|Cushman, Robert - Bob|
|ALLAN, MARK - Former ARS Employee|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/9/2010
Publication Date: 9/1/2010
Citation: Cushman, R.A., Allan, M.F., Mcdaneld, T.G., Kuehn, L.A., Rempel, L.A., Lindholm-Perry, A.K., Snelling, W.M., Freetly, H.C. 2010. Using growth traits and adipose function to identify indicators of heifer fertility [abstract]. Proceedings of 8th International Ruminant Reproduction Symposium. p. 130 (Abstract # M43).
Technical Abstract: The identification of early indicators of fertility would increase profitability by improving the quality of heifers chosen to enter the breeding herd. Growth traits are closely linked to age at puberty and could be predictors of initiation of reproductive cycles and heifer fertility. Adipose has been classically thought of as a tissue that stores excess energy; however, during the last decade it has been recognized as an endocrine organ that secretes hormones, growth factors, and adipokines. Therefore, the adipose represents an easily accessible tissue that could produce biomarkers of fertility that also could be linked to growth traits or feed efficiency. Crossbred beef heifers (n = 422) were observed for behavioral estrus with the aid of Estrotect patches starting at 6 months of age. At 363.7 ± 0.7 days of age, a subcutaneous adipose biopsy was collected from the tail head under epidural anesthesia; and at 416.3 ± 0.6 days of age heifers were pastured with fertile bulls for a 63-day breeding season. Heifers were examined by ultrasonography to determine pregnancy status 45 days after the end of the breeding season; pregnancy status was confirmed at calving. Random adipose samples from 22% of the heifers that were pre-pubertal (n = 15) or pubertal (n = 77) at the time of biopsy were analyzed by real-time RT-PCR to determine relative levels of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) mRNA because PPAR-gamma has been linked to adiposity, fertility, and ovarian function. Heifers that were pre-pubertal at biopsy were 10.2 ± 3.5 kg lighter at weaning (P = 0.004) and 6.3 ± 2.0 days younger at biopsy (P = 0.002) but did not differ in weight at breeding (P = 0.41) or in pregnancy rate (P = 0.42). Pre-pubertal heifers were 6.9 ± 3.0 days younger at calving (P = 0.02), but calving day did not differ between the groups (P = 0.64). Age at puberty did not differ between heifers that were diagnosed pregnant (n = 373) and heifers that were diagnosed open (n = 49; P = 0.83). Messenger RNA levels of PPAR-gamma did not differ between pre-pubertal and pubertal heifers (P = 0.88); however, PPAR-gamma mRNA levels tended to increase in a linear manner as age at puberty increased (P = 0.1). Heifers that were diagnosed pregnant (n = 84) and heifers that were diagnosed open (n = 8) did not differ in PPAR-gamma mRNA levels (P = 0.34). Messenger RNA levels of PPAR-gamma in the adipose were not a predictor of fertility. In future studies, biopsies will be collected at weaning because this is an ideal management point for making decisions on replacement heifers and because weaning weights were lower in heifers that reached puberty at a later age.