EFFECT OF RACTOPAMINE (Paylean) FEEDING PROGRAM ON GROWTH PERFORMANCE AND CARCASS VALUE

To determine if ractopamine (RAC) response can be enhanced by changing the levels in the diet during different phases of feeding, 100 barrows and 100 gilts (initial body weight = 156 lb) were randomly allotted to one of four dietary treatments. Treatments were: 1) Control diet containing no RAC wk 0-6; 2) Step-up RAC: 4.5g/t wk 1 and 2; 9g/t wk 3 and 4; and 18g/t wk 5 and 6; 3) Step-down RAC: 18g/t wk 1 and 2; 9g/t wk 3 and 4; and 4.5g/t wk 5 and 6; and 4) Average RAC: 10.5g/t wk 0-6. All diets were formulated to contain 1.2% lysine. Overall, ADG was increased (2.20 vs. 2.04lb/d; P < .05) and FCR decreased (2.77 vs. 3.21; P < .01) for pigs fed RAC compared to the control. Feed cost/lb gain did not differ between dietary treatments but total feed cost/pig was greater ($21.67 vs. $19.44; P < .01) for pigs fed RAC. Loin muscle area, lb of boneless trimmed ham and % fat free lean increased (P < .01) in pigs fed RAC. Carcass value was calculated using a common North Carolina pricing system and lean value of the carcass was based on USDA reported prices for boneless pork primal cuts. When value was adjusted to a common final weight, carcass value/pig did not differ (P > .10) across treatments but lean value/head was increased by $4.69 (P < .01) for pigs fed RAC. When value was not adjusted for final weight allowing a comparison of equal time on feed, a treatment x sex interaction (P < .01) was observed for carcass value with control gilts having the least value ($114.86) and barrows fed the average RAC treatment having the greatest value ($132.07) but not significantly different from control barrows ($130.59). Lean value per head was greater for the Step-up and Average RAC treatments than the Step-down or Control ($129.27^a, $128.11^a, $127.35^b, $123.49^c; P < .01) treatments. Ractopamine resulted in a favorable response in growth performance and yielded more lean pork at a greater feed cost. Carcass and lean value data indicate that the decision to feed RAC and the feeding program used with it should be made based on marketing plans. Economic benefits from RAC feeding may be achieved if pigs are sold on pounds of lean pork and not on a typical carcass value basis. Economic benefits of RAC feeding may also be achieved for pigs fed to a constant age rather than a constant weight.

 

Introduction

 

It has been previously reported (1) that the response to ractopamine (RAC) is not constant over the course of the feeding period. The RAC response increases, plateaus and then decreases during the course of the RAC feeding period. The reason for this response is not fully understood. Two potential reasons for the response are receptor down regulation and a changing RAC dose (per unit of weight), as the treated pigs grow heavier while consuming the same amount of feed. If either of these reasons is true, then it may be possible to maintain the RAC response for a longer period of time by changing the RAC dose throughout the feeding period. Therefore, the objective of this study was to determine if changing the levels of RAC in the diet during different phases of RAC feeding and what the impact of the observed response is on carcass value could enhance the RAC response. Specifically to determine if the RAC dose is increased, will the magnitude of the RAC response be maintained.

 

Materials and Methods

 

The trial was divided into three 14-day periods and during the trial, pigs were fed one of four treatments. The treatments were designed to evaluate the effects of increasing and decreasing RAC dose compared with a negative control and constant RAC treatment. Treatments were: 1) Control diet containing no RAC wk 0-6; 2) Step-up RAC: 4.5g/t wk 1 and 2; 9g/t wk 3 and 4; and 18g/t wk 5 and 6; 3) Step-down RAC: 18g/t wk 1 and 2; 9g/t wk 3 and 4; and 4.5g/t wk 5 and 6; and 4) Average RAC: 10.5g/t wk 0-6. Treatments were achieved by adding varying levels of Paylean 9g/lb at the expense of corn as described in Table 1. All diets were formulated to contain 1.2% lysine. Complete diet formulations are reported in Table 1.

 

One hundred barrows and 100 gilts (Newsham) were randomly assigned to pens at 90 lb. Pens were randomly assigned one of the four dietary treatments. There were 5 pigs per pen and 10 pens per treatment with 5 pens per treatment of barrows and 5 pens per treatment of gilts. Pigs were housed at the North Carolina Swine Evaluation Station (Clayton, NC) on solid concrete floors and provided ad libitum access to feed and water. After 33 days of acclimation treatments were imposed at an average weight of 156.5 lb. Starting weight was calculated based on expected performance so that the average weight at the end of six weeks on treatment would be 240 lb. Diet changes occurred at 2-week intervals. Due to scheduling at the slaughter facility the trial concluded at 41 days rather than 42 resulting in 13 days in the third feeding period.

