"Swine veterinarians discuss expectations of welfare, disease"

Feedstuffs, March 25, 2002 - SWINE FOCUS

By TIM LUNDEEN
Feedstuffs Staff Writer

When the American Association of Swine Veterinarians (AASV) gathered March 2-5 in Kansas City, Mo., discussion tended to revolve around welfare issues, emerging diseases and the latest on porcine reproductive and respiratory syndrome (PRRS) virus research.

Dr. Timothy Blackwell, a veterinarian from Belwood, Ont., presented the 2002 Howard Dunne Memorial Lecture titled “Exceeding Expectations.” He related some of his recent experiences with alternatives to sow gestation stalls. He described how “independent research establishments” – farms – have produced economically viable alternatives to housing sows individually during gestation. He focused on three systems where sows are housed in groups sized from 12 to 28 sows per pen with varying configurations of partitions and feeders. He said each of these systems maintain or improve sow productivity, were cheaper to build and easier to operate, particularly in large herds.

Blackwell said these systems are based on a principle that may seem counterintuitive: the more sows per pen, the less fighting there will be. He noted that producers who have experimented with loose sow housing systems reported that the worst injuries occur when sows are in small groups – two to eight sows – where dominant sows can bully smaller and passive sows, resulting in an unequal feed distribution. The initial solution to this problem, he said, was to individually house sows, an approach that worked well but was expensive and has come into conflict with the popular ethic.

The alternative approach, Blackwell said, is to increase group size to “12, 25, 50, 100 sows or more per pen.” He said feed suddenly dumped on the floor for 100 sows means that if a sow spends any time fighting, she wastes time she could have been eating. In order for her to maximize feed intake in this system, she must “keep her head down and eat.”

Even though some fighting can occur when sows are mixed, Blackwell said it has been hypothesized that the effort to establish a “boss sow or sows” is too overwhelming in very large groups, so fighting is therefore diminished.

Another feature of these systems, the veterinarian said, is that the cost is equal to or less than conventional crated gestation housing. He noted that although some of these systems require a larger total barn area per sow, significant cost savings occur in simpler requirements for floors and no cost for the crates.

Circovirus

Swine health concerns were a predominant topic at the AASV meeting, and there was much interest in emerging diseases, such as type 2 circovirus (PCV2), which is associated with postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome.

PMWS is a recently emerged/recognized disease complex characterized clinically by wasting, dyspnea and occasionally by icterus and/or diarrhea in nursery and grow-finish pigs, according to Dr. Steven Sorden of the veterinary diagnostic laboratory at Iowa State University. He said PCV2 is consistently demonstrated in PMWS lesions, and experiments performed by several groups have established that PCV2 causes these unique lesions.

Sorden noted that most growing pigs seroconvert to PCV2 during the finishing phase of production and most pigs exhibit no clinical signs in association with PCV2 infection. He said he has not found a U.S. herd in which all tested adult animals were PCV2-seronegative.

He reported that since 1999, when PCV2 immunohistochemistry became available, the Iowa State diagnostic lab has diagnosed 400-600 cases per year out of approximately 7,000 porcine tissue samples per year.

PRRS stability

Among the many presentations on PRRS encompassing the entire gamut of PRRS science, Dr. Darwin Kohler with Babcock Swine Inc. presented his findings on the role of herd stability in the control of PRRS.

He asked, “Is there enough of a difference in performance between PRRS-positive and PRRS-negative herds to justify depopulation and repopulation?” Kohler’s investigation had the goal of determining the differences between positive and negative herds in a closed-herd system.

In these systems, the herds are permanently closed to all live animal introduction, with gilts being raised on the sow site and semen coming from a single closed source. Kohler’s study included 42,500 sows located in four sates. Of these herds, 10 farms (16,200 sows) were PRRS-negative and 29 farms (6,275 sows) were PRRS-positive. Negativity was determined by all animals tested having an S/P ratio of less than 0.4.

He said his data show no production difference between the older PRRS-positive herds and the more recently populated PRRS-negative herds. He said one reason is the predictability of the production system in attaining and maintaining herd stability.

According to Kohler, on average, PRRS-positive farms had a farrowing rate of 83.9% compared to 86.5% for the PRRS-negative herds. The positive herds had a pre-weaning loss of 10.5% compared to 11.3% for the negative herds. Also, the PRRS-positive sows gave birth to 0.1 more pigs than the negative sows.

More PRRS

In the final session on scientific answers to commonly asked PRRS question, Dr. Scott Dee of the University of Minnesota’s College of Veterinary Medicine discussed five knowledge gaps relating to PRRS control/eradication.

He said the immune response in the pig following PRRS virus infection is poorly understood, and work is needed in this area before researchers and practitioners can “advance to the next level of understanding this disease.”

Dee noted that many biosecure herds have become infected through unknown routes because virus transmission, outside of pigs and semen, remains a mystery. There are also discrepancies between results from field studies and experimental data regarding the prevalence of persistently infected breeding animals, he said.

Finally, Dee said, with the co-existence of genetically diverse viruses within sow herds, the development of sub-populations within the breeding herd may be difficult for traditional gilt management – with or without vaccination – to control.