Using Growth and Feed Intake Data to Improve the Efficiency of Lean Pork Production

A. P. Schinckel

Department of Animal Sciences,
Purdue University, West Lafayette, IN 47907


Each commercial pork producer must evaluate the strengths and weaknesses of available genotypes. The difficulty in choosing the optimal genotype or genotypes is predicting the improvements on performance and profitability in the specific environmental-health status conditions, production costs and marketing system.

After making the key genetic decisions, each commercial producer must consider cost-effective management changes to optimize the expression of genetic potential of their pigs. A number of alternative management decisions must be evaluated including; 1) the number of diets fed during the growth period and the composition of each diet; 2) alternative diets for different seasons; 3) target slaughter weight or weights; 4) alternative stocking densities; and, 5) split-sex feeding and management. These decisions are influenced by production costs (i.e., feed, facilities, labor and interest costs) and the relative rate of payment for carcass lean vs. fat in the marketing system.

Protein accretion curves can be used to estimate the magnitude in which environmental conditions (health status, facilities, stressors) limit the expression of the pigs genetic potential for lean growth. A substantial difference between on-farm and maximum achievable protein accretion or lean growth rates are indicative of a major environmental limitation. In such cases the commercial producer must evaluate the benefits and costs of environmental- management changes.

A trial recently conducted by Dr. Tyler Holck, evaluated the difference in growth of pigs raised under average commercial and optimal environmental conditions. Pigs weighed an average of 32.5 kg at 77 days of age. The barrows were blocked by weight and allotted to either a commercial grow-finish facility (.70 m2/pig, 24 pigs/pen) or a test station (2.15 m2/pig, 3 pigs/pen). The pigs in the optimal environment grew faster with substantially high lean growth rates (Table 1). The protein accretion rates demonstrate that the pigs moved to the optimal environment almost immediately increased live weight growth and protein accretion. Protein accretion rates both declined as age (or liveweight) increased (Figure 1).

 

Table 1. Comparison of commercial versus optimal commercial conditions.

 

Environment

 

 

 

Commercial

Optimal

% Optimal/ Commercial

P value

Daily gain, kg/d

.730

1.038

142

<.001

Days to 118 kg

192

160

83

<.001

Daily fat-free lean gain, g/d

240

322

134

<.001

Daily fat gain, g/d

240

354

148

<.001

Daily feed intake, kg/d

2.45

3.00

122

<.05

Feed/gain

3.29

2.85

87

<.05

Feed/lean gain

10.39

9.30

90

ns

Backfat, cm

2.48

2.74

112

ns

M.S. Thesis Tyler Holck (DVM, MS), Iowa State University, School of Veterinary Medicine.

 

Analysis of protein accretion curves under both optimal and commercial environmental conditions indicate a consistent trend toward both decreased and flatter protein accretion curves under more limiting commercial conditions (Schinckel and de Lange, 1996). An example of representative protein accretion curves for a high protein accretion genotype under three commercial environments are presented in Figure 2. Under ideal conditions, high growth rates: 1.16 kg/day and feed efficiency (.65 gain:feed) were achieved from 25-52 kg live weight. Average daily gain approached 1.1 kg/day with .41 feed efficiency from 25-118 kg. The above average commercial producer has high health status pigs produced with three-site production which allows grow-finish growth rates of .90 kg per day. The primary environmental limitations are animal density, pen size, and social effects present in 10-20 pig pens. The averge commercial herd has implemented all-in, all-out production practices but has chronic health problems and generally has a lower level of management and feed intake. The lowest curve is for a poorly managed continuous flow unit with a number of chronic lingering diseases.

Three primary types of functions are currently being used to describe animals' responses to increased dietary intake of essential amino acids. The first approach is to model protein accretion or nitrogen retention as a linear-plateau response to increasing protein intake. This approach assumes a constant marginal efficiency, or slope, of protein accretion on ideal protein intake until the maximum protein accretion is attained, at which point the slope becomes zero. That is, each additional gram of protein consumed results in the same amount of protein retained up to the point maximum protein accretion, after which additional consumption is wasted.

