Gestation length in dogs and cats is approximately 63 days from the day of ovulation (Rickard, 2011). In unneutered cats, promiscuous behaviour, coupled with unrestricted access to an outdoor environment, often leads to unnoticed matings and inaccurate due dates. In dogs, determining gestation length is further complicated by the variability in the window of fertilisation. In dogs, determining gestation length is further complicated by the window of fertilisation. As a result, a due date of 57-73 days post mating is not unreasonable to consider, and a seemingly late 70 days gestation could in fact be a normal pregnancy (O'Dwyer, 2015).
Progesterone testing is a useful tool when a breeder presents with a bitch thought to be overdue. Progesterone levels decline transiently towards the end of pregnancy, with a significant drop below 2 ng/ml occurring approximately 24 hours before whelping (Smith, 2011). A progesterone level below 3 ng/ml is generally considered safe for delivery, while a level below 1 ng/ml necessitates delivery within 24 hours to improve pup viability (Greer, 2014). Pregnancies with more than five days remaining typically have progesterone levels exceeding 5 ng/ml (Greer, 2014). Progesterone testing, alongside clinical examination, is an effective method for determining whether a bitch requires a caesarean section due to apparent delayed whelping.
In queens, this method is unreliable as progesterone levels can exceed 6 ng/ml on the day of parturition (Roos, 2022).
Identifying preterm neonates
Certain breeds tend to give birth several days early while still producing fully formed neonates. Smaller breeds commonly produce immature puppies (Figure 1), even after a full-term pregnancy (Bloomfield, 2013a).
Occasionally, a litter may include a neonate that appears significantly less developed than the rest. This is more pronounced than a typical ‘runt’ and, in some cases, these neonates may not be viable. Such individuals are often the result of poor implantation within the uterus, typically in a thin, less vascular area. This reduces placental blood supply, restricting the fetus's access to nutrients throughout development. Other factors, such as illness, infection or stress in the dam, can also impede fetal development, leading to seemingly premature offspring despite a full-term pregnancy (Bloomfield, 2013b).
Puppies and kittens born in this way (Figure 2) are referred to as small for gestational age (SGA). For cases that are not truly premature, where maternal factors are involved, the terms ‘immature’ or ‘undeveloped’ are more appropriate. As a result of these differing causes, visual examination of neonates is more reliable than using apparent due dates to determine maturity. Low birth weight and lack of fur—particularly around the face and legs—are the most obvious signs of immaturity. These neonates often have a ‘jelly baby’ appearance rather than resembling a fully furred newborn.
Recognising a puppy or kitten that is premature or small for gestational age involves identifying specific signs and characteristics:
- Low birth weight: kittens should weigh more than 85g at birth. Those below 85 g are considered underweight, and those below 75 g are unlikely to survive. Puppy birth weights are breed-dependent
- Appearance: skinny or wrinkled
- Fur development: lack of fur on the feet, legs, abdomen, chest, face, or, in some cases, the entire body (Figure 3)
- Righting reflex: absent righting reflex (inability to roll onto their front when placed on their back)
- Suckle/swallow reflex: absent or weak
- Behaviour: lack of vocalisation or rooting behaviour when stimulated
- Temperature regulation: inability to maintain normothermia without increased environmental temperatures (32–36°C based on the author's experience).
Initial treatment of premature or small for gestational age patients
Ordinarily, the survival rate of neonates is better when they are cared for by their dam. However, premature neonates require nursing intervention, as many lack a strong suckle reflex and the ability to swallow effectively. Those who appear to be suckling may lack the strength to draw sufficient milk or the stamina to feed for an adequate duration. Milk may bubble from their nose and mouth as they struggle to swallow, often unsuccessfully. Furthermore, the energy expended in their attempts to feed can be detrimental, contributing to hypoglycaemia.
