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The effect of selection for rapid lean growth on the dietary lysine and energy requirements of pigs fed to scale
Livestock Production Science, 27 ( 1991 ) 185-198
185
Elsevier Science Publishers B.V., A m s t e r d a m
The effect of selection for rapid lean growth on the dietary lysine and energy requirements of pigs fed to scale C.P. McPhee, K.C. Williams and L.J. Daniels Department of Primary Industries, Animal Research Institute, 665 Fair~eld Road Yeerongpillv. Queensland 4105, Australia (Accepted 11 April 1990)
ABSTRACT McPhee, C.P., Williams, K.C. and Daniels, L.J., 1991. The effect of selection for rapid lean growth on the dietary lysine and energy requirements of pigs fed to scale. Livest. Prod. Sci.. 27:185-198. A line of pigs (S line) selected for weight of ham lean, a measure of lean growth, was compared with an unselected control line (C line) of common origin on a series of food regimens ranging in average daily intake from 23.7 to 27.2 MJ digestible energy and from 13.3 to 23.4 g total lysine. The comparison was made over a 12-week test period starting at 25 kg liveweight and measurements were made of growth rate, fat depth by ultrasonics and, from these, predicted weight of lean in the ham at the end of test. As energy and lysine in the diet were increased, growth rate and ham lean rose at rates and reached limits which were higher in the S than the C line. As a result of 4.4 standard deviations (SD) of selection differential accumulated over five generations of selection, the superiority of the S over the C line in ham lean ranged from 0.5 (SD) on a low energy-lysine diet to 2.7 SD on a high energy-lysine diet. Maximum growth rate and ham lean were reached in the S line on a diet which provided 1 MJ day- ~ more digestible energy and 3 g day- t more total lysine than the diet at which the maxima were reached in the C line. Increasing dietary energy raised fat depths in the C line and increasing lysine lowered fat depths in the S line. Pigs from both lines were most profitable on diets lower in energy and lysine levels than those which gave maximum growth. Net monetary returns were most responsive to changes in energy in the C line and to changes in lysine in the S line. Keywords: energy: growth; lysine: pigs: selection.
INTRODUCTION
Modern pig genotypes exhibit faster rates of growth of lean tissue than their progenitors. McPhee et al. (1988) demonstrated steady divergence between a line of pigs undergoing selection for rapid lean growth and an unselected control line. Annison ( 1987 ) found difficulty in defining the energy and lysine requirements of pigs because of a lack of information on the range of genotypes of varying rates of lean growth known to exist in the commercial pig population. In the present study, pigs from the selected and control lines of McPhee et al. ( 1988 ) were fed a range of dietary lysine and energy levels to 0301-6226/91/$03.50
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examine the effect of a measured amount and type of selection on changed requirements for these nutrients. MATERIALS AND METHODS
The lines Two lines, a selected (S) and a control (C), were formed from a c o m m o n synthetic foundation of Large White and Landrace. A detailed description of the conduct of the lines is given by McPhee et al. (1988 ). Briefly, the S line comprised six boars and 36 sows. Boars were replaced after siring six litters and sows after two farrowings, by their best offspring selected for high weight of lean in their hams, predicted from liveweight and ultrasonic measurements of fat made after a 12-week performance test commencing at 25 kg liveweight. Selection continued in this way for five generations. The 36-sow C line was maintained by the pedigree control technique of within-family selection with cyclical mating.
Conduct of the comparison For the purpose of farrowing, the 36 sows of both herds were placed in one of three batches of 12 with an interval of about 2 months between batches so that the whole herd was farrowed in each 6-month period. Male and female pigs were sampled for trial across all litters of a batch, grouped in pens of eight and fed in individual stalls once daily. The trial period commenced at 25 kg liveweight and continued for 12 weeks. Pigs were weighed weekly and at the end of trial, subcutaneous fat depths were measured ultrasonically at the P2 position (over the eye muscle 65 m m from the mid-line and level with the last rib). The weight of lean in the ham was estimated at the end of the trial using the equation: H L = 6 . 7 2 G R - 0.06 F + 1.56 where H L = w e i g h t of lean in the ham (kg), G R = g r o w t h rate (kg d a y - t ) , F--ultrasonic depth of fat ( m m ) . The derivation of this relationship is described by McPhee et al. ( 1988 ). Because of its high correlation with lean in the whole carcass (Evans and Kempster, 1979 ) weight of ham lean estimated at the end of the 12-week test was taken as indicative of growth rate of whole body lean. Net return was estimated from the difference in value of each pig at slaughter and the cost of feeding it over the 12-week trial period. Returns were affected by carcass weight and grade as determined by fat depth measured at the P2 position. The cost of feed was that of practical diets equivalent in nutrient specification to the experimental diets used. The compositions of the
EFFECTOFSELECTIONON DIETARYREQUIREMENTSOF PIGS
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practical diets were d e r i v e d using a least-cost diet c o m p u t e r p r o g r a m m e ( A d a and B l o o m f i e l d , 1985 ).
Rations and diets The ration scale fed is set out in Table 1. From preliminary trial work it was judged to provide a generous allowance with a minimum of refusals. Thirteen diets were fed. Each comprised two time phases; Weeks 1-6 and Weeks 7-12. The energy densities and lysine- energy ratios of the diets are set TABLE1
Daily food rations over the 12-week duration of the trial Week
Weight (kg)
Week
Weight (kg)
1 2 3 4 5 6
1.0 1.2 1.3 1.45 1.6 1.75
7 8 9 10 l1 12
1.9 2.0 2.1 2.2 2.3 2.4
TABLE 2 Lysine : energy ratios and energy densities of the 13 diets compared
Period fed (weeks) Digestible energy (MJkg -I )
Low energy
Medium energy
High energy
1-6
7-12
1-6
7-12
1-6
7-12
14
13
15
14
16
15
Lysine:energy (g MJ -~ ) Diet no. 1 0.65 2 0.70 3 0.75 4 0.80 5 0.85 6 7 8 9 10 11 12 13
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95
0.70 0.75 0.80
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C.P. McPHEE ET AL.
TABLE 3 C o m p o s i t i o n o f the basal diet f o r m u l a t e d for each energy density a n d time period Period fed (weeks) 1-6 Digestible energy ( MJ k g - ~) Lysine: digestible energy (g M J - t ) Feedstuffs (g kg ~) Wheat Barley Fishmeal ( t u n a ) Soybean meal ( Solv. ext ) Vegetable oil /-Lysine HCI Dicalcium p h o s p h a t e S o d i u m chloride Vitamin/mineral premix ~
14 0.85
511 200 80 190 9 2.5 2.5 5
7-12 15 0.85
631 120 190 49 2.5 2.5 5
16 0.85
543 160 190 97 2.5 2.5 5
13 0.7
14 0.7
15 0.7
796 45 140 4 1.5 6 2.5 5
721 75 140 49 1.5 6 2.5 5
652 105 140 90 1.5 4 2.5 5
~Composition as described by Williams et al. ( 1988 ).
out in Table 2 and the composition of the basal diet formulated for each energy density and each time phase is shown in Table 3. To obtain the desired lysine:energy ratio diets, the soybean contribution of the basal diet was altered by 30 g kg- 1 for every 0.05 change of the ratio and at the expense of the wheat portion. Very minor adjustments were also made to the contributions of vegetable oil and synthetic lysine at the expense of wheat in order to obtain the desired nutrient ratios. The vitamin and trace mineral premix was as described by Williams et al. ( 1988 ). Diets of varying energy and lysine levels were formulated using the composition tables prepared by Evans (1985). In varying the lysine levels, the other essential amino acids threonine, methionine, cystine and tryptophan were kept in balance. Added synthetic lysine did not exceed 0.25% of the diet to minimize variations in lysine availability which might arise with once per day feeding (Batterham, 1984).