The second approach, presented by Moughan (1989), models the relationship between the efficiency (E) with which absorbed essential amino acids are utilized and the level of empty body protein retention achieved (PA) expressed as a proportion of maximum protein retention. Using a fifth degree polynomial, the equation is

When the pigs are achieving 50 percent of their maximum protein accretion potential (PA = .5), the efficiency of utilization is 90 percent (E = .90). To achieve maximum protein accretion, PA = 1.0, absorbed ideal essential amino acid intake must be 1.59 times maximum protein accretion.

The third approach is a four parameter, non-linear function: PA = aDPb(c-DP)d. This is solved by Log10 transformation and multivariate regression analysis.

To describe the response of protein accretion on absorbed ideal protein intake:

The marginal efficiency is the efficiency with which the next unit of absorbed ideal amino acid intake is utilized. The marginal efficiency is:

When a number of research papers were re-examined, the following coefficients were derived: a = .822167, b = 1.0041, c = 1.95, d = .272027.

This function fits the data better than either the linear-plateau or polynomial function. The value of DP at which protein accretion is maximized (PA = 1) and the marginal efficiency equals zero is (b*c)/(b+d) and is 1.534 for the example.

The non-linear function predicts an almost linear increase in protein accretion as digestible protein intake increases, up to the point that the achieved protein accretion reaches approximately 85% of maximum protein accretion. Above that point, the increase in protein accretion achieved per unit increase in digestible protein intake (marginal efficiency)rapidly declines. As protein intake approaches the amount needed for maximum protein accretion, the marginal efficiency decreases to zero (Table 2).

 

Table 2. Relationship of absorbed ideal amino acid intake (as a fraction of maximum protein accretion potential) to the proportion of maximum protein accretion potential achieved.

DP

PA

Overall Efficiency

Marginal Efficiency

1.00

.811

.811

.58

1.10

.866

.787

.51

1.20

.913

.761

.43

1.30

.952

.732

.34

1.40

.980

.700

.22

1.50

.994

.663

.06

1.53

1.00

.652

0.0

PA = protein accretion divided by maximum protein accretion,DP = absorbed ideal amino acid intake divided by maximum protein accretion, c = constant, a = scale factor, b and d = exponential coefficients.

 

The protein accretion curves can be used to estimate the pigs daily requirements for essential amino acids. For the vast majority of swine diets in North America, lysine is the first limiting amino acid. Thus, it is assumed that the ratio of amino acids has been checked so that lysine is the first limiting amino acid.

Assuming an illeal digestibility of .76, the relationship between protein accretion and grams of lysine intake per day can be predicted for genotypes with different maximum protein accretion rates (Figure 3). At low to moderate lysine intake (12-20 g/day), the difference between the genotypes is reduced. At these lysine intakes, the high protein accretion genotypes are further away from achieving their maximum protein accretion and thus have a higher efficiency of utilization, allowing slightly higher achieved protein accretion rates.

Protein accretion data from the 1993 lean growth trial was used to evaluate genotype differences in dieal amino acid requirements. The protein accretion curves (Figure 4) were used to determine essential amino acid requirements. Assuming that the first limiting amino acid is lysine, the daily lysine requirements and percent lysine required for each genotype were determined (Figures 5 and 6). Line 2, which had the lowest protein accretion rate, especially after 80 kg liveweight, had the lowest lysine requirements. Line 1B had the highest amino acid requirement. The lysine percentage required by the Line1B barrows was 50-55% greater than the Line 2 barrows. Notice that the percent lysine requirements change more rapidly at the lighter weights. Requirements using these estimates of percent lysine requirements and a feed budget, the amount of each diet needed can be estimated.

