Keeping a litter of newborn puppies alive can be a perplexing problem for dog-breeders. The problem may lie in a range of diseases of genetic, environmental, physiologic, or nutritional origin. However, it should be understood that the causes of most puppy losses have not been determined.

Investigators have observed the following general pattern: percentage of puppy losses was highest in young bitches, gradually diminished as the age of the bitch approached three years, then increased after four years; most mortalities occurred during the first week of life; high inbreeding increased neonatal mortality while hybrids of inbred breeds resulted in significantly reduced losses. In a comparison of male and female survival rates of more than 400 English Setter pups, there was little or no difference during the first week of life; however, at three and four weeks of age the male survival rate was slightly greater than female with 90.4% of the males and 89.5% of the females surviving.

The neonatal period, here arbitrarily defined as the first three weeks of life, is one in which puppies are physiologically immature. Selected normal physiological values are listed in Table 1. These illustrate the relatively undeveloped function of most physiological and behavioral activities of puppies during the first few weeks of life. Puppies also are immunologically immature although certain elements of the immune system have been shown to be functional prior to birth. Certain agents which are relatively innocuous to the mature dog are lethal to the newborn puppy.

Noninfectious Causes of Neonatal Puppy Death
While it is very difficult to determine the relative significance of various factors that cause death of newborn puppies during the first week of life, it appears that noninfectious disease conditions account for a large percentage of them. Fetal anomalies (congenital malformations), poor mothering, parasitism by round worms and hookworms, and, on rare occasions, neonatal isoerythrolysis are blamed.

Difficult or prolonged labor is a major cause of stillbirth, but it cannot be blamed for all nonviable puppies. The loss is estimated to be about 8%. Uterine inertia is a major cause. Contributing factors are excessive weight and lack of exercise, especially hi certain small breeds. Obstruction of the birth canal also may contribute.This condition may result from old fractures or from fibrous bands across the vagina. Problems also may be caused by excessive puppy size, large heads of brachycephalic breeds, abnormal presentations, or fetal anomalies.

Because of the intense selection by many breeders for certain conformation characteristics, congenital abnormalities are becoming a more frequent cause of death of the newborn and now account for nearly 1 % of newborn puppy deaths. They may be hereditary or may result from failure of the embryo to differentiate properly. Among the hereditary conditions, chondro-dystrophla fetalis has been reported in Poodles, Scottish Terriers, and Fox Terriers. The fetus has a cretinous appearance with malformations of the limbs. Congenital hydrocephalus is not uncommon in the brachycephalic breeds and may be associated with malformation and doming of the cranium. Congenital diaphragmatic hernia has been reported to be hereditary, but it has been produced experimentally in pigs and rats by vitamin A deficiency. Cleft palate is considered to be a common hereditary cause of puppy death because of the inability of most affected puppies to suckle. Those puppies that do suckle have a high incidence of inhalation pneumonia. Harelip often is associated with cleft palate. Additional conditions have been described: congenital abnormalities of the lungs (alveolar dysplasia); failure of lungs to inflate (primary atelectasis) or a secondary atelectasis from inhalation of fluids at birth, aplasia of the kidneys; and occlusion of the anus, termed atresia ani. This condition produces a bloated pup that vomits sporadically and will cause death if not treated promptly.

Neonatal isoerythrolysis (neonatal hemolytic anemia) has occurred in A-positive pups born to A-nega-tive mothers that had been immunized by previous transfusions of A-positive blood. As transfusion technology becomes more widely practiced, this condition may become more common. (It does not occur as a result of breeding dogs with incompatible blood groups.) Affected puppies become very pale within one to two days after birth; deaths usually occur within the first 72 hours. If puppies survive beyond this time, they usually do not die.
Poor mothering is one of the principal causes of neonatal deaths. A nervous, inexperienced bitch may cause trauma to her newborn puppies. Overzealous removal of fetal membranes may result in evisceration, umbilical herniation, and cannibalism. The provision of an adequate whelping box and close attention to the bitch are of greater value than administration of tranquilizing drugs. Starvation may result from the inability of puppies to suckle, as with premature or "runt" puppies, especially when they are weak or chilled. As mentioned above, developmental defects may reduce food intake or preclude it. Occasionally, a bitch will not settle long enough to allow puppies to suckle. Caked udder (edema) may make milk unavailable. Lack of milk, technically termed agalactia, has a number of causes: underdeveloped mammae; uterine infections; septicemia; mastitis due to staphy-lococci, streptococci, or mixed infections with coli-form bacteria. A bitch with mastitis often will not allow puppies to suckle because of the pain.

