Energetics of lactation in domestic dog (Canis familiaris) breeds of two sizes.

The energetics of lactation was measured in two breeds of domestic dog during peak lactation. Labrador Retrievers (30 kg) had larger litter sizes than Miniature Schnauzers (6 kg). During the 7-day experimental period, Labrador pups increased more in mass than Schnauzer pups, both absolutely and relatively. Consequently, the energy demands of the litter, relative to maternal metabolism, were higher in Labradors than Schnauzers. Milk composition and gross efficiency of milk production were not significantly different between breeds and the costs of lactation were fuelled by increases in food intake. Metabolisable energy intake was higher than predicted in Labradors, but lower than predicted in Schnauzers. These patterns differ from interspecific expectations, which would predict larger animals to reproduce more slowly, have smaller litter sizes, and invest less energy in reproduction.