an as fed-basis) neither the DE nor the NE system was a good predictor of rate of gain. This is attributed to the fact that both equations were developed using data from predominantly high grain feedlot diets. Since carcass backfat thickness is strongly associated with rate of gain (Hironaka et al., 1979), a prediction of rate of gain should be beneficial in the prediction of carcass grade and assessment of diet and feeding programs for feedlot cattle. Information on rate of gain is also needed because it influences marketing date and carcass composition (Hironaka & Freeze, 1992).
REFERENCES Bailey, C. B. (1989) Rate and efficiency of gain, body composition, nitrogen metabolism, and blood composition of growing Holstein steers, given diets of roughage or concentrate. Canadian Journal of Animal Science, 69, 707-725. Epplin, P., Bhide, S. and Heady, E. 0. (1980) Empirical investigations of beef gain roughage-concentrate substitution. American Journal of Agricultural Economics, 62,468477.
Freeze, B. and Hironaka, R. (1990) Effect of form of hay and carcass quality on the economics of concentrate: hay substitution in cattle feedlot diets. Western Journal of Agricultural Economics, 15, 163-174. Hironaka, R. and Freeze, B. (1992) Feedlot finishing of cattle. Agr. Can. Pub 1591. Ottawa, ON.
Comparison of digestible and net energy models
431
Hironaka, R., Freeze, B., Kozub, G. C. and Beauchemin, K. A. (1994) The influence of cereal silage to concentrate ratio on rate and efficiency of gain, diet digestibility and carcass characteristics of beef steers. Canadian Journal of Animal Science, 74, 495-501.
Hironaka, R., Grigat, G. A. and Kozub, G. C. (1986) The voluntary intake of diets differing in digestible energy concentration and form of hay. Canadian Journal of Animal Science 66, 735-142.
Hironaka, R., Sonntag, B. H. and Kozub, G. C. (1979) Effects of feeding programs and diet energy on rate of gain, efficiency of digestible energy utilization, and carcass grades of steers. Canadian Journal of Animal Science, 59, 385-394. Kozub, G. C. and Hironaka, R. (1992) Digestible energy requirements for growth in Hereford and Charolais x Hereford steers. Canadian Journal of Animal Science 72, 651-661.
Mood, A. M., Graybill, F. A. and Boes, D. C. (1974) Introduction to the theory of Statistics, 3rd ed, Mcgraw-Hill Inc. p.291. National Academy of Sciences - National Research Council (1984) Nutrient Requirements of Beef Cattle. 6th edn. National Academy Press, Washington, D.C.
PII:
SO308-521X(96)00103-5
Systems, Vol. 54, No. 4. pp. 429431, 1997 0 1997 Published by Elsevier Science Ltd All rights reserved. P&ted in Great Britain 0308-521X/97 $17.00+0.00
ELSEVIER
A Comparison of Digestible and Net Energy Models to Predict Rates of Gain of Hereford Steers R. Hironaka,
B. Freeze & G. C. Kozub
Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada, Tl J 4Bl (Received 23 May 1996; accepted 26 November
1996)
ABSTRACT Equations to predict rates of gain and eficiency of feed utilization are widely used by feedlot operators to make decisions on what and how much to feed to maximize rates of gain and/or feed utilization. Two widely used systems to predict these parameters are the net energy (NE) and the digestible energy (DE) systems. A comparison of the two systems over a wide range of diets would be useful to select the system that is the more useful to the feedlot operator. The objective of this study was to compare the observed and predicted rates of gain of steers fed eight diets ranging from 100% silage to 100% concentrate. Data from an experiment in which 80 Hereford steers were fed diets containing barley-silage and concentrate in ratios of lOO:O, 75.1:24.9, 58.3:41.7, 34.4.656, 18.9:81.1, 8.0:92.0, 3.7:96.3 and 0:lOO on a dry matter (DM) basis were used to compare the accuracy of prediction of average daily gain (ADG) from equations using the NE and DE systems. For steers fed 100 or 75% silage, the NE system more closely predicted the observed rate of gain, but when the concentrate was greater than 40% of the diet, ADG was more closely predicted using the DE than the NE system. For steers fed the all-silage diet for one year then fed an all-concentrate diet, predictions from the NE system over-estimated ADG but were closer than those from the DE system. 0 1997 Published by Elsevier Science Ltd
INTRODUCTION
Feedlot operators use models to predict rates of gain and feed efficiency based on energy intake and utilization. Protein, minerals and vitamins are 429
430
