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Sixty Brangus bulls were evaluated live using two real-time ultrasound instruments and four technicians to estimate longissimus muscle area (LMA) and 12th rib fat thickness (FT) every 4 mo beginning at 4 and 12 mo of age, respectively, and continuing until 24 mo of age. Ten bulls were slaughtered every 4 mo to determine actual LMA and FT, 9-10-11th rib chemical composition, yield grade (YG) factors, and empty body weight (EBW). Live animal traits were used to predict 9-10-11th rib composition, YG, and EBW. Scanned mean FT was accurate (P less than .05) at 16 mo and was not different (P = .09) from the actual mean FT (95% of the time the error in estimation was less than or equal to .33 cm). Scanned mean LMA was accurate (P less than .05) at 12 mo (95% of the time the error in estimation was less than or equal to 20.0 cm2). Absolute differences between scanned and actual mean FT and LMA were different (P less than .05) from zero for the main effects of month, operator and(or) interpreter, and instrument. Increased level of operator skill did not improve the accuracy of FT or LMA measurements, whereas increased level of skill of the interpreter of scans did improve the accuracy of LMA estimations. There was no difference (P greater than .05) between ultrasound instruments in accuracy of estimating FT or LMA. The most accurate prediction of YG occurred at 12 mo and incorporated LW, hip height (HH), and ultrasound LMA (R2 = .95, SD = .14). The most accurate prediction of EBW occurred at 16 mo and incorporated LW, HH, and ultrasound FT (R2 = .99, SD = 6.65 kg), whereas the most accurate equation for combined slaughter periods incorporated LW, HH, and ultrasound LMA (R2 = .99, SD = 20.71 kg). We conclude that scanning of LMA at 12 mo and of FT at 12 or 16 mo were sufficiently accurate to characterize groups of bulls; however, some individual measurements were quite inaccurate. Measurements at other months should not be considered accurate for either individuals or groups of bulls. Yield grade and EBW can be accurately estimated from live animal and ultrasound measurements, which may be useful in identifying Brangus cattle with superior cutability and may eliminate the need for serial slaughter in research projects.

To determine whether the uterus was the source of serum pregnancy-specific protein B (PSPB) after calving, five beef cows were hysterectomized at 21 d postpartum and five served as intact controls. A single blood sample was taken from all cows immediately after calving and then twice weekly until 21 d postpartum. Beginning on d 22, blood samples were taken from all cows at 3-h intervals for 4 d and then twice weekly until 53 d postpartum. When the half-life calculated for the interval from d 1 to 21 was used as a covariate, the adjusted d-22 to -53 half-lives were 8.4 d for control cows vs 7.3 d for hysterectomized cows (P = .044). Data show that PSPB has a long half-life in the circulation and that the uterus is a minimal, if any, source of postpartum circulating PSPB. In another experiment, PSPB was measured weekly after calving in serum of 58 Polled Hereford and Simmental cows. Cows were exposed to fertile bulls and allowed to mate at every estrus. Observations were made for estrus, and progesterone concentrations in serum were measured to estimate the time of ovulations. Levels of PSPB were highest at approximately the time of calving, then decreased rapidly. Concentrations of PSPB were < 1 ng/mL by 80 d in eight cows that had not conceived since calving. Two cows eventually had nondetectable PSPB levels, one by 86 d and the other by 96 d after calving.(ABSTRACT TRUNCATED AT 250 WORDS)

Milk EPD, used to predict the milk production potential of a parent's daughters, have been reported by all major cattle breed associations. Our objectives were to determine the relationship of milk EPD of a dam to actual milk production (both fluid and components) and offspring weaning weight. Angus (AN; n = 114) and Simmental (SM; n = 82) cows were machine-milked at approximately 60, 104, and 196 d postpartum after overnight calf removal. In addition, one herd of AN was also milked at approximately 35 and 145 d postpartum. A lactation curve was fitted to these measurements to estimate total milk production during lactation. Simple correlations between 205-d total milk yields (TMY) and adjusted 205-d calf weaning weight (WW) were .30 (P < .001) and .47 (P < .001) for AN and SM, respectively. Furthermore, milk EPD was positively correlated to adjusted WW (r = .38 P < .001; r = .39, P < .001) and TMY (r = .32, P < .001; r = .44, P < .001) for AN and SM cows, respectively. A 1-kg change in TMY changed WW by .014 +/- .006 kg (P < .001) in AN and by .032 +/- .009 kg (P < .001) in SM. A 1-kg change in milk EPD resulted in a 4.85 +/- 1.14 kg change in WW (P < .001) in AN and a 3.74 +/- 1.73 kg (P < .05) change in SM. Corresponding changes in TMY were 42.1 +/- 16.6 kg (P < .01) and 69.3 +/- 16.0 kg (P < .001) for AN and SM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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