Professor 208C Brehm 2505 River Drive Knoxville, TN 37996-4574 (865) 974-2887 Fax: (865) 974-7297 Email: asaxton@utk.edu Research Appointment: 80% Teaching Appointment: 20%
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RESEARCH

  Hatch Projects

TEN 078: Feasibility of Independent Culling for more than Five Traits (CRIS PROJ NO: TEN00078)

OBJECTIVES
Test and compare various approximations and modifications to independent culling(IC), to find the best approach for IC calculations with 5 to 20 traits. 2. Study the sensitivity of IC to errors in parameter estimates. 3. Incorporate all results, plus multistage and restricted IC applications into the existing INDCULL computer software.

APPROACH
Within the past 5 years several published suggestions have been made concerning approximate IC, or approximating the multivariate normal integral. Computer programs will be obtained or written so these methods can be compared under an essentially complete range of test conditions. Similarly, the sensitivity of IC and approximations above to errors in genetic parameter estimates will be studied under a range of test conditions. Best performing methods will be made available through computer software (INDCULL).

PROGRESS: 1994/07 TO 1997/09
The goal of this project was to allow independent culling to handle as many traits as a selection index, as this has been a computational limit on independent culling. The selection index has no practical limit, as 20, 50 or even 100 traits can easily be handled on a personal computer. Given this goal, this project has been a failure, as available algorithms with the desired accuracy are simply too slow for more than 8 to 10 traits to be practically feasible. These findings refer to exact independent culling, based on numerical integration of the multivariate normal distribution. Perhaps approximate methods may be developed with sufficient accuracy to be practically useful (with errors in the culling levels small enough that genetic gain is not greatley reduced). But it should be noted that 8 to 10 traits covers the vast majority of quantitative genetic applications, so to that degree the number of trait limitation on independent culling has been removed.

TEN 079: Optimization of Feeder Cattle Production (CRIS PROJ NO: TEN00079)

OBJECTIVES
To simultaneously quantify and evaluate factors that influence productivity of beef cow-calf enterprises in Tennessee. To estimate the distributions of net income generated by beef cattle production strategies. To identify beef cattle management practices that optimize net income within the varying biological, environmental and economic conditions of Tennessee.

APPROACH
A fractional factorial design will simultaneously evaluate the pre- and post-weaning production responses of feeder cattle to four differing environments, two calving seasons, three mature cow weights, three cattle breed types, and three nutrition availability levels. Yearly production inputs will be recorded for risk management evaluations and production potentials of cattle types based on genotype-environmental interactions. Primary indicators will be calf growth performance, cow reproductive health, calf mortality of first-calf animals and external fat cover changes of cattle within each operating environment.

PROGRESS: 1994/06 TO 1999/09
Data from five spring and three fall calf crops have been collected representing 724 and 348 cow-calf pairs, respectively. The data indicates a location (loc) effect (P=.05) on calf weaning weight(wwt), and on forage availability levels (nutr) which reflect the temperature and elevation differences. Nutr impacted both wwt (p=.01) and cow reproduction (p=.05). Loc x nutr interactions (p=.01) indicated wwt will not be equal for differing biological types (bt). Bt were described by mature weight and breed. Nutr x bt interactions revealed (p=.01) the need for higher nutr by the heavier bt for comparable wwt. These results indicate that increased weaning performance can be improved through management systems designed for specific bt. Weigh suckle weigh estimates (wsw) at 74, 137 and 191 days showed less increase in wwt following 74 days (b=3.1, 1.5, 0.5, respectively). This indicates that selection for increased milk production is less important than improving nutr. Nutr effects (p=.05) were apparent following weaning when comparing calves going direct to the feedlot or to a grazing stocker program. Calves going direct to the feedlot from a higher nutr had greater (p=.05) live and carcass weight, rib and rump fat through the feedlot period, while the only difference with stocker cattle was found for live weight. This indicated that pre-weaning nutr differences are compensated by allowing time for calves to mature in a stocker program. For Tennessee producers this data indicates decisions to change bt for increased performance may also require changes in nutr to support normal reproduction and higher wwt.