Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 21, 2006
Publication Date: July 1, 2006
Citation: Echternkamp, S.E., Cushman, R.A., Allan, M.F. 2006. Effects of ovulation rate and fetal number on fertility in twin-producing cattle [abstract]. Journal of Animal Science. 84 (Supplement 1):152. (Abstract #209) Technical Abstract: Effects of ovulation rate (number of corpora lutea; OR) and of fetal number and distribution within the uterus on pregnancy rate (PR) and fetal survival were evaluated from 1994 to 2004 in nulliparous (n = 1230) and parous (n = 3104) females selected for twin births. Cattle were distributed equally between a spring (70 d) and fall (60 d) breeding season and bred by a combination of AI and natural service. Ovulation rate, PR, and fetal number and distribution were determined by real-time ultrasonography (US) of the uterus and both ovaries at 35 to 70 d post-breeding; PR was confirmed by rectal palpation at 75 to 135 d. For cows and heifers combined, OR increased (P < 0.01) from 1.46 in 1994 to 1.89 in 2004; number of calves/parturition increased from 1.34 to 1.56, respectively. Pregnancy rates at US and palpation diagnosis and at term for females with one (89.1, 85.1, and 85.1%, respectively), two (91.2, 86.5, and 82.7%), or three (91.5, 75.8, and 63.0%) ovulations were not affected by OR at US but PR decreased (P < 0.01) at calving with increasing OR. Cows with single ovulations had similar PR between seasons, but cows with twin or triplet ovulations had lower PR in the fall (OR x season; P < 0.05). Also, PR increased (P < 0.01) with postpartum interval but was decreased (P < 0.01) for dams with twins versus singles. For females diagnosed with one, two, or three fetuses at US, calving rate was 95.7%, 87.8%, and 54.9%, respectively, and differed (P < 0.01) among fetal groups. In addition, fetal survival was reduced (P < 0.01) for unilateral versus bilateral twins or triplets in heifers but did not differ in cows. Calf survival at birth was 97.2% for singles, 92.0% for bilateral twins, 83.2% for unilateral twins, 73.8% for bilateral triplets, and 51.9% for unilateral triplets and differed (P < 0.01) among single, bilateral twin, unilateral twin, and triplet births. Thus, increased calf production from increased OR in beef cattle is tempered by increased fetal and calf mortality, especially in nulliparous heifers.