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Comparative Lactation - Cats and Dogs


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This section discusses aspects of lactation in cats and dogs, including anatomy, milk composition, nutrition during lactation, pseudopregnancy, and eclampsia.


Mammary Anatomy

The number of teats in the dog varies from 8 to 12, with 4 to 6 gland complexes on each side of the midline. Ten is the most common number in larger breeds, four pairs are more common in the smaller breeds. In bitches with ten normal teats, the pattern is two pairs thoracic teats, two pairs abdominal teats, and one pair of inguinal teats.

Cats usually have four pairs, two thoracic and two abdominal, which are about equidistantly spaced. Supernumerary teats do occur in both dogs and cats, and are generally removed.

The number of ducts opening on a teat varies from 8 to 20 external openings per teat for the dog and 1 to 7 for the cat. The openings are located on the blunt end of the teat in an irregular pattern. Dog owners should remember that each milk exit can be an entry point for bacteria. Keeping the bitch's environment especially clean during the nursing period. The streak canal, or teat canal, is 1/4 to 1/3 the length of the dog's teat. The teat sinus extends upward from the teat canal into the parenchyma of the gland. The teat sinuses are small uniformly wide passages and not wide dilations as in cattle. The parenchyma, or secretory tissue, is present only during pregnancy, pseudopregnancy, during lactation, and for 40 to 50 days after weaning.

The blood supply of the mammary glands of dogs and cats are similar except for the thoracic glands. In the dog the first pair of thoracic mammary glands receives blood from two sternal branches of the internal thoracic artery, passing between the first and second ribs. The second pair of thoracic mammary glands is supplied by small branches of the mediastinal, or internal mammary, arteries before they anastamose with the sternal branches serving the first pair of glands.

The abdominal and inguinal gland pairs of glands are served by the femoral arteries. Branches pass anteriorly to become the external pudic, then the posterior mammary arteries. They supply the abdominal glands and anastamose with the anterior abdominal arteries which are extensions of the previously mentioned mediastinal, or internal mammary arteries.

Tumors are frequently seen in the mammary gland of the dog. They may belong to the connective tissue or the epithelial series of mammary tumors, or both. Tumors of the epithelial series are of great importance. Those observed are adenomas, carcinomas, and above all, mixed mammary tumors.

The mixed tumor of the mammary gland is the most frequent form of tumor found in the dog. It is of great comparative pathological importance due to its similarity to the mixed tumor of the parotid gland seen in man. The preferential site of these tumors is the posterior, or inguinal, mammary glands, although others may be involved. While in most cases only one tumor is seen, multiple tumors are also seen. These tumors vary in size; fist-size is not uncommon. The skin is generally freely movable over the tumor and the tumor itself is surrounded by a fibrous capsule, from which it can be readily removed surgically. These are mostly benign. It is different in the case of the cat. Tumors of the mammary gland are generally rare in cats, but if a tumor is present, it is generally an infiltrating carcinoma with early metastasis in the regional lymph nodes.


Milk Composition

Composition of milks at mid-lactation:

Species

% DM

% fat

% protein

% sugar

% ash

cat

-

10.8

10.6

3.7

1.0

pig

20.1

8.3

5.6

5.0

0.9

cow

12.4

3.7

3.2

4.6

0.7

dog

22.7

9.5

7.5

3.8

1.1

human

12.4

4.1

0.8

6.8

0.2


Composition of milks as a percent of dry matter:

Species

% fat

% protein

% sugar

% ash

gross energy
kcal/gm

cat

-

-

-

-

1.74

pig

41

23

25

4

1.24

cow

30

26

37

6

0.71

dog

41

33

17

5

1.46

human

33

7

55

2

0.69


Whey protein and casein (as percent of total composition) in milks:

Species

casein

whey protein

cat

3.7

3.3

pig

2.8

2.8

cow

2.8

0.6

dog

5.8

2.1

human

0.4

0.6

The milk of the dog changes composition during the course of lactation. Milk composition through the first 45 days of lactation has several changes:

protein concentration increased from 4.3% to 6.3%
fat concentration increased from 2.4% to 4.5% early in the period and then dropped to 2.7%
carbohydrate concentration did not change significantly
iron decreased from 13 ug/ml to 6 ug/ml
zinc decreased from 9.7 ug/ml to 8.7 ug/ml
calcium increased from 1366 ug/ml to 1757 ug/ml
copper did not change significantly
manganese did not change significantly
magnesium did not change significantly

The iron concentration in cat milk is 5 to 6 ug/ml decreasing to 3 ug/ml. The iron concentration of dog milk, about 10 ug/ml was much higher than human, 0.2 to 0.5 ug/ml or dairy animals (0.2 to 0.3 ug/ml), but about equal to rat milk. The iron concentration is strongly influenced by the stage of lactation, and decreases with time.


Nutrition During Lactation

This lactating bitch provides an example of the nutritional stresses associated with lactation. The characteristics of the litter which determine the level of nutritional stress on the mother are: the size of the puppies, the number of puppies in the litter, and their age. The peak energy needs of the bitch occur when puppies are 3 to 4 weeks old. If a bitch is nursing more than 4 to 5 puppies she should receive a diet containing 28 to 30% protein and 20 to 25% fat during heavy lactation.