Experimental design and data analysis The trial was performed on 432 pigs, 24 of each sex from nine successive batches so that the whole experiment was carried out over an 18-month period. The pigs were the progeny of 35 sires in the S line and 32 sires in the C line. An unbalanced design was employed so that not all treatments appeared in each batch. Analyses of variance were carried out according to Harvey ( 1985 ). Fixed effects were line, batch, energy, sex and their first-order inter-
EFFECTOFSELECTIONONDIETARYREQUIREMENTSOFPIGS
189
actions and polynomial regressions to the fifth degree on lysine intakes. Random effects were sire and residual. RESU LTS
Occasional feed refusals reduced the food intake achieved below that allocated by the feeding scale but no significant effects of the factors considered in the analysis were detected. Compared with the average food allocation of 1.77 kg day-1 the actual daily food intake over the 12-week trial period was 1.74 _+0.07 kg. During this period the pigs grew from a starting weight averaging 25.3 _+0.1 kg to finishing weights averaging 81.6 + 0.2 kg in the S line and 80.3 _+0.2 kg in the C line. In Table 4 are given the least squares means of the measured traits fitted for the main effects in the analysis of variance model. Line and sex effects were significant for all traits ( P < 0.05 ), the S line being faster growing, leaner and more profitable than the C line and males having the same advantages over females. Increasing the energetic value of the diet increased fat and reduced net return. The only significant effect of energy on either growth rate or ham lean was an increase in growth rate between the low and m e d i u m energy levels. Sire effects were significant for all traits ( P < 0 . 0 1 ) and sire×energy interactions were significant for growth rate and fat depth (P<0.05). In Fig. 1, polynomial regressions, orthogonal with the above main effects, give the response in each trait to increasing lysine intakes. Regressions were fitted separately for each line and energy level. Although attempts were made to fit polynomials to the fifth degree, as seen from the regression parameters TABLE 4 Least squares means of the measured traits to which have been fitted the main effects of line, energy and sex in the analyses of variance Trait
Line S
Growth rate (kg day 1) Fat depth (mm) Ham lean (kg) Net return ($pig ')
0.77 12.2 6.37 64.6
Energy C 0.69 14.5 5.71 54.8
SE ~ 0.01 0.35 0.06 1.2
Low 0.72 12.4 5.98 64.7
Sex Medium 0.75 13.5 6.09 60.2
~SE = average standard error of difference between means.
High 0.74 14.2 6.02 54.4
SE 0.01 0.5 0.09 1.6
Male 0.76 12.9 6.21 62.3
Female
SE
0.71
0.01
3.8
0.4
5.85
0.06
57.2
1.1
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C,P. M c P H E E E T AL.
in Table 5, all responses were either curvilinear, linear or zero. Where zero, responses are plotted as horizontal lines parallel to the X axis. It is seen in Fig. 1 that the two ends of the medium-energy graphs overlap the high lysine levels of the low-energy graphs and the low lysine levels of the high-energy graphs. The lysine intakes were similar between energy levels in
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1 91
EFFECT O F SELECTION ON DIETARY R E Q U I R E M E N T S OF PIGS
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Fig. 1. Fitted means and regressions of measured traits on daily lysine intakes. Separate regressions are fitted for the selected (S) and control (C) lines and for low, medium and high energy levels.
192
C.P. McPHEE ET AL.
TABLE 5 Performance and economic traits measured on the S and C lines fed diets of the three energy levels. The polynomial regression y = ~
b i ( x - x ) i relates traits (y) to daily lysine intakes ( x ) . Mean daily
i=O
lysine intakes ( x ) were 16.9 +_0.1 g, 18. l ± 0. l g and 19.3 _+0.2 g for the low, m e d i u m and high energy levels, respectively Trait
Line
Energy
Mean
SE 1
Regression coefficients bo
Growth rate (kg day i)
Fatdepth
Net return
b2
SE I
S
Low Medium High
0.75 0.78 0.79
0.01 0.01 0.01
0.75 0.76 -
0.19;< l0 -3 0 . 9 6 X 1 0 -4 NS 2
- 0 . 3 6 × 10 .6 - 0 . 4 4 X 1 0 -6 NS
0.20X 10 -6 0.19X10 o -
C
Low Medium High
0.69 0.71 0.70
0.01 0.01 0.01
0.76 -
0.12X10 NS NS
3
_0.50X10-6 NS NS
0.22X10-6 -
S
Low Medium High
11.6 12.5 12.6
0.4 0.4 0.6
13.6 12.6 -
-0.48X10 -0.35X10 NS
2 '
- 0 . 1 6 X 1 0 -4 0.14X10 ~ NS
0.94X10 5 0 . 8 3 X 1 0 -5 -
C
Low Medium High
13.2 14.4 15.8
0.4 0.3 0.6
-
NS NS NS
S
Low Medium High
6.3 6.4 6.4
0.1 0.1 0.1
6.09 6.22 -
0.17×10 2 0 . 8 6 X 1 0 -3 NS
NS - 0 . 3 9 X 1 0 -5 NS
0.28X 10 -3 0 . 1 5 X 1 0 -5 -
C
Low Medium High
5.7 5.8 5.6
0.1 0.1 0.1
6.18
0 . 7 5 X 1 0 -3 NS NS
-0.35X10 NS NS
~
0.17X10
S
Low Medium High
67.8 65.1 61.0
1.3 1.1 1.7
0 . 1 4 × 10 -~ - 0 . 2 9 X 1 0 -2 - 0 . 1 9 X 10 -~
NS -0.45N10 NS
4
0 . 5 2 × 10 -2 0.28X10-4 0.10X 10 l
Low Medium High
61.5 55.2 47.6
1.3 1.1 1.7
(mm)
H a m lean (kg)
bl
( $ p i g -1)
C
59.9 61.4 59.9
NS NS NS
NS NS NS
NS NS NS
-
5
-
t SE = standard error of the means and highest order regression coefficients. 2NS = not significantly different from zero ( P < 0.05 ).
these overlapping regions. The performances of pigs on these overlapping diets, different in energy but similar in lysine level, are given in Table 6. Despite appearances from Fig. 1 the only cases of significant difference ( P < 0.05 ) between energy levels at the same lysine intakes were an increase in fat from low to medium energy in the S line and a decrease in net return with both changes of energy in the C line. The similarity of the responses in growth rate and ham lean to increasing nutrient density of the diets is evident in Fig. 1. The responses of the two lines
193
EFFECT OF SELECTION ON DIETARY REQUIREMENTS OF PIGS
TABLE 6 A comparison of performances on diets with similar lysine levels but differing energy levels. These results were drawn from diets used where the different energy levels are seen to overlap in Fig. I Lysine intake (g d a y - t )
Growth rate ( kg d a y - ~)
Fat ( m m )
Ham lean ( kg )
Net return ($ pig- t )
Lines S and C
Line S
Line C
Line S
Line C
Line S
Line C
Line S
Line C
Energy change Lowto medium
17.2 17.2
0.76 0.77
0.70 0.72
11.1 13.2
13.8 14.7
6.29 6.25
5.74 5.81
69.0 65.3
59.5 55.2
Medium to high
21.0 21.0
0.81 0.82
0.73 0.71
11.5 11.9
13.9 14.7
6.67 6.71
5.92 5.77
65.1 63.1
54.9 50.3
SE (diff.) t
0.01
0.6
0.11
2.2
SE = average standard error of difference between column means. TABLE 7 Diets on which the maximum differences were recorded between the S and C lines. Values are fitted means of pigs fed the diets indicated Trait
Growth rate (kg day -~ )
Fat depth (mm)
Ham lean (kg)
Net return ($ pig -z )
Diet no. Energy Lysine (gday -1 ) Line S Line C Line diff. ( S - C ) SE (diff.) ~
12 High 21.5 0.83 0.70 0.13 0.02
13 High 23.0 11.11 15.49 -4.38 1.0
12 High 21.5 6.75 5.74 1.01 0.18
12 High 21.5 62.7 50.0 12.7 3.5
~SE = standard error of difference between line means.
diverged but each reached a plateau within the range of diets tested. The approximate levels at which this occurred were 20 g day-i lysine on medium energy for the S line and 17 g day- l lysine on low energy for the C line. The responses in fat depth to increasing energy and lysine levels were quite different for the S and C lines. As seen in Fig. 1, increasing lysine had no effect in the C line but increasing energy markedly increased fat depth in that line. Conversely, in the S line, energy had no effect on fat depth but within the low and medium energy levels, fat declined with increasing lysine intake. Although fat depth continued to fall in the S line at the highest lysine intake on low energy, a minimum fat depth appears to have been reached at 20 g day- i on the medium level of energy.
