Relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls

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Relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls A. N. Hafla, P. A. Lancaster, G. E. Carstens, D. W. Forrest, J. T. Fox, T. D. A. Forbes, M. E. Davis, R. D. Randel and J. W. Holloway J ANIM SCI 2012, 90:3937-3944. doi: 10.2527/jas.2011-4029 originally published online June 4, 2012

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Relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls
A. N. Hafla,* P. A. Lancaster,† G. E. Carstens,*1 D. W. Forrest,* J. T.Fox,‡ T. D. A. Forbes,§ M. E. Davis,# R. D. Randel,║ and J. W. Holloway§
*Department of Animal Science, Texas A&M University, College Station 77843;†Department of Animal Science, Oklahoma State University, Stillwater 74078; ‡JBS Five Rivers Cattle Feeding LLC, Greeley, CO 80634; §Texas AgriLife Research, Uvalde 78801;# Department of Animal Sciences, Ohio State University, Columbus 43210; and║Texas AgriLife Research, Overton 75684

ABSTRACT: A meta-analysis was conducted to examine phenotypic relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls. Data evaluated were obtained from 5 postweaning trials involving Angus (n = 92), Bonsmara (n = 62), and Santa Gertrudis (n = 50) bulls fed diets that ranged from 1.70 to 2.85 Mcal ME/kg DM. Afteran adaptation period of 24 to 28 d, feed intake was measured daily, and BW was measured at 7- or 14-d intervals during the 70- to 77-d trials. Ultrasound carcass traits (12th-rib back fat thickness, BF; LM area, LMA) and scrotal circumference (SC) were measured at the start and end of each trial. Semen samples were collected by electroejaculation within 51 d of the end of the trials when the ageof bulls averaged from 365 to 444 d and were evaluated for progressive sperm motility and morphology. Residual feed intake (RFI) was calculated as the difference between actual DMI and expected DMI

from linear regression of DMI on ADG and midtest BW0.75, with trial, trial by ADG, and trial by midtest BW0.75 as random effects. Across all studies, bulls with low RFI phenotypes (0.5 SD above themean RFI of 0). Gain to feed ratio was strongly correlated with ADG (0.60) and weakly correlated with initial BW (−0.17) and DMI (−0.26). Residual feed intake was not correlated with ADG, initial age, or BW but was correlated with DMI (0.71), G:F (−0.70), and BF (0.20). Initial SC (−0.20), gain in SC (−0.28), and percent normal sperm (−0.17) were correlated with G:F, but only sperm morphology wasfound to be weakly associated with RFI (0.13). These data suggest that RFI is not phenotypically associated with SC or sperm motility but is weakly associated with sperm morphology.

Key words: residual feed intake, scrotal circumference, sperm morphology, sperm motility © 2012 American Society of Animal Science. All rights reserved.
INTRODUCTION Feed cost is the single largest variable expenseassociated with the production of beef, and it accounts for approximately 65% of the expense required to maintain a breeding herd (Arthur et al., 2004; Van der Westhuizen et al., 2004). Ratio-based traits like G:F have been used to measure feed efficiency, but favorable selection will result in increased growth and ma1Corresponding

J. Anim. Sci. 2012.90:3937–3944 doi:10.2527/jas2011-4029author: g-carstens@tamu.edu Received March 4, 2011. Accepted May 18, 2012.

ture cow size. Residual feed intake (RFI) is a measure of feed efficiency that is independent of growth traits (Herd and Arthur, 2009) and moderately heritable (Herd et al., 2003). Progressive seed stock producers are adopting technology to measure daily intake to assess feed efficiency of growing bulls and heifers....
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