Fertilization rates and embryonic development in superovulated cattle inseminated in different sites within the reproductive tract

Transuterine embryo migration, distribution of sexes within uterine horns, and fetometry in Nellore (Bos indicus) cattle

There is no consensus about the occurrence of transuterine embryo migration under natural breeding circumstances, neither data related to this phenomenon for zebu cattle. In this study, 5431 reproductive tracts of Nellore cows and heifers were evaluated in an abattoir in the state of Mato Grosso do Sul. A total of 1030 animals (19.0%) were pregnant at the time of slaughter (including 2 twin pregnancies). Regarding singleton pregnancies (n = 1028), 39.5% of them, the fetus was located in the left uterine horn and the remaining 60.5% in the right. These frequencies differed statistically from parity. In all 1028 (100.0%) cases, the presence of a single CL was perceived in the ovary ipsilateral (whether right or left) to the pregnant uterine horn, indicating the absence of transuterine embryo migration of the conceptus. The overall sex ratio found was 51.5%, considering only pregnancies with sex identified, not differing significantly between the number of males and the number of females. The sex frequencies obtained from the total number of singleton pregnancies were 46.5% males, 43.9% females, and the remaining 9.6% corresponding to unknown sex fetuses. The supposed sex predilection for uterine horns was not observed because the difference between the numbers of males and females for the same uterine horn was not statistically significant. The crown-rump (CR) and crown-nose (CN) measures, for the conceptus with CR length 2.00 cm to 15.00 cm, showed a high linear correlation coefficient (r = 0.990865), being CN = (0.3027 × CR) + 0.4491, r² = 0.9818, the equation that describes the behavior between the variables for this length interval. In conclusion, in Nellore cattle, the transuterine migration of conceptus may not exist, or consists of a rare event. In addition, the sex ratio and predilection are not distinguished from the symmetrical distribution, and regarding fetometry, an equation that involves CR and CN, could be useful for the veterinary field routine, especially in reproductive evaluation.

Effects of deep-horn AI on fertilization and embryo production in superovulated cows and heifers

The primary objective of this study was to determine the effect of site of semen deposition on fertilization rate and embryo quality in superovulated cows. The hypothesis was that deposition of semen into the uterine horns would increase the fertilization rate compared with deposition of semen into the uterine body. The secondary objective was to evaluate the effect of uterine environment on fertilization rate and embryo quality. It was hypothesized that subclinical endometritis at the onset of superstimulation would decrease the fertilization rates and embryo quality. In experiment 1, 17 superovulated heifers were randomly assigned to receive artificial insemination (AI) into the uterine body or uterine horns. The total number of fertilized structures and fertilization rate from superovulated heifers was increased (P = 0.04 and P = 0.02, respectively) when semen was deposited into the uterine horns compared with the uterine body. Other embryo characteristics did not differ based on the site of semen deposition. In experiment 2, 14 lactating dairy cows were superovulated twice and were randomly assigned to receive AI into the uterine body or deep into the uterine horns using a crossover design. Neither fertilization rate nor any other embryo characteristics were improved when semen was placed deep into the uterine horns compared with the uterine body. In experiment 3, 72 superovulated lactating dairy cows were randomly assigned to receive AI into the uterine body or uterine horns. Before initiation of superstimulatory treatments, an endometrial cytology sample was collected from each cow. Ova/embryos were collected by a nonsurgical technique at 70 ± 3 days in milk. Similar to experiment 2, neither fertilization rate nor any other embryo characteristics differed based on the site of semen deposition in experiment 3. The percentage of cows with subclinical endometritis did not differ between treatments. Interestingly, there was a tendency (P = 0.09) for a reduction in embryo recovery rate and a reduction (P = 0.01) in the fertilization rate for cows with subclinical endometritis. In conclusion, deposition of semen into the uterine horns rather than into the uterine body did not improve the fertilization rate or embryo quality in superovulated cows. Subclinical endometritis decreased the fertilization rate in superovulated cows.

