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Glen Almond, Kathryn Brightwell and Morgan Morrow
College of Veterinary Medicine
North Carolina State University
Raleigh, NC 27606


Most producers are cognizant of the various causes of neonatal or preweaning mortality. Our traditional classifications of the major categories of preweaning death include both infectious and noninfectious causes. Noninfectious mortality includes low viability (and weak) pigs, traumatic injuries (crushed and stepped on) pigs, starvation (colostrumdeprived and hypoglycemic pigs) and miscellaneous abnormalities such as congenital anomalies, shaker pigs and splayleg.

The most common classifications of death due to infectious agents included diarrheas, joint infections, central nervous system infections, greasy pig and pneumonia. Without diagnostic evaluations, these traditional classifications were considered adequate.

Risk Factors

Numerous risk factors contribute to the causes of neonatal mortality. Risk factors associated with the sow include breed, size, body condition and genetics.

Decreased milk production due to noninfectious causes or mastitis also increase the risk of pig death. Neonatal mortality is more common in large litters, litters with large variations in piglet size at birth or litters with pigs less than 2 lb. at birth.

Piglets have inherent risk factors that decrease their likelihood to survive to weaning. Most preweaning deaths occur in the first 1-3 days and a 2 lb. pig is more likely to die than a 5 lb. pig. Weak pigs at birth, i.e. pigs with low viability, rarely reach weaning age.

Farrowing house environment and facilities play major roles in neonatal mortality. Both the absolute temperature of the pigs' microenviroment and temperature fluctuations influence pig survival.

Hence, auxiliary heating devices, such as heating pads, heat lamps and other heaters are used (and misused) in farrowing crates. To decrease preweaning mortality, producers adjust the heights and positions of heaters and assess the response of the pigs to changing ambient temperatures. Table 1 summarizes the probability of an association between factors and different categories of causes of neonatal mortality.

Additional risk factors include:
air flow and drafts
moisture on floor surfaces
evaporative cooling
use of drippers
(type) use of cooling devices
auxiliary fans
fan capacity
air distribution
water delivery
water consumption
water quality
crate type
crate location in a room
crate side panels

Table 1. Association between factors and causes of mortality between birth and weaning in pigs (Adapted from Vaillancourt and Tubbs, Vet Clinics of North America: Swine Reproduction 1992; 8:685-706).

Preweaning Mortality
Factors Low Viability Trauma Scours Infection
Age 0-3 days 0-3 days 1-3, > 10 days > 10 days
Animal Factors .
Birth weight +++ ++ + +
Litter weight +++ +++ ++ ++
Duration of Farrowing +++ +++ ++ +
Parity +++ +++ +++ ++
Environmental Factors .
Temperature +++ +++ +++ ++
Equipment +++ ++ + -
Floor type ++ + + -
Season ++ ++ ++ +
Management Factors .
Nutrition/feeding +++ + ++ -
Crossfostering +++ + ++ -
Induction +++ ++ - -
Attendance at farrowing +++ +++ + ++
Piglet processing + + + ++
Medical treatment - - + +

Management of the farrowing house often is taken for granted; however, certain people are exceptional at managing the sows and piglets. One component of effective management is the crossfostering program.

Original Recommendations for Crossfostering and Nurse Sow Utilization

Many, if not all, recommendations for crossfostering were based on studies conducted by Peter English in the UK. Fostering of piglets was viewed as a necessity and was based on the observations that malnutrition or starvation was the single most important cause of pre-weaning deaths, chilling contributed to piglet deaths and the competition for teat positions and teats by baby pigs.

The primary "achievements" of effective crossfostering were:

reduced risk of chilling or hypothermia
improved resistance to prevailing disease problems
reduced risk of malnutrition
reduced pre-weaning mortality
English developed ten basic principles of successful fostering:

Prepare piglets for fostering. Ensure colostrum intake before fostering.

Foster promptly. Foster immediately after colostrum intake.

Be kinder to smaller, weaker pigs. Fostering is based on the best interests of the weaker pigs. Move the stronger pigs, if the weak ones will do better with the original dam. If weaker pigs are fostered, select a recently farrowed sow with a small litter of small piglets.

Assess rearing capacity when deciding on fostering. This takes into account the number of functional teats and the number of those exposed to piglets at nursing.

Even up birth weights within litters by crossfostering. To be used with batch farrowing. Small piglets go to a docile dam with fairly slender teats of medium length and at the appropriate height for suckling by small piglets.

Use suckling behavior to guide fostering of older piglets. To be used when piglets are 8 or more hours old at the time fostering. Piglets which do not have a settled teat are the ones to be moved. Conversely, a small piglet in a litter of large piglets, which has a stable suckling position is best left where it is.

Make arrangements for a surplus of newborn piglets. Foster the largest of newborn pigs on to a docile, good milking sow which has farrowed 1 week previously. In turn, the 1-week old litter can be fostered on to a docile and milky sow (i.e., nurse sow) weaned at the normal stage. Leave one or two of the smallest of her piglets for up to 24 hours.

Colostrum sharing soon after birth. In the case of large litters, without an available recipient sow, move 9-10 of the largest piglets into a warm heated area away from the sow for 2 hours. This allows the small pigs an opportunity to suckle colostrum.

Cater for ill-thriving pigs in older litters. Individual piglets which are ill-thriving in older litters because of malnutrition rather than disease can be fostered to newly farrowed sows. Match pigs in size and strength.