194
c.P. McPHEE ET AL.
As with fat depth, the pattern of change in net monetary return with increasing dietary energy and lysine differed markedly between the S and the C lines. The decline in economic value with increasing energy occurred in both lines but to a much greater extent in the C than the S line. The distribution of fitted means plotted in Fig. 1 suggests a maximum net return for the C line at lysine and energy levels lower than those examined in the present study. For the S line maximum net returns are obtained on low- or medium-energy diets offering 18-20 g lysine dayTable 7 indicates the diets which gave the greatest differences in performance between the S and C lines. All of these occurred on high-energy and highlysine diets. DISCUSSION
The object of this study was to examine the changed nutritional requirements of pigs resulting from selection for increased rate and leanness of growth by subjecting the S and C lines to a range of energy and lysine intakes within which the optima of performance traits were likely to fall as judged by previous studies on a variety ofgenotypes (ARC, 1967; Yen et al., 1986a,b; Annison, 1987; Campbell and Taverner, 1988 ). The lysine and energy levels were stepped down from a growth to a finish phase, each of 6 weeks, in recognition of normal commercial practice to account for the higher lysine and energy requirements of young pigs. It is possible that the true optima were not found since the lysine and energy levels chosen, particularly those of energy, were necessarily limited and were correlated. Nevertheless, both response and plateau phases were revealed, particularly for traits measured in the S line. The similarity of the ham lean and growth rate graphs arise from the dominance of growth rate over fat in the equation used to predict ham lean. This equation was developed by dissecting hams from a wide range of pigs drawn from the foundation herd from which the S and C lines were developed. It may have lost some accuracy as the S line was moved outside this range by selection. Where increasing levels of nutrient produce response-plateau outcomes, a number of mathematical forms have been fitted (e.g. curvilinear, 'bent stick' ), the advantages and disadvantages of which have been discussed by Fisher et al. ( 1973 ). In the present study, increasing lysine intake was expected to have diverse outcomes depending on the genotype and energy level. The fitting of polynomials to the fifth degree permitted a considerable degree of flexibility in fitting these diverse responses. Polynomials also had the advantage of being orthogonal to the other effects in the analysis of variance, e.g. line, batch. As it turned out, the highest order polynomial found to be significant was the second, the remainder being linear or zero. Where responses were curvilinear, estimates of optimum lysine-energy levels were possible. These are probably overestimates (Fisher et al., 1973) but the upward bias should be the same
EFFECT OF SELECTION ON DIETARY REQUIREMENTS OF PIGS
19 5
for the two lines since they both had the same nutrient intakes. It follows that the difference observed in o p t i m u m intakes between the S and the C lines should be relatively free of bias. In the C line, response in ham lean to increases in energy and lysine occurred up to a level 17 g d a y - l of lysine on the low-energy diet. Further increases in energy and lysine were converted into fat. The high energy cost of this tissue relative to that of lean (Webster, 1977) prevented these higher nutrient intakes being expressed as significant increases in growth rate. In the S line, lean conti~nued to respond to increases in nutrient density until a lysine intake of 20 g day-J on the m e d i u m energy level was attained so that the steady increase in fatness with increasing energy was not seen in the S line as it was in the C line. Yen et al. ( 1986a, b) fed British Large W h i t e x Landrace crossbred pigs a range of lysine levels. Viewing their results in terms of this study, they obtained an o p t i m u m level for growth rate of about 20 g day- 1 on an average energy intake of 28 MJ day-1, close to the o p t i m u m of the S line in the present study. Annison ( 1987 ) interpreted the results of several experiments by Giles et al. (1984, 1986) and Batterham et al. (1985) exposing two sexes and genotypes to a range of lysine and energy intakes, as suggesting that the o p t i m u m lysine intake for all was constant at 16 g day- 1 and that pigs adjusted their food intakes to achieve that level. The work of Campbell and Taverner (1988) contrasts with these findings. They compared the rate of protein deposition in males from an improved and an unimproved genotype grown from 45 to 90 kg and subject to a range of energy and lysine intakes and found that the improved strain had both a higher appetite and higher optimum requirements for lysine and energy. Response in the improved strain continued in a linear fashion up to a m a x i m u m intake of 41 MJ d a y - l and 30 g d a y - l lysine. Results for the sexes are not given separately in the present study, but responses in growth rate and ham lean in the last 6 weeks of trial are known to have been diminishing in S line males before the highest levels of 32 MJ d a y - 1 energy and 26 g d a y - 1 lysine were reached. This suggests that the S line had not yet attained the same potential for lean growth as the improved genotype of Campbell and Taverner ( 1988 ). It is intended in a future study to compare the nutrient requirements of the S and C lines on ad lib. feeding but in the present study the ration scale was chosen to be the same as the one used for performance testing the S line during selection (McPhee et al., 1988). That it was generous in a m o u n t is evidenced by the high daily energy intakes (up to 36 MJ at Week 12) and by occasional food refusals which were not so frequent as to permit the higher appetite known to exist in the S line to be expressed. The selection was designed to favour those animals which grew quickly because they partitioned their fixed food ration in favour of lean and away from fat, lean deposition having only one-fifth of the energy cost of fat deposition (Webster, 1977).
196
C.P. McPHEE ET AL.
The present study demonstrated that this objective had been met. The possibility that the maintenance requirement of the S line had been lowered, allowing more energy to be retained as growth, seems small. On the contrary it is probable that the higher lean body mass of the S line would have caused it to have a higher maintenance requirement than the C line (Campbell et al., 1988). The relationship between the amount of selection in the background of the S line and its altered o p t i m u m nutrient requirements can be quantified. At the time of this study the S line had been subjected to 4.4 standard deviations of selection differential in ham lean since its c o m m o n origin with the C line (McPhee et al., 1988). This raised the nutrient levels at which m a x i m u m expression of the trait was observed by 1 MJ d a y - l energy and 3 g d a y - ' lysine. The diet used during selection in the S line was equivalent to the low-energy diet supplying lysine at an average rate of 17.5 g d a y - 1. On this diet selection response in ham lean was estimated as 0.72_+0.16 kg. This contrasts with 1.01 _ 0.15 kg or 2.7 standard deviations (SD), the m a x i m u m response observed on the high-energy diet supplying 22 g lysine day- 1 and 0.18 + 0.15 kg or 0.5 SD, the m i n i m u m response observed on the low-energy diet supplying 13.2 g lysine day- '. Although no change in the ranking of the S and C lines occurred between the diets, this dependence of the magnitude of the line difference on diet represents a form of genotype X environment interaction, the consequences of which for genetic improvement programmes in pigs have been discussed by Merks (1988). It is tempting to conclude that selection response in ham lean, per unit of selection differential, would have been greater had the better quality diet been used for performance testing. This would be the case if the enhanced genetic difference seen between the lines on the best diet also occurred between families within the S line. There is evidence for this in the significant sire X energy interactions revealed by the analysis of variance. In contrast to the conclusions which can be drawn from the results on the performance traits, those from the responses in net monetary return will be of a more transient nature. They depend on pig meat prices, premiums paid for lean content and the cost of food ingredients, all of which are subject to change with time. The net return figures were included to show that decisions on the choice of the best diet for a particular genotype could be quite misleading if made on the basis of performance traits (e.g. growth rate). It is seen that the quality of the diets giving highest net returns in both the S and C lines was below those on which the pigs grew fastest or were leanest. Disagreement between the performance and net return trends was related more to the energy than the lysine content of the diets. Increasing the energetic value of the diets enhanced growth rates but this was accomplished by the expensive addition of fat.