Site of semen deposition in cattle: a review

The breeding of cattle using conventional artificial insemination methods involves the deposition of semen in the uterine body. However, it has been recently proposed by several authors that the site of semen deposition be changed to the uterine horns. This suggestion is based on 2 facts: the acceptance that the major preovulatory sperm reservoir may be the uterotubal junction rather than the cervical canal, and the lack of accuracy by inseminators in depositing semen. In over 50% of cases, inseminators were not sufficiently trained to deposit semen into the uterine body, so that intracervical insemination was often performed resulting in reduced fertility. The advantage of deep uterine insemination, whether bicornual or unicornual, is that it favors the deposition of semen nearer to the uterotubal junction and thus reduces the incidence of cervical deposition. This review updates the literature on the ideal site of semen deposition, including cervical, uterine body, cornual and intraperitoneal. Also analyzed are the effects of right vs. left side activity of the female reproductive tract on the optimum site of semen deposition as it affects fertilization. Finally, the question of whether the clinical training of inseminators should be reevaluated is discussed.

Side of gestation in dairy heifers affects subsequent sperm transport and pregnancy rates after deep insemination into one uterine horn

Effects of side of previous gestation on sperm transport and pregnancy rates after deep cornual insemination were evaluated in 1686 Friesian cows in their first lactational period. Only single ovulating animals were used. At insemination, semen was deposited deep into the uterine horn ipsilateral or contralateral to the preovulatory follicle. A total of 876 cows (52%) ovulated in the ovary ipsilateral to the postgravid horn, and 810 cows ovulated in the contralateral ovary. Semen was deposited into the previously nongravid uterine horn of 832 cows, and into the gravid horn of 854 cows. The pregnancy rate was higher (P < 0.00001) for semen deposition into the previously nongravid horn (46.6%) than for semen deposition into the gravid horn (35.7%). For inseminations ipsilateral to the side of impending ovulation, pregnancy rates were higher (P = 0.0004) when ovulations occurred on the opposite side to the postgravid horn than on the same side. Pregnancy rates were higher (P = 0.002) for contralateral inseminations when ovulations occurred on the same side to the postgravid horn than on the opposite side; they were higher (P = 0.0001) for total ipsilateral than for total contralateral inseminations. There was no difference between ipsilateral and contralateral inseminations (P = 0.64) when ovulation occurred ipsilateral to the postgravid horn, but pregnancy rates were higher (P < 0.00001) when ipsilateral insemination was carried out into the nonpostgravid horn. Results indicate that the side of gestation in dairy heifers affects subsequent pregnancy rates after deep insemination into one uterine horn, possibly by affecting sperm transport.

Effect of side of insemination on transuterine transport of spermatozoa in superovulated dairy cattle

Eleven superovulating Friesian lactating cows were inseminated deep into one uterine horn with one unit of frozen semen, containing 2.5 million total spermatozoa, with more than 40% postthaw progressive motility and with 14% morphologically abnormal spermatozoa. Semen was deposited into the right or left uterine horns of alternate cows. There was no difference in the proportions of fertilized recovered ova from ipsilateral horns between right and left inseminations (P>0.05). The fertilization rate in the contralateral horns was higher (P<0.01) for right uterine horn insemination (50%) than for left uterine horn insemination (15.6%).

Does intrauterine site of insemination in cattle really matter?

Two trials were conducted to determine the influence of semen placement on pregnancy rate in dairy heifers and cows. Seventy-two dairy heifers were artificially inseminated (AI) 10 to 12 h after the first detection of estrus. Control heifers (n = 25) were inseminated at the junction of the uterine body and internal cervical os. The remaining heifers were inseminated deep in one uterine horn, 3 to 5 cm anterior to the external bifurcation. Twenty-three heifers were inseminated in the horn ipsilateral to the ovary bearing the ovulatory follicle, and 24 heifers were inseminated in the contralateral horn. Pregnancy rates did not differ for the three groups of heifers. In a second trial, 64 inseminations were performed in 38 nonlactating, adult dairy cattle. Thirty-one inseminations were made deep in the uterine horn ipsilateral to the ovary bearing the ovulatory follicle and 33 in the contralateral horn. Pregnancy rates were similar for both groups. Combining both trials, pregnancy rates for ipsilateral and contralateral inseminations were equal (32 54 = 59% and 34 57 = 60% , respectively). Therefore, placement of semen in one horn of the uterus does not appear to be a cause of decreased or increased pregnancy rate with AI.

Effects of single deep insemination on transferable embryo recovery rates in superovulated dairy cows

Thirty superovulated Friesian lactating cows were randomly assigned to two groups. Group I donors were inseminated with one unit of semen deposited into the uterine body at 8, 20 and 32 h after the onset of estrus. Group II donors were inseminated with one unit of semen deposited deep into the uterine horns at 15 h after the onset of estrus. Neither the mean rates of fertilized ova nor the mean rates of transferable embryos were different between treatments (P > 0.05).