Premature neonates are at an increased risk of hypoglycaemia because of inefficient hepatic gluconeogenesis, decreased adipose tissue, and elevated metabolic demands associated with their comparatively larger brain size (Abramowski et al, 2024). Oral glucose supplementation is typically the most practical approach to manage hypoglycaemia in these cases, given the difficulty of venous access.
If neonates appear to be suckling successfully and the dam is lactating, an attempt can be made to keep them with her. However, extreme vigilance is required to ensure they remain active, continue to suckle and stay warm.
It is essential to weigh premature neonates several times a day to monitor for appropriate weight gain. Maintaining their body temperature between 35 and 37°C and ensuring they produce urine and faeces should also be closely observed. If the dam is producing milk but her young are weak, her milk can be hygienically expressed into a sterilised container, refrigerated and used for feeding. This approach ensures the transfer of passive immunity, which can also be achieved by administering plasma or serum via a feeding tube (The National Kitten Coalition, 2023).
The author recommends administering plasma or serum on an empty stomach to avoid interference with its composition (Figure 4). Neonates older than 24 hours can no longer absorb antibodies through the gastrointestinal tract, requiring administration via subcutaneous or intravenous routes.
Fewer than 5% of maternally-derived antibodies are transferred through the placenta in puppies and kittens (Rickard, 2011). The ingestion of colostrum is particularly critical in cases of prematurity, where the immune system is further compromised. Additionally, as with all neonates, premature individuals must be barrier nursed in a practice setting because of their heightened susceptibility to infection. Strict hygiene protocols, cold sterilisation of all feeding equipment and isolation from other animals should be implemented.
Hand-rearing a premature neonate
If it has been established that the young require hand-rearing, supportive care and treatment, alongside basic hand-rearing principles, should be applied. These additional measures not only enhance their viability but also improve their quality of life during the fragile days and weeks ahead. Most premature paediatric patients will require tube feeding initially (Figure 5) until they develop strong suckle and swallow reflexes. Some may only need assisted feeding for a few days and may then be strong enough to return to the dam's care, provided she is accepting and lactating.
Tube feeding can be demonstrated to owners wishing to hand-rear themselves. However, it is important to note that premature neonates are unlikely to vocalise, which can be disconcerting for those who use the method of squeezing an ear or foot to elicit a cry, which establishes the tube has been placed in the stomach, rather than the lungs. Newborn puppies and kittens may also lack a gag or cough response, meaning they might not react to an incorrectly placed feeding tube. If there is any doubt about tube placement, the feed should not be given.
Support of the respiratory system and other organs
A significant factor contributing to mortality in premature neonates is underdeveloped lungs, specifically a lack of surfactant, which is produced in the final days of gestation. Surfactant is the fluid that allows the alveoli to remain open, preventing atelectasis. Additionally, surfactant plays a role in the immune response and pathogen defence (Chroneos et al, 2009). In its absence, each exhalation causes the alveoli to collapse, leading to airway closure and oxygen depletion (NHLBI, 2018). Dyspnoea develops as the neonate takes deeper breaths in an attempt to inflate the lungs. Eventually, the neonate exhausts its energy reserves trying to breathe.
Neonates with underdeveloped lungs may benefit from oxygen supplementation to preserve energy and meet oxygen demands. However, prolonged oxygen use can be counterproductive, reducing pulmonary function as a result of oxygen toxicity. General guidelines recommend using a fraction of inspired oxygen (FiO2) greater than 0.6 (equivalent to 60% oxygen) for no longer than 24 hours (Mosley, 2015).
Steroids such as betamethasone have been widely administered as a prenatal precaution in humans and tested in animals. This treatment is pre-emptive, as it takes 2–7 days for the steroid to be most effective. In practice, however, most premature neonates present after birth, making steroid administration potentially futile and accompanied by risks. Steroid use in young animals has been linked to behavioural abnormalities and altered endocrine function. Additionally, administering pharmaceuticals to premature neonates must be approached with caution because of their reduced liver and kidney function. The liver's ability to eliminate toxins is compromised, and the kidneys have limited capacity to regulate electrolytes and acid-base balance (Aarnes, and Muir, 2011).