R. Hironaka, B. Freeze, G. C. Kozub
assumed to be present in sufficient concentration not to limit rate and efficiency of gain. Accurate estimates of rates of gain and energy requirements allow feedlot operators to develop economically sound diets and feeding programs and maximize their returns. Kozub & Hironaka (1992) derived empirical equations based on daily digestible energy (DE) intake per day and body weight to predict rates of gain for steers fed an all-concentrate diet to appetite (C-A), an all-concentrate diet restricted to limit average daily gain (ADG) to about 0.5 kg between six and 12 months (C-R) and a 50% hay diet fed to appetite (H-A). These equations consider several factors such as age of the cattle, composition of the diet (and, by implication, the associative effect of roughage and concentrate in the diet), level of DE intake, type of animal and the previous level of feed intake; these are the basis for a feedlot model (Hironaka & Freeze, 1992). This DE-based method for predicting gain is referred to as the ‘DE system’ in this study. The DE system provides several equations for different situations. However, which equation to use for a particular diet is not clear. The data used to derive the equations did not have a wide range of roughage to concentrate ratios and did not include high hay or silage diets. Therefore, predictions for very high roughage diets may lack precision. The NE system, widely used to express energy requirements and predict rates of gain (National Academy of Sciences-National Research Council, 1984) assigns efficiencies of utilization of feed energy for maintenance and gain (NE, and NE,) to different feeds. As with the DE-based equations, rates of gain, or NE, and NE,, can be calculated for animals of different weights and a given feed intake. The NE system assumes a constant efficiency of utilization of the NE for maintenance and gain for a given feedstuff and does not allow for associative effects between feeds or animals gaining at different rates. Both systems (the DE and NE) are used to predict rate of gain from a given feed intake or, conversely, to calculate the feed intakes required to obtain a desired rate of gain. However, the prediction of rate and efficiencies of gain over a wide range of diets of the two systems have not been compared. The purpose of this study was to compare the predicted rates of gain using DE and NE equations with the actual rates of gain observed in a feeding trial with Hereford steers fed eight diets differing in silage:concentrate ratios.
MATERIALS
AND METHODS
Data from an experiment (Hironaka et al., 1994) in which 80 Hereford steers were fed diets containing barley-silage and concentrate in ratios of lOO:O,
Comparison of digestible and net energy models
431
751:24.9, 58.3:41.7, 34.465.6, 18.9:81-l, 8.0:92.0, 3.7:96.3 and 0:lOO on a dry matter (DM) basis were used to compare predicted and actual rates of gain using the DE and NE systems. For 24 weeks (Period l), the rations provided about equal DE per unit live weight with a target ADG of 0.6 kg. Data from the period of feed restriction were used to compare the rates of gain among groups to avoid the confounding effects of variation in level of DE intake. After week 24, the steers were fed their respective diets to appetite until they reached a market weight of about 515 kg (Period 2), except the all-silage group (group 1). Steers in group 1 were fed the all-silage diet until week 52, then the all-concentrate diet from week 52 until they reached market weight. Data from steers in group 1 fed the all-concentrate diet to appetite after 52 weeks on the all-silage diet were used to examine ADG of steers in a period of compensatory gain after 1 y of feed restriction. Rates of gain were predicted using all three DE equations for Hereford steers (Kozub & Hironaka, 1992) (Table 1) and the NE, and NE, for barley silage and barley (National Academy of Sciences-National Research Council, 1984). Root mean squared forecast error (RMSFE) (Mood et al., 1974; Epplin et al., 1980) of the difference between the predicted and the observed rates of gain for each diet was calculated and used to evaluate the precision of prediction of the two systems. In each period (period 1 = 24 weeks; period 2 = variable length), until the steers reached about 5 15 kg live weight, the equation: RMSFE = J[X(Gi - Gi)2], where Gi and G’i are the observed and predicted mean daily gains, respectively, for steer i(i= 1,2...8) in a diet group, was used to calculate RMSFE.
