title: Evaluation of reproductive traits in Bos taurus and Bos indicus crossbred heifers: effects of postweaning energy manipulation.
abstract: Reproductive traits were evaluated in Bos taurus and Bos indicus crossbred heifers that were fed different diets during the postweaning period. The study was designed in a 2 x 2 x 2 factorial arrangement of treatments. Angus x Hereford (AH; n = 148) and Brahman x Hereford (BH; n = 148) heifers were sorted after weaning by body weight into light (LW) and heavy (HW) weight blocks. Heifers in each weight block were assigned to diets calculated to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weights by the start of the breeding season. Puberty was determined after a 160-d observation period and characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 6 to 10; estrus = d 0), and 3) rise in serum progesterone above 1 ng/ml (d 6 to 10). A higher (P = .01) proportion of AH heifers than of BH heifers reached puberty by the breeding season (93% vs 67%). Interactions of breed x weight block and energy level x weight block also contributed to this difference. Weight at puberty was heavier (P = .001) among HE than among LE heifers and greater for heifers in HW than for those in LW blocks (P = .02). Differences in prebreeding weight, body condition, average daily gain, hip height, and pelvic area were influenced selectively by breed, energy level, or weight block. Pregnancy rates were higher (P = .01) among AH than among BH heifers. Incidence and severity of dystocia was influenced by the breed x energy level interaction (P = .01). Brahman x Hereford heifers had less (P = .01) dystocia than AH heifers, HE heifers had less (P less than .02) dystocia than LE heifers, and HE-AH heifers had less (P less than .01) dystocia than LE-AH contemporaries. Subsequent duration of the postpartum interval to estrus was shorter (P = .002) among AH than among BH females. Pregnancy rates at the end of the 2nd yr were higher (P = .02) among LW than among HW females and weights were heavier (P = .001) at weaning among calves weaned from BH dams.
authors.affiliation: Kansas State University, Manhattan 66506.
authors.forename: D J
authors.initials: DJ
authors.lastname: Patterson
authors.forename: L R
authors.initials: LR
authors.lastname: Corah
authors.forename: J R
authors.initials: JR
authors.lastname: Brethour
authors.forename: M F
authors.initials: MF
authors.lastname: Spire
authors.forename: J J
authors.initials: JJ
authors.lastname: Higgins
authors.forename: G H
authors.initials: GH
authors.lastname: Kiracofe
authors.forename: J S
authors.initials: JS
authors.lastname: Stevenson
authors.forename: D D
authors.initials: DD
authors.lastname: Simms
mesh_terms: D000821:Animal Feed; D000818:Animals; D001947:Breeding; D002417:Cattle / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D002418:Cattle Diseases / Q000453:epidemiology; D003433:Crosses, Genetic; D004420:Dystocia / Q000453:epidemiology / Q000662:veterinary; D002149:Energy Intake; D004971:Estrus / Q000502:physiology; D005260:Female; D005298:Fertility; D005838:Genotype; D016018:Least-Squares Analysis; D009752:Nutritional Status; D010388:Pelvis / Q000033:anatomy & histology; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy; D012098:Reproduction / Q000235:genetics*; D012741:Sexual Maturation; D015430:Weight Gain