|Gregory, Keith - FORMER ARS EMPLOYEE|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 7, 2003
Publication Date: June 20, 2003
Citation: ECHTERNKAMP, S.E., GREGORY, K.E. REPRODUCTIVE EFFICIENCY IN CATTLE SELECTED FOR OVULATION AND TWINNING RATE. JOURNAL OF ANIMAL SCIENCE 81 SUPPLEMENT 1:183. 2003. Technical Abstract: Effect of ovulation rate on cow productivity was evaluated in the MARC Twinner herd by comparing ovulation rate (i.e., corpora lutea) at pregnancy diagnosis to calving results and progeny performance. Numbers of fetuses and corpora lutea were determined by scanning the uterus and ovaries transrectally with a 3.5 MHz, convex-array, real-time, ultrasound probe at 75 d after first d of the 1995 to 2002 spring and fall breeding seasons; females < 35 d of gestation were re-examined 35 d later. Progeny body weight was measured at birth and 200 d of age. Effects of type birth on progeny body weight and survival were analyzed by GLM ANOVA with age of dam, sex of calf, dystocia, year, season, and uterine location in the model and on calf survival by Chi-square analysis. Incidence of fetal mortality (abortions) from ultrasound to calving was 6.0% for single, 12.2% for twin, and 50.0% for triplet pregnancies (P < 0.01; n = 890, 583, and 28 cows, respectively). Percentage of females calving did not differ (P > 0.1) between single ovulations occurring on the left vs right ovary (84.9 vs 82.8%), but twinning rate was greater (P < 0.01) for bilateral twin ovulations (61.3% twins and 20.9% singles) compared with unilateral twin ovulations on left (55.4% twins and 27.9% singles) or right (53.6% twins and 27.0% singles) ovary. Calf birth weight and survival were also greater (P < 0.01) for bilateral vs unilateral twins (38.5 ± 0.3 kg and 91.8 ± 1.1% vs 36.8 ± 0.3 kg and 82.3 ± 1.1%, respectively). Single-born calves were heavier (P < 0.01) than twin or triplet calves at birth (48.7 ± 0.1 vs 37.6 ± 0.1 or 30.5 ± 0.6 kg) and at 200 d of age (256.9 ± 1.4 vs 222.4 ± 1.4 or 210.6 ± 7.0 kg); whereas, number weaned and total 200-d body weight per cow calving increased (P < 0.01) from single (0.89 ± 0.01 calf and 220.8 ± 2.5 kg) to twin (1.54 ± 0.01 calves and 343.6 ± 3.4 kg) to triplet (1.80 ± 0.08 calves and 378.3 ± 17.8 kg) birth. Bilateral twin ovulations produced the greatest increase in reproductive efficiency in cattle; whereas, increased pre- and postnatal mortality for triplet ovulations and births compromise such gains.