No abstract

. 1993. Maternal factors and the prediction of dystocia in beef heifers. Can. J. Anim. . Stepwise discriminant analysis was used to determine maternal factors associated with dystocia in 564 2-yr-old heifers bred to bulls with below breed average birth weights-. Calf birth weight (n : 556) was consistently the most significant (P < 0.001) factor correlated (Rr = 0.31) with dystocia. Other significant (P < 0.001) factors were weight at breeding (n : 376) and calving (n = 559: R' = 0.11 for both traits). Other factorsconsideredwereageatbreeding(n:446), pelvicareaatbreeding (n = ll2) andpregnancy evaluation (n:297), heifer birth weight (n --564), gestation length (n : 467) and age at calving (n:559) but none were significant (P > 0.05). Heifers requiring caesarian section were heaviest (P < 0.05) at breeding and their calves were heaviest (P < 0.05) at birth. Unassisted heifers were heavier at calving (P < 0.05) than assisted heifers. It was concluded that none ofthe factors examined in this study was a reliable predictor of dystocia in beef heifers but that heifers should be bred atl 5 ir la dystocie chez 564 g6nisses de deux ans mises i la reproduction avec des taureaux dont les poids d la naissance 6taient inf6rieurs d la moyenne de la race. La poids des veaux ir la naissance (n : 556) 6tait r6gulidrement le facteur le plus significatif (P<0,001) corr6l6 ir la dystocie (R' : 0,31). Egalem-ent significatif (P< 0,001) 6tait le poids ir la mise ir la reproduction (n : 376) et au v€lage (n = 559, Rr : 0,11 pour les deux caractbres), D'autres facteurs consid6r6s 6taient l'Age d la mise ir la reproduction(n = 446),lasurfacepelvienneirlamiseirlareproduction(n:112)et1'6valuationdelagravidit6 (n : 29'7), le poids des g6nisses ir la naissance (n : 564), la dur6e de la gestation (n : 467) et I'Age au vdlage (n : 559), mais aucun de ces caractdres ne s'est rdv6l6 significatif (P > 0,05). Les g6nisses qui requ6raient une c6sarienne 6taient les plus lourds (P < 0,05) ir la mise ir la reproduction et leurs veaux 6taient les plus lourds (P < 0,05) d la naissance. Les g6nisses vClant sans aide 6taient plus lourdes au v€lage (P < 0,05) que celles qui avaient besoin d'aide. On conclut qu'aucun des facteurs examin6s n'6tait un pr6diteur fiable de la dystocie chez les g6nisses, mais on peut dire toutefois que, pour rdduire les risques de dystocie, le poids des g6nisses h la mise d la reproduction devrait €tre de 75 it80% de leur poids pr6vu au vdlage.

Charolais (C), Maine-Anjou (MA), Simmental (S) and Brown Swiss (SB) bulls were evaluated using production traits of their steer calves from birth to slaughter. Traits measured were calving ease, birth weight, preweaning average daily gain (ADG), adjusted weaning weight, ADG to slaughter; liveweight at slaughter, days on feed, carcass weight, grade fat, loin-eye area, cutability and dressing percent. For most traits the ranking was MA ≥ C ≥ S ≥ SB. Key words: Beef sire, calving ease, growth, carcass

. Theeffectof zeranol implants on growth and pregnancy loss in beef heifers. Can. J. . Live weight, average daily gain (ADG) and reproductive performance were compared between heifers implanted with zeranol at birth, 100 and 200 d of age (n : 54) and those not implanted (n : 50). Zeranol implantation resulted in increased (P < 0.05) ADG from birth to weaning, weaning weight, ADG from weaning to breeding, breeding weight and calving weight but did not affect (P > 0.05) calf birth weights, incidence of dystocia, calf survival or gestation lengths. Zeranol implants did not affect (P > 0.05) the incidence or magnitude of the pre-ovulatory LH surge or the number of heifers that ovulated between 48 and 168 h after cloprostenol injection. Pregnancy rate 42 d after bull entry did not differ between the two groups (P > 0.10), tended toward a difference at72 d (P < 0.10), and was different at 133 d (P < 0.05), with implanted heifers having a lower pregnancy rate than non-implanted heifers. Between day 72 and day 133 after bull entry there was a 70% embryonic or fetal mortality rate in zeranol-implanted heifers, which differed from the 0% loss in non-implanted heifers (P < 0.05). We conclude that serial implants of zeranol from birth reduced the pregnancy rate in heifers and that this effect was due to early fetal loss. de la gestation. Le z6ranol n'a pas eu d'influence (P > 0,05) sur la fr6quence ou l'amplitude de la d6charge pr6ovulatoire de LH, ni sur le nombre de g6nisses qui ovulaient entre 48 et 168 h aprbs injection de cloprostdnol. Le taux de gestation, 42 j aprbs l'exposition au taureau ne diff6rait pas entre les deux groupes (P > 0,10). A 72 j, cependant, on observait une diff6rence (P < 0,10) et d 133 j on notait une diff6rence significative (P < 0,05), les g6nisses implant6es ayant un taux de gestation moins 6lev6 que les g6nisses non implant6es. Entre le72 et le 133" j aprbs I'admission des taureaux, on observait un taux de mortalitd embryonnaire-foetale de I0% chez les g6nisses implant6es, contrastant avec l'absence totale de ce type de mortalit6 chez les g6nisses non trait6es (P < 0,05). Les auteurs en concluent que I'implantation s6quentielle de z6ranol d partir de Ia naissance abaisse le taux de gestation chez les g6nisses et que cet effet serait d0 d la mortalit6 en d6but de d6veloppement foetal.