title: Seasonal and breed effects on reproductive parameters in bitches in the tropics: a retrospective study.
abstract: OBJECTIVE
  To investigate the influence of season and breed on reproductive parameters in bitches raised under tropical climatic conditions.
  
  
  METHODS
  Over a seven year period, from 1998 to 2004, 310 oestrous periods of 53 bitches were observed. The dogs were of various breeds; dobermann (number of bitches/number of oestrous cycles) (n=2/19), German shepherd dog (n=35/211), Labrador retriever (n=14/68) and Rottweiler (n=2/12). In 250 of the 310 oestrous periods, natural matings took place on days 9 and 11 after the onset of pro-oestrus. The whelping rate was analysed for bitches of each breed. Variables, including breed and the whelping rate, by month of the year, were used for analysis of the inter-oestrus interval, gestation length, total number of pups born, number of live pups born and the weight of the pups at birth.
  
  
  RESULTS
  A low frequency of oestrous activity was found during the summer. Breeding dogs in the summer resulted in a low whelping rate. No difference (P>0.05) was seen in the whelping rate of each breed: dobermann (70.5 per cent), German shepherd dog (61.5 per cent), Labrador retriever (67.9 per cent) and Rottweiler (100 per cent). The Labrador retriever had a longer inter-oestrus interval (252 [114] and 190 [61] days) (P<0.01) and a larger litter size (8.2 [1.8] and 6.6 [2.8]) (P<0.05) than the German shepherd dog.
  
  
  CONCLUSIONS
  The environmental factors in summer tend to reduce oestrus incidence and fertility in the bitches. According to litter size, the Labrador retriever seems to have a more efficient reproductive performance than the German shepherd dog. The Labrador retriever had a longer inter-oestrus interval than the German shepherd dog.
authors.affiliation: Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand.
authors.forename: K
authors.initials: K
authors.lastname: Chatdarong
authors.forename: P
authors.initials: P
authors.lastname: Tummaruk
authors.forename: S
authors.initials: S
authors.lastname: Sirivaidyapong
authors.forename: S
authors.initials: S
authors.lastname: Raksil
mesh_terms: D000818:Animals; D001947:Breeding / Q000706:statistics & numerical data*; D004285:Dogs; D004971:Estrus / Q000502:physiology; D005260:Female; D008098:Litter Size / Q000502:physiology; D010375:Pedigree; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D012189:Retrospective Studies; D012621:Seasons; D013785:Thailand / Q000453:epidemiology; D014329:Tropical Climate