Purdue University researchers find a phase-fed diet, adjusted weekly, more adequately meets the crude protein needs of pigs fed this supplement.

The maximum benefit of feeding Paylean in late finishing diets can only be realized if hogs are also fed higher levels of crude protein (CP).

Research at Purdue University shows today's leaner pigs require more lysine than the 16% CP recommended on the product label.

Paylean, the trade name for ractopamine hydrochloride, is a feed additive produced by Elanco Animal Health. The product shifts the animal's metabolism to direct nutrients from fat deposition to muscle growth.

To evaluate performance of pigs fed Paylean during the last six weeks of finishing period, researchers conducted a feeding trial in April and May 2000.

Four dietary treatments fed during the study included:

- a 16% CP diet with 0.82% lysine;

- a 16% CP diet with 18 g./ton Paylean and 0.82% lysine;

- an 18% CP diet with 18 g./ton Paylean and 0.97% lysine;

- a phase-fed diet, containing 18 g./ton Paylean, with 18% CP and 1.08% lysine during weeks 1 and 4; 20% CP and 1.22% lysine in weeks 2 and 3; 16% CP and 0.94% lysine in week 5; and 16% CP and 0.82% lysine in week 6.

The phase-feeding diet sequence was designed to match previous lean accretion curves, in which pigs fed Paylean increased fat-free lean gain by 50% in weeks 2 and 3, then Paylean response declined to 11%, as compared to control pigs, by week 6.

Ninety-six PIC barrows were blocked by weight into 24 pens (4 pigs/pen; 10 sq. ft./pig). The four diets were randomly assigned to each pen within a block. Pigs were weighed and feed intakes were recorded every week to determine average daily feed intake (ADFI) and average daily gain (ADG), from which feed-to-gain ratio (F:G) was calculated. Backfat depth and loineye areas were measured weekly with real-time ultrasound.

Pigs were marketed at 240 lb. Data collected at marketing included loin depth, carcass length, percent lean, carcass weight, carcass premium, 10th rib loineye area, fat thickness and pork quality characteristics.

Week-by-week performance results are shown in Table 1. Pigs receiving the phase-fed Paylean diet grew 15% faster in week 1, decreased ADFI by 5.2% and F:G by 16%, as compared with the control diet. By week 5, no significant differences were observed between the four dietary treatments.

Carcass characteristics for each dietary treatment are shown in Table 2. Pigs fed Paylean had reduced 10th rib backfat depth and increased predicted percent lean. Loineye area and percent lean were higher for pigs receiving the phase-fed, Paylean diet. Paylean-fed pigs showed no difference in pork quality measurements.

Fifteen pigs/dietary treatment were tested for loin pH, drip loss and Hunter color values. Dietary treatment had no effect on loin characteristics.

Table 3 shows the cost for the last 90 lb. of gain and premiums received for the pigs. All pigs fed Paylean had a lower feed cost. Pigs fed 16% and 18% CP returned about $2/pig more than the control. The phase-fed diet pigs returned $3/pig more than the control.

Based on this research, Purdue animal scientists suggest a four-week finishing program feeding Paylean with phase feeding. Higher diet costs in a four-week program would be offset by performance improvements.

Phase-Feeding Advantages In another study, researchers found the predicted lysine requirements for pigs fed 18 g./ton of Paylean rapidly increases, plateaus during the second and third weeks and then rapidly declines. This curve follows the same pattern shown in the performance data.

Therefore, phase feeding will be required if lysine requirements are to be closely met. Without phase feeding, pigs will not achieve maximum performance during the peak Paylean response and lysine will be overfed during the period of decreased Paylean response. A model for weekly lysine requirements for gilts is shown in Table 4.