The optimal series of diets are those which most cost-effectively meet the daily amino acid requirements. Each day, the optimum amino acid intake is determined as the point at which the marginal cost of increasing amino acid concentration equals the marginal return of the increased protein accretion. The increased protein accretion results in changes in lean growth, feed conversion and fat accretion. Future research will focus on determining the optimum series of diets (i.e., 2, 3, 4 or 5 diets) from 40 lb to market weight. This optimization with restrictions such as the number of diets and length of feeding period of each diet is much more complex than determining optimal daily requirements.

The protein accretion curves and highly related fat-free lean growth rates are needed to evaluate optimal slaughter weights with different pricing systems and production costs. The objective of the optimization is to maximize average daily profit per day ($1/day) not dollar profit per pig. The calculation of profit per day requires an allocating of all costs including initial cost of the pig entering the grower-finishing facility, feed, labor and operating expenses. The value of the pig must be based on the actual premiums and discounts related to carcass weight and composition. If carcass value is primarily determined by fat-free lean mass, the modeling of the relationship between fat-free lean mass and live weight is crucial. The use of an augmented allometric function to describe protein mass will increase predicted daily lean growth rates below 50 kg live weight and decrease lean growth rates above 90 kg live weight. In general, the optimal slaughter weight of gilts is 10 kg heavier than barrows.

Commercial producers are considering health management changes to improve both the rate and efficiency of lean growth. Substantial differences in performance exist between different environments and health management strategies. In a recent Purdue trial, pigs with minimal diseases via segregated early weaning (SEW) and fed a series of nonlimiting diets achieved 105 kg at 136 days of age and 120 kg at 151 days of age. Pigs raised on the original commercial farm conventionally weaned with all-in, all-out production required 180 days to attain 105 kg liveweight.

Substantial genetic variation for lean growth rate, lean efficiency, carcass percent lean and feed intake exists between different genetic populations of pigs. Lean growth trials conducted in the late 1980's at Purdue University and the University of Kentucky, found substantial variation for lean growth between different genetic populations or genotypes of pigs. In the early 1990's, seedstock were imported from Canada and Europe resulting in additional genetic variation in percent lean and feed intake.

Commercial producers who have implemented or are considering implementing SEW to improve health status, may want to reconsider their genetic choices. The best combination of traits for high health status pork production must be based on swine growth concepts.

The first concept is that lean growth increases after 20 kg liveweight, reaches a plateau and then declines. In general, high lean growth genotypes achieve their maximum lean growth rate later and maintain higher lean growth rates to heavier weights. The second concept of swine growth is that as feed intake increases, a linear response in lean growth and fat rate occurs. The change in protein accretion (or lean growth) per unit increase in energy intake is called the slope. As energy intake increases, protein accretion increases until a plateau occurs (Figure 7). The plateau is achieved when the energy required for maximum protein accretion is reached. Energy supplied in excess of a pig's maximum lean growth rate requirements will be utilized for fat deposition. This causes a rapid increase in lipid accretion and the ratio of rapid to protein accretion (Figure 8). Pigs with high lean growth rate potentials respond to higher energy intakes by increasing lean growth rate.

To optimize lean feed conversion, producers must aim to achieve high lean growth rates without excessive fat deposition (Table 9). Animals with reduced intakes achieve lower lean growth rates, grow slower and allocate a higher proportion of their energy intake to maintenance. As feed intake is increased in the linear response range, lean growth increases with only small increases in the ratio of lipid gain to protein accretion. In the linear feed intake response range, backfat marginally increases with increased feed intake. As energy intake increases above that needed for maximum lean growth, increases occur in the ratio of fat:protein deposition, backfat thickness and lean feed conversion. The most efficient lean growth is achieved when pigs consume enough energy to achieve 95-100% of their lean growth potential (Figure 10).