Proper vitamins and trace minerals must be provided also. Work has been reported on B complex vitamins, detrimental excesses of Vitamin D and calcium, and deficiencies of zinc and Vitamin C. Supplementation may be necessary, but a proper calcium:phosphorus ratio should be carefully maintained.

The lactating bitch should be fed 1.5 times maintenance for the first week, 2 times maintenance for the second, and 2 to 3 times maintenance amounts for the third week of lactation. Ontko and Phillips noted little or no loss of weight when lactating bitches were fed a basal diet of 427 calories per 100 gm. of ration, but a weight loss occurred when bitches nursing four or more puppies were fed a diet containing 310 calories per 100 gm. Therefore, increasing the caloric density of the diet assures improved lactation. Care must be exercised in adding fat or a diet of higher caloric density. Problems in low birth weights and high death rates occurred in litters which have only an increased fat percentage. Fat must be balanced by protein increases, so that 17% protein should balance with 7.5% fat, 25% protein should balance with 20% fat, and 29% protein should balance with 30% fat to assure that increased caloric density will not induce protein deficiency. Increases of fat also make the diet more palatable.

The digestive capacity of the pet must be considered when increasing the ration of a companion animal during lactation. If the quantity of food required exceeds the amount she can eat in one feeding, then divide that into three or four feedings per day.

A protein intake of 25 to 50% of the diet on a dry weight basis appears optimal. A commercial maintenance diet should have 2 to 4% animal protein added, such as liver.

The behavior of both lactating cats and their kittens is affected by a protein restricted diet. Vocalization and movement in the home box are both higher in kittens whose mothers are not receiving enough protein in the diet. Nursing behavior was abnormal in those queens, also.

Most puppies are weaned at 6 to 7 weeks of age. This appears to be the optimum time from both the nutritional and behavioral standpoints. At this age they are sufficiently adapted to their species yet young enough so that they adapt well to people and, therefore, become good pets.

It is helpful to restrict the food intake of the bitch before and during weaning to prevent excessive distention of the mammary glands and discomfort after weaning, particularly for good milk-producing bitches with large litters. This may be accomplished by separating the bitch from the litter during the day and withholding all food the day before weaning, but reuniting the bitch and pups that night and removing the food from the pups. Then gradually increase the amount fed the bitch after the pups are completely removed so that by several days after weaning she is receiving the amount needed for maintenance.


Pseudopregnancy

Turner and Gomez, in their 1934 work on the mammary gland of the dog described a condition called "complete pseudopregnancy." In the dog this condition extends for a period comparable to normal pregnancy and the development of the mammary gland includes the growth phase during the first half and the gradual initiation of lactation during the second half of the false pregnancy. Therefore, normal secretory activity is not dependent either upon the fetus or fetal membranes. The uterus is apparently not necessary either, as a hysterectomized female was given hormones and began the glandular growth phase.

Pseudopregnancy can be very helpful to the breeder who needs a foster mother to nurse orphaned, abandoned, or extra puppies. On the other hand, the home owner with a single, female dog who is not allowed to mate during estrus will frequently have to contend with unwanted milk dripping. Veterinarians can administer bromocriptine to "dry up" the milk. Behaviorists note nesting behavior and even straining movements which simulate parturition about nine weeks after estrus. The dog owner is counseled to discourage nesting behavior, not to let the dog "nurse" any rolled-up socks she has stolen, and provide interesting outside activities.


Eclampsia

Eclampsia (convulsions not associated with other cerebral conditions such as epilepsy or cerebral hemorrhage) can occur in the dog as a result of lactation. The greater the quantity of milk produced, the more likely it is that eclampsia will occur. When calcium is lost in the milk faster than it is absorbed, or than it can be mobilized from the skeletal system, hypocalcemia results. Signs are muscle fasciculations, tetany, and death. The treatment is to slowly (10-15 min) administer a calcium solution intravenously. As you treat, the amplitude of heart sounds will increase, and the heart rate will decrease. If the heart rate increases, or becomes arrhythmic immediately stop calcium administration.

A bitch with a large litter two to four weeks into lactation is especially susceptible to eclampsia. Some would suggest giving extra Ca prior to the time it is needed. However, this does not help, because excess Ca intake decreases the efficiency of Ca absorption from the intestine, inhibits parathyroid hormone secretion, and stimulates thyrocalcitonin secretion. These changes decrease the ability of the dog to mobilize Ca from the bone, when additional Ca is needed; it takes 1 to 3 weeks to reverse the effects. Of course, this is not fast enough, and hypocalcemia and eclampsia occur. Giving Ca when it is needed, during the first week through the fourth or fifth week of lactation, may be helpful; 500 mg of calcium carbonate (about one Tums, the antacid you take for upset stomach) per 5 kg of body weight per day, but only for the bitch in which eclampsia has previously occurred. The best treatment is to get the puppies off the dam as quickly as possible, either onto solid food or a bitch's milk replacer.


 
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