Cayden Sanchez
Biology 1615
Breed and sex differences in growth curves for two breeds of dog guides
There is a number of different things to consider when deciding whether a dog is capable
of being a guide dog, one of which being weight. A guide dog needs to weigh enough to guide
the owner comfortably, but not so heavy that the dog cannot be controlled. A desirable guide dog
will normally weigh between 18 to 32 kg as an adult. Estimating a puppy’s adult weight can be
difficult because research of growth patterns is limited. Most studies have looked at specific
breed, but not the entire growth curve.
The purpose of the study was to provide a model of growth for male and female German
shepherd and Labrador retriever dogs using mathematical functions. This would help to better
predict a dog’s adult weight, thus decreasing the cost of production. It would decrease the cost of
production by making it possible to train fewer dogs to benefit the same number of blind
individuals.
To construct the model 18,235 weight observations were taken on 1,558 different
German shepherd and Labrador retrievers raised from 1992 to 1997 by the Seeing Eye, Inc.,
Morristown, NJ. For the first week of life weights were recorded daily, then weekly until the
puppies were 6 to 8 weeks old. After this the puppies were placed in homes and their weights
were recorded sporadically. Observations would be deleted if the dogs were older than 550 d, of
if there was no observations on the dog from 290 to 550 d of age. After taking deleted
observations into account the data set consisted of 10,484 observations for 809 dogs. This
included dogs from 109 German shepherd litters coming from 42 dams and 12 sires, as well as
75 Labrador retriever litters coming from 29 dams and 10 sires. Dams were mated to 2.21 ± .12
sires, 7/10 of the dams were mated to more than one sire. Weight observations per dog were
11.91 ± .07, with each dog being weighted 8 to 20 times. The Gompertz Function was used to
display the growth curve of the dogs observed.
After everything was said and done the average mature weight for male Labrador
retrievers was 31.4 kg and for females was 26.8 kg. The average mature weight for Male German
shepherds was 29.1 kg and for females was 24.4 kg. The duration of growth for Male Labrador
retrievers was 335 d and for females was 319 d, for male German shepherds the average duration
of growth was 326 d and for females 325 d. The point of inflection For male Labrador retrievers
was 87.4 d and for females was 82.7 d. The point of inflection for male German shepherds was
86.6 d and for females 84 d. The estimated mature weight for Labrador retrievers was 2.4 ± .3
kg higher than German shepherds; males were an estimated 4.7 ± .2 kg heavier than females.
Males also grew an estimated 8 ± 5 d longer than females. Also males point of flection was an
estimated 3.6 ± 1.2 d greater than females.
Another study modeled growth in male and female beagles, Brittany Spaniels, and
Labrador retrievers from birth to 1 year of age using the Gompertz Function. However this study
used weekly weights, four groups of dogs for each breed, one group for 0 to 8 weeks of age, one
for 9 to 18 weeks of age, another for 19 to 26 weeks of age, and one more for 27 to 52 weeks of
age. The number of dogs used in each group decreased as the study went on, leaving less dogs to
determine the average mature weight. One concern for this study is that the fewest observations
were recorded between 61 and 332 d of age. Data in this time period could change the results.
This growth curve provides useful information on the mature weight and average growth
term for dogs in this population. This may help to develop a section protocol to increase the
chance that dogs will attain a mature weight within the desirable weight for guide dogs, 18 to 32
kg.