NCSU Extension Swine Husbandry 1999

February, 1999 . Volume 22, Number 1


Water is an important nutrient required by swine. It is important in the digestion of food and is required for almost all chemical reactions in the body. In addition to being essential for the pig, water can be used as a carrier for nutrients and/or medication in pig production facilities. An estimate of the water intake of pigs is needed to supply the correct levels of nutrients or drugs. Although the water intake estimates for the different classes of pigs varies substantially, some general recommendations can be made. As a rule of thumb, water intake can be estimated as a ratio to feed intake of approximately 3:1 (3 liters of water per kg of feed, or 0.36 gallons per lb of feed). Estimates for different weight classes of pigs are given in the table below.

Pig Age or Class

Approximate Weight (lbs)

Water Intake (gallons/day)

Piglets (to 55 days)

10 to 65


55 to 95

65 to 110


96 to 156

110 to 185


157 to 230

185 to 250





Pregnant Sows



Lactating Sows






Adapted from Weckowicz et al., 1978 as cited by Miller et al., 1991.

Eric van Heugten


To compete in today's global markets the USA pork industry is rapidly changing from treating pork as a commodity product to one focused on functional and conformance quality. The outbreak of E. coli O157:H7 in 1993 has increased government and industry focus on enhancing the safety of meat and lead to the adoption of HACCP principles to improve pork quality. Pork retailers have indicated that their top four quality concerns are: excessive color variation, too much purge, short shelf life, and lack of uniformity or consistency (NPPC, Pork Chain Quality Audit). Unfortunately, a recent survey indicated that 26% of the pork evaluated at 14 major plants had unacceptable muscle quality (Kauffman 1992). Many of these quality problems are related to Porcine Stress Syndrome (PSS).

To decrease the proportion of PSE pork, producers are recommended (Eikelenboom 1991) to withdraw feed from hogs 12-24 hours prior to slaughter. Because producers are penalized for selling hogs outside a narrow weight range, most who have all-in/all-out facilities will send their hogs to slaughter over 3-4 weeks. In most cases, they withdraw feed from the last load but earlier loads are usually on full feed until they are shipped. The benefits of feed withdrawal are not without risks including a possible rise in the proportion of pigs with gastric ulcers or an increase in the proportion of pigs excreting Salmonella spp.

Salmonellosis currently costs the USA between $0.6 billion and $3.5 billion annually making it the most costly bacterial foodborne disease. From an estimated 696,000 to 3,840,000 cases, 690 to 3,800 people die each year in the United States (Buzby, AER, #741). Since 1970, there has been a steady increase in non-typhoid salmonellosis in humans caused by non-host adapted serotypes, particularly S. typhimurium, with the majority of outbreaks traced to foods of animal origin (Tauxe 1991) Pork is a major cause of foodborne salmonellosis throughout the world.

Studies of pork in retail stores found 15-22% of samples were contaminated. In Denmark in 1993, pork was the most important source of foodborne salmonellosis when meat contaminated with S.infantis accounted for an outbreak of 20 cases per 100,000 inhabitants. Although slaughter equipment is often the primary source of contamination, the initial source is the carrier pig and transmission is thought to occur by pig-to-pig contact or from exposure to the contaminated environment. The handling and transport of pigs to slaughter has long been recognized as increasing the prevalence of Salmonella spp. To counteract these inherent risks researchers have been investigating techniques that may decrease the risk of contaminating the carcasses. Withholding feed from pigs before slaughter decreases gastrointestinal contents and appears to decrease the risk of gastrointestinal spillage and consequent carcass contamination. However, feed withdrawal is stressful and may increase the proportion of pigs excreting Salmonella spp.

In addition to the effects of feed withdrawal on carcass quality the possibility that it will also increase the proportion of pigs with gastric ulcers must be considered. The echanisms by which gastric ulcers develop are not understood, however, if acid is a major factor and the pH of proximal stomach contents declines as time post-feeding progresses, then it is possible that feed withdrawal will initiate damage to healthy mucosa or accentuate damage where it exists already. The impact of feed withdrawal would likely be magnified if repeated several times. The result could be decreased growth rate due to severe lesions or death.


