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A new study confirms antibiotic-free production strategies leave pigs at considerable risk of exposure to disease and responsible use of antibiotics can significantly improve animal health. Prior to this study, no data has been available regarding the production performance and health of animals raised antibiotic-free when under a disease challenge such as PRRSV, the most significant pathogen in the global swine industry.

“No one has ever done an experiment of this size under representative conditions comparing antibiotic-free production to production strategies utilizing judicious use of antibiotics,” says Scott Dee, DVM, lead researcher of the study and director of research with Pipestone Applied Research.

As public concern regarding the role of antibiotic use in livestock increases, so has the interest in raising livestock under antibiotic-free (ABF) conditions to decrease antibiotic use in farm animals, despite the lack of scientific data supporting this position. 

A team of researchers from Pipestone Applied Research, the University of Minnesota and Zoetis recently set out to compare production strategies. 

A multi-pronged approach

The study compared 2,200 pigs in three different research groups that started in the farrowing house. Three different medication programs were assigned. Treatment group one received a standard use of antibiotics. Pigs were treated at processing and weaning, received a feed medication, and were treated with injectable and water-soluble antimicrobials as needed. 

Meanwhile, pigs in group two received a processing injection, but no weaning injection. They received water medication and injectable medications when needed, but did not receive feed medication.

Group three did not receive antibiotics – even from birth. They received nothing in the lactation period, then moved on to the antibiotic-free program during the wean-to-finish period. They could receive aspirin in water, but no antimicrobials were administered at any time.

Following weaning, all groups were inoculated with PRRS Virus 174 using a seeder pig challenge model and researchers let virus roll through the barn naturally. The research team measured clinical response and mortality, average daily gain, feed efficiency, percentage of animals removed (if they had to be treated with antibiotics, they were removed from study), and individual pig care over time.

In addition, the researchers went a step further and measured personnel response and economics – the cost of raising each group per head. 

“One of the things that made this study unique is that we wanted to know what people working on the farm thought,” Dee says. “We gave the workers a survey and asked how they felt about what they could and couldn’t do with each group of pigs as they watched the disease move through the pigs.” 

An immediate response

Right away, Dee’s team started seeing a response in the farrowing house between the three groups of pigs. The mortality and removals in the ABF production protocol were significantly higher. 

The ABF group experienced problems prior to weaning, including rotavirus and E.coli. 

“The pigs you could treat responded well, but the pigs you couldn’t, suffered,” he says. “After moving the pigs into the wean-to-finish facility and were exposed to PRRSV, the problems continued.”

Groups one and two did well, but group three did not. After three weeks, the team had to terminate the ABF group according to their welfare protocol. 

“We made a decision with our welfare director and Zoetis that if we reached a specific mortality level, we would continue the study but discontinue the ABF component,” Dee says. “The welfare aspects of the pigs were very well monitored. Every day clinical scores of all animals were collected and the data tabulated for analysis.”

Lucina Galina Pantoja, DVM, co-researcher and director of pork technical services at Zoetis, says this aspect of the study – using the individual pig care monitoring system to obtain clinical scores – is unique. 

“When you think about mortality in these studies, it’s very abstract.  You forget that pigs are actually suffering,” Galina says. “In this study, we did a lot of clinical evaluations to help determine the toll our decisions are making on the pigs.”

Research results

Across the three groups, the results were striking, Dee says. The percentage of full-value pigs marketed was significantly greater in groups one and two (68.09% and 65.33%) when compared to group three (33.05%). In addition, the percentage of mortalities and removals was significantly greater in group three (57.98%) when compared with groups T1 and T2 (20.94% and 24.89%). The actual number of pigs removed from the study and placed in a designated hospital pen, and the actual number of pigs that either died or were euthanized across all three groups was as follows: T1: 15 removals and 132 mortalities, T2: 23 removals and 152 mortalities and T3: 60 removals and 347 mortalities.

From an economic standpoint, the net revenue per pig was 3.1-fold greater for the group one versus the group three pigs ($105.43 vs. $33.81) and 2.9-fold greater for the group two versus the group three pigs ($98.79 vs. $33.81). 

Between groups one and two, there were not a lot of differences statistically, Dee says. 

“Group one’s more intensive antibiotic protocol is fairly typical of many production systems,” he adds. “Both programs were far better than antibiotic-free on performance, welfare and economics.”

Results of caregiver responses to the survey question ‘Are you satisfied with the efficacy of the care being given to the study animals?’ for the first 11 weeks of the study were most favorable for group one and group two pigs at each time point compared to scores for ABF pigs. 

The least favorable health satisfaction scores occurred just before and after PRRSV challenge. Scores began to improve in the ABF group following antibiotic treatment initiated at week 8 of the trial.

Galina says although the caregiver scoring was subjective and not evaluated statistically, it captured a valid aspect of food animal production, namely that humane production methods are consistent with avoidance of disease and optimum productivity outcomes. 

“The ABF group of pigs put a high toll on the caregivers because these pigs were not doing well,” Galina says. “Caregivers had to be there more often, checking on sick pigs and making hard decisions on what treatments they could do within an antibiotic-free environment. Few studies measure the toll this type of production puts on the caregiver.”

Improper antibiotic use leads to antimicrobial resistance

When pigs are sick, they need to be treated with antibiotics just like sick babies or sick dogs and cats, Dee says. 

“We need to use antibiotics correctly – the right dose and duration. We can’t lose those tools,” he says. “If we do, and then get infections like PRRS, it will be disastrous and end in a lot of suffering.”

Although PRRS is a viral disease, due to its immunosuppressive capabilities, the effect of secondary bacterial pathogens on infected pigs is significant and requires the ability of the veterinarian to use antibiotics in a responsible manner to treat affected animals. 

In the study, many pathogens were identified by direct culture or PCR from several tissues across these pigs including, Haemophilus parasuis, Streptococcus suis, Pasteurella multocida, Salmonella cholerasuis, Bordetella bronchiseptica, Mycoplasma hyosynoviae,Mycoplasma hyorhinis, E. coli, influenza virus A of swine, porcine circovirus type 2 and rotavirus A, B and C.

Many herds are PRRS positive, Galina says. Because of this, their research team wanted to generate solid data to evaluate the impact of ABF production under this disease pressure. She believes ABF may work in a healthy herd, but most farms don’t have perfect health and judicious use of antibiotics is necessary to provide the best care possible for the pig.

“Antibiotic reduction is a race to the bottom. It’s not a good practice and it will result in the inability to use antibiotics responsibly to treat sick animals,” Dee says. “We believe we can control resistance better through responsible use – proper diagnosis and doing everything possible to reduce pathogen load through proper sanitation and proper care of animals. Medications are just a part of it.”

The study, “A randomized controlled trial to evaluate performance of pigs raised in antibiotic-free or conventional production systems following challenge with porcine reproductive and respiratory syndrome virus,” was published in PLOS One in December. Authors include Scott Dee, Jose Ezequiel Guzman, Dan Hanson, Noel Garbes, the late Robert Morrison, Deborah Amodie and Lucina Galina Pantoja. 

“Reprinted by permission of Farm Journal media, January 2019”

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