Unused mammary glands take 3 days to dry off. Surplus, newborn pigs can be fostered to a sow which has farrowed up to 3 days previously. In this case, the stronger pigs are moved, not the smaller ones.
These principles have been modified, contorted and changed by farrowing house personnel. Piglets often are fostered with little planning. Considerable knowledge of piglet and sow behavior and excellent pig husbandry skills are required for effective fostering. The best written guidelines are often misinterpreted or ignored.

Effects of Crossfostering on Pig Performance

Few prospective studies with appropriate controls have been conducted to examine the influence of crossfostering on pig performance prior to and after weaning. One study (Neal and Irvin, 1991, J. Anim. Sci.) determined the effects of crossfostering pigs on survival and growth.

Crossfostered pigs were compared to pigs raised by the foster dam; however, the performance of non-fostered pigs in litters from which fostered pigs were taken, was not evaluated. Only first parity sows were used in the study and all pigs were crossfostered with 48 hours. Recipient litters received pigs of similar age and weight. Birth vigor of piglets was scored by subjective evaluation. Results of this study are given in Table 2.

Table 2. Effects of crossfostering on selected pig traits (Adapted from Neal and Irvin, 1991).

Unadjusted for birth vigor Adjusted for birth vigor
Trait NC C NC C
Birth wt (kg) 1.45 1.48 1.47 1.43
21 d wt (kg) 5.09 4.99 5.08 5.00
Weaning (42 d) wt 10.22 10.10 10.21 10.11
Survival to 21 d 75% 86% (.01) 80% 75% (.10)
Survival to weaning 74% 83% (.05) 79% 72% (.05)
NC = Non-crossfostered, C = fostered
Values in parentheses are p-values for differences between NC and C.

Growth of a small subset (n=46) of the crossfostered pigs was compared to growth of non-fostered pigs (n=764) from weaning to 100 kg.

There were few differences between the groups. Some of the obvious questions regarding this study are; How many farms wean at 42 days? What happened to the non-fostered pigs on orphaned sows? What happens with older parity sows? The final conclusion was that crossfostering pigs of greater vigor at birth negated the detrimental effects of crossfostering on survival. One final comment on this report - it failed to indicate any disease problems, which is surprising considering the high preweaning mortality.

Published reports can be misleading.

We recently conducted a preliminary trial at the Unit II Swine Educational Facility (NCSU). Pigs were weighed at processing (day after birth) and at 14 days after birth. Crossfostering typically occurred within 48 hours of birth.

Table 3. The effect of crossfostering on pig weights at 14 days after birth.

Group N Wt (lb) at Processing Wt (lb) at Weaning Mortality
CF 44 (50)* 3.1 + 0.06 8.8 + 0.16 12%
N 222 (251) 3.3 + 0.02 10.1 + 0.06** 11.5%

CF = Crossfostered pigs, N = non-fostered pigs.
* Numbers in parentheses is the initial number of pigs in the group.
** Crossfostered pigs weighed less (P < 0.05) than non-fostered pigs at 14 days.

These results could be interpreted several different ways. Initially, it would appear that crossfostering resulted in lighter pigs at 14 days. Conversely, the argument would be that these pigs would have died or not gained weight if they were not fostered. Few, prospective studies have been conducted to examine the influence of fostering on piglet performance.

What are the crossfostering "trends" in North Carolina sow herds?

Most producers record the number of pigs added or removed from sows. Using PigChampR records from 14 farms, the following tables illustrate the movement of piglets on sow farms.

Table 4. Crossfostering in fourteen North Carolina sow farms for a 2-year period.

Parameter Mean SEM Range (by farm)
Litters 6082 1192 815 to 19,575
Pigs born live/litter 10.1 0.11 9.43 to 11.04
Preweaning mortality 14.12 0.71 8.53 to 18.99
Disrupted litters (%) 74.2 2.64 55 to 86
Multi-foster litters* (%) 36.8 3.9 4.5 to 65
Multi-day foster litters* (%) 31.8 4.1 3.7 to 60
Mortality intact litters (%) 2.16 0.35 0.6 to 4.8
Mortality disrupted litters (%) 18.58 1.34 11.03 to 29.6
*The percentage of multi-foster or -day litters is in respect to the number of disrupted litters.

Table 5. Net-foster of pigs between different parity sows.

Parity Mean SEM Range
Parity 1 950.7 203 -215 to 2112
Parity 2 276.1 841 -104 to 1075
Parity 3-6 -1178 300 -4496 to 32
Parity > 6 -249 99 -1240 to 69

As mentioned previously, there is more than one way to interpret the findings of this retrospective report. It demonstrates that most producers generally move pigs from parity 3-7 sows to parity 1 and 2 sows. Older parity sows have greater numbers of pigs born than parity one or two sows. Consequently, the pigs are moved to younger parity animals. Litters that remain intact have extremely low preweaning mortality.

This low mortality in the intact litters probably indicates that the sow and litter are perfectly matched and that no problems existed. From the data, it is evident that the majority of sows and/or litters have problems.

In summary, it is clear that most pork producers crossfoster most of their pigs. Sometimes the crossfostering is well-planned and conducted by exceptional farrowing house personnel. Other times, crossfostering looks completely random.

Most of this discussion omitted the impact and role of diseases on neonatal mortality and crossfostering. Disease situations, such as TGE and PRRS, create unique and challenging factors that need to be considered for a crossfostering program.

Take-Home Message

Most neonatal mortality is due to non-infectious causes.
Plan your crossfostering program according to the level of expertise and knowledge demonstrated by farrowing house personnel.
Re-evaluate crossfostering programs when neonatal diseases are present.