Location: Range and Livestock ResearchTitle: Identification and analysis of beef heifers with superior capacity for fertility Author
|Bruno, Ralph G|
Submitted to: International Congress on Animal Reproduction
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2012
Publication Date: 7/29/2012
Citation: Minten, M.A., Bilby, T.R., Bruno, R.S., Allen, C.C., Roberts, C.A., Wang, Z., Sawyer, J.E., Tibrary, A., Neibergs, H.L., Geary, T.W., Spencer, T.E. 2012. Identification and analysis of beef heifers with superior capacity for fertility. International Congress on Animal Reproduction Abstract No. 1703. Interpretive Summary: n/a
Technical Abstract: Cattle production is highly dependent upon reproductive efficiency. Early pregnancy loss, estimated to be at least 25% in beef cattle and 45% in dairy cattle, is economically detrimental to both the beef and dairy industries. The majority of embryonic loss occurs between days 8 and 16 of gestation. To identify heifers of contrasting fertility, serial synchronized artificial insemination (AI) of pubertal beef heifers (1/4 Bos indicus, 3/4 Bos taurus, n=201) was conducted. Pregnancy was determined on day 35 post-timed AI. Heifers were ranked from highest to lowest fertility based on number of pregnancies in the four timed AI opportunities. Thirty-nine (39) heifers were classified as having high fertility (pregnant 4/4, n=14) or low fertility (pregnant 1/4, n=17; pregnant 0/4, n=8). The selected heifers were superovulated and flushed; embryos were graded and transferred into synchronized recipients. There was no effect of fertility classification on quantity of embryos recovered per flush or their quality. Pregnancy rates of recipient cows receiving embryos from either high fertility or low fertility donors were not different. These results indicate embryo quality is not the reason for contrasting fertility observed in these heifers. Two embryos (stage 4 or 5, grade 1 or 2) were then transferred into the heifers on day 7 after observation of estrus, and pregnancy determined by ultrasonography approximately 25 days later. Pregnancy rates were higher (P=0.03) in high fertile (69%) than low fertile (33%) heifers. Circulating levels of progesterone were not different in the heifers during the estrous cycle or at embryo transfer. Genome-wide association studies of DNA from the heifers using the Illumina 770K SNP BovineHD Genotyping BeadChip detected 7 (P< 2.0x10-5) associations with fertility that were present on 6 different chromosomes. The uteri from the selected heifers were collected on Day 14 of the estrous cycle. No obvious histological differences were present in the endometrium of the high versus low fertility heifers. Further analysis of uterine tissues and secretions from these animals will be used to elucidate physiological and genetic markers associated with fertility in cattle.