The slope of lean gain (or protein accretion) on energy intake determines the extent to which energy intake is partitioned into lean versus fat gain. Pigs with moderate feed intakes during this time deposit a high proportion of lean and little fat. For this reason, improving management to increase feed intake at these liveweights can be very cost effective because the additional nutrients will efficiently be used to increase lean gain. As a pig grows, the slope becomes less steep and the partitioning of energy changes so that at moderate energy intakes 70-80% of the intake is needed for maximum lean growth, the ratio of lean gain to fat gain declines. The slope of lean gain to energy intake decreases rapidly at heavier liveweights (70-120 kg) as the pig's maximum lean growth rate declines. In other words, once a pig matures, and its lean growth rate declines, the partitioning of energy shifts so that even at moderate energy intakes the ratio of lean gain to fat gain decreases. Therefore, genotypes that decline rapidly in lean growth at lighter weights will also have more fat and less lean deposition at moderate feed intakes. This makes it very difficult to produce uniform lean carcasses from early maturing low lean growth genotypes.

Another pig growth concept is that fat requires substantially more energy to deposit that lean. The energy cost of protein gain is 10.53 Mcal/kg, while the energy cost of lipid accretion is 12.64 Mcal/kg. For each gram of protein accretion, there is an accompanying 3.5-4.2 grams of water (higher in young pigs) deposited. For each gram of protein accretion, 2.53 grams of fat-free lean is deposited. Therefore, carcass fat accretion requires 3 times more energy per kg than fat-free lean gain. For this reason, lean lines depositing a high proportion of lean due to steep slopes of protein accretion on energy intake require less energy to achieve the same lean growth rate. These genotypes have the potential to achieve very efficient lean growth due to their high ratio of lean to fat growth.

However, if these lean genotypes will also respond differently to environments which limit feed intake. Because of their low feed intakes under ideal conditions and the fact that they are gaining a higher proportion lean, these genotypes will respond to feed intake limiting environments with larger absolute and percentage drops in liveweight and lean growth.

In the future, U.S. pork processors will probably pay premiums on 110-120 kg pigs that produce heavier lean cuts. It is very difficult to produce efficiently lean 120 kg barrows unless the genotype maintains a high lean growth rate to heavier weights have higher growth rates and continue to deposit a high ratio of lean to fat (1.6-2.0:1). Thus, to produce lean pork efficiently, commercial producers should identify high lean growth genotypes. The pigs must also have adequate feed intakes under commercial conditions in order to achieve a high percentage of their genetic potential for lean growth. Such pigs must also be able to maintain high lean growth rates to heavier weights, resulting in improved lean efficiency from 100 kg to market weight.

Pigs of improved health status have higher growth rates, feed intakes and lean growth rates. The changes observed in carcass composition and backfat thickness will be highly dependent upon the characteristics of the genotype. Pigs with high lean growth potential and primarily gaining lean (low lipid:protein accretion as the result of a steep slope of lean growth on energy intake) will respond to improved health status and increased feed intakes with drastically increased lean growth rates. The pigs become substantially more feed efficient (i.e., 3.2 to 2.7). Loin eye areas increase by approximately .5 square inches larger. Pigs with a low- medium lean growth potential and average percent lean will respond differently to improved health status. Feed intake will increase by 20-30 percent. The pigs, especially barrows, have too high feed intake after 90 kg liveweight. As lean growth declines, feed intake becomes excessive, above that needed for the pigs maximum genetic potential for lean growth. For this reason, fat accretion and backfat depth rapidly increase. When low to medium lean growth genotypes have grown 900 g per day, backfat thickness has increased from 20-25 mm at 100 kg to 27-35 mm at 120 kg liveweight.

Based on concepts of pig growth, lean genotypes with high lean growth potentials and moderate feed intakes will respond most favorably to improved health status and environmental conditions. The genotypes best suited to high health status, high level management conditions are low-moderate in feed intake and maintain high lean growth rates to heavier weights.

