title: Higher feeding diets effects on age and liveweight gain at puberty in crossbred Nelore × Hereford heifers.
abstract: This study was conducted to determine the age and liveweight at puberty of 120 crossbred beef heifers submitted to four diets to achieve predetermined weight gains (kg/day): 0.5 (G500; n = 32), 0.75 (G750; n = 32), 1.0 (G1000; n = 29), and 1.25 (G1250; n = 27). Animals were classified depending on their level of crossing between Nelore (N) and Hereford (H): 25%N-75%H, 37.5%N-63.5%H, 43.7%N-56.7%H, 50%N-50%H, and 75%N-25%H. Reproductive evaluation was performed at the beginning and at the end of the experimental period by ultrasonography and hormone analysis. The average age and liveweight at puberty were 388.0 ± 1.9 days and 331.4 ± 1.3 kg, respectively. Animals from the 25%N-75%H group reached puberty earlier than heifers from other genetic groups supplemented with G1250 diet (P < 0.05). Heifers with higher degree of Nelore (75%N-25%H) fed with G1000 diet showed estrus 42 days prior to mating, but only 57% reached puberty at mating (P < 0.05). Heifers with follicles of higher diameter reached puberty (P < 0.05) earlier. Higher average daily weight gain showed a positive effect on follicular diameter and IGF-I level at puberty (P < 0.01). Concentrations of GH were lower in heifers fed G1250 compared to G1000 diet (P < 0.05). There was a significant interaction between nutritional level and insulin levels at puberty (P < 0.01). We demonstrated the relationship between IGF-I and average daily gain on the onset of puberty in heifers. In conclusion, heifers submitted to the higher feeding level showed a higher follicular diameter and were younger at puberty.
authors.affiliation: Department of Animal Science, Núcleo de Estudos em Sistemas de Produção de Bovinos de Corte e Cadeia Produtiva - NESPRO, Federal University of Rio Grande do Sul, UFRGS, Ave. Bento Gonçalves 7712, 91540-000, Porto Alegre, RS, Brazil.
authors.forename: Júlio Otávio Jardim
authors.initials: JO
authors.lastname: Barcellos
authors.forename: Gabriel Ribas
authors.initials: GR
authors.lastname: Pereira
authors.forename: Eduardo Antunes
authors.initials: EA
authors.lastname: Dias
authors.forename: Concepta
authors.initials: C
authors.lastname: McManus
authors.forename: Leonardo
authors.initials: L
authors.lastname: Canellas
authors.forename: Mari Lourdes
authors.initials: ML
authors.lastname: Bernardi
authors.forename: Adriana
authors.initials: A
authors.lastname: Tarouco
authors.forename: Enio Rosa
authors.initials: ER
authors.lastname: Prates
mesh_terms: D000367:Age Factors; D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D001947:Breeding / Q000379:methods; D002417:Cattle / Q000235:genetics* / Q000254:growth & development*; D003433:Crosses, Genetic; D004032:Diet / Q000662:veterinary*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D012098:Reproduction / Q000502:physiology; D012741:Sexual Maturation / Q000502:physiology*; D014463:Ultrasonography; D015430:Weight Gain / Q000502:physiology
chemical_list: D012739:Gonadal Steroid Hormones; D007334:Insulin-Like Growth Factor I
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