Evaluation of Selection Practices in Three Lines of Beef Cattle

Selection practices in three synthetic lines of beef cattle were evaluated based on data collected over 12 to 13 years. Sires from the Jersey, Angus and Simmental breeds were mated to three lines of foundation crossbred dams to produce first generation progeny. Subsequent calves were produced mating crossbred parents of the same generation. Crossbred sires were selected based on an index that included hip height and weight at weaning. At Rhodes, a total of 2.84 to 3.07 generations of selection have been carried out. This provided a mean generation interval of 4.33, 4.23 and 4.58 years in small, medium and large lines, respectively. At McNay, the corresponding generation interval values were 4.15 years for small and medium lines and 5.29 years for the large. The mean weighted sire selection differential for the index in the small line was 1.28 s/generation. In the medium cattle these values were -.57 s/generation (Rhodes) and -.36 s/generation (McNay). For the large synthetic cattle the index differential ranged from .71 s/generation at McNay to .92 s/generation at Rhodes. Of the total mean parental selection differential, sire contribution ranged from 86% to 95%. Selection differential values for components of the index indicated that the index equations often favored weaning weight, and this was very pronounced in the medium line. Regardless of the line, selection criteria have been strictly followed. However, all the maximum potential sires have not been utilized

IMPUTING CHARACTERISTIC VALUES OF AGRICULTURAL SEED-STOCK

Statistical methods of regression and mathematical (linear) programming are employed to combine principles of economics and genetics in a conceptual, multi-step, model of valuation for biotechnical change. The resulting model has the capacity to estimate the value of changes in specific characteristics for specific production environments, whether those changes are accomplished by traditional plant and animal breeding methods or by genetic engineering. The application of the model is illustrated with an example of commercial cow-calf production under conditions typical of the Texas Panhandle using a total of 32 breed groups

Individual descriptive record system

An electronic individual descriptive record system for storing the individual\u27s identification and descriptive data on a programmable electronic identification and data storage module carried with the individual so that the individual\u27s identification, the individual\u27s descriptive data and the individual itself become one. The system includes an implantable programmable electronic identification and data storage module carried by the individual, and a reading and recording device which communicates with the electronic identification and data storage module

An Evaluation of Four Procedures to Rank Centrally Tested Boars

Four procedures, one using genetic relationships, were evaluated to rank centrally tested boars from records on 9,093 boars tested in central stations. Breeds with larger numbers of tested boars were found to have more total relationship ties than were breeds with smaller numbers of boars tested. Of the breeds with greater tested numbers, Durocs and Yorkshires Were genetically more tied than were the Hampshire or Spotted breeds. Among breeds with fewer observations, Berkshires had the most relationship ties, while Poland Chinas had the fewest. When the number of ties between boars in each season-year with boars in the most recent season-year were evaluated, only the last six or seven-season-year groups were needed to provide sufficient relationship ties with pigs currently tested. The four evaluation procedures were performance value (PV), deviation of the performances value from the station-season-year subclass mean (SSYD), mixed model without relationships (MM) and mixed model including relationships (MMR). The MM procedure produced much lower prediction error variances than did the PV or SSYD procedures; whereas the MMR procedure produced the lowest prediction error variances. Although the MM and MMR procedures gave far more precise estimates than did PV and SSYD, they do involve more complex computing procedures. When the cost of these morecomplex computations is reasonable, the MMR procedure should be considered to evaluate centrally tested boars because it allows a fair comparison of boars across stations in the same season. The value of across station evaluation is discussed

Prediction of Percent Retail Product, Retail Product Weight and Hot Carcass Weight From Serially Measured Live Animal Traits

