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Made available in DSpace on 2022-04-29T08:29:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-01 Context: Knowing the broilers' response to the intake of balanced protein allows nutritionists to choose the optimal level to be used in the feed. Aims: The objective of the present study was to describe the response of male and female broilers of two commercial strains to a range of dietary balanced protein levels. Methods: In total, 2496 sexed chicks (equal numbers of Ross 308 and Cobb 500) were used. Six dietary balanced protein levels × two strains × two sexes (24 treatments) were randomly allocated to 96-floor pens, using four replications of 26 chicks each. Feed intake, bodyweight, feed conversion efficiency, carcass weight and the weights of the breast without skin, thigh plus drum (leg) and wing were measured at 14, 28, 42 and 56 days of age. Key results: Feed intake in all periods in both strains and sexes increased as the dietary balanced protein level decreased, and then decreased markedly at the lowest balanced protein levels. Only at 14 days did the responses differ between strains and sexes; in all other cases, the responses differed only between sexes. At 14 days, the response in bodyweight differed between strains and sexes, whereas at all other samplings they differed only between sexes. The response in carcass, breast and wing yield at 14 days was the same for both strains and sexes but differed between strains and sexes at 28 days. At 42 and 56 days, the response differed only between sexes. The response in leg (thigh-plus-drum) weight at 14 days was the same for both strains and sexes, but after that differed between sexes only. Body lipid content increased linearly initially, and then quadratically, as dietary protein content was reduced. Conclusions: Appropriate equations are presented for describing the above responses of broiler chickens, male and female, from two commercial strains. Implications: The fitted equations may be used to calculate the optimum economic level of dietary balanced protein to be used under different economic circumstances. Departamento de Zootecnia UNESP-Universidade Estadual Paulista (Unesp) Faculdade de Ciências Agrárias e Veterinárias, Via de Acesso Professor Paulo Donato Castellane, s/n São Paulo School of Agricultural Earth and Environmental Sciences University of KwaZulu-Natal, Carbis Road, Scottsville Evonik Operations GmbH, Rodenbacher Chaussee 4 Departamento de Zootecnia UNESP-Universidade Estadual Paulista (Unesp) Faculdade de Ciências Agrárias e Veterinárias, Via de Acesso Professor Paulo Donato Castellane, s/n São Paulo

Made available in DSpace on 2019-10-06T05:12:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Programa de Estudante Convenio de Pos GraduacAo (PEC-PG) The objective of the present study was to describe the growth of reproductive organs and, on the basis of this information, predict feed intake during the pre-laying phase of laying-type pullets and to evaluate the results of the models. Ninety-six ISA-Brown pullets from 15 to 28 weeks of age were used in the first experiment. The weights of the birds with and without feathers, ovaries and oviducts were measured, and samples were taken to analyse dry matter, gross energy and crude protein. Seventy-six ISA-Brown and 76 Hy-Line pullets from 15 to 24 weeks of age were used in the second experiment. Feed intake was measured daily for each hen until the first egg was laid. The energy for maintenance (EEM) was calculated on the basis of the actual protein content and protein weight at maturity. The effective energy (EE) requirement was calculated as EER = EEM + 50 deposition of protein (DP) + 56 deposition of lipids (DL). Feed intake was calculated by dividing the EE requirement by the EE content in the feed. The simulation of feed intake overestimated values of 0.41 g/day (P > 0.05) and 2.65 g/day (P < 0.001) for Hy-Line and ISA-Brown respectively. A significant linear bias was observed for Hy-Line (P < 0.001) but not for ISA-Brown (P > 0.05). The assessment of the results indicated that the models for predicting feed intake were more accurate and less precise for Hy-Line than for ISA-Brown. Thus, there was an agreement between the calculated and measured values for feed intake, which shows that the models provide a true estimation of feed intake during the pre-laying phase. Univ Estadual Paulista, BR-14884900 Sao Paulo, Brazil Univ Estadual Paulista, BR-14884900 Sao Paulo, Brazil FAPESP: 2013/25761-4