RESULTS Observed rates of gain of steers fed diets with 100 and 75% silage in the restricted feeding period were more closely predicted with the NE equations than with the DE equations (Table 2). For groups fed 42% or greater concentrate, the DE equation predictions for C-A and H-A in period 1 were closer to the observed ADG than those from NE equations. At high levels of concentrate, rates of gain predicted from the NE system were lower than those observed. The average RMSFE during the period of feed restriction was O-129 for the NE predictions compared to O-103 and O-118 for the DE predictions using the H-A and C-A equations, respectively. However, when
432
R. Hironaka, B. Freeze, G. C. Kozub
groups fed 100 or 75% silage were not considered, the corresponding RMSFE values were 0.135, 0.071 and 0.08 1 for the NE, H-A and C-A equations. For period 2 (feeding to appetite), a faster rate of gain (O-95 kg d-l predicted vs 0.63 kg d-l observed) was predicted using the DE equation derived from the 50% hay diet (H-A equation) than was observed in steers fed the 100% silage diet (Table 3). At 75% silage, predictions from the DE equations derived from the 50% hay diet (H-A equation) (predicted 0.98 kg d-l) and from the NE equations (predicted 0.96 kg d-l) were close to the observed ADG (0.98 kg d-l) and their RMSFEs were similar. For cattle fed diets with 42% or higher concentrate, the DE equations derived from the restricted (C-R equation) or fed to appetite all-concentrate diets (C-A equation) were more effective in predicting the observed ADG. The ADG predicted with the NE equation (0.82 kg d-l) was higher than observed for the 100% silage diet (0.63 kg d-l) but this prediction was closer than that predicted using the DE equations. For diets with 42% and higher concentrate, the NE-predicted ADG were lower than observed. During the period of feeding to appetite, the average RMSFE for the NE predictions was 0.215 when all-silage and 90% silage diets were omitted, compared to 0.158 and 0.159 for the C-R and C-A predictions, respectively. For steers fed the all-silage diet for 52 weeks and then fed the all-concentrate diet, the observed rate of gain was 1.35 kg d-l on the all-concentrate diet compared to DE-predicted rates of 0.57, 1.06 and 0.97 kg d-’ for the HA, C-R and C-A equations, respectively. The rate of gain predicted using the NE system was 1.49 kg d-l. The rate of gain predicted using the NE system was higher than the observed but closer than that from any of the DE equations. TABLE 1 Digestible Energy (DE) Equations Used to Predict Rates of Gain (Kozub & Hironaka,
1992)
Breed and feeding typs’
Daily gain (kg) prediction equationb
C-A
G=-1.526+0.02145 DEI+0.007719 W +0.0004388 DEI*W -0~000120 DE12-O~OOO02001W2 G=-0.3631+0~01574 DEI+OXlO2302 W+O.O0001897 DEI*W-O.00005257 DE12-0~0000082341 W2 G=-1~700+0~001048 DEI+0.01452 W+O.O00139 DEI*W -0.000195 DE12-O~OO04396W2
C-R H-A
“Feeding type: C-R, all concentrate diet with feed restriction in periods 1 and 2 and ad Zibitum feeding in period 3; C-A, all-concentrate diet fed ad libitum in periods l-3; and H-A, hay (50%) and concentrate mixture fed ad libitum in periods 1-3. bVariables in regression equations: DEI, mean daily digestible energy intake (MJ); G, mean daily gain (kg); and W, mean weight (kg).
245 254 257 254 251 256 254 254
loo:o 75.11249 58.3:41.7 34.4~65.6 18.9:18.1 8.0:92.0 3.7:96.3 0:lOO Average Adjusted averaged
0.39 0.52 0.56 0.51 0.51 0.54 0.51 0.51
Observed ADG (kg a’) 0.68 0.68 0.64 0.56 0.52 0.53 0.47 0.49
Predicted ADG (kg a’) 0.293 0.167 0.105 0.084 0.063 0.065 0.089 0.077 O-1 18 0.08 1
(kg d-l)
RMSFE
-
0.76 0.74 0.71 0.66 0.63 0.63 0.59 0.60
Predicted ADG (kg a’)
C-Rb
0.367 0.235 0.167 0.161 0.134 0.114 0.110 0.105 0.174 0.132
(kg d-l)
RMSFE
0.64 0.64 0.62 0.56 0.53 0.54 0.48 0.50
Predicted ADG (kg a’)
H-A”
0.53 0.53 0.48 044 0.41 0.42 0.34 0.38
of age.
0.118 0.100 0,110 0.118 0.122 0.134 0.192 0.134 0.129 0.135
(kg ii’)
RMSFE
about six and 12 months
0.253 0.141 0.089 0.084 0.063 0.045 0.084 0.063 0.103 0.071
(kg a’)
Predicted ADG (kg d-l)
Net Energy (NE)
system
of Steers Fed Diets
error ( RMSFE)e
RMSFE
“C-A prediction equation based on all-concentrate diet fed to appetite. bC-R prediction equation based on all-concentrate diet restricted to obtain an ADG of about 0.5 kg between ‘H-A prediction equation based on 50% hay dietfed to appetite. dAdjusted average eliminating 100% silage and 75.1:24.9 diets. ‘RMSFE = root mean square forecast error.
