Introduction

The neonatal period is a major risk period in the dog, since approximately 20% of live-born puppies die before they are 21 days old; 70% of deaths are in the first week post-partum 12. Puppy survival within the early weeks is particularly dependent on colostrum, a specific secretion of the mammary gland produced during the first two days post-partum. Colostrum is both a source of nutrients and a source of immunoglobulins (Ig), as puppies are almost agammaglobulinemic at birth. The risk of neonatal mortality therefore depends on two factors: the quality of the transfer of passive immunity (evaluated by circulating IgG levels at 2 days of age) and the growth of the puppy between birth and 2 days old (at worst, weight loss should not be more than 4% of birth weight) 34. The immunity and energy supplied to the puppy by colostrum is therefore essential, but there is no guarantee that all puppies in a litter will receive sufficient colostrum; at two days of age, about 20% of puppies have a passive immunity deficit and 30% show insufficient early growth 34. 

Colostrum formation and composition

Colostrum is the first mammary secretion produced after delivery (and is occasionally present before parturition), with the transition to milk occurring between day two and three of lactation (Table 1). The actual quantity of colostrum produced by a lactating bitch is unknown.

Trypsin inhibitors are also found in the colostrum (but not in the milk), reducing degradation of colostral Ig and potentially increasing its absorption by the newborn 14. Colostrum also contains antimicrobial factors (such as lactoferrin and lysozyme), hormones (cortisol, thyroxine, insulin and growth hormone) and growth factors (e.g., insulin-like growth factors, epidermal growth factor and nerve growth factor 15. These are involved in the development and maturation of various organs such as the thyroid and intestines, as well as being vital for general puppy growth (see below).

Canine colostrum has high levels of two enzymes, gamma-glutamyl transferase and alkaline phosphatase, respectively 100 times and 10 times more concentrated than in maternal serum 16. These two chemicals are essentially absent from the circulating blood at birth, and so detection of these enzymes in a puppy’s serum will confirm ingestion of colostrum (although the enzyme levels do not correlate to the IgG concentration). 

Finally, canine colostrum also contains various cells including macrophages, neutrophils and lymphocytes. These cells are absorbed by the puppy before the intestinal barrier closes, and either enter the circulation, or play a role in cellular, humoral or local digestive immunity 17.

Roles of canine colostrum

• Firstly, colostral IgG decreases rapidly in the first few hours post-partum.

• Secondly, the rapid closure of the intestinal barrier; this is the point at which macromolecules (including IgG) can no longer cross the intestinal wall to enter the bloodstream, so that while a puppy absorbs ~ 40% of ingested colostral IgG at birth, only 20% is absorbed four hours after delivery and 9% twelve hours after delivery. 24 hours post-partum, absorption is nil 20.
  
   

The immunological quality of the colostrum, in terms of IgG concentration, is quite variable, both between female dogs and between teat pairs of the same female (Figure 3). In one study looking at the colostrum of 44 female dogs from 13 different breeds in a single breeding kennel, the IgG levels varied between females by a factor of 5; neither the dam’s age or breed size, nor the litter size, appeared to influence the colostrum’s immunological quality 12. The IgG concentration in 180 samples from different teat pairs varied between 0.8 and 61 g/L, with a variation coefficient of 42% between teat pairs of the same bitch 12. However, the teat pair producing the highest-quality colostrum varies from one animal to another, so there is no value in advising puppies should suckle from one particular teat. Nevertheless, the marked variation in immunological quality between dams (and between the teats of the same female) may mean that certain litters have an increased risk of neonatal mortality. 

The colostrum supplies most of the IgG for systemic immunity, while IgA ensures local and digestive immunity, and in particular mucosal immunity. Colostral IgA is involved in local defense of the digestive tract and this role is continued with the ingestion of milk, which is rich in IgA. Other than the fraction absorbed into the bloodstream before closure of the intestinal barrier, IgA is distributed throughout both digestive and non-digestive mucosal sites 2023. 

Although transfer of maternal Ig helps reduce neonatal mortality, at the end of the pediatric period, when a puppy is 6-8 weeks of age, maternal immunity can interfere with puppy vaccination. The higher the IgG concentration acquired by two days of age, the higher it is during the pediatric period 24, and this increases the risk that a puppy may not be protected after vaccination. However, the interference is variable, being dependent on the individual animal, the immunogenicity of the vaccine, and the dose given.

The energy value of colostrum is at least 20% greater than milk, although the energy content can vary between dams (albeit within a fairly small range, by a factor of 1.6) and there can be slight differences between teat pairs of the same dog (a variation coefficient of around 8%, as opposed to 42% for the immunological value). Age, breed and litter size have not been shown to affect the energy value. 52% of the energy supplied by the colostrum is protein and 40% comes from lipids; variations in the energy value are principally explained by variations in the lipid levels 25.