 

Feed allocation was recorded on a daily basis and pigs were weighed and feed weighed back when diets were changed to determine average daily gain (ADG) and average daily feed intake (ADFI) from which feed conversion ratio (FCR) was calculated. Backfat and loin eye area was measured on all pigs and percentage fat free lean estimated (NPPC, 2000) at the end of the trial using real-time ultrasound (Aloka 500; Corometrics) Two pigs per pen were randomly selected for blood sample collection at days -1, 7, 21, 35 and 41 and for slaughter on day 42. Blood samples were separated and the serum froze at -20 C and subsequently analyzed for serum urea nitrogen.

 

Eighty pigs were sent to a commercial slaughter facility and were killed approximately 16 hours after being weighed off treatment. Carcass data collected at the slaughter facility included hot carcass weight, leaf fat weight, loin eye area, tenth rib backfat depth, and carcass length. Dressing percentage was calculated using off-test weight and hot carcass weight and percentage fat free lean estimated using equations recommend by the NPPC (2000). The right side of each carcass was separated into the 4 primal cuts, ham, loin, belly and shoulder, and each primal was weighed. Each primal cut was then boned and trimmed to 1/8″ and the weights of the boneless loin, tenderloin, boneless ham, belly, and shoulder were collected. The belly was boned but not trimmed to 1/8″.

 

Costs and values were determined based on the observed performance and carcass data. Feed cost per pound of gain and total feed cost was estimated based on current ingredient prices (Table 1). Carcass value was estimated by applying the observed hot carcass weight, fat depth and loin depth for each carcass (n = 80) to a payment matrix that is commonly used in North Carolina. Lean value is the estimated total value of the lean cuts in the carcass comprised of the sum value of whole boneless loins ($1.87/lb), Tenderloin ($2.80/lb), Boneless ham – 5 muscle group ($1.27/lb), Seedless belly – skin-on ($.735/lb), and whole primal shoulder ($.5257/lb) as reported by the USDA.

 

Statistical analysis of the data was performed using the GLM procedure of SAS. Dietary treatment, sex and interaction were examined to determine their effects on growth and carcass characteristics. Carcass data was also evaluated with hot carcass weight used as a covariate to adjust carcass parameters and primal characteristics to a common slaughter weight.

 

Results and Discussion

 

Growth performance and feed cost data are summarized in Table 2. Treatments did not differ (P = .70) in starting weight nor were they significantly different (P = .18) in pre-test ADG. However barrows were both heavier and faster growing (P < .05) than gilts throughout the study. Dietary treatments did not result in differences (P > .10) in live weight at the end of each two-week period. Average daily feed intake was not affected during the first 28 d but pigs on the control diet did consume more feed (P < .01) during the last 13 d and over the entire study. During the first 2 periods pigs on the RAC treatments showed increased ADG (P < .05). However, there was no advantage (P = .10) in ADG for the RAC treatments during the third period. Feed cost per lb of gain was less (P < .01) for the UP and Average treatments than for the Down and Control treatments in the first period. However, no differences were observed between treatments for feed cost per pound of gain in the second period and during the third period and overall feed cost was lower (P < .01) for the Control as compared to the RAC treatments. Overall, ADG was increased (2.20 vs. 2.04lb/d; P < .05) and FCR decreased (2.77 vs. 3.21; P < .01) for pigs fed RAC compared to the control. Feed cost per kg gain did not differ between dietary treatments but total feed cost per pig was greater ($21.67 vs. $19.44; P < .01) for pigs fed RAC.

 

Regardless of whether pigs were considered to be on the dietary treatment for an equal length of time or fed to a common final weight (Tables 3 and 5) loin eye area (LEA) and % fat free lean (FFL) increased (P < .01) and BF decreased (P < .01) in pigs fed RAC. This result is true whether the measurements were taken on the carcass or by real-time ultrasound measurement of the live animal. If pigs were considered to be on feed for an equal time period significant advantages (P < .05) were observed for weight of boneless trimmed ham, shoulder and loin for the Up and Average RAC treatments as compared to the control animals. Treatment by sex interactions (P < .05) were observed for weight of rough cut hams when marketed at either a common market weight or at an equal time on feed and for weight of the rough cut shoulder when pigs were considered to be on feed for an equal time and no adjustment was made for carcass weight. These interactions are most likely a result of the observed treatment by sex interaction for hot carcass weight (P < .05). However, the observed treatment by sex interactions with rough-cut primals did not translate to significant differences when these primals were boned and closely trimmed. Therefore, it can be assumed that much of the weight difference is due to fat content of these cuts. Weight of the rough cut and trimmed primals expressed as a percentage of hot carcass weight are summarized in Table 5 and are similar to those results when primal weight data were adjusted to a common final weight (Table 4). Less leaf fat and more boneless ham was observed (P < .05) from RAC treated pigs as compared to the controls.