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REFERENCES Ada, R.L. and Bloomfield, R.C., 1985. Least Cost Diets. Users Manual. Queensland Department of Primary Industries, Brisbane, Australia. Agricultural Research Council, 1967. The Nutrient Requirements of Farm Livestock. No. 3. Pigs. Agricultural Research Council, London. Annison, E.F. (Editor), 1987. Feeding Standards for Australian Livestock - Pigs. Standing Committee on Agriculture, Canberra, 226 pp. Batterham, E.S., 1984. Utilization of free lysine by pigs. Pig News Inform., 5: 85-88. Batterham, E.S., Giles, L.R. and Dettmann, E.B., 1985. Amino acid and energy interactions in growing pigs. 1. Effects of food intake, sex and live weight on the responses of growing pigs to lysine concentration. Anim. Prod., 40:331-343. Campbell, R.G. and Taverner, M.R., 1988. Genotype and sex effects on the relationship between energy intake and protein deposition in growing pigs. J. Anim. Sci., 66: 676-686. Evans, M., 1985. Nutrient Composition of Feedstuffs for Pigs and Poultry. Queensland Department of Primary Industries, Brisbane, Australia, 135 pp. Evans, D.G. and Kempster, A.J., 1979. A comparison of different predictors of the lean content of pigs' carcases. 2. Predictors for use in population studies and experiments. Anim. Prod., 28: 97-108. Fisher, C., Morris, T.R. and Jenning, R.C., 1973. A model for the description and prediction of the response of laying hens to amino acid intake. Br. Poult. Sci., 14: 469-484. Giles, L.R., Dettmann, E.B. and Batterham, E.S., 1984. Daily gain response to dietary lysine of growing pigs as influenced by sex, liveweight and cereal. Proc. Aust. Soc. Anita. Prod., 15: 361-364. Giles, L.R., Batterham, E.S. and Dettmann, E.B., 1986. Amino acid and energy interactions in growing pigs. 2. Effects of food intake, sex and live weight on responses to lysine concentration in barley-based diets. Amin. Prod., 42:133-144. Harvey, W.R., 1985. User's guide to LSMLMW mixed model least-squares and maximum-likelihood computer program. Ohio State Univ., Columbus (Mimeo), 46 pp. McPhee, C.P., Rathmell, G.A., Daniels, L.J. and Cameron, N.D., 1988. Selection in pigs for increased lean growth on a time-based feeding scale. Anim. Prod., 47:149-156. Merks, J.W.M., 1988. Genotypex Environment Interactions in Pig Breeding Programmes. IVO Report B-310, Institute for Animal Production 'Schoonoord', Zeist, The Netherlands. Webster, A.J.F., 1977. Selection for leanness and the energetic efficiency of growth in meat animals. Proc. Nutr. Soc., 36: 53-59. Williams, K.C., Blaney, B.J. and Magee, M.H., 1988. Responses of pigs fed wheat naturally infected with Fusarium graminearum and containing the mycotoxins 4-deoxynivalenol and zearalenone. Aust. J. Agric. Res., 39:1095-1105. Yen, H.T., Cole, D.J.A. and Lewis, D., 1986a. Amino acid requirements of growing pigs. 7. The response of pigs from 25 to 55 kg liveweight to dietary ideal protein. Anim. Prod., 43: 141154. Yen, H.T., Cole, D.J.A. and Lewis, D., 1986b. Amino acid requirements of growing pigs. 8. The response of pigs from 50 to 90 kg liveweight to dietary ideal protein. Anim. Prod., 43:155165. RESUME McPhee, C.P., Williams, K.C. et Daniels, L.J., 1991. Les effets de la selection pour une croissance rapide de viande maigre sur les besoins en lysine et en 6nergie de porcs alimentes suivant un plan de rationnement. Livest. Prod. Sci., 27:185-198 (en anglais ).
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Une serie de rdgimes alimentaires couvrant des niveaux quotidiens d'ingestion de 23,7 a 27,2 MJ d'dnergie digestible et de 13,3 h 23,4 g de lysine totale a dt6 utilis6e pour comparer une lignde de porcs (lignde S ) sdlectionnde sur le poids de maigre du jambon, qui mesure la croissance des tissus maigres, avec une lignde tdmoin non sdlectionnde (lignee C) de mSme origine. La comparaison dtait effectude pendant une pdriode de 12 semaines ddbutant au poids vifde 25 kg. Les critbres retenus dtaient la vilesse de croissance, l'dpaisseur de lard mesurde aux ultra-sons et, partir de ces mesures, la prddiction du poids de maigre du jambon ~ la fin du test. Au fur et mesure que les apports d'6nergie et de lysine augmentaient, la vitesse de croissance et le maigre du jambon s'accroissaient plus rapidement et atteignaient des limites supdrieures dans la lignde S que darts la lignde C. A la suite des 4,4 dcart-types (SD) de sdlection diff6rentielle accumulds au cours de cinq gdndrations de sdlection, la supdrioritd sur le maigre du jambon de la lignde S par rapport a la lignde C allait de 0,5 (SD) pour un rdgime ~ faibles teneurs en dnergie et en lysine a 2,7 SD pour un rdgime a teneurs en energie et en lysine dlevdes. Les maximums de vitesse de croissance et de tissu maigre du jambon dtaient obtenus dans la lignde S avec un regime apportant 1 MJ jour ~de plus d'dnergie digestible et 3 g j o u r - ~de plus de lysine qu'avec le rdgime permettant les maximums dans la lignde C. L'augmentation de l'dnergie alimentaire accroissait l'dpaisseur de lard dans la lignee C et l'augmentation de la lysine diminuait l'dpaisseur de lard dans la lignde S. Les profits rdalisds dans les deux ligndes dtaient plus dlevds avec les apports d'dnergie et de lysine les plus faibles qu'avec ceux permettant la croissance maximale. Le b6ndfice net rdpondait davantage aux modifications des apports d'dnergie dans la lign6e C et aux changements des apports de lysine darts la lignde S. KURZFASSUNG McPhee, C.P., Williams, K.C. und Daniels, L.J., 1991. Wirkung der Selektion ftir hohes Wachsrum aufden Bedarfan Energie und Lysin von rationiert geffitterten Schweinen. Livest. Prod. Sci., 27:185-198 (aufenglisch). Eine Schweinelinie (S), die als MaB ftir Wachstum von Magerfleisch auf Gewicht des mageren Schinkens selektiert war, wurde verglichen mit einer nichtselektierten Kontrolllinie (C) herk6mmlichen Ursprungs in einer Serie von Ffitterungsregimen, die im t~glichen Verzehr von 23,7 bis 27,2 MJ verdauliche Energie und von 13,3 bis 23,4 g Gesamtlysin schwankten. Der Vergleich erstreckte sich fiber zw61f Wochen mit einer anf'anglichen Lebendmasse yon 25 kg. Gemessen wurde neben der Zuwachsrate die Speckdicke durch Ultraschall woraus das Gewicht des Magerfleischs im Schinken am Ende des Tests berechnet wurde. Mit Erh6hung von Energie und Lysin im Futter stiegen Zuwachsrate und Magerfleisch im Schinken schrittweise bis zu Grenzen, die in der Linie S h6her waren als in der Linie C. Als Ergebnis einer Ansammlung von 4,4 Standardabweichungen (SD) des Selektionsdifferentials fiber ffinf Selektionsgenerationen lag die Oberlegenheit der Linie S fiber die Linie C im mageren Schinken zwischen 0,5 (SD) bei niedriger Energie/Lysin-Versorgung und 2,7 SD bei hoher Energie/Lysin-Versorgung. Maximalwerte ftir Zuwachsrate und mageren Schinken wurden in der Linie S erreicht mit einem Futter, welches 1 MJ Tag- ' mehr verdauliche Energie und 3 g Tag- ~ mehr Lysin zuffihrte als dasjenige Futter, welches in der Linie C die entsprechenden Maxima bewirkte. Die Steigerung der Futterenergie steigerte die Speckdicke in tier Linie C und Steigerung des Lysins senkte die Speckdicke in der Linie S. In beiden Linien ergab sich ffir die Schweine tier h6chste Gewinn mit Futtermischungen, die niedriger im Gehalt an Energie und Lysin waren als diejenigen, welche maximalen Zuwachs erzielten. Der geldliche Reinertrag reagierte am st~rksten auf A,nderungen im Energiegehalt in Linie C und aufAnderungen im Lysingehalt in Linie S.
