Placental weight and puppies’weight at birth and during the first week of life in toy and small breeds: preliminary study.

Canine perinatal and neonatal mortality can be as high as 23.3%, when no supervision at delivery and additional nursing or hand rearing is performed (1). Low birth weight, early growth, Apgar score and glucose concentration identify puppies at risk (1,2). Low birth weight might be due to a smaller placenta, as described in pigs (3). The relation between placental weight and puppy weight and mortality, however, in the dog is not known. Methods: Eighteen bitches belonging to toy (<5 kg, n=8, range 2.2-3.8 kg) or small (5 to 10 kg, n=10, range 5-8.5 kg) breeds were included in the study. Puppies were weighted at birth (D0) and daily until Day 6 (D6). Placentas (n=62) were deprived of amniotic membrane and placed in absorbent paper for 5 minutes before being weighted. Puppies that died, within 24 hours or 10 days, were recorded. Birth and placental weights were classified into quartiles, separately for toy and small breeds. The first quartiles (Q1) represent the lowest 25% of weights (1,2). Groups were compared by the Mann-Whitney test. Results: Mean litter size in toy and small breeds was 3.0±0.8 and 5.4±1.8, respectively, and overall mortality in each group was 0/24 and 6/54 (overall it was 7.7%). In each group, three litters were born by planned Caesarian sections (C-S). Median weight at birth was 134 grams (Q1: ≤125 grams, range 89-182 grams) and 196 grams (Q1: ≤178.7 grams, range 114-253 grams) for toy and small breeds’ puppies (P<0.001) respectively. There was no difference between males and females. All puppies had an Apgar score ≥8 at birth, except for two small breed puppies delivered by C-S, which survived. Median weight of placentas was 18.5 grams (Q1: ≤17 grams, range 14-29 grams) and 28 grams (Q1: ≤23.7 grams, range 15-46 grams) in toy and small breeds (P<0.05). There was a statistically significant correlation between puppy weight at birth and placental weight in small (P<0.001) but not in toy breeds. Three/6 (50%), 4/5 (80%) and 3/6 (50%) of the dead puppies had Q1 birth weight, Q1 placental weight (one was lost) or were from C-S, respectively. Four puppies died at birth or within 24 hours, two after D6. On Day 3 after birth, small breeds puppies reached a relatively higher weight than toy puppies (131% vs 125% of D0 weight, respectively, P<0.05), however this difference was not present at D6 (173% vs 170%). When breeders carefully monitor and support parturient bitches and neonates, mortality rate can be greatly reduced. Only 3/21 (14%) of Q1 birth weight puppies died. The identification of the Q1 puppies and placentas was more precise dividing toy from small breeds, respect to the use of previous classifications (1,2). This is confirmed by the statistically significant differences between the two groups in the weight of puppies at D0 and placentas. Most dead puppies had Q1 placentas, however more data are needed before the role of this structure in peri-birth mortality can be elucidated.