DM basis
Animal weight (kg)
C-A”
system
rates of gain and root mean squared forecast
Digestible energy (DE)
Predicted
TABLE 2 Daily Gains (ADG) (kg d-t) Observed and Predicted by Digestible Energy (DE) and Net Energy (NE) Systems with Different Silage to Concentrate Rations During the Restricted Feed Period (168 days)
Ratio silage:conc
Average
d 3 & $
r$ F 3 Q. g : g
$
Q 2 a E. 8 q
TABLE 3
344 426 425 425 421 423 420 418
100:o 75.1:24.9 58.3:41.7 34.4656 l&9:81.1 8*0:92.0 3.7:96.3 0:lOO Average Adjusted averaged
0.486 0.257
1.11 1.22 1.22 1.33 1.29 1.24 1.25 1.24
0.98
0.63
1.15 1.31 1.30 1.23 1.25 1.24
0.158 0.138 0.176 0.105 0.232 0.145 0.212 0.159
(kg a’)
RMSFE
Predicted ADG (kg d-‘)
Observed ADG (kg a’)
0.167 0.126 0.176 0.110 0.221 0.148 0.206 0.158
0446 0.255
1.07 1.22 1.23 1.35 1.32 1.24 1.26 1.25
(kg a’)
RMSFE
Predicted ADG (kg a’)
C-Rb
0.97 1.09 l-04 0.99 1.oo 1.00
0.95 0.98
Predicted ADG (kg a’)
0.224 0.259 0.319 0.263 0440 0.352 0.287 0.310
0.336 0.100
(kg a’)
RMSFE
H-AC
0.99 1.22 1.20 1.11 1.11 1.15
0.82 0.96
Predicted ADG (kg a’)
0.212 0.155 0.212 0.158 0.332 0.221 0.199 0.215
0.214 0.089
(kg a’)
FiUSFE
Net energy (NE) system
“C-A prediction equation based on all-concentrate diet fed to appetite. bC-R prediction equation based on all-concentrate diet restricted to obtain an ADG of about 0.5 kg between about six and 12 months of age. ‘H-A Prediction equation based on 50% hay diet fed to appetite. dAdjusted average eliminating 100% silage and 75.1:24.9 diets. ‘RMSFE = root mean square forecast error.
DM basis
Animal weight (kg)
Ratio silage:conc
C-A”
Digestible energy (DE) system
Predicted rates of gain and root mean squared forecast error (RMSFE)’
Daily Gains Observed and Predicted by Digestible Energy (DE) and Net Energy (NE) Systems of Steers Fed Different Ratios of Silage and Concentrate Fed to Appetite
g &
a 2 a m a 9
-;
3 8 %
P
Comparison of digestible and net energy models
435
DISCUSSION We attribute the smaller RMSFE from the DE- than the NE-system for diets with more than 40% concentrate in the feed restricted period to allowance in the DE system for variation in efficiency of DE utilization of different mixes of roughage and concentrate and to different efficiencies of DE utilization at different rates of gain. The equations used were derived using diets with about 50% concentrate, and the efficiency of DE utilization for gain increases between 21 and 41% concentrate in the diet and levels off at higher levels of concentrate (Hironaka et al., 1986). This is likely to be why the 50% hay equation over-estimated the efficiency of DE utilization for gain on the all-silage diet. When the diets contained more than 40% concentrate, the RMSFE using the DE equation remained constant and smaller than RMSFE for the NE system. Over this range of concentrates in the diet, the DE system was a better predictor of ADG than the NE system. Within the DE system, the lower than predicted ADG observed for the allsilage and the 75.1% silage diets supports observations of other workers that rates of gain of steers on all-roughage diets are lower than those on isocaloric high concentrate diets (Bailey, 1989). We attribute the larger difference between observed and predicted ADG on the 100% silage diet than on diets with concentrate to the development of prediction equations using data from diets with a maximum of 50% roughage. The equation based on data from a 50% roughage diet over-estimated the efficiency of DE utilization for gain on a 100% silage diet. This suggests that the efficiency of DE utilization declines between 60 and 100% silage DM in the diet. Rates of gain for the restricted feed period were most closely predicted using the H-A and C-A equations. In the period of feeding to appetite, for the 100 and 75% silage diets, RMSFE was lowest using the equation derived from the 50% hay diet. At 42% or higher levels of concentrate, predictions made using C-R and C-A equations produced the smallest RMSFE. Thus, the point at which the products of digestion change resulting in a change in efficiency of DE utilization is between 25 and 42% concentrate in the diet. Using the NE equation, the ADG was over-estimated on high silage diets. As the concentrate in the diet increased, the predicted ADG increased. At about 25% concentrate the observed and predicted rates of gain were similar. However, as the level of concentrate was increased above about 25%, the predicted ADG was less than observed, apparently due to a non-linear substitution between DE of barley-silage and barley for maintenance and gain. This view agrees with that of Epplin et al. (1980) and Freeze and Hironaka (1990) that the gain to roughage-concentrate ratio isoquant is not convex to the origin.
