title: Parallel distribution of sexes within left and right uterine horns in Holstein dairy cows: evidence that the effect of side of pregnancy on sex ratio could be breed-specific in cattle.
abstract: Dissimilar distribution of male and female calves within left and right uterine horns has been observed in beef cows. A retrospective study was conducted to investigate the effect of side of pregnancy on secondary sex ratio in Holstein dairy cows. Data associated with sex of calves, side of pregnancy, sire, dam, parity number of dam, AI technician, season and year were retrieved from the database of a Holstein dairy farm. In total, data consisted of 6515 birth records from 3155 dams and 244 sires across years 2001-2010. Data were analyzed using logistic regression. There was no difference in proportion of male and female calves between left (52.9% and 47.1%, respectively) and right (53.2% and 46.8%, respectively) uterine horns (P>0.05). AI technician, year, season and parity of dam did not affect secondary sex ratio (P>0.05). Secondary sex ratio of left and right uterine horns, and consequently, overall secondary sex ratio (53.1%) were skewed toward males as compared with hypothetical secondary sex ratio of 50% (P<0.05). Incidence of right pregnancy (60.5%) was higher than hypothetical 50% incidence of right pregnancy. In conclusion, the present study revealed similar secondary sex ratio of calves between left and right uterine horns in Holstein dairy cows.
authors.affiliation: Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
authors.forename: F
authors.initials: F
authors.lastname: Gharagozlou
authors.forename: M
authors.initials: M
authors.lastname: Vojgani
authors.forename: V
authors.initials: V
authors.lastname: Akbarinejad
authors.forename: A
authors.initials: A
authors.lastname: Niasari-Naslaji
authors.forename: M
authors.initials: M
authors.lastname: Hemmati
authors.forename: R
authors.initials: R
authors.lastname: Youssefi
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001723:Birth Rate; D001947:Breeding / Q000706:statistics & numerical data*; D002417:Cattle; D003612:Dairying; D005187:Fallopian Tubes / Q000166:cytology / Q000502:physiology*; D005260:Female; D008297:Male; D011247:Pregnancy; D011270:Pregnancy, Animal; D012744:Sex Ratio; D013045:Species Specificity
keywords: Dairy cows; Secondary sex ratio; Uterine side of pregnancy