A number of genotypes were evaluated in the 1993 lean growth trial. The pigs were reared under near optimal conditions (1.9 m2 per pig). In the 1993 lean growth trial, genotypes 7 and 1 had moderate feed intakes and high lean growth rates (Tables 4, 5 and 6). Line 8 had high lean growth, low feed intake and had a high ratio of lean gain to fat gain. Under average environmental-health status conditions, with 20-30% lower feed intakes, genotype 8 pigs would grow slowly due to limited feed intakes. Line 8 pigs are consuming just enough under ideal conditions to achieve high lean growth rates and subsequently are very efficient in converting feed to lean. For this reason, line 8 would only be recommended in the best managed, high health status production units. When reared under good conditions, high lean growth genotypes offered a substantial increase in profitability (Table 7).

In the past three years a number of European, Canadian and Australian sources of breeding stock have entered the United States. This importation of seedstock has added genetic variation for lean growth, fat accretion and lean efficiency. Thirty percent differences in feed intake exist between different genotypes (Schinckel, 1994a). The differences for digestible energy consumed above maintenance approached 60 percent. In a recent trial, three European terminal cross genotypes and four U.S. genotypes (2 Hampshire-Duroc [HD] x Yorkshire-Landrace [YL], one H x YL, one D x YL) were evaluated. The European pigs grew 4.3% slower, had 10.5% higher lean growth rates, consumed 13.7% less feed, and had substantially lower daily carcass fat growth rates (Table 8). This resulted in the European genotypes having higher ratios of carcass lean gain to fat gain (1.65 vs. 1.06), and 21.2% better lean feed conversion than U.S. genotypes.

To evaluate genetic by health status interactions, a trial has been intiated. Two genotypes will be evaluated, one high lean growth low-medium feed intake and one low- medium lean growth with medium to high feed intake. Each genotype will be reared under two health-management environments, SEW and .70 m2 per pig in grow- finish versus conventional weaning and continuous flow grow-finish with 1 m2 per pig. The pigs farrowed in early April, 1996. Measures of immune system activation, growth factors and gene expression for muscle growth are being evaluated to investigate the underlying biological changes between genotypes and health status.

In the future, pork production will become more intensively managed. Improved health status and facilities will allow pigs to grow faster with higher feed intakes. Producers will also consider high lean growth genotype's feed intakes to maximize profitability per head per day.

 

Table 3. Growth of gilts at different energy intakesa.

 

Energy intake, Mcal ME/Day

 

7.7

8.3

8.9

9.5

Carcass lean gain (g/day)

322

363

390

391

Carcass fat gain (g/day)

150

163

204

231

Lean gain:fat gain

2.16

2.15

1.91

1.63

Backfat, 10th rib (cm)

1.88

1.93

2.00

2.23

Average daily gain (kg/day)

0.72

0.78

0.83

0.87

Kg feed/kg lean gain

6.80

6.28

6.28

6.62

a 58-104 kg liveweight, maximum lean growth achieved at an intake of 8.7 Mcal ME/day; 36 gilts per energy intake.

 

Table 4. Means for growth and performance traits (1993 trial).

Genotype

Sex

N

ADG, kg/day

Feed Intake, kg/day

Feed Conversion

7

F

32

.91

2.34

2.50

8

F

32

.85

2.08

2.46

9C

F

16

.90

2.52

2.82

1

B

28

1.01

2.49

2.47

2

B

16

.94

2.68

2.82

7

B

32

.96

2.62

2.78

8

B

32

.93

2.22

2.41

9C

B

16

.92

2.60

2.84

 

Table 5. Means for fat standardized lean gain, carcass fat gain, and lean feed conversion (1993 trial).

Genotype

Sex

Lean gain/day, g/daya

Carcass fat gain/day,
g/day

Lean Feed Conversion

7

F

.793

.519

6.46

8

F

.773

.470

5.93

9C

F

.702

.610

7.93

1

B

.837

.624

6.53

2

B

.653

.782

9.03

7

B

.739

.708

7.82

8

B

.781

.593

6.27

9C

B

.666

.724

8.60

a Lean gain is standardized to contain 10% fat in the dissected lean

 

Table 6. Means for carcass measurements (1993 trial).