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The effect of selection for rapid lean growth on the dietary lysine and energy requirements of pigs fed to scale C.P. McPhee, K.C. Williams and L.J. Daniels Department of Primary Industries, Animal Research Institute, 665 Fair~eld Road Yeerongpillv. Queensland 4105, Australia (Accepted 11 April 1990)
ABSTRACT McPhee, C.P., Williams, K.C. and Daniels, L.J., 1991. The effect of selection for rapid lean growth on the dietary lysine and energy requirements of pigs fed to scale. Livest. Prod. Sci.. 27:185-198. A line of pigs (S line) selected for weight of ham lean, a measure of lean growth, was compared with an unselected control line (C line) of common origin on a series of food regimens ranging in average daily intake from 23.7 to 27.2 MJ digestible energy and from 13.3 to 23.4 g total lysine. The comparison was made over a 12-week test period starting at 25 kg liveweight and measurements were made of growth rate, fat depth by ultrasonics and, from these, predicted weight of lean in the ham at the end of test. As energy and lysine in the diet were increased, growth rate and ham lean rose at rates and reached limits which were higher in the S than the C line. As a result of 4.4 standard deviations (SD) of selection differential accumulated over five generations of selection, the superiority of the S over the C line in ham lean ranged from 0.5 (SD) on a low energy-lysine diet to 2.7 SD on a high energy-lysine diet. Maximum growth rate and ham lean were reached in the S line on a diet which provided 1 MJ day- ~ more digestible energy and 3 g day- t more total lysine than the diet at which the maxima were reached in the C line. Increasing dietary energy raised fat depths in the C line and increasing lysine lowered fat depths in the S line. Pigs from both lines were most profitable on diets lower in energy and lysine levels than those which gave maximum growth. Net monetary returns were most responsive to changes in energy in the C line and to changes in lysine in the S line. Keywords: energy: growth; lysine: pigs: selection.
INTRODUCTION
Modern pig genotypes exhibit faster rates of growth of lean tissue than their progenitors. McPhee et al. (1988) demonstrated steady divergence between a line of pigs undergoing selection for rapid lean growth and an unselected control line. Annison ( 1987 ) found difficulty in defining the energy and lysine requirements of pigs because of a lack of information on the range of genotypes of varying rates of lean growth known to exist in the commercial pig population. In the present study, pigs from the selected and control lines of McPhee et al. ( 1988 ) were fed a range of dietary lysine and energy levels to 0301-6226/91/$03.50
© 1991-
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examine the effect of a measured amount and type of selection on changed requirements for these nutrients. MATERIALS AND METHODS
The lines Two lines, a selected (S) and a control (C), were formed from a c o m m o n synthetic foundation of Large White and Landrace. A detailed description of the conduct of the lines is given by McPhee et al. (1988 ). Briefly, the S line comprised six boars and 36 sows. Boars were replaced after siring six litters and sows after two farrowings, by their best offspring selected for high weight of lean in their hams, predicted from liveweight and ultrasonic measurements of fat made after a 12-week performance test commencing at 25 kg liveweight. Selection continued in this way for five generations. The 36-sow C line was maintained by the pedigree control technique of within-family selection with cyclical mating.
Conduct of the comparison For the purpose of farrowing, the 36 sows of both herds were placed in one of three batches of 12 with an interval of about 2 months between batches so that the whole herd was farrowed in each 6-month period. Male and female pigs were sampled for trial across all litters of a batch, grouped in pens of eight and fed in individual stalls once daily. The trial period commenced at 25 kg liveweight and continued for 12 weeks. Pigs were weighed weekly and at the end of trial, subcutaneous fat depths were measured ultrasonically at the P2 position (over the eye muscle 65 m m from the mid-line and level with the last rib). The weight of lean in the ham was estimated at the end of the trial using the equation: H L = 6 . 7 2 G R - 0.06 F + 1.56 where H L = w e i g h t of lean in the ham (kg), G R = g r o w t h rate (kg d a y - t ) , F--ultrasonic depth of fat ( m m ) . The derivation of this relationship is described by McPhee et al. ( 1988 ). Because of its high correlation with lean in the whole carcass (Evans and Kempster, 1979 ) weight of ham lean estimated at the end of the 12-week test was taken as indicative of growth rate of whole body lean. Net return was estimated from the difference in value of each pig at slaughter and the cost of feeding it over the 12-week trial period. Returns were affected by carcass weight and grade as determined by fat depth measured at the P2 position. The cost of feed was that of practical diets equivalent in nutrient specification to the experimental diets used. The compositions of the
EFFECTOFSELECTIONON DIETARYREQUIREMENTSOF PIGS
187
practical diets were d e r i v e d using a least-cost diet c o m p u t e r p r o g r a m m e ( A d a and B l o o m f i e l d , 1985 ).
Rations and diets The ration scale fed is set out in Table 1. From preliminary trial work it was judged to provide a generous allowance with a minimum of refusals. Thirteen diets were fed. Each comprised two time phases; Weeks 1-6 and Weeks 7-12. The energy densities and lysine- energy ratios of the diets are set TABLE1
Daily food rations over the 12-week duration of the trial Week
Weight (kg)
Week
Weight (kg)
1 2 3 4 5 6
1.0 1.2 1.3 1.45 1.6 1.75
7 8 9 10 l1 12
1.9 2.0 2.1 2.2 2.3 2.4
TABLE 2 Lysine : energy ratios and energy densities of the 13 diets compared
Period fed (weeks) Digestible energy (MJkg -I )
Low energy
Medium energy
High energy
1-6
7-12
1-6
7-12
1-6
7-12
14
13
15
14
16
15
Lysine:energy (g MJ -~ ) Diet no. 1 0.65 2 0.70 3 0.75 4 0.80 5 0.85 6 7 8 9 10 11 12 13
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95
0.70 0.75 0.80
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C.P. McPHEE ET AL.
TABLE 3 C o m p o s i t i o n o f the basal diet f o r m u l a t e d for each energy density a n d time period Period fed (weeks) 1-6 Digestible energy ( MJ k g - ~) Lysine: digestible energy (g M J - t ) Feedstuffs (g kg ~) Wheat Barley Fishmeal ( t u n a ) Soybean meal ( Solv. ext ) Vegetable oil /-Lysine HCI Dicalcium p h o s p h a t e S o d i u m chloride Vitamin/mineral premix ~
14 0.85
511 200 80 190 9 2.5 2.5 5
7-12 15 0.85
631 120 190 49 2.5 2.5 5
16 0.85
543 160 190 97 2.5 2.5 5
13 0.7
14 0.7
15 0.7
796 45 140 4 1.5 6 2.5 5
721 75 140 49 1.5 6 2.5 5
652 105 140 90 1.5 4 2.5 5
~Composition as described by Williams et al. ( 1988 ).
out in Table 2 and the composition of the basal diet formulated for each energy density and each time phase is shown in Table 3. To obtain the desired lysine:energy ratio diets, the soybean contribution of the basal diet was altered by 30 g kg- 1 for every 0.05 change of the ratio and at the expense of the wheat portion. Very minor adjustments were also made to the contributions of vegetable oil and synthetic lysine at the expense of wheat in order to obtain the desired nutrient ratios. The vitamin and trace mineral premix was as described by Williams et al. ( 1988 ). Diets of varying energy and lysine levels were formulated using the composition tables prepared by Evans (1985). In varying the lysine levels, the other essential amino acids threonine, methionine, cystine and tryptophan were kept in balance. Added synthetic lysine did not exceed 0.25% of the diet to minimize variations in lysine availability which might arise with once per day feeding (Batterham, 1984).