 

Payment to pork producers is commonly based on a formula that accounts for hot carcass weight, fat depth and loin muscle depth. Dietary treatment did not have a significant effect (P < .10) on any of the individual premiums and/or discounts for weight, muscle or leanness (Tables 6 and 7). However, a treatment x sex interaction (P < .01) was observed for CV, total payment received for the pig, when value was not adjusted for a common final weight allowing a comparison of equal time on feed (Figure 1), with control gilts having the least value ($114.86) and barrows fed the average RAC treatment having the greatest value ($132.07) but not significantly different from control barrows ($130.59). However, when pigs were considered to be fed to a common slaughter weight payment to producer (CV) did not differ (P > .10) across dietary treatment. Lean value is an estimate of the value of the four lean primal cuts of the pork carcass. Lean value per head (Table 6) was greater for the Up and Average RAC treatments than the Down or Control (P < .01) treatments. When lean value was adjusted to a common final wt it was increased by $4.69 (P < .01) for pigs fed RAC. Therefore, these results would indicate that dietary treatment would result in a greater potential return in a more vertically coordinated system or if payment received by the producer was based on the true lean content of the carcass. This is in part due to the fact that most buying systems do not measure the lean content of the ham where most of the benefit in lean gain was observed in this study. In addition, the buying system used in this report to determine carcass value provides the optimum premium when backfat depth is at .60 inches and this premium is reduced for both fatter and leaner hogs. Therefore the leaner carcass from the RAC treatments did not provide an advantage in carcass value.

 

Implications

 

Carcass and lean value data indicate that the decision to feed RAC and the feeding program used with it should be made based on marketing plans. The payment system on which the value of the pig is determined, as well as, the length of time on feed and the objective of equal time or equal weight at slaughter must all be considered to determine the appropriate RAC feeding program. Economic benefits from RAC feeding may be achieved if pigs are sold on pounds of lean pork and not on a typical carcass value basis. Economic benefits of RAC feeding may also be achieved for pigs fed to a constant age rather than a constant wt. These results indicate RAC feeding may provide an opportunity to minimize variation in weight and lean content at a given age, especially when feeding both barrows and gilts.

 

References

 
Williams, N.H., T.R. Cline, A.P. Schinckel, and D.J. Jones. 1994. The Impact of Ractopamine, Energy Intake, and Dietary Fat on Finisher Pig Growth Performance and Carcass Merit. J. Anim. Sci. 72:3152-3162.

 

Table 1. Experimental Diets.

^aMixing charge included of $10.00 per ton.

 

Table 2. Effect of Paylean Feeding Program and sex on bi-weekly growth performance and feed cost per pound of gain.

 

Table 3. Effects of Paylean feeding program and sex on ultrasonic and plant carcass characteristics that are not adjusted for final weight allowing for a comparison of equal time on feed.

^aTreatment by sex interaction, P < .05.

 

Table 4. Effects of Paylean feeding program and sex on ultrasonic and plant carcass characteristics that are adjusted for final weight allowing for a comparison of feeding to a common market weight.

^aTreatment by sex interaction, P < .05.

 

Table 5. Effects of Paylean feeding program and sex on rough-cut and boneless, trimmed primal weights expressed as a percentage of hot carcass weight.

 

Table 6. Effect of Paylean feeding program and sex on producer premiums and payments and lean carcass values that are not adjusted for final weight allowing for a comparison of equal time on feed.

^xTreatment by sex interaction, P < .01.
^#Premiums are based on payment matrix from a common swine-buying program in the southeast.  Base carcass price of $68.17/cwt.
⁺Total payment is dollars received per head adjusted for premiums and discounts. Base carcass price of $68.17/cwt.
^{^}Lean value is value of lean cuts in the carcass comprised of whole boneless loins ($1.87/lb), Tenderloin ($2.80/lb), Boneless ham – 5 muscle group ($1.27/lb), Seedless belly – skin-on ($.735/lb), and whole primal shoulder ($.5257/lb).

 

Table 7. Effect of Paylean feeding program and sex on producer premiums and payments and lean carcass values that are  adjusted for final weight allowing for a comparison feeding to a common market weight.

^#Premiums are based on payment matrix from a common swine-buying program in the southeast.  Base carcass price of  $68.17/cwt.
⁺Total payment is dollars received per head adjusted for premiums and discounts. Base carcass price of $68.17/cwt.
^{^}Lean value is value of lean cuts in the carcass comprised of whole boneless loins ($1.87/lb), Tenderloin ($2.80 /lb), Boneless ham – 5 muscle group ($1.27/lb), Seedless belly – skin-on ($.735/lb), and whole primal shoulder ($.5257/lb).

 

Table 8. Effect of Paylean feeding program and sex on Blood Urea Nitrogen (mg/dl).