Nevertheless, natural surfactant production can be encouraged by nebuliser treatments and maintaining higher levels of environmental humidity (Figure 6). Humidity levels above 80% should be avoided, as they can lead to congestion and promote bacterial growth (Bloomfield, 2013). Spaulding (2023) recommends humidity levels of approximately 60% for premature neonates. From a respiratory perspective, maintaining humidity helps to keep airways open and alveoli functional, preventing airway collapse until natural surfactant is produced.
The author advocates using F10 antiseptic solution (F10 Products) in nebuliser treatments, as it is commonly used to treat respiratory infections. This approach aims to promote a healthy respiratory environment, reducing susceptibility to infection (F10 Products, 2024). Some incubators include built-in humidity, oxygen and nebuliser functions, making this management strategy more achievable.
Thermoregulation
An incubator is essential for vulnerable neonates, who are particularly susceptible to draughts and airborne infections. Full-term neonates are born with a layer of insulating brown fat, which aids in heat retention. In contrast, those born prematurely or underdeveloped lack this fat reserve and can become chilled within seconds. The author recommends an incubator capable of maintaining a constant ambient temperature of 32–36°C for these neonates, ensuring optimum core body warmth (Table 1).
Table 1. Some neonates require higher or lower incubator settings based on factors such as breed, body condition and health
| Puppy age | Incubator temp °C | Kitten age | Incubator temp °c |
|---|---|---|---|
| Premature | 32-36.5°C | Premature | 32-36.5°C |
| <7 days | 29.5-32.5°C | <7 days | 30-32.5°C |
| 8-12days | 26.7-28°C | 7-10 days | 29.5°C |
| 2-3 weeks | 24°C | 14 days | 26.6-29.5°C |
| 4-weeks | 22.5°C | 4 weeks | 22.5°C |
A heat pad that provides surface heat is insufficient to support thermoregulation in these patients and may also impair their ability to digest nutrients. Heat lamps, meanwhile, create a drying atmosphere that reduces humidity and contributes to dehydration. In the author's opinion, neither of these methods can provide the consistent and controlled temperature environment that an incubator offers.
Microwave heat pads, such as the Snuggle Safe, are valuable during feeding times. They can be wrapped in a blanket and used to maintain the neonate's body temperature, reducing the risk of chilling during the brief periods they spend outside the incubator. Time outside the incubator should be minimised wherever possible.
Supporting the digestive system
Retarded digestive function is a significant concern in neonatal immaturity, with reduced peristalsis being a common finding. As discussed, premature neonates are often hypothermic, which substantially increases their susceptibility to ileus. Consequently, bloating, constipation and diarrhoea are common issues.
These conditions may lead to necrotising enterocolitis (NEC), also referred to as ‘leaky gut syndrome,’ which is a leading cause of morbidity and mortality in preterm infants (Monzon, 2023). An underdeveloped digestive system struggles to adapt to changes in blood flow when nutrition is introduced. This can result in inflammation of the intestines, bacterial colonisation and weakening of the intestinal walls, leading to leakage of their contents. The underlying causes of NEC remain unclear; an animal study highlighted that much about this condition is still unknown (Won, 2023).
As a precaution, the author recommends initially feeding small amounts of pure rehydration fluid supplemented with liquid glucose to accustom the neonate's stomach to nutrition gradually. Spaulding (2023) supports this approach when rearing premature neonates, clarifying that nutrition should not be introduced until the neonate is normothermic. Formula is then introduced incrementally to reduce the likelihood of NEC in critical neonates. The author also uses a mixing ball—commonly used for preparing smoothies—to dissolve larger particles, which may be challenging for neonates to digest. While this may seem excessive, the liver in premature neonates has minimal capacity to produce the enzymes required for digestion (The National Kitten Coalition, 2023). This limitation impedes protein synthesis, so smaller particles are easier for neonates to digest.