Genotype

Sex

Fat Depth, 10th Rib, cm

Loin Eye Area, cm2

Backfat Last Rib, cm

7

F

2.00

43.8

2.36

8

F

2.16

40.6

2.16

9C

F

2.82

38.6

2.69

1

B

2.26

41.5

2.56

2

B

3.65

32.8

3.68

7

B

2.64

38.6

2.87

8

B

2.49

38.5

2.46

9C

B

3.23

35.4

3.05

 

Table 7. Economic returns above feed costs for the three highest and four lowest genotypes with either liveweight or carcass value marketing.

 

$ Economic Returna

Lean Growth Genotype

Average Daily Gain, kg/day

Feed Intake kg/day

Lean Gain g/day

Fat Gain g/day

Live
Market

Carcass Value

High

.984

2.43

371

277

.666

.760

Low

.916

2.60

297

327

.567

.550

a U.S. dollars daily return of either liveweight gain ($105.6 U.S./100 kg liveweight) or carcass value (lean at $2.73/kg, fat at $.44/kg). Feed cost is $.154/kg.

 

Table 8. Summary of performance differences observed between European and U.S. terminal cross.

 

ADG,
kg/d

Feed
Intake,
kg/d

Livewt.
Feed
Conver.

Fat
Depth,
cm

Fat-Free
Lean
Gain,g/d

Carcass Fat Gain,
g/d

kg. Feed/
kg. Lean

Barrows

European

.957

2.19

2.30

2.05

345

236

6.36

U.S.

.975

2.46

2.54

3.15

304

313

7.95

Gilts

European

.875

1.99

2.27

1.57

327

172

6.10

U.S.

.939

2.38

2.52

2.85

304

254

7.87

Overall

European

.916

2.09

2.28

1.81

336

204

6.23

U.S.

.957

2.42

2.53

3.00

304

286

7.91

Difference

.041

.33

-.25

1.19

32

82

1.68

Difference as % of U.S.

-4.3

-13.7

-9.9

-39.7

+10.5

-28.7

-21.2

*The data included three European and four U.S. terminal cross genotypes 28 or 32 pigs per genotype-sex group. Test period was from 27 to 113.5 kg live weight.

 

Moughan, P.J. (1989) Simulation of the daily partitioning of lysine in the 50 kg live weight pig. A factorial approach to estimating amino acid requirements for growth and maintenance. Res. Dev. Agric. 6:7.

Schinckel, A.P. (1994a) Nutrient requirements of modern pig genotypes. In P.C. Garnsworthy and D.J.A. Cole (Eds.). Recent Advances in Animal Nutrition. p 133. Univ. of Nottingham Press, Nottingham, U.K.

Schinckel, A.P. and C.F.M. de Lange. (1996) Characterization of growth parameters needed as inputs for pig growth models. J. Anim. Sci. 74:2021.


Figures are not yet ready for web presentation, and will be added later. (6-3- 97)

Figure 1. Protein accretion curves for barrows raised under commercial or ideal conditions to 118 kg live weight.

Figure 2. Protein accretion curves for a high lean growth barrow genotype reared in four management level environments.

Figure 3. Relationship between protein accretion and lysine intake in three genotypes with different maximum protein accretion potentials (50 kg liveweight). (Genotypes 115, ------ 135 and 150 g/day protein accretion).

Figure 4. Protein accretion curves for four genotypes of barrows.

Figure 5. Daily lysine requirements for four genotypes of barrows from the 1993 Lean Growth Trial.

Figure 6. Percent lysine required for four genotypes of barrows from the 1993 Lean Growth Trial.

Figure 7. Predicted daily protein accretion rates for three genotypes at 53 kg live weight 50 kg empty body weight at different energy intakes. Maximum daily protein accretion rates of 110, 150 and 150 g, slope of protein accretion (g) per Mcal ME intake of 21.3, 24.8 and 28.3.

Figure 8. Daily lipid accretion rates at different energy intakes.

Figure 9. Ratio of lipid gain to protein gain at different energy intakes.

Figure 10. Ratio of lean gain to ME intake at different energy intakes.


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