Thoughts on Cross-Fostering


By Thomas Long, PhD.,
Quality Control Manager,
Norsvin USA

Over the past few decades the US swine industry has made quantum leaps in the prolificacy of its sow herds. In the past, when people talked of production levels of 30 pigs/sow/year, they were considered “dreamers”. Today some top managed sow farms are achieving this level of production, and many more are pushing hard on this milestone. To achieve these levels of production the goal must be to wean as many good, healthy pigs as is possible, and a number of farrowing facilities have implemented a variety of Cross-fostering strategies in an attempt to achieve this goal. Although well intended, many of these strategies are counter-productive to this goal, and some management groups have implemented rules of no Cross-fostering within their farrowing facilities as a method to control over-Cross-fostering. However, there may be times when Cross-fostering may be needed. Examples of when it is needed include:

  1. Breeding department overbred for farrowing spaces available
  2. The conception rate on a group was better than planned for
  3. A sow dies during the birth process, but did produce some live pigs
  4. A sow stops milking (agalacia) early in lactation and no artificial rearing options are available
  5. There are a number of large litters born of good healthy pigs on sows with poor underlines such that these sows will not support these litters through lactation, but NOT just to “even out” litters

The purpose of this paper is to discuss some of the critical control points during early lactation that need to be considered by a production unit, to maximize the number of good, healthy pigs weaned.


How a sow is fed during gestation can affect how she milks in farrowing. A sow entering farrowing in a negative energy balance has the potential to be one of those sows who has her pigs and then does not eat much after farrowing, subsequently drying up. The last trimester of gestation is not the time to correct body condition on over-conditioned bred sows, and restricting their feed during this period can set them up for failure during lactation. Body condition on all gestating sows needs to be monitored weekly and any major feed adjustments made on specific sows needs to be made in the first or second trimester of gestation. Also, make sure each sow in lactation gets up every day and is eating. Remember she is the milking machine for her piglets, and their nutrition and survival is dependent on her eating and lactating optimally.


While perhaps seemingly straightforward, it is worth noting that the number of functional teats a sow has needs to be counted after she farrows. This establishes the upper limit of how many piglets the sow can nurse.


Every piglet needs to receive a good dose of colostrum within 24 hours of birth, preferably from its birth dam. Not getting colostrum before gut closure is a death sentence for the piglet. Some of the pre-weaning mortality seen in swine operations may be due to piglets in large litters being pushed off of teats while the colostrum is flowing, such that they receive suboptimal levels of colostrum. Split suckling is a procedure that can be used to help ensure the majority of piglets in large litters receive colostrum. It entails taking half the litter and putting it in a “hot box” under a heat lamp while the other half of the litter nurses. After ¾-1 hour, the two groups of piglets are switched. Both groups of piglets have reduced competition for teats and a better chance of getting a good suckle during the initial lactations when colostrum is flowing.

Also, colostrum is not just about antibodies. It also contains a number of growth factors (EGF, Insulin, IGF-1, IGF-2 and TGF-Beta, for example) that help develop the piglet in its first early days of life. How piglets get started in life can affect their immediate survival, but it can also affect subsequent performance in the nursery and finishing. Managers sometimes say they can’t afford the time and/or labor to implement this type of procedure in farrowing. The question should be “Can they afford not to implement such procedures?” given the large litter sizes we now have being born in the US.


Piglets having birth weights below 2 lbs. have a much greater risk of not surviving to weaning, or dying in the nursery, compared to piglets born with heavier weights. The graph below suggests a 2 lb piglet at birth has a 50/50 chance of surviving to weaning -- dropping off dramatically with piglets who weigh less. When considering Cross-fostering, managers need to consider if these small piglets will survive, or if they will take up resources in extra care and space in the farrowing crate that will result in no piglet produced at weaning. Whether these small piglets should be allocated the sow’s resources or whether they should be humanely euthanized needs to be determined at each farrowing.


The majority of Cross-fostering should be done within the first 1-3 days of life for the piglet. Some Cross-fostering may be needed in the middle of lactation if a sow’s udder dries up, but this should be the exception, rather than the rule. Some production units will continually cross-foster during lactation, moving piglets around, thinking they are improving chances for piglet survival and weaning weights. However, each farrowing crate needs to be seen as a micro environment, within the larger farrowing room environment and sow farm.

Each movement affects that micro environment and piglet growth within that environment. Work at Michigan State University has demonstrated that restricting Cross-fostering to the first two days of life improves weaning weight by 20% compared to a system where Cross-fostering occurs throughout lactation. If the goal is to raise more good quality pigs, it seems prudent to try and do all Cross-fostering within 1-3 days of birth.


Some units strive to even out all litters within a group to a single number nursing per litter, 12 pigs per litter, for example. The hope is to have more uniform piglets at weaning. While this might be a workable protocol in large units with minimal staff, as stated above, each farrowing crate is a micro environment and movement of a piglet to another litter/environment can be a stressful event impacting piglet growth rate. If a sow has 15-16 functional nipples and 12-14 piglets, leaving the piglets where they are may be the optimal solution. Implementing one rule for micro environments across a production unit might be less optimal than doing Cross-fostering on a sow by sow basis.


Vigorous, healthy piglets should be the candidates to cross-foster. Being moved from the birth environment is stressful on a piglet. Research at The Ohio State University has showed, when above average pigs, relative to vigor, were cross-fostered, they had better liveability and heavier weaning weights than non-cross-fostered piglets.

This research also showed that when average vigor pigs were cross-fostered they had poorer liveability and lower weaning weights than non-cross-fostered piglets. These results suggest that when selecting cross-foster candidates from large litters, strong, healthy piglets should be chosen. This should optimize performance in both the piglets that were crossfostered, as well as the piglets that remained with their birth dams.


pre-weaning and nursery survival

pre-weaning and nursery survival

Dr. Tom Long has more than 30 years of experience in swine genetic improvement programs and their implementation into production systems. After receiving his PhD from the University of Nebraska, he worked for 5 years in Australia with swine genetic improvement software for the Australian swine industry. He then spent 5 years on the University of Nebraska faculty in a Research and Extension position followed by 8.5 years with Smithfield Premium Genetics as a Geneticist and Genetics System Manager. He is currently the Quality Control Manager for Norsvin USA.