title: Calves' sex ratio in naturally and artificially bred cattle in central Ethiopia.
abstract: A study was undertaken with the objective to identify some intrinsic (genotype of the cow, estrus time and parity) and extrinsic factors (service type, service time and estrus seasons) that affect calf sex ratio in naturally and artificially bred cattle in the central highlands of Ethiopia. A total of 4657 calving events were extracted from the long-term dairy cattle genetic improvement experiment at Holetta Agricultural Research Center. Factors that affect the logit of the probability of a female calf being born were obtained by using PROC GENMODE in Statistical Analysis System. Moreover, multivariate analysis was performed using PROC LOGISTIC procedure using forward selection procedure. Accordingly, genotype of the cow, parity, estrus season, and service type had considerable influences on calf sex ratio. However, estrus time and service time did not affect calf sex ratio (χ(2) = 0.83 and 0.79, respectively). In Ethiopia, smallholder dairy farmers often complain that artificial insemination (AI) skewed to producing more male calves. However, our study showed that AI did not alter female-to-male calf sex ratio. On the contrary, natural mating increases the probability of female calves born (odds ratio 1.38) over AI. Heifer/cows that showed estrus and bred during the harsh seasons of the years produced more female calves than those that bred during the good seasons of the year. This strongly agreed with Trivers and Willard sex allocation theory.
authors.affiliation: Ethiopian Institute of Agricultural Research, Holetta Agricultural Research Center, Holetta, Ethiopia. Electronic address: kefenaol@yahoo.com.
authors.forename: Effa Kefena
authors.initials: EK
authors.lastname: Delesa
authors.affiliation: Ethiopian Institute of Agricultural Research, Holetta Agricultural Research Center, Holetta, Ethiopia.
authors.forename: Aster
authors.initials: A
authors.lastname: Yohannes
authors.affiliation: Ethiopian Institute of Agricultural Research, Holetta Agricultural Research Center, Holetta, Ethiopia.
authors.forename: Mengistu
authors.initials: M
authors.lastname: Alemayehu
authors.affiliation: College of Veterinary Medicine, Nursing and Allied Health (CVMNAH), Department of Pathobiology, Tuskegee University, USA.
authors.forename: Temesgen
authors.initials: T
authors.lastname: Samuel
authors.affiliation: College of Veterinary Medicine, Nursing and Allied Health (CVMNAH), Department of Pathobiology, Tuskegee University, USA.
authors.forename: Teshome
authors.initials: T
authors.lastname: Yehualaeshet
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle; D005002:Ethiopia; D005260:Female; D007315:Insemination, Artificial; D008297:Male; D016017:Odds Ratio; D012744:Sex Ratio
keywords: Artificial insemination; Calf sex ratio; Estrus season; Natural mating