Weaning age in baby pigs has seen its ups and downs over the years in U.S. pig production. Recently, we've seen a trend toward stabilizing and increasing weaning age in many sow farms (Figure 1).
The South Central Veterinary Associates database, representing clients across southern Minnesota and north central Iowa, has shown a decrease in the number of sows/farrowing crate over the past two years, reflecting the move to older ages at weaning.
The changes that have occurred with pork production in general, and as a result of the switch to older weaning age in particular, raise five key questions that must be considered:
Do preweaning mortality levels increase as weaning age increases?
What is the impact of weaning age on the incidence rate of sickness and death loss in the nursery?
Have there been any negative health consequences as a result of the trend to earlier weaning that developed over the past 25 years?
How much has weaning age been influenced by barn limitations and economics?
Do all infectious agents respond in a positive way when pigs are weaned earlier?
Weaning Age Effect on Preweaning Mortality
All indications from research and field data, up until a few years ago, are that in many cases, decreasing weaning age allowed for a healthier pig at weaning. At the same time, conventional wisdom suggested that as weaning age decreased, so did preweaning mortality (PWM).
In fact, a review of the U.S. and Canadian databases in the PigChamp recordkeeping system shows no direct correlation between average age at weaning and PWM (Table 1).
One explanation for this apparent contradiction is the high percentage of mortality that occurs within the first 14 days after farrowing (Table 2). If 6% of the total PWM is occurring after 14 days of age, this accounts for only 0.066 pigs/litter weaned (assuming an average of 11 pigs born alive/litter with a 10% PWM).
As farrowing facilities and management techniques have improved, any negative impacts on PWM associated with weaning age seem to have been eliminated.
Segregated Early Weaning Programs
Swine health innovators, such as the late Al Leman, DVM, helped the industry understand the true benefit of all-in, all-out production. Emptying rooms, barns and, ultimately, production sites, could make large linear gains in health.
Work by researchers, including swine veterinarians Tom Alexander of the United Kingdom, and D.L. (Hank) Harris and Barry Wiseman of the United States, has shown the positive contributions of segregated early weaning (SEW) on elimination of some known swine disease agents (Table 3 on p. 20).
|Wean Age, Days||Percent PWM||Year||Wean Age, Days||Percent PWM|
|18.6||12.0||1st half ‘05||20.0||12.1|
|Age||0-3 Days||4-7 Days||8-14 Days||15+ Days|
|*South Central Vets PigChamp data 2004|
At about the same time, the need for improved facility and labor efficiencies began impacting the size of herds. These factors helped foster the development of multi-site production systems throughout the 1980s and 1990s that were very conducive to implementation of SEW programs.
Early Weaning Successes, Failures
The SEW program has proven successful, in some cases, in helping eliminate diseases such as Mycoplasmal pneumonia, swine dysentery, Actinobacillus pleuropneumonia (APP) and pseudorabies.
The management strategies necessary to properly implement early weaning programs are very detailed and require precise implementation. These health strategies are most successful with high-quality facilities, nutrition and management.
Unfortunately, there have been many instances where earlier weaning of pigs has led to higher mortality and disease problems in the nursery. Placing very young pigs into nurseries that do not meet those stringent requirements can quickly lead to disaster.
During the last decade, emphasis has been placed on maximizing throughput of systems and facilities, while compromises have been made to some of the critical control points that make SEW work. Some compromises include:
Not understanding the diseases that pigs are being exposed to at the sow farm;
Not implementing the proper medication programs prior to weaning and postweaning to help eliminate infectious disease agents;
Not sticking strictly to low variation in weaning age when trying to adapt a true SEW program;
Weaning pigs into a “motel style” nursery (pigs weaned into different rooms in the same barn) that allows for lateral infections to occur between age groups at one site;
Locating too many pigs on one site;
Overcrowding pigs in a poor environment;
Improper training of nursery personnel to handle very young, weaned pigs;
Not feeding pigs the proper diets for their age at weaning;
Mixing multi-sourced weaned pigs into one nursery at an early age;
Weaning pigs that are shedding the porcine reproductive and respiratory syndrome (PRRS) virus into a population of healthy, early-weaned pigs.
