Energy

The nutrient of greatest increased demand during pregnancy and especially lactation is energy. Because daily caloric need of a given individual also is influenced greatly by body size, breed, age, activity, and environmental conditions, perhaps the best means of expressing energy needs for pregnancy and lactation is as a proportion of the normal energy requirements of the same animal at maintenance. However, to do that requires knowledge of the dam’s energy needs at maintenance.

A number of equations are used to determine maintenance energy requirements of the dog, but perhaps the most widely accepted equation provided by the National Research Council (NRC, 2006) is for metabolizable energy (ME) in kilocalories per day:

Although some equations do not rely on an exponent and thus are easier to calculate, determination of metabolic body weight by this method best accounts for the great diversity in adult body size in dogs. The constant in the formula (130) was determined in dogs under laboratory conditions; thus it assumes the dog to be at a moderate activity level and in environmentally favorable conditions during most of the day. Actual maintenance requirements of a given individual may vary up to 30% either way. A mostly indoor, sedentary house pet requires less to maintain body weight than an outdoor, kenneled dog. Breed and body size are also factors. For example, the equation coefficient may vary from 94 for a large pet dog to 175 for a highly active pet Border collie.

For cats, the equations recommended by NRC (2006) for estimating maintenance energy requirements are similar in format to the dog equation. Cats have less of a range of adult body sizes and are less apt to be highly active or exposed to extreme environmental conditions compared with dogs. Therefore variability in caloric requirements between individuals may be narrower. However, differences in requirements are seen with increasing body condition score (BCS); overweight cats require fewer calories per kilogram (kg) to maintain body weight. To account for this difference, ME can be calculated by two equations, one for “lean” (BCS ≤5 on a scale of 1 to 9) and one for “overweight” (BCS >5):

Because of the potentially large variation in caloric requirements, especially in dogs, perhaps a more practical means of determining needs of an individual is simply to monitor the amount of a given food (and number of calories that amount of food delivers) required to keep the animal in optimum body condition during prebreeding. During gestation and lactation the amount of the same food then can be adjusted by the appropriate proportion. If a more calorie-dense food is fed during these periods, the proportional increase would be modified relative to the calorie content of the old and new diets.

In the bitch the energy requirements for early and midgestation are approximately the same as those for maintenance (Figure 210-2). Although the fetuses are developing rapidly, they remain relatively small. Only in the last few weeks of gestation are additional calories needed for growth of the fetuses and maternal tissues. Depending on the number of fetuses, total weight gain by the time of parturition should be around 15% to 25%. At this time the bitch likely is consuming approximately 150% of her normal maintenance needs. Expressed differently, the increase in energy requirements above maintenance from the fourth week after mating until parturition is approximately 26 kcal of ME per kilogram of body weight per day.

Unlike in the bitch, increase in body weight and therefore caloric requirements of the gestating queen between mating and parturition are linear; that is, weight gain is steady and consistent throughout gestation. The weight gain in the queen during early pregnancy is not associated with fetal growth but apparently serves as an energy reserve to support later demands for lactation. Depending on the number of kittens, the mean body weight gain at the end of gestation is usually around 40% over premating body weight.

In the bitch, dramatic increases in energy needs are seen after the first week of lactation, even though the dam may be approaching or even falling below her prebreeding body weight after delivery. This effect is tempered somewhat in queens; she remains above prebreeding weight at parturition but then uses the fat stored during early pregnancy for lactation. Still, increased energy is needed in bitches and queens to meet the monumental nutritional demands of milk production for the ever-growing offspring. For both species, the calorie requirement of a given individual depends on the amount of milk production, which in turn is correlated with the number of offspring. In bitches with litters of one to four neonates, milk production can be estimated at 1% of the bitch’s body weight per pup, which increases the bitch’s energy requirement by 24 kcal of ME per kilogram of body weight per day for each puppy in the litter. For litters larger than four, milk production and caloric needs per additional pup are approximately half of these values, and the increase in milk yield as litters exceed eight pups is negligible. Put more simply, in a bitch during peak lactation (4 weeks after parturition) with a moderate-to-large litter, energy needs could be three or even up to four times the normal maintenance requirements. As the offspring are weaned and milk production declines, the calorie needs for lactation drop, and more energy can be directed toward reestablishing normal body weight.

The increase in caloric requirements for the queen may not be as dramatic as in the bitch, because the queen still is using energy she stored during early gestation and continues to lose weight during lactation. In the lactating queen, NRC (2006) recommends energy requirements in kilocalories (kcal) per day above maintenance by the following equation:

For example, a 4-kg queen with three kittens in peak lactation (fourth week) would require 288 kcal per day above the 253 kcal/day required for maintenance. As a rule of thumb, an energy need 2 to 2.5 times the maintenance requirement is expected during lactation.

Other Essential Nutrients

In addition to calories, the needs for most other essential nutrients (e.g., amino acids, minerals, vitamins) increase during this life stage. For example, more protein, calcium, and phosphorus are needed for proper growth and bone development of the puppies and kittens. The Association of American Feed Control Officials (AAFCO) Dog and Cat Food Nutrient Profiles indicate for which nutrients are increased dietary needs above maintenance of the reproducing bitch or queen. For example, increased intake of dietary salt above maintenance needs is indicated to support normal milk production in the bitch, whereas the dietary levels of vitamins A and D are higher for reproducing queens versus cats at adult maintenance. Although many of the nutrient requirements in the AAFCO profiles appear the same for all life stages, absence of an established difference in the profiles between growth and reproduction versus maintenance reflects the lack of data showing a decreased need in the adult at maintenance (especially for many of the trace minerals and vitamins). Furthermore, although the amount in the diet may appear to remain the same, the actual daily intake of a given nutrient is higher in the gestating/lactating bitch or queen because of increased food intake.