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OCR for page 148
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Appendix 2
Equations for Determining Lean Growth Rate of Pigs
The lean growth rate of pigs is influenced by their total body growth rate and by the leanness of their carcass. Lean growth rate, or lean gain, is the rate at which a pig's carcass accretes lean tissue (muscle). In the past, measurements of carcass lean tissue were standardized to 10 percent fat, then later they were standardized to 5 percent fat. Today, carcass lean tissue is measured on a fat-free basis.
Carcass fat-free lean gain of pigs, in pounds per day, can be determined by estimating the pounds of fat-free lean in the carcass at the beginning and end of a prescribed test period, subtracting one weight from the other to determine the gain in weight of the fat-free lean, then dividing by the number of days from beginning to end.
Final carcass fat-free lean, as a percent of the carcass (referred to as ''fat-free lean index"), can be estimated at the packing plant from either (1) ruler measurement of the backfat at the last rib at the midline of the hot carcass or (2) fat probe between the third and fourth rib, 7 cm off the midline of the hot carcass, according to the following (National Pork Producers Council, 1994):
The pounds of carcass fat-free lean is then determined by multiplying the fat-free index (or percentage of fat-free lean in the hot carcass) by the weight of the hot carcass, as follows:
A more sophisticated approach for measuring carcass fat-free lean weight and gain involves the determination of loin eye area in carcasses. If that measurement is obtainable, the lean gain can be calculated by the following (adapted from National Pork Producers Council, 1991):
Initial carcass fat-free lean weight can be estimated by the following formula:
After estimating the pounds of fat-free lean in the carcass at slaughter and in the carcass of the initial pig, the lean gain is calculated as follows:
Lean gain in lb/day is then converted to g/day by multiplying by 454.
Because lean gain is not constant from one day to the next, the calculated lean growth rate will be influenced by the initial and final weights of the pigs. The mean lean growth rate in the growth model assumes initial and final weights of 20 and 120 kg, respectively (approximately 45 and 265 lb). If the calculated lean growth rate is determined with pigs having different initial and/or final weights than these, the adjustment factors in Appendix Table 2-1 can be used to adjust the lean gain to a 20- to 120-kg basis.
OCR for page 149
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Appendix Table 2-1 Factors for use when the lean growth rate is measured over a period other than 20 to 120 kg.
Initial Wt (kg)
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Final Wt (kg)
40
1.07
1.04
1.02
1.00
45
1.05
1.02
1.00
0.99
0.97
50
1.03
1.01
0.99
0.97
0.96
0.95
55
1.02
1.00
0.98
0.96
0.95
0.94
0.94
60
1.01
0.99
0.97
0.96
0.95
0.94
0.93
0.93
65
1.00
0.98
0.96
0.95
0.94
0.94
0.93
0.93
0.93
70
0.99
0.97
0.96
0.95
0.94
0.93
0.93
0.93
0.93
0.93
75
0.98
0.97
0.96
0.95
0.94
0.93
0.93
0.93
0.93
0.93
0.93
80
0.98
0.97
0.96
0.95
0.94
0.94
0.93
0.93
0.93
0.93
0.94
0.94
85
0.98
0.97
0.96
0.95
0.94
0.94
0.94
0.94
0.94
0.94
0.94
0.95
0.96
90
0.98
0.97
0.96
0.95
0.94
0.94
0.94
0.94
0.94
0.95
0.95
0.96
0.96
0.97
95
0.98
0.97
0.96
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.96
0.97
0.97
0.98
0.99
100
0.98
0.97
0.96
0.96
0.95
0.95
0.95
0.95
0.96
0.96
0.97
0.97
0.98
0.99
1.00
1.01
105
0.98
0.98
0.97
0.96
0.96
0.96
0.96
0.96
0.97
0.97
0.98
0.98
0.99
1.00
1.01
1.03
1.04
110
0.99
0.98
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.98
0.99
1.00
1.00
1.01
1.03
1.04
1.05
115
0.99
0.99
0.98
0.98
0.97
0.97
0.98
0.98
0.98
0.99
1.00
1.01
1.02
1.03
1.04
1.05
1.07
120
1.00
0.99
0.99
0.98
0.98
0.98
0.99
0.99
0.99
1.00
1.01
1.02
1.03
1.04
1.05
1.07
1.08
Instructions: Find the cell in the table that corresponds to the initial and final weights over which the mean lean growth rate in the situation of interest is measured. Multiply the measured mean lean growth rate by the factor in that cell.
Note: These factors are correct only for the default lean accretion curve.
References
National Pork Producers Council. 1991. Procedures to Evaluate Market Hogs. Third ed. National Pork Producers Council, Des Moines, IA.
National Pork Producers Council. 1994. Fat-Free Lean Index. National Pork Producers Council, Des Moines, IA.
Representative terms from entire chapter:
lean gain
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