title: Residual feed intake and blood variables in young Nellore cattle.
abstract: This study was conducted to evaluate associations of performance traits, feed efficiency, and blood variables with residual feed intake (RFI) in growing Nellore cattle. A total of 118 growing Nellore animals, 62 males and 56 females, were used. A diet containing 2 Mcal/kg was offered ad libitum and individual DMI was measured over a period of 84 d. Animals were classified as low (≤0.128 kg/d; = 40), medium (-0.128 to 0.135 kg/d; = 42), or high RFI (>0.135 kg/d; = 36). Blood samples were collected at the beginning and at the end of the test for determination of plasma concentrations of different blood variables. Data were analyzed using a mixed model that included the random effect of facility the fixed effects of sex, RFI class, and linear effect of the covariate age within sex; and the interaction between RFI class and sex. Least squares means were compared using a -test. Animals of different RFI classes presented similar performance traits and different DMI. Low-RFI animals consumed, on average, 0.670 kg/d less DM than high-RFI animals. Among the blood variables analyzed, significant differences among RFI classes were observed for urea, IGF-1, and insulin. Plasma urea concentrations were lower (5.58 vs. 5.91 mmol/L) and insulin (4.45 vs. 3.70 μIU/mL) and IGF-1 (433 vs. 399 ng/mL) concentrations were higher in low-RFI animals when compared to high-RFI animals. Plasma concentrations of urea, IGF-1, and insulin can be used as indicators of feed utilization efficiency in Nellore cattle.
authors.forename: C F
authors.initials: CF
authors.lastname: Nascimento
authors.forename: R H
authors.initials: RH
authors.lastname: Branco
authors.forename: S F M
authors.initials: SF
authors.lastname: Bonilha
authors.forename: J N S G
authors.initials: JN
authors.lastname: Cyrillo
authors.forename: J A
authors.initials: JA
authors.lastname: Negrão
authors.forename: M E Z
authors.initials: ME
authors.lastname: Mercadante
mesh_terms: D000375:Aging; D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D014508:Urea / Q000097:blood
chemical_list: D007328:Insulin; D007334:Insulin-Like Growth Factor I; D014508:Urea