| dc.description.abstract | Bos indicus influenced primiparous heifers (n = 300) and yearling Beefmaster
heifers (n = 172) were evaluated to determine relationships between serial carcass
ultrasound traits and ability to breed in short (45 to 90 d) breeding seasons. Data
collected included carcass ultrasound traits: ribeye area (REA), intramuscular fat
(IMF), rump fat (UFAT), ribfat, weight, and body condition score taken at yearling
age, pregnancy determination, before breeding, and after the breeding season when
pregnancy status was recorded. A logistic regression analysis was used to determine
the influence of ultrasound traits and body condition on pregnancy status. Odds
ratios suggested the likelihood of primiparous cattle rebreeding would have been
increased by 93% if IMF would have averaged 3.5% instead of 2.5% as yearlings, or
an increase in the average ribfat as yearlings from 0.287 to 0.387 cm would have
increased the odds of rebreeding by 88%. Increased average body condition score of
6.5 rather than 5.5 at 30 days postpartum in primiparous cows was estimated to have
increased rebreeding 367%. The odds of yearling Beefmaster heifers successfully
breeding during a 45-day season would have been increased by 73% (year 1) or 274% (year 2) by increasing REA 6.4 to 6.5 cm^2 at a year of age. Steers were
serially scanned beginning at approximately 265 kg of body weight through harvest
in 56 day +/- 6 intervals. Data collected included ultrasound measurements (ribeye
area (REA), 12th rib fat thickness (RibFat), percent intramuscular fat (IMF), and
rump fat (UFAT)), weight, and carcass data. Days to choice was calculated for each
steer based on a linear regression. The IMF deposition was quantified as quadratic
from scans 1-6 and linear when cattle were on full feed. Prediction models at scans
1, 2, 3, 4, 5, and 6 yielded R-square values of 0.20, 0.25, 0.41, 0.48, 0.59, and 0.49,
respectively for days to choice. Odds ratios suggested that if steers in this study had
averaged 3.78% at day 0 rather than 2.78, the odds of cattle grading premium choice
or greater would have been increased by 300%. | en |
