The impact of feeding ractopamine hydrochloride (RAC) on growth performance and responses to handling and transport in heavy pigs was evaluated in a study reported by C.M. Pilcher at the University of Illinois Urbana and co-authors there and with the USDA-ARS Livestock Behavior Research Unit in West Lafayette and Elanco Animal Health in Journal of Animal Science.

The experiment was performed as a split-plot design with a 3×3 factorial arrangement of treatments:

1. RAC level (0 versus 5.0 versus 7.5mg per kg of feed) and
2. handling intensity (HI; gentle versus moderate versus aggressive)

RAC level was the main plot and HI was the subplot.

A total of 288 pigs housed in groups of eight were used to evaluate growth performance over a 28-d RAC feeding period (98.5 ± 4.58 to 131.5 ± 7.45kg bodyweight).

On day 29 of the study, the HI treatment was applied to 216 pigs (six per pen; two per pen on each HI). This was followed by transportation for one hour on a livestock trailer at the end of which pigs were subjected to a final handling procedure.

Blood samples (to measure acid–base, cortisol and catecholamine levels) were collected and rectal temperature was measured two hours before the HI treatment (baseline) and after the final handling procedure (final).

Feeding RAC (5.0 and 7.5mg per kg) improved (P<0.01) average daily gain (9.9 and 9.0 per cent for 5 and 7.5 mg/kg RAC, respectively) and gain:feed ratio (8.8 and 11.8 per cent, respectively) compared to controls, with no differences (P>0.05) between the two RAC levels.

Increasing the intensity of handling decreased (P<0.001) final blood pH, bicarbonate and base excess and increased (P<0.001) final blood lactate and plasma cortisol and norepinephrine levels.

Aggressive compared to gentle handling increased (P<0.05) the incidence of pigs exhibiting open-mouth breathing and skin discoloration after the final handling procedure but had no effect (P>0.05) on the incidence on non-ambulatory, uninjured pigs.

There was no effect (P>0.05) of feeding RAC on final rectal temperature or blood acid–base measurements.

Compared to the control, feeding 7.5mg but not 5.0mg per kg RAC increased (P<0.05) final plasma epinephrine levels and the incidence of non-ambulatory, uninjured pigs.

This study confirms the improved growth performance of pigs fed RAC and the negative effects of aggressive handling on physical, metabolic and physiological responses of pigs, observed Pilcher and co-authors.

It also suggests that pigs fed 5.0mg compared to 0mg per kg RAC showed similar responses to transport and handling.

However, pigs fed 7.5mg per kg of RAC had a greater incidence of non-ambulatory, uninjured pigs when subjected to the handling/transport model and this warrants further investigation, Pilcher and co-authors suggested.

Reference

Peterson C.M., C.M. Pilcher, H.M. Rothe, J.N. Marchant-Forde, M.J. Ritter, S.N. Carr, C.L. Puls and M. Ellis. 2015. Effect of feeding ractopamine hydrochloride on growth performance and responses to handling and transport in heavy-weight pigs. J. Anim. Sci. 93:1239-1249.

Further Reading

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April 2015