Browsing by Author "Amen, Tonya Sue"

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    Birth, weaning, carcass, and meat traits in Bos indicus-Bos taurus reciprocal backcross calves produced through embryo transfer
    (Texas A&M University, 2005-02-17) Amen, Tonya Sue; Herring, Andy; Gill, Clare; Dahm, P. Fred; Sanders, Jim
    Angus - Bos indicus (Brahman or Nellore) reciprocal backcross embryo transfer calves belonging to 28 full-sib families were evaluated for differences in birth weight (BW), gestation length (GL), weaning weight (WW), carcass weight (HCW), longissimus muscle area (REA), fat thickness (adjusted (ADJFAT) and actual(ACTFAT)), intramuscular fat (MARB), and Warner-Bratzler shear force tenderness (WBSF). Family types with a greater proportion of Bos indicus in the sire in relation to the amount in the dam (F1 x A and B x F1) averaged longer GL and heavier BW than their respective reciprocal crosses (A x F1 and F1 x B). Calves had longer GL when the F1 parent was BA as opposed to AB. Small differences (statistically insignificant) were detected for BW, but no consistent difference was found between offspring of AB and BA parental types, with the exception of male F1-sired calves. F1 x A and B x F1 crosses also showed a large BW difference between males and females (about 5.0 kg), while A x F1 and F1 x B crosses showed no BW difference between males and females. Further examination within each sex showed a difference between male reciprocals that was two times that of females. Calves with a higher percentage of Bos indicus in the sire compared to the proportion in the dam showed the same trend, as they were still heavier at weaning, and produced heavier carcasses than the reciprocal crosses, though these differences were not significant. As a whole, A backcross calves had more ACTFAT, more ADJFAT, larger REA, more MARB, and lower WBSF than B backcross calves, though no significant differences were detected between reciprocal crosses for any of these traits. These results suggest that for weight related traits, especially BW, both the breed constitution of the calf and the cross that produces the calf play an important role in its ultimate performance for Bos indicus crossbred calves. For carcass and meat related traits, it appears that the breed make-up of the calf itself is more significant in influencing performance than the cross used to produce the calf.
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    Feed efficiency, carcass, and temperament traits in F2 Nellore-Angus steers
    (2009-05-15) Amen, Tonya Sue; Gill, Clare A.; Herring, Andy D.; Derr, James; Sanders, James O.; Sawyer, Jason E.
    Feed efficiency in fed F2 Nellore-Angus steers produced through embryo transfer was evaluated using two methods: residual feed intake (RFI) and NRC-based model predicted residual consumption (MPRC). Sire and family(sire) both contributed to differences in model predicted residual consumption (P = 0.036 and P < 0.001, respectively), but not in RFI (P = 0.117 and 0.455, respectively). This indicates that variation exists among the sires and families studied, and the opportunity exists to improve MPRC through selection; it also indicates these 2 evaluation methods could result in different conclusions about feed efficiency. Five aspects of temperament were also evaluated (aggressiveness, nervousness, flightiness, gregariousness, and overall temperament) on a 9-point scale shortly after weaning. Sire had a significant effect on all 5 aspects of temperament evaluated, but family was only responsible for variation in aggressiveness, nervousness, and overall temperament. Contemporary group had no effect on aggressiveness, but did contribute significantly to variation in all other temperament traits. All temperament traits were highly correlated with one another (r = 0.81 to 0.98). Recipient dam temperament was lowly correlated with gregariousness and overall temperament (r = 0.16 and 0.15, respectively), and the correlations with recipient dam temperament approached significance for aggressiveness, nervousness and flightiness. This suggests that the temperament of the recipient female may have a small effect on the temperament of the calf. This population was structured to identify QTL for economically important traits and appears to be useful to identify genetic markers for feed efficiency and animal temperament.