Kauffman RG, RG Cassens, A Scherer, and DL Meeker. 1992. Variations in Pork Quality. National Pork Producers Council publication, Des Moines, IA. USA.

Eikelenboom, GA, AH Bolink, and W Sybesma. 1991. Effect of feed withdrawal before delivery on pork quality and carcass yield. Meat Sci. 29:35.

Tauxe RV. Salmonella: A Postmodern Pathogen. J. Food Protection. 54, 7(July 1991):563-568.

Morgan Morrow


Tremendous progress has been made in the eradication of PRV in North Carolina. All Coharie Farms, Murphy Family Farms, and Brown's of Carolina quarantines have been released.

To our knowledge, NO PRV positive breeding animals remain in North Carolina.

STAGE III (4-26-99)

Breeding 2 4,336
Finishing 3 17,800
Nurseries 1 12,160
TOTAL 6 34,296

STAGE II (12-28-98)

Breeding 7 6,818
Finishing 56 218,944
Nurseries 6 25,776
TOTAL 69 251,538

The PRV Advisory Committee approved three policy statements at the December meeting of the Committee. They are:

1. Policy Statement for Discontinuing the Use of PRV Vaccine in North Carolina.
2. Herds Circulating PRV Virus
3. Minimum Surveillance in 1999

These policies became an official part of the North Carolina PRV eradication program January 1, 1999 and are explained below.

Policy Statement for Discontinuing The Use of Pseudorabies Vaccine in North Carolina

The use of pseudorabies vaccine has been a tremendous tool in reducing the spread of the pseudorabies virus, and has allowed North Carolina to advance to its current status. Therefore, when trying to determine how we reduce the usage of the vaccine, every possible scenario needs to be examined to prevent future outbreaks and the possibility of virus spread. This will require a lot of planning, because we don't want to stop prematurely, which could be devastating to the program. We would like to see producers relieved of the burden of continuous vaccination, which is time consuming and costly, especially with the price of pork these days. But, if we stop too early, the price of pork within North Carolina may become cheaper when the other states restrict the importation, such as in the case of South Dakota.

Recommendations for discontinuing vaccination: 

1. Continue the current vaccination program through the winter (the risk of disease spread is greater during the colder months). By April 1999, consider defining the areas of Sampson and Duplin counties which are "high incidence" and continue to vaccinate all finishers in those areas until quarantine release. Eliminate the vaccination requirement in low incidence areas. The areas designated as "high incidence" should be re-evaluated quarterly or as needed.

 2. Vaccinate all swine within a 2 mile radius of any herd with virus circulation.

 3. Confine all pigs sourced from farms with active circulation to placement only into areas with active circulation, or high incidence areas, where vaccination is continuing. Movement of these animals should be carefully and actively monitored by NCDA/USDA personnel.

 4. The continued vaccination of sow herds; and proper isolation, testing, and vaccination of all incoming gilts and boars. The timing and frequency of vaccination and the selection of product used should be determined by the producer and his/her veterinarian in association with the NCDA/USDA personnel, but at least at 6 month intervals. 

II. New Outbreaks: 

1. Vaccinate all adjacent farms within a 2 mile radius.

 2. Vaccinate all farms within the pyramid flow.

 3. Vaccination of all sow herds exposed to the new outbreak.

 4. Restrict the movement of progeny into designated high incidence areas as described in I.3 above. 

III. Considerations: 

1. These will be the minimal requirements, additional steps may be needed to protect the swine population in North Carolina. Each herd will be treated with respect to it's specific needs. Additional steps may be needed depending on the origin or destination of the specific animals.

2. The above recommendations are to be based on the following criteria:

-no circulation is found in any of the finishing floors during the 1998 finishing floor project.