A total of 1,072 observations collected over a six-year period were used to develop prediction models for retail product (percentage and weight) and hot carcass weight from live cattle measures. Independent variables used were: ultrasound fat thickness (UFAT), ultrasound longissimus muscle Area (ULMA), age, hip height (HT), live weight (WT), ultrasound-predicted percent Intramuscular fat (UIMF) and breed composition. Pearson product moment correlations between the dependent and independent variables were often significant (P \u3c .01, P \u3c .05). In the prediction of percent retail product, UFAT accounted for 29 to 42% of the variation. A complete model including all the independent variables explained 20% more of the variation. In the prediction of retail product weight, WT remained a highly significant independent variable accounting for 32 to 78% of the variation. Similarly, WT accounted for 38 to 81% of the variation in hot carcass weight. When independent variables were adjusted to a constant age, models from data adjusted to earlier ages (M-414, M-382) explained more variation than models from data adjusted to a mean age at slaughter (M-448)

Prediction of Marbling Scores From Percentage Intramuscular Fat

In this study two separate sets of data were used to develop prediction equations for Marbling Scores (MS) from actual percentage intramuscular fat. All regression parameters were significantly (P\u3c.01) different from zero. Model-I explained only 49% of the variation in MS as compared with 83% for model- II. When these equations were validated on an independent data set, the correlations between the predicted and actual marbling scores were similar at 0.69 and 0.66 for model-I and model-II, respectively. Model-I has correctly classified 45.45%, 67.62%, 63.83%, and 42.86% of the bservations in trace, slight, small and modest classes, respectively. Model- II performed better than model-I for the extreme MS classes (practically devoid and moderate)

Validation of a Model for Prediction of Percent Intramuscular Fat on Live Feedlot Cattle

A prediction model from a previous study was utilized to evaluate the degree of fit when this model is applied to an independent data set. The degree of fit was evaluated using means, regression analysis, correlation coefficient, distribution of residuals, and mean square error of prediction (MSEP). The model provided a reasonably accurate prediction of intramuscular fat with a mean bias of 0.13%. For 47.1% of the steers, percent intramuscular fat was predicted within ± 0.5%, and for 77.6% of the steers, prediction of percent intramuscular fat was made within ± 1%. Pearson product moment correlation between predicted and actual percent intramuscular fat was 0.74 (p \u3c .01), and the square root of MSEP indicated a prediction error of 0.9%

Evaluation of Ultrasound Measurements of Fat Thickness and Ribeye Area, I. Assessment of Technician Effect on Accuracy

Data from two feeding trials were used to estimate accuracy of ultrasound measurements of fat thickness and ribeye area. In each trial, steers were scanned three or four times by one technician. Two beef improvement federation (BIF)-certified technicians with different levels of experience interpreted images from the last scan taken just before slaughter. Each technician interpreted the image of an individual steer twice on two different days. Accuracy of interpretation was evaluated using simple statistical measures, including means, standard deviations, regression and correlation coefficients, RMSE, and ESD. The overall technician biases for ultrasound measurements of fat thickness and ribeye area were -0.17 cm and 0.63 cm2, respectively. Mean bias by technician indicated a similar direction and amount of bias (-0.14 vs -0.20 cm). However, bias in the measurement of ribeye area by the two technicians took an opposite direction ( -1.28 vs 2.54 cm2). In all cases, technician bias was within the acceptable range for BIF certification. Pearson product moment correlations between carcass and ultrasound measurements of fat thickness and ribeye area were 0.70 and 0.40, respectively. In general, fat thickness for 52% of the steers was measured within ±0.254 cm and for 85.2 % of the steers, fat thickness was measured within ±0.508 cm. For ribeye area, ±51.2 % and ±71.4 % of the steers had measurements within ±6.65 cm2 and ±12.99 cm2, respectively

Evaluation of Ultrasound Measurement of Fat Thickness and Ribeye Area, II. Repeatability of Measurements.

Data from two feeding trials were used to evaluate repeatability of ultrasound measurements of fat thickness and ribeye area. In each trial, steers were scanned three or four times by one technician. Two beef improvement federation (BIF)-certified technicians with different levels of experience interpreted images from the last scan. Each technician interpreted the image of an individual steer twice on two different days. Repeatability was evaluated as an intra-class correlation. Additional statistics used to evaluate repeatability were the slope and intercepts from a regression analysis, RMSE, and ESD. Ultrasound measurements of fat thickness and ribeye area were repeatable both within and across technicians. The only exception was the across-technician measurements of ribeye area, where an apparent difference in variances of measurements was observed