Rethinking Neonatal Assessment: Why Birthweight Still Matters Most

Neonatal survival in canine practice is not determined at the moment of birth alone. It is the culmination of intrauterine development, maternal health, and fetal growth. A well-developed fetus enters the world with the physiological maturity required to adapt to extrauterine life, while compromised intrauterine growth often translates into immediate postnatal challenges. Among all measurable parameters available at birth, neonatal bodyweight (NBW) remains one of the most reliable indicators of both maturity and survival potential^1,2,3,4. 

Interpreting Birthweight in Clinical Context 

In routine practice, NBW is often interpreted relative to adult bodyweight within the same breed size category. Small breeds typically show NBW ranging from 2.5% to 5% of adult weight, medium breeds from 1.7% to 2.5%, and large to giant breeds between 1% and 1.7%¹. While these ranges provide a general framework, they are often insufficient in clinical settings due to the extreme variability across breeds. A puppy that appears small in one context may be physiologically appropriate in another, making isolated interpretation unreliable. 

This variability becomes clinically significant because low birthweight has consistently been associated with increased neonatal mortality, particularly within the first week of life^1,5. For veterinarians, this reinforces the need to move beyond visual assessment and adopt a more structured approach to evaluating neonatal size. 

Determinants of Neonatal Bodyweight 

Neonatal bodyweight is influenced by multiple interdependent factors, beginning with maternal bodyweight. Heavier dams tend to produce heavier puppies, reflecting the influence of maternal physiology and uterine capacity. Gender also plays a role, especially in larger breeds where sexual dimorphism is evident even at birth, with female puppies often weighing less than males. Litter size further complicates interpretation, as larger litters typically result in smaller individual puppies due to intrauterine competition¹. 

These variables highlight a critical clinical challenge: NBW cannot be interpreted in isolation. Instead, it must be contextualized within maternal and litter-related factors to accurately assess neonatal risk. 

Limitations of Traditional Reference Methods 

Over time, several methods have been proposed to define low birthweight, including breed-specific reference ranges, litter-based quartiles, and growth curves. While scientifically valid, these approaches are often limited in their practical application. They tend to be highly specific to particular breeds or populations and require data that may not be available in everyday clinical practice. Given the vast diversity in canine breeds, with adult bodyweights ranging from under 2 kg to over 100 kg, a universally applicable system remains a necessity ^1,6. 

A Practical Shift Toward Maternal-Based Evaluation 

A more clinically adaptable approach involves evaluating neonatal bodyweight relative to maternal bodyweight, expressed as N-MBW%. This method offers a practical advantage by removing breed dependency and allowing veterinarians to assess neonatal adequacy using readily available data. It simplifies decision-making without compromising clinical accuracy¹. 

Importantly, evidence shows that neonatal survival within the first week is significantly influenced by this ratio. Puppies with lower N-MBW% are more likely to experience early mortality, whereas those within expected ranges demonstrate better survival outcomes across all size categories¹. 

Clinical Implications for Early Decision-Making 

The first week of life represents the most vulnerable period for canine neonates, with mortality rates reported between approximately 7% and 25% depending on breed and conditions¹. During this time, early identification of at-risk puppies can significantly alter outcomes. 

In practice, this means that birthweight should not be recorded merely as part of documentation but actively used to guide intervention. Puppies falling below expected thresholds relative to maternal size should be considered high-risk and monitored more closely from the outset. 

Bridging the Gap Between Measurement and Care 

One of the persistent challenges in neonatal medicine is delayed intervention. Clinical deterioration in neonates can be rapid, and by the time overt signs appear, the opportunity for optimal intervention may already be reduced. Incorporating NBW into early assessment allows veterinarians to anticipate complications rather than react to them. 

This approach also supports better communication with breeders, enabling them to understand which puppies require additional attention and why. In settings where veterinary supervision during parturition is limited, this knowledge becomes even more critical¹. 

Conclusion 

Neonatal bodyweight remains one of the simplest yet most powerful tools available to veterinary practitioners. When interpreted in relation to maternal bodyweight and litter dynamics, it provides meaningful insight into neonatal viability. Moving beyond traditional breed-based references toward more adaptable metrics allows for earlier identification of at-risk puppies and more effective clinical intervention. In modern veterinary practice, NBW should be viewed not just as a measurement, but as a cornerstone of neonatal care. 

References 

1. Alonge S, Beccaglia M, Trovò C, Melandri M, Migliaretti G. Neonatal–Maternal Bodyweight Ratio at Birth: An Indicator for First-Week Survival Prognosis in Canine Newborns. Animals. 2023 Nov 1;13(21):3397. https://www.mdpi.com/2076-2615/13/21/3397 

2. Pereira KH, Fuchs KD, Corrêa JV, Chiacchio SB, Lourenço ML. Neonatology: topics on puppies and kittens neonatal management to improve neonatal outcome. Animals. 2022 Dec 5;12(23):3426. https://www.mdpi.com/2076-2615/12/23/3426 

3. Uchańska O, Ochota M, Eberhardt M, Niżański W. Dead or alive? A review of perinatal factors that determine canine neonatal viability. Animals. 2022 May 30;12(11):1402. https://www.mdpi.com/2076-2615/12/11/1402 

4. Mugnier A, Gaillard V, Chastant S. Relative impact of birth weight and early growth on neonatal mortality in puppies. Animals. 2023 Jun 9;13(12):1928. https://www.mdpi.com/2076-2615/13/12/1928 

5. Mugnier A, Mila H, Guiraud F, Brevaux J, Lecarpentier M, Martinez C, Mariani C, Adib-Lesaux A, Chastant-Maillard S, Saegerman C, Grellet A. Birth weight as a risk factor for neonatal mortality: Breed-specific approach to identify at-risk puppies. Preventive Veterinary Medicine. 2019 Nov 1;171:104746. https://www.sciencedirect.com/science/article/am/pii/S0167587719301060 
6. Kocevar G, Rioland M, Laxalde J, Mugnier A, Adib-Lesaux A, Gaillard V, Bodin J. Growth charts for small sample sizes using unsupervised clustering: Application to canine early growth. Veterinary Research Communications. 2023 Jun;47(2):693-706. https://link.springer.com/content/pdf/10.1007/s11259-022-10029-2.pdf