title: Fertilization and early embryonic development in heifers and lactating cows in summer and lactating and dry cows in winter.
abstract: Two experiments in two seasons evaluated fertilization rate and embryonic development in dairy cattle. Experiment 1 (summer) compared lactating Holstein cows (n = 27; 97.3 +/- 4.1 d postpartum [dppl; 40.0 +/- 1.5 kg milk/d) to nulliparous heifers (n = 28; 11 to 17 mo old). Experiment 2 (winter) compared lactating cows (n = 27; 46.4 +/- 1.6 dpp; 45.9 +/- 1.4 kg milk/d) to dry cows (n = 26). Inseminations based on estrus included combined semen from four high-fertility bulls. Embryos and oocytes recovered 5 d after ovulation were evaluated for fertilization, embryo quality (1 = excellent to 5 = degenerate), nuclei/embryo, and accessory sperm. In experiment 1, 21 embryos and 17 unfertilized oocytes (UFO) were recovered from lactating cows versus 32 embryos and no UFO from heifers (55% vs. 100% fertilization). Embryos from lactating cows had inferior quality scores (3.8 +/- 0.4 vs. 2.2 +/- 0.3), fewer nuclei/embryo (19.3 +/- 3.7 vs. 36.8 +/- 3.0) but more accessory sperm (37.3 +/- 5.8 vs. 22.4 +/- 5.5/embryo) than embryos from heifers. Sperm were attached to 80% of UFO (17.8 +/- 12.1 sperm/UFO). In experiment 2, lactating cows yielded 36 embryos and 5 UFO versus 34 embryos and 4 UFO from dry cows (87.8 vs. 89.5% fertilization). Embryo quality from lactating cows was inferior to dry cows (3.1 +/- 0.3 vs. 2.2 +/- 0.3), but embryos had similar numbers of nuclei (27.2 +/- 2.7 vs. 30.6 +/- 2.1) and accessory sperm (42.0 +/- 9.4 vs. 36.5 +/- 6.3). From 53% of the flushings from lactating cows and 28% from dry cows, only nonviable embryos were collected. Thus, embryos of lactating dairy cows were detectably inferior to embryos from nonlactating females as early as 5 d after ovulation, with a surprisingly high percentage of nonviable embryos. In addition, fertilization rate was reduced only in summer, apparently due to an effect of heat stress on the oocyte.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
authors.forename: R
authors.initials: R
authors.lastname: Sartori
authors.forename: R
authors.initials: R
authors.lastname: Sartor-Bergfelt
authors.forename: S A
authors.initials: SA
authors.lastname: Mertens
authors.forename: J N
authors.initials: JN
authors.lastname: Guenther
authors.forename: J J
authors.initials: JJ
authors.lastname: Parrish
authors.forename: M C
authors.initials: MC
authors.lastname: Wiltbank
mesh_terms: D000818:Animals; D002417:Cattle / Q000196:embryology* / Q000502:physiology*; D005314:Embryonic and Fetal Development; D005260:Female; D007315:Insemination, Artificial / Q000662:veterinary; D007774:Lactation / Q000502:physiology*; D008297:Male; D009865:Oocytes / Q000254:growth & development / Q000502:physiology; D010298:Parity; D011247:Pregnancy; D018873:Pregnancy Rate; D012621:Seasons; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology; D013997:Time Factors