Experimental design and data analysis The trial was performed on 432 pigs, 24 of each sex from nine successive batches so that the whole experiment was carried out over an 18-month period. The pigs were the progeny of 35 sires in the S line and 32 sires in the C line. An unbalanced design was employed so that not all treatments appeared in each batch. Analyses of variance were carried out according to Harvey ( 1985 ). Fixed effects were line, batch, energy, sex and their first-order inter-
EFFECTOFSELECTIONONDIETARYREQUIREMENTSOFPIGS
189
actions and polynomial regressions to the fifth degree on lysine intakes. Random effects were sire and residual. RESU LTS
Occasional feed refusals reduced the food intake achieved below that allocated by the feeding scale but no significant effects of the factors considered in the analysis were detected. Compared with the average food allocation of 1.77 kg day-1 the actual daily food intake over the 12-week trial period was 1.74 _+0.07 kg. During this period the pigs grew from a starting weight averaging 25.3 _+0.1 kg to finishing weights averaging 81.6 + 0.2 kg in the S line and 80.3 _+0.2 kg in the C line. In Table 4 are given the least squares means of the measured traits fitted for the main effects in the analysis of variance model. Line and sex effects were significant for all traits ( P < 0.05 ), the S line being faster growing, leaner and more profitable than the C line and males having the same advantages over females. Increasing the energetic value of the diet increased fat and reduced net return. The only significant effect of energy on either growth rate or ham lean was an increase in growth rate between the low and m e d i u m energy levels. Sire effects were significant for all traits ( P < 0 . 0 1 ) and sire×energy interactions were significant for growth rate and fat depth (P<0.05). In Fig. 1, polynomial regressions, orthogonal with the above main effects, give the response in each trait to increasing lysine intakes. Regressions were fitted separately for each line and energy level. Although attempts were made to fit polynomials to the fifth degree, as seen from the regression parameters TABLE 4 Least squares means of the measured traits to which have been fitted the main effects of line, energy and sex in the analyses of variance Trait
Line S
Growth rate (kg day 1) Fat depth (mm) Ham lean (kg) Net return ($pig ')
0.77 12.2 6.37 64.6
Energy C 0.69 14.5 5.71 54.8
SE ~ 0.01 0.35 0.06 1.2
Low 0.72 12.4 5.98 64.7
Sex Medium 0.75 13.5 6.09 60.2
~SE = average standard error of difference between means.
High 0.74 14.2 6.02 54.4
SE 0.01 0.5 0.09 1.6
Male 0.76 12.9 6.21 62.3
Female
SE
0.71
0.01
3.8
0.4
5.85
0.06
57.2
1.1
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C,P. M c P H E E E T AL.
in Table 5, all responses were either curvilinear, linear or zero. Where zero, responses are plotted as horizontal lines parallel to the X axis. It is seen in Fig. 1 that the two ends of the medium-energy graphs overlap the high lysine levels of the low-energy graphs and the low lysine levels of the high-energy graphs. The lysine intakes were similar between energy levels in
GROWTH 0
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1 91
EFFECT O F SELECTION ON DIETARY R E Q U I R E M E N T S OF PIGS
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Fig. 1. Fitted means and regressions of measured traits on daily lysine intakes. Separate regressions are fitted for the selected (S) and control (C) lines and for low, medium and high energy levels.
192
C.P. McPHEE ET AL.
TABLE 5 Performance and economic traits measured on the S and C lines fed diets of the three energy levels. The polynomial regression y = ~
b i ( x - x ) i relates traits (y) to daily lysine intakes ( x ) . Mean daily
i=O
lysine intakes ( x ) were 16.9 +_0.1 g, 18. l ± 0. l g and 19.3 _+0.2 g for the low, m e d i u m and high energy levels, respectively Trait
Line
Energy
Mean
SE 1
Regression coefficients bo
Growth rate (kg day i)
Fatdepth
Net return
b2
SE I
S
Low Medium High
0.75 0.78 0.79
0.01 0.01 0.01
0.75 0.76 -
0.19;< l0 -3 0 . 9 6 X 1 0 -4 NS 2
- 0 . 3 6 × 10 .6 - 0 . 4 4 X 1 0 -6 NS
0.20X 10 -6 0.19X10 o -
C
Low Medium High
0.69 0.71 0.70
0.01 0.01 0.01
0.76 -
0.12X10 NS NS
3
_0.50X10-6 NS NS
0.22X10-6 -
S
Low Medium High
11.6 12.5 12.6
0.4 0.4 0.6
13.6 12.6 -
-0.48X10 -0.35X10 NS
2 '
- 0 . 1 6 X 1 0 -4 0.14X10 ~ NS
0.94X10 5 0 . 8 3 X 1 0 -5 -
C
Low Medium High
13.2 14.4 15.8
0.4 0.3 0.6
-
NS NS NS
S
Low Medium High
6.3 6.4 6.4
0.1 0.1 0.1
6.09 6.22 -
0.17×10 2 0 . 8 6 X 1 0 -3 NS
NS - 0 . 3 9 X 1 0 -5 NS
0.28X 10 -3 0 . 1 5 X 1 0 -5 -
C
Low Medium High
5.7 5.8 5.6
0.1 0.1 0.1
6.18
0 . 7 5 X 1 0 -3 NS NS
-0.35X10 NS NS
~
0.17X10
S
Low Medium High
67.8 65.1 61.0
1.3 1.1 1.7
0 . 1 4 × 10 -~ - 0 . 2 9 X 1 0 -2 - 0 . 1 9 X 10 -~
NS -0.45N10 NS
4
0 . 5 2 × 10 -2 0.28X10-4 0.10X 10 l
Low Medium High
61.5 55.2 47.6
1.3 1.1 1.7
(mm)
H a m lean (kg)
bl
( $ p i g -1)
C
59.9 61.4 59.9
NS NS NS
NS NS NS
NS NS NS
-
5
-
t SE = standard error of the means and highest order regression coefficients. 2NS = not significantly different from zero ( P < 0.05 ).
these overlapping regions. The performances of pigs on these overlapping diets, different in energy but similar in lysine level, are given in Table 6. Despite appearances from Fig. 1 the only cases of significant difference ( P < 0.05 ) between energy levels at the same lysine intakes were an increase in fat from low to medium energy in the S line and a decrease in net return with both changes of energy in the C line. The similarity of the responses in growth rate and ham lean to increasing nutrient density of the diets is evident in Fig. 1. The responses of the two lines
193
EFFECT OF SELECTION ON DIETARY REQUIREMENTS OF PIGS
TABLE 6 A comparison of performances on diets with similar lysine levels but differing energy levels. These results were drawn from diets used where the different energy levels are seen to overlap in Fig. I Lysine intake (g d a y - t )
Growth rate ( kg d a y - ~)
Fat ( m m )
Ham lean ( kg )
Net return ($ pig- t )
Lines S and C
Line S
Line C
Line S
Line C
Line S
Line C
Line S
Line C
Energy change Lowto medium
17.2 17.2
0.76 0.77
0.70 0.72
11.1 13.2
13.8 14.7
6.29 6.25
5.74 5.81
69.0 65.3
59.5 55.2
Medium to high
21.0 21.0
0.81 0.82
0.73 0.71
11.5 11.9
13.9 14.7
6.67 6.71
5.92 5.77
65.1 63.1
54.9 50.3
SE (diff.) t
0.01
0.6
0.11
2.2
SE = average standard error of difference between column means. TABLE 7 Diets on which the maximum differences were recorded between the S and C lines. Values are fitted means of pigs fed the diets indicated Trait
Growth rate (kg day -~ )
Fat depth (mm)
Ham lean (kg)
Net return ($ pig -z )
Diet no. Energy Lysine (gday -1 ) Line S Line C Line diff. ( S - C ) SE (diff.) ~
12 High 21.5 0.83 0.70 0.13 0.02
13 High 23.0 11.11 15.49 -4.38 1.0
12 High 21.5 6.75 5.74 1.01 0.18
12 High 21.5 62.7 50.0 12.7 3.5
~SE = standard error of difference between line means.
diverged but each reached a plateau within the range of diets tested. The approximate levels at which this occurred were 20 g day-i lysine on medium energy for the S line and 17 g day- l lysine on low energy for the C line. The responses in fat depth to increasing energy and lysine levels were quite different for the S and C lines. As seen in Fig. 1, increasing lysine had no effect in the C line but increasing energy markedly increased fat depth in that line. Conversely, in the S line, energy had no effect on fat depth but within the low and medium energy levels, fat declined with increasing lysine intake. Although fat depth continued to fall in the S line at the highest lysine intake on low energy, a minimum fat depth appears to have been reached at 20 g day- i on the medium level of energy.