It is important to note that the PRRS virus is an example of an infectious disease agent that has been proven to infect pigs at or around the time of farrowing. It has been clearly shown that early weaning of baby pigs cannot successfully eliminate this virus.
Increasing Weaning Age To Reduce Mortality
As data has accumulated on the positive effect that extending weaning age has on sow performance, producers have begun to realize the potential benefits to health and performance from weaning an older, bigger pig.
It is important to note that there is actually very little science to observe what happens to the health of a population of pigs in a nursery or a wean-to-finish barn when the average weaning age changes on a farm.
In extensive field trials conducted by Kansas State University (KSU) researchers, there was a significant reduction in nursery mortality as weaning age increased (Figures 2 and 3). These differences were measured from a 7,300-sow commercial farm in trials on over 2,000 and 3,000 pigs, respectively, in a uniform environment with one source of pigs. Weaning pigs at less than 15 days of age increased mortality rates dramatically; weaning pigs from 15 to 21.5 days of age resulted in near linear improvements.
The trials concluded that a significant improvement could be made not only in mortality but in average daily gain and pounds sold/weaned pig. Modeling of the two trials showed that for every day added to weaning age, wean-to-finish mortality decreased by 0.47%.
The level of change in mortality expected from increasing weaning age will depend on individual farm parameters such as baseline mortality rates, pig flow and other farm-specific challenges. Farms that are heavily infected with PRRS virus probably will not see substantial changes.
Effect of Weaning Age on Nursery Pigs' Behavior
Recently published work (Journal of Swine Health and Production, September-October 2005, Vol. 13) by the KSU group has shown significant differences in the chronic problem of navel sucking (belly nosing) in weaned pigs. Pigs that were weaned at a younger age had a much higher prevalence of belly-nosing behavior.
The most significant change in rate of belly nosing occurred in pigs weaned at less than 15 days of age. Over 20% of all weaned pigs at 12 days of age showed this detrimental behavior. Only 6% of pigs weaned at 21 days of age had these tendencies.
At the same time, over 30% of pigs weaned at 12 days of age had umbilical lesions. These types of umbilical lesions can lead to bacterial infections and umbilical hernias. Average daily gain in the belly-nosing pigs was 4% less in comparison to the control group.
Overall, the KSU researchers concluded that increasing weaning age and using bowl waterers appear to be the two main management inputs that reduce belly nosing.
Impact of Increased Weaning Age
Over the past few years, a significant increase has occurred in a few diseases caused by bacteria that are found in just about all pigs' mucous populations. This group includes the “suicide” diseases of Haemophilus parasuis and Streptococcus suis.
Carlos Pijoan, University of Minnesota expert on Haemophilus parasuis and Streptococcus suis, has done significant studies on how these two normal mucosal bacteria cause disease.
Pijoan explains that pigs don't always suffer disease when exposed to bacterial agents as young pigs. This is because of a process called colonization.
Pijoan theorizes that baby pigs get colonized with the bacteria while still under maternal protection, which would prevent the bacteria from invading the pig and causing disease.
Disease prevalence and severity has increased with the transition to off-site SEW. In older, conventional farms with continuous pig flow on the same site as the sow herd, baby pigs get infected very quickly from older animals.
Pijoan's work has shown that some disease-causing strains of Haemophilus parasuis and Streptococcus suis require late colonization in an older pig because of their low prevalence in sow herds. In order to produce disease from one of these bacteria, only a few pigs are infected, causing spread to non-colonized pigs in the nursery. A higher prevalence of the virulent or infectious strain of bacteria prior to weaning will not cause disease in the nursery.
Inoculation of baby pigs with live cultures of disease-causing Hemophilus parasuis has proven successful in some cases in reducing disease levels in nurseries. Caution needs to be exercised before trying these procedures, however. Weaning an older pig may play an important role in allowing natural colonization of these two potential pathogens prior to movement to off-site segregated production.