Premature neonates are also prone to dehydration as a result of impaired renal function. This can be managed effectively with subcutaneous fluid administration, which minimises strain on their digestive system. Additionally, a high-quality prebiotic and probiotic can help support a healthy gut environment. Any probiotics should be added to the formula immediately before feeding, as leaving them for extended periods may result in fermentation.
Development
Premature puppies and kittens are expected to develop and grow at a slower rate and should be treated according to their developmental stage. For example, a kitten born 10 days premature should be treated as a newborn at 10 days of age. Subsequently, milestones such as opening of the eyes, teething, mobility and weaning will be delayed (Figure 7).
As the kitten or puppy gains strength and develops in a manner typical of hand-reared animals, the transition from tube feeding to teat feeding can begin. This process may seem daunting after relying on tube feeding; however, it will soon be seen as the safer option. A 1–2 ml syringe attached to a teat provides the lowest milk flow and the least risk of aspiration. If the neonate takes to the teat well, it is possible to progress to a 2–5 ml syringe, depending on their size and strength. Syringes with a rubber plunger often do not require depressing if the neonate is suckling well, allowing them to regulate their own milk flow. A bottle can be used once a strong suckle has been established, but care must be taken when setting the flow of a bottle. The bottle should be tipped before feeding to ensure milk is not free-flowing (some brands have pre-set holes that are too large for most paediatric patients). It is far better for the hand rear to maintain full control over milk flow and express milk manually rather than allowing it to drip uncontrollably, which may flood the neonate's mouth.
Weaning can be the easiest or the most challenging phase of the rearing process. Premature neonates take significantly longer to wean, and their development will be delayed, so this stage should not be rushed. The dental development of a hand rear provides a reliable indicator for the appropriate introduction of weaning (Shaw, 2024). Typically, this occurs when the premolars emerge in kittens and when the incisors appear in puppies. If there are concerns about progress because of weight loss or delayed weaning, a calorie supplement such as Nutri-Cal (Vetquinol Care) can be added to the formula until weaning begins. Once weaned and thriving, vaccination protocols should be resumed, albeit postponed until the juvenile reaches the age at which they would typically receive vaccinations if born full-term.
Conclusions
Deciding to treat or hand rear a premature puppy or kitten is certainly a decision to be approached with careful consideration. This endeavour requires significant commitment and necessitates additional equipment, time, energy and vigilance, particularly in cases where hand rearing is involved. It is possible that ultimately, despite all efforts, the situation may result in disappointment due to their low viability. Owners should be well informed of the challenges if they choose to undertake the responsibility of rearing themselves. Even with an experienced rearer, the likelihood of success remains low, and it is short-sighted to entrust someone who may approach the task with a lack of commitment or who may resort to shortcuts.
More knowledge is being gained from rearing such cases, which brings hope to similar scenarios that may be seen in practice. Much like premature humans, there is ongoing insight and discovery into the care of paediatric patients. Cases seen as non-viable previously can be supported through to being healthy juveniles with no evidence of abnormality, and have the potential to live a healthy life at full life expectancy. The cause of immaturity, whether it is because of early labour or an inadequate implantation site within the uterus, will influence the likelihood of the individual achieving the typical growth and size associated with their breed. Figure 8 shows a kitten that was born approximately 10 days premature, yet achieved full breed potential in regards to her health and size.
KEY POINTS
- Gestation length is unreliable for assessing prematurity; progesterone testing aids overdue pregnancy evaluations
- Premature neonates often display low birth weight, absent reflexes and underdeveloped fur or features
- Premature care requires maintaining warmth, assisted feeding and vigilant monitoring for hypoglycaemia and dehydration
- Underdeveloped lungs increase respiratory risks; oxygen supplementation and humidity aid survival
- Gradual nutrition introduction prevents gastrointestinal issues; formula is adjusted as neonates develop digestive capacity.