-certain herds and/or areas may need to be vaccinated longer, such as areas around previously infected herds (particularly the more recently infected herds) or finishing floors receiving pigs from recently released breeding herds. 

3. Certain areas within Sampson and Duplin counties may be approved for stopping vaccination of finishing floors ahead of the rest of the county. The delineation of these areas will be determined as soon as the appropriate conditions for stopping vaccination are met.

Herds Determined to be Circulating PRV Virus 

As of November 12, all herds that are determined to be circulating PRV will be required to institute the following procedures, as specified by herd type below:

 Breeding Herds: 

1. Immediately re-vaccinate the whole herd. NCDA/USDA, VS personnel will monitor. Continue to vaccinate the whole herd quarterly (4 times per year) at least until the QT is released.

 2. New breeders (gilts and/or boars) will be uniquely identified (double tagged or tattooed) and tested. If negative, at least 30 of these negative G1 vaccinated breeders (vaccinated sentinels) will be tested monthly (every 30 days) until it can be determined that virus circulation has ceased.

 3. As required by the national and NC Program Standards, all breeding groups will be tested at or before farrowing and the positives removed at weaning. Also, all boars will be tested and the positives removed within 15 days of receiving the test results.

 4. NCDA will assure that a circle test around the farm is completed within 1 week after detection if virus circulation and again at the time of virus eradication/QT release.

 5. Routine on-farm visits will be conducted by NCDA/USDA, VS personnel and the designated veterinarian to assist in determining what additional steps may need to be taken and to evaluate all aspects of the vaccination and biosecurity programs. 

Finishing Herds: 

1. Immediately revaccinate the whole herd with the exception of any finishers to be marketed within the next 3 weeks. NCDA/USDA, VS personnel will monitor.

 2. A booster vaccination will be given 3-4 weeks after the initial vaccination for all newly placed animals. NCDA/USDA, VS personnel should be onsite to actively monitor biosecurity and movement protocols. Sell all non-vaccinated animals that are within 3 weeks of market age, and vaccinate and hold the remainder to allow for reduction in the risk of spread as a result of transport.

 3. Premises determined to be circulating virus should not add any PRV negative animals until premises is depopulated and thoroughly cleaned and disinfected. This process should be actively monitored by NCDA/USDA, VS personnel. The next animals placed on this site would be tested in accordance with NCDA protocol to insure no continued circulation.

 4. NCDA will assure that a circle test within a 1.5 radius of the farm is completed within 1 week after detection of virus circulation and again at the time of virus eradication/QT release.

 5. Routine on-farm visits will be conducted by NCDA/USDA, VS personnel and the designated veterinarian to assist in determining what additional steps may need to be taken and to evaluate all aspects of the vaccination and biosecurity programs. 

Minimum PRV Surveillance for 1999

 The PRV surveillance requirements that will be needed for both Stage II and Stage III are as follows: 

Gilt Replacement Finishers: The current requirements (monthly testing of a minimum of 95/10 or 30 animals for continuous flow for Stage II) will be maintained.

 Breeding Herds: A minimum of 60 animals per quarter (or 20 per month) for herds in the current Stage II counties. Herds in Stage III counties should test 60 randomly selected animals annually, but must have a test during the first 6 months of 1999.

 Finishing Premises: A minimum of once a year for all finishing premises but every six months for those that are positive for PRV or within 6 months for those recently positive premises released from quarantine. All houses containing animals that have been on the farm a minimum of 30 days should be tested.

 VQ Herds and Boar Studs: Surveillance requirements will remain the same (monthly or quarterly for VQ herds and monthly for Boar Studs).

 All herds will be subject to an epidemiological evaluation to determine if the above surveillance requirement are sufficient. These minimum surveillance requirements may be increased for some herds depending on the epidemiological evaluation.

Adapted by Morgan Morrow

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Last modified January 28, 1999