Recent outbreaks of postweaning multisystemic wasting syndrome (PMWS), potentially caused by porcine circovirus Type 2, have been difficult to control.
In certain areas of pig production, such as the United Kingdom and Quebec, Canada, significant nursery mortality has occurred with this disease syndrome. Severity also increases when PMWS cases in Quebec have been linked with the PRRS virus, according to new research presented at the 2005 Leman Swine Conference by Laura Batista, DVM, of the University of Montreal. Field experiences are indicating that increasing weaning age reduces the severity of pigs showing signs of wasting from PMWS.
|Disease||Maximum Wean Age, Days|
|Pasteurella multocida||8 to 10|
|Mycoplasmal pneumonia||17 to 21|
|Porcine reproductive and respiratory syndrome||0|
|Salmonella||14 to 16|
|Swine influenza virus||21|
There are still diseases such as Mycoplasmal pneumonia, atrophic rhinitis and Actinobacillus pleuropneumonia where weaning an older pig may cause an increase in disease prevalence if not properly medicated and vaccinated (Table 3).
Over the next few years, more individualized weaning strategies will be implemented based on recognized scientific methods of disease prevention. Certainly, weaning age will be a cornerstone of those strategies.
What to Look for When Buying Weaned Pigs
Many weaned pigs are purchased on the spot open market in North America today.
While spreadsheets may show potential profit for putting pigs on feed, developing a checklist of items to understand the health of the animals prior to purchasing is critical. This has been commonly referred to as a vet-to-vet consult.
It is important to note that in spite of a thorough investigation before purchasing pigs, unforeseen health problems can arise. Still, the industry standard is that pigs are purchased on an “as is” basis.
Review this checklist before purchasing weaned pigs:
Are the pigs being sold because of health problems, such as depopulation/repopulation situations?
How many different sites are the pigs coming from? Pigs can be represented as a single source from a “system” instead of from an individual site.
What are the demographics of the source site farm (size, location, population, facility type, genetics, pig flow and production data).
Who is the herd health veterinarian? Often, the system veterinarian may not see the sale animals. Talking with the local veterinarian may be important to understanding the pigs' health.
What health issues has the sow farm dealt with during the past two years?
Is testing being done to understand the porcine reproductive and respiratory syndrome (PRRS) status of the sow herd?
When was the last PRRS break?
What is the level of preweaning mortality? Scour problems could be an indicator of potential nursery problems.
What vaccination programs are in place?
Has the herd experienced a swine influenza virus break?
What is the Mycoplasmal pneumonia status of the sow herd?
What other diagnostic tests have been done?
What is the track record of this source of pigs? Get reference information on other pigs sold and fed recently.
What are the mortality rates in the nursery and finisher?
What health problems have been seen? Are there signs of respiratory, enteric, sudden death or central nervous system problems?
What have been the performance parameters for average daily gain, feed efficiency and cost per pound of gain?
What medications and vaccines have been used in the nursery and finisher?
Would the referral party buy these pigs again?
Finally, what are the average and range of age and weight of the pigs being sold?
|Weaned Pigs Purchased||Avg. Weight In||Avg. Weight Out||Feed:Gain||Feed Cost||Cost/Lb. Of Gain||Mortality||Days On Feed|
Many systems are now selling weaned pigs on a sliding scale with each additional pound over a base weight bringing $0.50 to $0.75/lb.
What does the purchase weight/age of weaned pigs mean to the physical health of the pig and the financial health of the producer? The average difference in weaning age can be as much as one day per ½ lb. of weight.
A review of two groups of purchased pigs that had a wide variation in purchase weights was conducted. Performance data from 2004 in the South Central Management Services (SCMS) database are summarized in Table 1.
An SCMS evaluation of purchased pigs suggests that weaning weight affects three key elements of production in the nursery:
Death loss on heavier pigs equals 0.85% less death loss.
Feed cost savings on a heavier pig is 1¢/lb. of gain.
Heavier exit weights equal significant financial value.