Submission Number: ROB-4-8-4

Abstract Number: 125

EARLY EMBRYONIC DEVELOPMENT DURING SUMMER IN LACTATING DAIRY COWS AND NULLIPAROUS HEIFERS.

Roberto Sartori* ¹, Renata Sartor-Bergfelt ², Siegrid A Mertens ¹, Jerry N Guenther ¹, John J Parrish* ² and Milo C Wiltbank* ¹

Department of Dairy Science, University of Wisconsin-Madison, Madison, WI, USA ¹
Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI, USA ²

Abstract:
Lactating cows with high milk production have much lower fertility than heifers with similar genetic potential. This experiment was designed to compare early embryonic development in lactating cows (C) with nulliparous heifers (H) and to evaluate if summer heat stress preferentially compromises oocyte/embryo quality in lactating animals. During the summer of 1999, Holstein cows (n=27; 50130 d postpartum; average milk production >40 Kg/d) and heifers (n=28; 1117 months old) were bred at estrus with a straw containing combined semen from 4 high fertility bulls. Five days after ovulation, embryos/oocytes were recovered and evaluated for fertilization, embryo quality (1=excellent to 5=degenerated), cell nuclei count (by fluorescent microscopy), and number of accessory sperm. On d 7 and 8, animals received PGF2, and were bred again at estrus. Daily ultrasonography confirmed ovulation. Each animal was flushed 2 or 3 times. Thirty-two embryos and no unfertilized oocyte (UFO) were recovered from H, and 21 embryos and 17 UFOs were recovered from C (100.0% vs. 55.3% fertilization rate; p<.01). The quality of fertilized embryos from C was inferior to H (3.8.4 vs. 2.3.2 [meansem]; p<.01). The cell nuclei count showed that embryos from C had fewer cells than from H (20.13.4 vs. 37.93.3; p<.01). Surprisingly, the number of accessory sperm in the embryos from C was greater than H (36.46.2 vs. 19.64.6; p<.01). Another interesting observation was that 80.0% of the UFOs had sperm attached to them (17.812.1 sperm/oocyte). Thus, high milk production may increase the negative effect of heat stress on fertilization and early embryonic development. These reductions do not appear to be due to a sperm problem based on attached sperm to UFOs and the high accessory sperm numbers in embryos from C. Further trials are needed to confirm the effect of lactation on fertilization rate and early embryonic development, independent of season, age and size of the animals.

Keywords: Fertility, Embryo, Dairy cattle

This abstract is being presented at: 8:00 AM in session:
Fertility Regulation I