This research aimed to evaluate the effects of zilpaterol hydrochloride (ZH; MSD Animal Health, São Paulo, SP, Brazil) on the performance, carcass traits, serum metabolites, body composition, and gain composition of nonimplanted Nellore heifers. Nellore heifers ( = 72; average BW = 267 ± 16 kg; average 18 mo of age) were maintained in a feedlot system for 118 d. Heifers were separated into 2 groups: Control and ZH. The ZH group received ZH (8.3 mg/kg diet DM) for 30 d with 3 d of withdrawal before slaughter. Heifers were allotted to 18 pens, 9 pens per treatment, and assigned to a randomized block design. The animals were weighed, blood samples were collected, and subgroups of heifers were slaughtered at the beginning of supplementation and after 20 and 33 d to evaluate performance, blood metabolites, empty BW (EBW), and EBW composition. Hot carcass and kidney-pelvic fat weights were recorded at slaughter. At 24 h postmortem, carcasses were fabricated and the 9-10-11th rib (HH) section was removed from the primal rib to analyze moisture, protein, ash, and ether extract (EE) content in empty body (EB) and gain composition. Heifers fed ZH had gains in HCW that were 19.7 kg greater than controls, reflecting the 30% increase ( < 0.01) in ADG. There was no change in DMI, resulting in a 20% greater G:F ratio ( < 0.01) for heifers fed ZH. Heifers supplemented with ZH had carcass dressing percentages that were 3% greater than controls ( < 0.01), and there was also a 19% reduction in kidney-pelvic fat ( = 0.05) in ZH-treated heifers. Zilpaterol increased serum creatinine ( < 0.01), tended to increase ( = 0.06) serum triacylglycerol, decreased serum NEFA ( = 0.04), and tended to decrease ( = 0.06) serum glucose. The EBW composition was changed after 20 d of ZH supplementation ( = 0.02), with ZH increasing the moisture, ash, and protein contents, whereas carcass fat was decreased by ZH by 14%. Consequently, the carcass CP:EE ratio after 20 d was increased ( = 0.03) by 24% with ZH supplementation. There was no change on EBW composition after 30 d of ZH supplementation ( = 0.17). Regarding carcass gain composition, ZH increased EBW gain ( = 0.02) by 842 g/d from d 0 to d 30, EB protein gain by 221 g/d ( = 0.05) from d 0 to d 20, and by 180 g/d ( = 0.01) from d 0 to d 33. In conclusion, ZH supplementation in nonimplanted Nellore heifers altered the composition of body weight gain, promoting greater lean tissue deposition and improving feed efficiency.
RESUMO-Trinta e dois tourinhos da raça Santa Gertrudis com peso inicial de 230 kg e idade média de 9 meses foram utilizados em um experimento de abate comparativo com delineamento de blocos ao acaso em esquema fatorial 2 x 2, com dois níveis de concentrado na dieta, 20 ou 80%, e dois ingredientes energéticos no concentrado, milho ou polpa de citros peletizada. Quatro animais foram abatidos após o período de adaptação para determinação da composição corporal inicial do lote e os que receberam dietas com 80 e 20% de concentrado foram abatidos após 123 e 172 dias de confinamento, respectivamente. O tratamento com 80% de concentrado à base de milho resultou em ganhos de peso vazio de 1,038 kg/dia, 40% maior que os demais. A substituição do milho pela polpa de citros decresceu o ganho a níveis abaixo dos tratamentos com 20% de concentrado, nos quais não foi observada diferença entre as fontes de energia. A composição química corporal, estimada por intermédio da composição do corte da 9-10-11 a costelas com equações obtidas em outro grupo de animais Santa Gertrudis, não revelou diferenças entre os tratamentos. Palavras-chave: composição corporal, polpa de citros, taxas de deposição, tourinhos Santa Gertrudis ABSTRACT-Thirty two Santa Gertrudis young bulls with an initial weight of 230 kg and 9 months of age were used in a comparative slaughter experiment with a 2 x 2 factorial arrangement with two concentrate levels, 80 and 20%, and two energetic ingredients in the concentrate, corn grain or pelletized citrus pulp. Four animals were slaughtered after the adaptation period for the determination of the initial body composition of lot and those that received diets with 80 and 20% of concentrate were slaughtered after 123 or 172 days, respectively. The treatment with 80% of corn grain based concentrate resulted in empty body weight gain of 1.038 kg/day, 40% greater than the others. The substitution of corn grain by citrus pulp decreased the body weight gain below those of the treatments with 20% concentrate, in which no difference due to energy source was observed. The chemical body composition, estimated by means of the 9-10-11 th rib cut composition with equations obtained from another group of Santa Gertrudis animals, did not show differences among treatments. Introdução Na determinação das exigências de energia e pro-teína para o ganho de peso, há necessidade de medir a mudança na composição corporal ao longo do cresci-mento, a qual pode ser influenciada por fatores como idade, sexo, raça e nível nutricional (AGRICULTURAL RESEARCH COUNCIL-ARC, 1980). A raça e o sexo, segundo o ARC (1980), afetam mais a composi-ção do ganho de peso que a taxa diária de ganho de peso. Raças de maturidade precoce, segundo REID et al. (1980), têm mais gordura e menos proteína, para deter-minado peso, que as raças de maturidade tardia. Segundo OWENS (1995), o crescimento é defini-do como a deposição de proteína, gordura e minerais. A deposição de proteína decresce a zero, quando o animal atinge seu peso adulto, embora ainda continue a depo...
RESUMO FRASSETO, M. O. Avaliação da eficiência biológica e doses crescentes de adubação em pastagens de capim-marandu e capim-mombaça durante o verão e outono em sistema de cria. [Biological efficiency evaluation of increasing doses of fertilizers on marandu and mombaça pasture prairies during summer and autumn in a calf rearing system]. 2015. 92 f.
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