194
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As with fat depth, the pattern of change in net monetary return with increasing dietary energy and lysine differed markedly between the S and the C lines. The decline in economic value with increasing energy occurred in both lines but to a much greater extent in the C than the S line. The distribution of fitted means plotted in Fig. 1 suggests a maximum net return for the C line at lysine and energy levels lower than those examined in the present study. For the S line maximum net returns are obtained on low- or medium-energy diets offering 18-20 g lysine dayTable 7 indicates the diets which gave the greatest differences in performance between the S and C lines. All of these occurred on high-energy and highlysine diets. DISCUSSION
The object of this study was to examine the changed nutritional requirements of pigs resulting from selection for increased rate and leanness of growth by subjecting the S and C lines to a range of energy and lysine intakes within which the optima of performance traits were likely to fall as judged by previous studies on a variety ofgenotypes (ARC, 1967; Yen et al., 1986a,b; Annison, 1987; Campbell and Taverner, 1988 ). The lysine and energy levels were stepped down from a growth to a finish phase, each of 6 weeks, in recognition of normal commercial practice to account for the higher lysine and energy requirements of young pigs. It is possible that the true optima were not found since the lysine and energy levels chosen, particularly those of energy, were necessarily limited and were correlated. Nevertheless, both response and plateau phases were revealed, particularly for traits measured in the S line. The similarity of the ham lean and growth rate graphs arise from the dominance of growth rate over fat in the equation used to predict ham lean. This equation was developed by dissecting hams from a wide range of pigs drawn from the foundation herd from which the S and C lines were developed. It may have lost some accuracy as the S line was moved outside this range by selection. Where increasing levels of nutrient produce response-plateau outcomes, a number of mathematical forms have been fitted (e.g. curvilinear, 'bent stick' ), the advantages and disadvantages of which have been discussed by Fisher et al. ( 1973 ). In the present study, increasing lysine intake was expected to have diverse outcomes depending on the genotype and energy level. The fitting of polynomials to the fifth degree permitted a considerable degree of flexibility in fitting these diverse responses. Polynomials also had the advantage of being orthogonal to the other effects in the analysis of variance, e.g. line, batch. As it turned out, the highest order polynomial found to be significant was the second, the remainder being linear or zero. Where responses were curvilinear, estimates of optimum lysine-energy levels were possible. These are probably overestimates (Fisher et al., 1973) but the upward bias should be the same
EFFECT OF SELECTION ON DIETARY REQUIREMENTS OF PIGS
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for the two lines since they both had the same nutrient intakes. It follows that the difference observed in o p t i m u m intakes between the S and the C lines should be relatively free of bias. In the C line, response in ham lean to increases in energy and lysine occurred up to a level 17 g d a y - l of lysine on the low-energy diet. Further increases in energy and lysine were converted into fat. The high energy cost of this tissue relative to that of lean (Webster, 1977) prevented these higher nutrient intakes being expressed as significant increases in growth rate. In the S line, lean conti~nued to respond to increases in nutrient density until a lysine intake of 20 g day-J on the m e d i u m energy level was attained so that the steady increase in fatness with increasing energy was not seen in the S line as it was in the C line. Yen et al. ( 1986a, b) fed British Large W h i t e x Landrace crossbred pigs a range of lysine levels. Viewing their results in terms of this study, they obtained an o p t i m u m level for growth rate of about 20 g day- 1 on an average energy intake of 28 MJ day-1, close to the o p t i m u m of the S line in the present study. Annison ( 1987 ) interpreted the results of several experiments by Giles et al. (1984, 1986) and Batterham et al. (1985) exposing two sexes and genotypes to a range of lysine and energy intakes, as suggesting that the o p t i m u m lysine intake for all was constant at 16 g day- 1 and that pigs adjusted their food intakes to achieve that level. The work of Campbell and Taverner (1988) contrasts with these findings. They compared the rate of protein deposition in males from an improved and an unimproved genotype grown from 45 to 90 kg and subject to a range of energy and lysine intakes and found that the improved strain had both a higher appetite and higher optimum requirements for lysine and energy. Response in the improved strain continued in a linear fashion up to a m a x i m u m intake of 41 MJ d a y - l and 30 g d a y - l lysine. Results for the sexes are not given separately in the present study, but responses in growth rate and ham lean in the last 6 weeks of trial are known to have been diminishing in S line males before the highest levels of 32 MJ d a y - 1 energy and 26 g d a y - 1 lysine were reached. This suggests that the S line had not yet attained the same potential for lean growth as the improved genotype of Campbell and Taverner ( 1988 ). It is intended in a future study to compare the nutrient requirements of the S and C lines on ad lib. feeding but in the present study the ration scale was chosen to be the same as the one used for performance testing the S line during selection (McPhee et al., 1988). That it was generous in a m o u n t is evidenced by the high daily energy intakes (up to 36 MJ at Week 12) and by occasional food refusals which were not so frequent as to permit the higher appetite known to exist in the S line to be expressed. The selection was designed to favour those animals which grew quickly because they partitioned their fixed food ration in favour of lean and away from fat, lean deposition having only one-fifth of the energy cost of fat deposition (Webster, 1977).
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The present study demonstrated that this objective had been met. The possibility that the maintenance requirement of the S line had been lowered, allowing more energy to be retained as growth, seems small. On the contrary it is probable that the higher lean body mass of the S line would have caused it to have a higher maintenance requirement than the C line (Campbell et al., 1988). The relationship between the amount of selection in the background of the S line and its altered o p t i m u m nutrient requirements can be quantified. At the time of this study the S line had been subjected to 4.4 standard deviations of selection differential in ham lean since its c o m m o n origin with the C line (McPhee et al., 1988). This raised the nutrient levels at which m a x i m u m expression of the trait was observed by 1 MJ d a y - l energy and 3 g d a y - ' lysine. The diet used during selection in the S line was equivalent to the low-energy diet supplying lysine at an average rate of 17.5 g d a y - 1. On this diet selection response in ham lean was estimated as 0.72_+0.16 kg. This contrasts with 1.01 _ 0.15 kg or 2.7 standard deviations (SD), the m a x i m u m response observed on the high-energy diet supplying 22 g lysine day- 1 and 0.18 + 0.15 kg or 0.5 SD, the m i n i m u m response observed on the low-energy diet supplying 13.2 g lysine day- '. Although no change in the ranking of the S and C lines occurred between the diets, this dependence of the magnitude of the line difference on diet represents a form of genotype X environment interaction, the consequences of which for genetic improvement programmes in pigs have been discussed by Merks (1988). It is tempting to conclude that selection response in ham lean, per unit of selection differential, would have been greater had the better quality diet been used for performance testing. This would be the case if the enhanced genetic difference seen between the lines on the best diet also occurred between families within the S line. There is evidence for this in the significant sire X energy interactions revealed by the analysis of variance. In contrast to the conclusions which can be drawn from the results on the performance traits, those from the responses in net monetary return will be of a more transient nature. They depend on pig meat prices, premiums paid for lean content and the cost of food ingredients, all of which are subject to change with time. The net return figures were included to show that decisions on the choice of the best diet for a particular genotype could be quite misleading if made on the basis of performance traits (e.g. growth rate). It is seen that the quality of the diets giving highest net returns in both the S and C lines was below those on which the pigs grew fastest or were leanest. Disagreement between the performance and net return trends was related more to the energy than the lysine content of the diets. Increasing the energetic value of the diets enhanced growth rates but this was accomplished by the expensive addition of fat.
