A retrospective analysis on determinants of litter size in a colony of working dogs

Successful breeding and increased litter size are paramount to increasing working dogs’ numbers for national security. We determined key factors affecting pregnancy and litter size in Canine Performance Sciences (CPS) breeding colony. Specific aims of this research were to elucidate factors that improved breeding outcomes in the colony. Data from CPS breeding population for 55 breeding cycles for 26 females over 5 years were analyzed. Factors analyzed were: age of dam at breeding, semen type (fresh, cooled-shipped, frozen), insemination method (vaginal AI, transcervical insemination [TCI], live cover), and total number of inseminations. Multiple regression model was used. Above factors influenced (p < 0.001) and explained 57% of the variance in litter size. Addition of 1 TCI increased (p = 0.005) litter size. Addition of 1 live breeding, although not different (p = 0.07) had clinical relevance (increased litter size). Average litter size of a 30 month old dam using fresh semen AI was 5.45 puppies and cooledshipped semen AI was 7 ± 1 puppies. Age of dams at breeding ranged from 13 - 88 months and there was no effect of age or parity on litter size. Results indicated that maximum litter size occurred when fresh semen was utilized, with cooled-shipped semen being equivalent. Use of frozen semen was least successful, resulting in negative effects on pregnancy rate in this population. Scrutiny of insemination methods revealed that addition of 1 live cover increased litter size by 2 puppies, whereas addition of 1 TCI increased litters by 3 puppies. In summary, incorporation of 1 live breeding and 1 TCI utilizing fresh semen increased average litter size in CPS breeding colony.

Keywords: Canine, semen, transcervical, litter, breeding

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.