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- Title
Relationship between residual feed intake and onset of puberty in Brangus heifers.
- Authors
Lancaster, P. A.; Carstens, G. E.; Forrest, D. W.; Randel, R. D.; Welsh Jr., T. H.; Forbes, T. D. A.
- Abstract
Objectives of this study were to examine relationships between residual feed intake (RFI) and onset of puberty and ultrasound estimates of carcass composition in growing, purebred heifers. Average (± SD) initial ages of Brangus heifers (Camp Cooley Ranch) used in this study were 225 ± 9 and 236 ± 11 d for years 1 (N = 114) and 2 (N = 115). Heifers were individually fed a roughage-based diet (ME = 2.2 Mcal/kg) using Calan-gate feeders, and BW and DMI were measured weekly for 70 d. Rfiwas calculated as the residual from the linear regression of DMI on mid-test BW0.75 (MBW) and ADG. Ultrasound measures of 12th rib fat thickness (BF), longissimus muscle area (LMA), and percent intramuscular fat (IMF) were measured on d 0 and 70. Progesterone analyses of weekly blood samples were used to determine onset of puberty. Heifers exhibiting a progesterone concentration ≥ 2 ng/mL for one wk or ≥ 1 ng/mL for two consecutive wk were considered to be pubertal. Ovarian ultrasound performed on d 63 of each year's study was used to confirm pubertal heifers. Average (± SD) ADG, DMI and Rfiwere 0.90 ± 0.15 and 1.06 ± 0.16 kg/d, 9.1 ± 1.1 and 9.5 ± 1.0 kg/d, and 0.00 ± 0.75 and 0.00 ± 0.68 kg/d for year 1 and 2, respectively. Rfiwas phenotypically correlated (P < 0.01) with DMI (0.67) and feed conversion ratio (FCR; 0.56), but not ADG or initial BW. Rfitended to be correlated (P < 0.10) with LMA (-0.16) and BF (-0.12) on d 0, but not with LMA or BF on d 70. Heifers with low Rfi(< 0.5 SD; n = 73) consumed 17% less (P < 0.01) DMI and had 16% lower (P < 0.01) FCR than heifers with high (> 0.5 SD; n = 66) RFI, even though final BW and ADG were similar. Across both years, 29% of the heifers were pubertal by d 70. Chi-square analysis revealed that the percentage of heifers that were cycling by d 70 within low (35.6%), medium (27.8%) and high (22.7%) Rfiphenotypes were similar (P > 0.20). Moreover, of those heifers that were pubertal by 70 d, age at puberty and maximum progesterone concentration were similar between low and high Rfiheifers. These data suggest that onset of puberty had a negligible association with phenotypic variation in RFI.
- Subjects
HEIFERS; PUBERTY; BLOOD testing; ANIMAL feeds; ANIMAL carcasses; BLOOD sampling
- Publication
Journal of Animal Science, 2006, Vol 84, p417
- ISSN
0021-8812
- Publication type
Article