Chilling accounts for many puppy deaths. A newborn puppy requires warmth, and an ambient temperature of at least 70 °F should be provided during the first week of life if puppies are with the bitch. Thermo-regulation is poor for the first eight days of age.

Newborn Puppy Deaths Caused by Bacteria and Viruses
Bacterial Infections: Many cases of early death of puppies have been attributed to viral diseases; however, those that occur within the first few days of life, especially during the first 72 hours, usually have not been associated with any known virus. The principal viral cause of puppy losses, canine herpesvirus, affects primarily the one-to-three-week-old age group. It normally does not cause "fading pups." The clinical terms "acid milk syndrome," "toxic milk syndrome," and "puppy septicemia" have been ascribed to a variety of causes, usually bacterial. Although useful to the veterinarian or breeder in describing common clinical signs, the causes of these conditions are largely unknown. The "toxic milk syndrome" has been ascribed to incompatibility of neonatal puppies to bitch's milk. The puppies cry, become bloated, and have greenish diarrhea and red, swollen rectums. Most cases of "fading pups," however, are believed to be caused by bacterial infections. Affected puppies crawl away from the mother, or are disregarded, become chilled, cry, strain, and develop cyanosis. They become weak and die within 18 hours after birth, usually within a few hours after the first appearance of clinical signs. Temperatures are not elevated; they usually are subnormal. Often, a bitch will lose several litters in sequence. In such instances, litters of weak or stillborn puppies suggested the possibility of chronic uterine infection (metritis) in the bitch. This is a very insidious disorder whose clinical signs generally are not apparent to the owner. Bitches with a history of puppy losses should be examined carefully by a veterinarian for chronic metritis, endometritis, and vaginitis. If found to be infected, they should be treated intensively with systemic antibiotics at the time of estrum and at breeding. Treatment also should be given at or before the time of whelping to prevent infection of the newborn puppies. In general, during the first week of life, puppies from bitches that have suffered previous losses should be kept warm (80-85 F), given oral glucose, and treated with antibiotics. If the quality of the bitch's milk is questioned, puppies should be hand fed with a commercial formula such as Esbilac (Borden).

It should be emphasized that treatment is based on signs and general experience since the cause of puppy deaths is rarely determined.

The most common bacteria associated with neonatal pup deaths are streptococci and E. coli, with some losses reportedly caused by staphylococci and pseudomonas infections. Pseudomonas and E. coli infections have been associated with severe hemor-rhagic enteritis whereas streptococci and staphylococci frequently are associated with umbilical infections. Brucella canis is associated with abortions after 45-55 days of gestation, stillbirths, early embryonic deaths, and occasional death of pups from infected bitches, but this organism is not a proven cause of neonatal puppy death.

Streptococcal infections (beta-hemolytic streptococci) are associated with puppies that are born vigorous and healthy, suckle well for the first 24 hours, then become suddenly weak and restless. They cry, show incoordination, develop tetanic spasms, and die. Affected puppies often are rejected by the bitch. All puppies in the litter may not die, and the bitch may not whelp infected litters subsequently. Affected puppies have peritonitis, a dark and enlarged liver, a blue-black and swollen umbilicus, and sometimes severe hemorrhagic enteritis. In such cases, streptococci may be isolated from the freshly obtained organs of dead puppies and from the vagina of the mothers. One author has shown transmission of beta-hemolytic streptococci within a kennel where several abortions occurred. He considers transmission from bitch to bitch by the male important. Also, carrier bitches have been identified.

Viral Infections: Although several viruses may infect puppies, only the canine herpesvirus has been associated with naturally occurring neonatal illness and death. Occasionally, pups may die from canine adenovirus infections (canine hepatitis virus) or distemper, but these have been reported only in laboratory studies. These studies have shown that both distemper and hepatitis viruses may infect embryos with resultant stillbirth or birth of weak pups that later die. The low incidence of neonatal mortality caused by these viruses may be one of the benefits of widespread vaccination preventing the spread of virulent virus. There are no reports that either attenuated distemper or hepatitis viral vaccines given to pregnant bitches have produced abortions or infections of the fetus.
From Cornell Research Laboratory for Diseases of Dogs.