A reservoir for sperm has been found in the oviductal isthmus in several species. Sperm are apparently trapped in the reservoir by binding to the oviductal epithelium, although other factors may be involved. We hypothesized that binding sites for bovine sperm are limited to the isthmus and are regulated by the hormonal state of the cow. Ipsilateral oviducts were obtained from heifers that were preovulatory (in estrus), had ovulated recently (within 12 h), or were in diestrus (Day 10). The isthmic and the ampullar epithelium were milked out and incubated separately in serum-free (SFRE-199-2) medium, at 39 degrees C in 5% CO2. Frozen-thawed sperm from bulls were added to the epithelium and coincubated for 15 min. The number of spermatozoa that bound to explants was not affected by stage of cycle or by anatomic origin of the explants (p > 0.05). In an additional experiment, oviducts were infused with sperm in vivo and then prepared for scanning electron microscopy, which revealed that sperm were associated with ciliated epithelium in both the isthmus and ampulla. Thus, bovine sperm may form a reservoir in the isthmic end of the oviduct because it is the first oviductal region that they encounter.
Our objective was to determine whether pregnancy rates in heat-stressed dairy cattle could be enhanced by timed embryo transfer of fresh (nonfrozen) or frozen-thawed in vitro-derived embryos compared to timed insemination. Ovulation in Holstein cows was synchronized by a GnRH injection followed 7 d later by PGF2 alpha and a second treatment with GnRH 48 h later. Control cows (n = 129) were inseminated 16 h (d 0) after the second GnRH injection. On d 7, a fresh (n = 133) or frozen-thawed (n = 142) in vitro-derived embryo was transferred to cows assigned for timed embryo transfer after categorizing the corpus luteum by palpation per rectum as 3 (excellent), 2 (good or fair), 1 (poor), and 0 (nonpalpable). Response to the synchronization treatment, determined by plasma progesterone concentration (ng/ml) < or = 1.5 on d 0 and > or = 2.0 on d 7, was 76.2%. Mean plasma progesterone concentration on d 7 increased as the quality of corpus luteum improved from category 0 to 3. Concentrations of progesterone in plasma were elevated (> or = 2.0 ng/ml) at 21 d in 64.7 (fresh embryo), 40.3 (frozen embryo), and 41.4 +/- 0.1% (timed insemination) of cows, respectively. Cows that received a fresh embryo had a greater pregnancy rate at 45 to 52 d than did cows that received a frozen-thawed embryo or timed insemination (14.3 > 4.8, 4.9 +/- 2.3%). Body condition (d 0) of cows influenced the pregnancy rate and plasma progesterone concentrations. In summary, timed embryo transfer with fresh in vitro-produced embryos in heat-stressed dairy cattle improved pregnancy rate relative to timed insemination.
Genetic parameters were estimated for scrotal circumference (SC; n=287), age at puberty in heifers (AP; n=292), and hip height in both sexes (HH; n=684) for Brahman cattle born from 1984 to 1994 at the Subtropical Agricultural Research Station, Brooksville, Florida. Age at puberty was defined as the age (days) at first detected ovulatory estrus. Measurements of SC and HH were taken at 18 mo of age. Fixed effects considered in the SC model were year of birth (YOB), age of dam (AOD), and age at measurement (AGE) as a linear covariate. Fixed effects fitted to the AP model were YOB and AOD. Fixed effects in the HH model were YOB, sex, AOD, and AGE as a linear covariate. Variances and covariances were estimated using REML with a derivative-free algorithm and fitting a multiple trait animal model. Estimates of heritability for SC, AP, and HH were .28, .42, and .65, respectively. Estimates of genetic correlations between SC and AP, SC and HH, and AP and HH were -.32, .19, and .25, respectively. Estimates of environmental correlations were .19 between SC and HH, and -.13 between AP and HH. Estimates of genetic parameters indicate a favorable genetic relationship between SC in Brahman bulls and AP in Brahman heifers under subtropical conditions. There was also evidence that selecting Brahman bulls for HH would not adversely affect SC but would have some detrimental effect on AP in female progeny.
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