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Effects of Added Zinc in Diets with Ractopamine on Growth Performance, Carcass Characteristics and Zinc Concentrations in Plasma, Loin and Liver of Finishing Pigs

28 March 2014

As in previous studies, the addition of ractopamine hydrochloride (RAC) improved the growth and carcass performance of finishing pigs, according to C.B. Paulk and co-authors at the 2013 Kansas Swine Day. Adding zinc to the finisher diets containing RAC did not improve overall performance.

Two experiments were conducted to determine the effects of added zinc from zinc oxide (ZnO) or Availa-Zn (AZ; Zinpro, Eden Prairie, MN) on growth performance and carcass characteristics of finishing pigs fed ractopamine HCl (RAC; Paylean; Elanco Animal Health, Greenfield, IN).

In Experiment 1, a total of 320 pigs (PIC 327 × 1050, initially 215.9 lb) were used in a 35-day study. Pens of pigs were randomly allotted to one of eight dietary treatments, with either two barrows or two gilts per pen and 20 pens per treatment.

Dietary treatments included:

  • a corn-soybean meal–based negative control - 0.66 per cent standardised ileal digestible (SID) lysine
  • a positive control diet (0.92 per cent SID lysine) containing 10ppm of RAC and
  • the RAC diet plus 75, 150 or 225ppm added zinc from ZnO or AZ.

The trace mineral premix provided a basal level of 55ppm zinc from zinc sulphate (ZnSO4) in all diets.

In Experiment 1, overall (days 0 to 35), pigs fed RAC had improved (P<0.04) average daily gain, feed:gain ratio, 35-day bodyweight, caloric efficiency on an ME and NE basis, hot carcass weight, carcass average daily gain and feed:gain, loin depth, percentage lean and carcass caloric efficiency on an ME and NE basis, and reduced (P<0.01) average daily feed intake and backfat thickness compared with pigs fed the control diet. No evidence of a zinc effect or an interaction between zinc source and level was observed. Performance and income over feed cost did not differ in pigs fed diets with added zinc from either source.

In Experiment 2, a total of 1,234 pigs (PIC 337 × 1050; initially 228.6lb) were used in a 28-day study. Pens contained 23 to 28 pigs with either all barrow, all gilt or mixed-sex allotments. Pens of pigs were blocked by bodyweight, feeder type and gender and were randomly assigned to diets.

The four dietary treatments consisted of:

  • a corn-soybean meal–based negative control diet (0.70 per cent SID lysine)
  • a positive control diet (0.92 per cent SID lysine) containing 10ppm RAC or
  • the RAC diet plus 50ppm added zinc from ZnO or AZ.

All diets contained 80ppm zinc from ZnO provided by the trace mineral premix.

On day 14, the six heaviest pigs from each pen (determined visually) were individually tattooed by pen and harvested to allow for carcass data collection, and on day 28, the remaining pigs were individually tattooed by pen and harvested to allow for carcass data collection.

Overall (days 0 to 28), pigs fed RAC had improved (P<0.001) average daily gain, feed:gain ratio, final bodyweight and caloric efficiency on an ME and NE basis.

Added zinc or zinc source did not affect (P>0.20) growth performance.

For pigs harvested on day 14, pigs fed RAC had improved (P<0.001) carcass average daily gain, feed:gain ratio, income over feed cost and carcass caloric efficiency on an ME and NE basis and a tendency for increased hot carcass weight, loin depth and percentage lean compared with those fed the negative control diet.

No differences were observed in carcass characteristics (P>0.11) between pigs fed RAC diets and diets containing added zinc. However, pigs fed diets with added zinc from ZnO had increased (P<0.05) carcass feed:gain ratio, carcass yield, carcass income over feed cost and carcass caloric efficiency on an ME and NE basis than those fed zinc from AZ.

For pigs harvested on day 28, pigs fed RAC had improved (P<0.01) hot carcass weight, carcass average daily gain and feed:gain ratio, backfat thickness, loin depth, percentage lean, carcass income over feed costs and carcass caloric efficiency on an ME and NE basis.

No differences were observed in carcass characteristics between pigs fed RAC and no additional zinc and diets containing added zinc from either source. Carcass characteristics did not differ in pigs fed diets with added zinc from ZnO or AZ.

Paulk and co-authors concluded they observed improvements in growth and carcass performance from adding RAC similar to previous studies. However, in contrast with their previous research, adding zinc to finishing pig diets containing RAC did not improve overall performance. Consistent with the earlier research, income over feed cost was numerically increased with the addition of zinc.

Reference

Paulk C.B., M.D. Tokach, J.L. Nelssen, S.S. Dritz, J.M. Gonzalez, J.M. DeRouchey, R.D. Goodband, G.M. Hill, and K.D. Haydon. 2013. Effects of added zinc in diets with ractopamine HCl on growth performance, carcass characteristics and zinc concentrations in plasma, loin, and liver of finishing pigs. Proceedings of 2013 Kansas Swine Day, p133-144.

Further Reading

You can view the full paper by clicking here.
Read other papers presented at the 2013 Kansas Swine Day by clicking here.

March 2014

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