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REFERENCES Ada, R.L. and Bloomfield, R.C., 1985. Least Cost Diets. Users Manual. Queensland Department of Primary Industries, Brisbane, Australia. Agricultural Research Council, 1967. The Nutrient Requirements of Farm Livestock. No. 3. Pigs. Agricultural Research Council, London. Annison, E.F. (Editor), 1987. Feeding Standards for Australian Livestock - Pigs. Standing Committee on Agriculture, Canberra, 226 pp. Batterham, E.S., 1984. Utilization of free lysine by pigs. Pig News Inform., 5: 85-88. Batterham, E.S., Giles, L.R. and Dettmann, E.B., 1985. Amino acid and energy interactions in growing pigs. 1. Effects of food intake, sex and live weight on the responses of growing pigs to lysine concentration. Anim. Prod., 40:331-343. Campbell, R.G. and Taverner, M.R., 1988. Genotype and sex effects on the relationship between energy intake and protein deposition in growing pigs. J. Anim. Sci., 66: 676-686. Evans, M., 1985. Nutrient Composition of Feedstuffs for Pigs and Poultry. Queensland Department of Primary Industries, Brisbane, Australia, 135 pp. Evans, D.G. and Kempster, A.J., 1979. A comparison of different predictors of the lean content of pigs' carcases. 2. Predictors for use in population studies and experiments. Anim. Prod., 28: 97-108. Fisher, C., Morris, T.R. and Jenning, R.C., 1973. A model for the description and prediction of the response of laying hens to amino acid intake. Br. Poult. Sci., 14: 469-484. Giles, L.R., Dettmann, E.B. and Batterham, E.S., 1984. Daily gain response to dietary lysine of growing pigs as influenced by sex, liveweight and cereal. Proc. Aust. Soc. Anita. Prod., 15: 361-364. Giles, L.R., Batterham, E.S. and Dettmann, E.B., 1986. Amino acid and energy interactions in growing pigs. 2. Effects of food intake, sex and live weight on responses to lysine concentration in barley-based diets. Amin. Prod., 42:133-144. Harvey, W.R., 1985. User's guide to LSMLMW mixed model least-squares and maximum-likelihood computer program. Ohio State Univ., Columbus (Mimeo), 46 pp. McPhee, C.P., Rathmell, G.A., Daniels, L.J. and Cameron, N.D., 1988. Selection in pigs for increased lean growth on a time-based feeding scale. Anim. Prod., 47:149-156. Merks, J.W.M., 1988. Genotypex Environment Interactions in Pig Breeding Programmes. IVO Report B-310, Institute for Animal Production 'Schoonoord', Zeist, The Netherlands. Webster, A.J.F., 1977. Selection for leanness and the energetic efficiency of growth in meat animals. Proc. Nutr. Soc., 36: 53-59. Williams, K.C., Blaney, B.J. and Magee, M.H., 1988. Responses of pigs fed wheat naturally infected with Fusarium graminearum and containing the mycotoxins 4-deoxynivalenol and zearalenone. Aust. J. Agric. Res., 39:1095-1105. Yen, H.T., Cole, D.J.A. and Lewis, D., 1986a. Amino acid requirements of growing pigs. 7. The response of pigs from 25 to 55 kg liveweight to dietary ideal protein. Anim. Prod., 43: 141154. Yen, H.T., Cole, D.J.A. and Lewis, D., 1986b. Amino acid requirements of growing pigs. 8. The response of pigs from 50 to 90 kg liveweight to dietary ideal protein. Anim. Prod., 43:155165. RESUME McPhee, C.P., Williams, K.C. et Daniels, L.J., 1991. Les effets de la selection pour une croissance rapide de viande maigre sur les besoins en lysine et en 6nergie de porcs alimentes suivant un plan de rationnement. Livest. Prod. Sci., 27:185-198 (en anglais ).
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Une serie de rdgimes alimentaires couvrant des niveaux quotidiens d'ingestion de 23,7 a 27,2 MJ d'dnergie digestible et de 13,3 h 23,4 g de lysine totale a dt6 utilis6e pour comparer une lignde de porcs (lignde S ) sdlectionnde sur le poids de maigre du jambon, qui mesure la croissance des tissus maigres, avec une lignde tdmoin non sdlectionnde (lignee C) de mSme origine. La comparaison dtait effectude pendant une pdriode de 12 semaines ddbutant au poids vifde 25 kg. Les critbres retenus dtaient la vilesse de croissance, l'dpaisseur de lard mesurde aux ultra-sons et, partir de ces mesures, la prddiction du poids de maigre du jambon ~ la fin du test. Au fur et mesure que les apports d'6nergie et de lysine augmentaient, la vitesse de croissance et le maigre du jambon s'accroissaient plus rapidement et atteignaient des limites supdrieures dans la lignde S que darts la lignde C. A la suite des 4,4 dcart-types (SD) de sdlection diff6rentielle accumulds au cours de cinq gdndrations de sdlection, la supdrioritd sur le maigre du jambon de la lignde S par rapport a la lignde C allait de 0,5 (SD) pour un rdgime ~ faibles teneurs en dnergie et en lysine a 2,7 SD pour un rdgime a teneurs en energie et en lysine dlevdes. Les maximums de vitesse de croissance et de tissu maigre du jambon dtaient obtenus dans la lignde S avec un regime apportant 1 MJ jour ~de plus d'dnergie digestible et 3 g j o u r - ~de plus de lysine qu'avec le rdgime permettant les maximums dans la lignde C. L'augmentation de l'dnergie alimentaire accroissait l'dpaisseur de lard dans la lignee C et l'augmentation de la lysine diminuait l'dpaisseur de lard dans la lignde S. Les profits rdalisds dans les deux ligndes dtaient plus dlevds avec les apports d'dnergie et de lysine les plus faibles qu'avec ceux permettant la croissance maximale. Le b6ndfice net rdpondait davantage aux modifications des apports d'dnergie dans la lign6e C et aux changements des apports de lysine darts la lignde S. KURZFASSUNG McPhee, C.P., Williams, K.C. und Daniels, L.J., 1991. Wirkung der Selektion ftir hohes Wachsrum aufden Bedarfan Energie und Lysin von rationiert geffitterten Schweinen. Livest. Prod. Sci., 27:185-198 (aufenglisch). Eine Schweinelinie (S), die als MaB ftir Wachstum von Magerfleisch auf Gewicht des mageren Schinkens selektiert war, wurde verglichen mit einer nichtselektierten Kontrolllinie (C) herk6mmlichen Ursprungs in einer Serie von Ffitterungsregimen, die im t~glichen Verzehr von 23,7 bis 27,2 MJ verdauliche Energie und von 13,3 bis 23,4 g Gesamtlysin schwankten. Der Vergleich erstreckte sich fiber zw61f Wochen mit einer anf'anglichen Lebendmasse yon 25 kg. Gemessen wurde neben der Zuwachsrate die Speckdicke durch Ultraschall woraus das Gewicht des Magerfleischs im Schinken am Ende des Tests berechnet wurde. Mit Erh6hung von Energie und Lysin im Futter stiegen Zuwachsrate und Magerfleisch im Schinken schrittweise bis zu Grenzen, die in der Linie S h6her waren als in der Linie C. Als Ergebnis einer Ansammlung von 4,4 Standardabweichungen (SD) des Selektionsdifferentials fiber ffinf Selektionsgenerationen lag die Oberlegenheit der Linie S fiber die Linie C im mageren Schinken zwischen 0,5 (SD) bei niedriger Energie/Lysin-Versorgung und 2,7 SD bei hoher Energie/Lysin-Versorgung. Maximalwerte ftir Zuwachsrate und mageren Schinken wurden in der Linie S erreicht mit einem Futter, welches 1 MJ Tag- ' mehr verdauliche Energie und 3 g Tag- ~ mehr Lysin zuffihrte als dasjenige Futter, welches in der Linie C die entsprechenden Maxima bewirkte. Die Steigerung der Futterenergie steigerte die Speckdicke in tier Linie C und Steigerung des Lysins senkte die Speckdicke in der Linie S. In beiden Linien ergab sich ffir die Schweine tier h6chste Gewinn mit Futtermischungen, die niedriger im Gehalt an Energie und Lysin waren als diejenigen, welche maximalen Zuwachs erzielten. Der geldliche Reinertrag reagierte am st~rksten auf A,nderungen im Energiegehalt in Linie C und aufAnderungen im Lysingehalt in Linie S.