Differential impact of birth weight and early growth on neonatal mortality in puppies

Breeding kennels face a high rate of neonatal mortality, on which the impact of nutrition remains to be determined. This study was designed to evaluate the impact of birth weight (reflecting intrauterine growth) and early growth rate (reflecting colostrum intake) on risk of neonatal mortality in puppies and to determine the critical thresholds of both parameters. Puppies from various breeds were weighed at birth (n = 514) and at 2 d of age, and the growth rate over that period (early growth rate) was calculated for all survivors (n = 477). Linear mixed models evaluated the effect of birth weight on mortality between birth and 2 d of age and the effect of both birth weight and early growth rate on mortality between 2 and 21 d of age. Birth weight was influenced by litter size (P = 0.003), with more low-birth-weight puppies (the lightest 25% within a breed size) in large litters compared with smaller litters. Mortality over the first 2 d after birth was associated with birth weight (P < 0.001), with 81.1% of dying puppies characterized by a low birth weight. Mortality between 2 and 21 d of age was not related to birth weight but was found to be associated with early growth rate (P < 0.001), with higher risk of death in puppies with growth rate at or below -4% after the first 2 d of life. This study demonstrates the differential effect of intrauterine nutrition impacting mortality during the first 2 d of life and that of colostrum intake impacting mortality until 21 d of life. Birth weight and early growth rate thresholds provided in this study allow identification of puppies at risk, whereby provision can be made for adequate nursing to increase their chances to survive.