by Bretaigne Jones, DVM
Most breeders recognize the need for optimal nutrition for the female during pregnancy and lactation. However, little notice is taken of the period between the completed weaning of one litter and the first signs of the next estrous cycle. For those dogs that will be rebred during the next estrous cycle, it is imperative that they receive the appropriate food, both in energy density and nutrient quality, during this interval. Lower quality food can lead to breeding issues such as failure to settle, and smaller litters, as well as higher incidences of pregnancy toxemia and eclampsia.
The concept of "eating for two" is widely recognized in association with pregnancy. Typically this phrase refers to necessary nutrition for the mother and the babies, but the nutritional needs during pregnancy go well beyond just the maintenance needs of the dam and the developmental needs of the fetuses. In addition to those needs are the generation of uterine tissue, miles of blood vessels, placental tissue, and development of mammary tissue.
Regardless of the stage of reproduction, the breeding bitch will deferentially provide nutrients to the babies, directly or through milk, regardless of her own needs. Consequently, she is drawing upon her own body reserves for necessary minerals, proteins, fats, and vitamins to meet the needs of her offspring. This is why a lactating bitch is often haggard looking. It is this depletion of body stores that necessitates a higher plane of nutrition between breedings in order to restore those nutrients reserves.
By the end of the first 6 weeks of pregnancy, there is only a 10% increase in energy necessary. By the end of pregnancy, the average bitch has increased her energy needs to 140% of maintenance. By the third and fourth week of lactation, depending on number of pups and breed, the bitch may demand 300% of her maintenance energy levels, with necessary elevations in most nutrients as well. During late pregnancy, throughout lactation, and through the recovery interim between breedings, differing levels of increased energy and nutrient content is critical to the health and well-being of the mother and pups.
The interval between weaning and the next estrus can be confusing nutritionally because while the bitch is back at maintenance energy needs, she needs higher levels of certain nutrients than are recognized for maintenance health. Calcium and phosphorous are good examples. According to the National Research Council (NRC) 2006 edition of Nutrient Requirements of Dogs and Cats, the minimum requirement for calcium for adult dog maintenance is 0.50 gram calcium per 1,000 Kcal metabolizable energy (ME). The recommended level is reported at 1.0 gram per 1,000 Kcal ME for calcium and 0.75 g/1,000 Kcal ME for phosphorous.
Compare to the recommended levels for late gestation (last 4 weeks of pregnancy) and peak lactation (weeks 3 and 4) where the recommended allowance for calcium is 1.9 grams per 1,000 Kcal and for phosphorous is 1.2 grams per 1,000 Kcal. These levels are 190% and 160%, respectively, of the normal maintenance levels. If the bitch carried an average size litter and successfully nursed to complete weaning at 6 weeks after whelping, she not only utilized every gram of nutrient provided in the diet, but also drew on her own body reserves in her bones to some extent. In the case of a larger litter, that body reserve resource provides even more to meet the needs of the growing pups during late pregnancy and throughout lactation.
When this bitch has totally weaned her pups, she's technically back to maintenance energy needs. However, her body is still repairing from the pregnancy and delivery, and her mammary tissue is returning to a normal non-productive state. The deficits created by providing all the nutritional needs of the developing and growing pups for months need to be corrected. The breeder cannot depend on the visual appearance of the bitch's body condition score to reliably assess her nutritional needs. She may look good, but still have deficient nutrient reserves.
Other nutrients that typically need to be restored (in addition of calcium and phosphorous) include omega-3 and omega-6 fatty acids, zinc, copper, manganese, taurine, arginine, and tyrosine.
If a bitch is going to be bred on her next estrous cycle, it is imperative that she be provided the optimal diet after weaning to rebuild her body stores. The drain on her reserves will compound with each pregnancy. So with pregnancy number 2, there may not be an appreciable difference in her reproductive performance, but with pregnancy 3 and 4 there will be decreases in litter size, viable puppies, milk production, and her "resting" body condition score. There is definitely an additive effect with successive pregnancies and lactations to the detriment of the bitch's base reserves, and her health.
A vitally important component of lactation is the production of colostrum, rich in maternal antibodies, to provide immune protection for the newborns. The wear and tear on the bitch bred repeatedly with inadequate nutrition between litters, will result in a compromised immune system, meaning lower levels of antibodies in the colostrum resulting in unprotected puppies. So not only are litters smaller and the puppies less vigorous, they are much more vulnerable to viruses, bacteria and parasites.