Whilst the immunoglobulins and energy supplied from colostrum influence the risk of puppy mortality during the neonatal period 34 it is interesting to note that the immunological quality and energy value of colostrum are not correlated 28. In addition, the quantity of average colostrum that must be ingested for satisfactory immunity is 1.3 mL per 100 g of puppy body weight (assuming the puppy’s IgG serum levels reach 2.3 g/L, with a digestive absorption rate of 40%, a hematocrit of 35%, and IgG levels in the colostrum of 20 g/L). In contrast, the average quantity of ingested colostrum required to cover energy needs is much higher, at 12 mL per 100 g of puppy body weight (energy need of 212 kcal/kg per day if the colostrum supplies 1800 kcal/L).

Although it seems much more difficult to cover the energy need than the immunological need, a slightly higher proportion of puppies are deficient in energy (30%) than in Ig (20%) (Figure 5). Whilst the threshold levels of colostral IgG and energy required to control neonatal mortality have been determined in some species, they are currently unknown for the dog.

Organ development 

In addition to growth, colostrum is also involved in the development and maturation of certain organs, in particular the digestive tract. This is linked to colostral hormones and growth factors. One study reported that puppies fed colostrum had gastrointestinal tracts 60-95% better developed when compared to puppies of the same body weight given a synthetic milk formulation 26, although other studies do not consistently observe this 27. 

Induction of colostrum production and release

Sometimes a dam produces little or no colostrum at birth or immediately post-partum. This agalactia may be as a result of premature birth, cesarean section, endotoxemia or malnutrition, but it is most commonly due to post-partum stress, particularly in primiparous females. A quiet, calm area should always be provided at whelping, and in some cases medication may be recommended for anxious dams to encourage colostrum production (Table 2).

Alternatives to colostrum

When the dam is absent or does not produce enough colostrum, it is essential to source a substitute in order to limit neonatal mortality. At the very least an energy supply must be provided for the puppies, but a supply of immunoglobulins is also desirable. The ideal scenario is to have another bitch who has given birth less than 2-3 days previously, and either make her adopt the puppies or draw colostrum from her to administer to the puppies. If an adoptive dam whelped more than 2-3 days previously, her milk will ensure sufficient energy supply (since the energy value of milk is only 20% less than that of colostrum), but the supply of IgG will be insufficient: milk contains only 1-2 g/L of IgG compared to 20 g/L in colostrum, so a puppy will require 13-26 mL of milk to supply the same quantity of IgG obtained from 1 mL of colostrum. Data is not available for puppies, but kittens fed with milk from a foster cat had no significant transfer of IgG 28. Formula milks are void of canine immunoglobulins and have an energy concentration of about 1 kcal/mL (i.e., half that of colostrum) 29 and so again ensure a nutritional supply but no immunological supply. 

Conversely, serum drawn from an adult dog will contain immunoglobulins, but at a concentration around 3 times less than that of colostrum, and will have only a limited energy value. Trials administering canine serum orally at birth to puppies deprived of colostrum showed an increase in circulating IgG, but at a much lower level than that obtained from standard colostrum 1819.

However, one study 18 showed that oral administration of canine serum at birth to puppies deprived of colostrum did result in reasonable IgG levels. This suggests that, in some puppies at least, administering serum may ensure that the minimum protective IgG concentration (i.e., 2.3 g/L) is reached.

Currently bovine colostrum as a source of heterologous immunoglobulins is of interest, as it is easy to collect and readily available, but it has yet to be evaluated in puppies for its immunological or nutritional value. Another source of abundant Ig is IgY (from immunized hen eggs), with recent work showing that serum containing specific antibodies against canine pathogens (E.coli and CPV2) obtained from hyper-immunized eggs can be administered to puppies to provide immunity; the authors trialed administration of oral IgY to puppies before closure of the intestinal barrier and obtained promising results in terms of overall health, with improved growth over the first three weeks of life (unpublished data). 

In the absence of an ideal substitute, the only solution currently available is to establish a colostrum bank, as currently practised for cattle and horses. Breeders can draw milk from a bitch on the second day post-partum (which ensures her own puppies have acquired passive immunity). Generally, milking a lactating bitch is easy; after cleaning the skin with a chlorhexidine-based soap the colostrum can be collected in small-volume plastic tubes and frozen (Figure 6). Small quantities of colostrum can then be thawed (at 37°C (98.6°F); under no circumstances should a microwave oven be used) as necessary and administered by bottle or feeding tube at a dose of 1.5 mL per 100 g of puppy body weight per day. 

Conclusion

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