R. Hironaka, B. Freeze, G. C. Kozub
436
Steers on restricted feed for 52 weeks had greater ADG than predicted using the DE equation for steers on restricted feed for 24 weeks, suggesting the efficiency of feed utilization during realimentation increases with the length of moderate feed restriction. The wide discrepancy between the predicted and observed rates of gain is attributed to the high efficiency of energy utilization due to compensatory gain in steers that have been restricted in feed for an extended period of time. The smaller RMSFE using the NE system than any of the DE equations is attributed to an increase in the efficiency of feed utilization due to compensatory gain. The DE system predicted rate of gain better than the NE system under most feeding conditions encountered in practical feedlot feeding conditions. The prediction of rate of gain in the restricted period of feeding was similar and best using the C-A and the H-A derived equations. During the period of feeding to appetite, the prediction of rate of gain was similar and best using the C-A and C-R derived equations. Since the C-A derived equation was common to both feeding situations, it appears that the C-A equation may be used in practical situations when the diet contains at least 40% concentrate, a condition that is common to practical feedlot practice. With very high silage diets (100 or 90% on an as fed-basis) neither the DE nor the NE system was a good predictor of rate of gain. This is attributed to the fact that both equations were developed using data from predominantly high grain feedlot diets. Since carcass backfat thickness is strongly associated with rate of gain (Hironaka et al., 1979), a prediction of rate of gain should be beneficial in the prediction of carcass grade and assessment of diet and feeding programs for feedlot cattle. Information on rate of gain is also needed because it influences marketing date and carcass composition (Hironaka & Freeze, 1992).
REFERENCES Bailey, C. B. (1989) Rate and efficiency of gain, body composition, nitrogen metabolism, and blood composition of growing Holstein steers, given diets of roughage or concentrate. Canadian Journal of Animal Science, 69, 707-725. Epplin, P., Bhide, S. and Heady, E. 0. (1980) Empirical investigations of beef gain roughage-concentrate substitution. American Journal of Agricultural Economics, 62,468477.
Freeze, B. and Hironaka, R. (1990) Effect of form of hay and carcass quality on the economics of concentrate: hay substitution in cattle feedlot diets. Western Journal of Agricultural Economics, 15, 163-174. Hironaka, R. and Freeze, B. (1992) Feedlot finishing of cattle. Agr. Can. Pub 1591. Ottawa, ON.
Comparison of digestible and net energy models
431
Hironaka, R., Freeze, B., Kozub, G. C. and Beauchemin, K. A. (1994) The influence of cereal silage to concentrate ratio on rate and efficiency of gain, diet digestibility and carcass characteristics of beef steers. Canadian Journal of Animal Science, 74, 495-501.
Hironaka, R., Grigat, G. A. and Kozub, G. C. (1986) The voluntary intake of diets differing in digestible energy concentration and form of hay. Canadian Journal of Animal Science 66, 735-142.
Hironaka, R., Sonntag, B. H. and Kozub, G. C. (1979) Effects of feeding programs and diet energy on rate of gain, efficiency of digestible energy utilization, and carcass grades of steers. Canadian Journal of Animal Science, 59, 385-394. Kozub, G. C. and Hironaka, R. (1992) Digestible energy requirements for growth in Hereford and Charolais x Hereford steers. Canadian Journal of Animal Science 72, 651-661.
Mood, A. M., Graybill, F. A. and Boes, D. C. (1974) Introduction to the theory of Statistics, 3rd ed, Mcgraw-Hill Inc. p.291. National Academy of Sciences - National Research Council (1984) Nutrient Requirements of Beef Cattle. 6th edn. National Academy Press, Washington, D.C.