Sperm motion and rheological behavior of the vaginal fluid of superovulated dairy heifers

The present study was conducted to determine whether there is any correlation between sperm motion and rheological behavior of the anterior vaginal fluid of superovulated dairy heifers. Vaginal fluid samples were collected from 16 superovulated dairy heifers from 12 to 20 h after estrus detection. Flow behavior was evaluated. The mean consistency index was 56.6 +/- 23.9 miliPascals per second(n) (mPa.s(n)) and ranged from 2.2 to 278 mPa.s(n). Of 16 samples of anterior vaginal fluid, 11 (69%) behaved as Newtonian fluids, while 5 (31%) behaved as non-Newtonian fluids. Concentrations and motility parameters of bull spermatozoa were evaluated into vaginal fluid samples after 30 min of incubation. The sperm concentrations were lower (P=0.01) in non-Newtonian than in Newtonian samples and were negatively correlated (P=0.009; r = - 0.62) with the index of consistency. The motility parameters such as average path velocity (VAP), curvilinear velocity (VCL) and linear velocity (VSL) were significantly higher in non-Newtonian than in Newtonian samples and were positively correlated with the index of consistency. Our data show that as mechanical resistance of vaginal fluid to sperm increases, the motility parameters increase while the migration efficiency appears to decrease.     

Rheological behavior of the vaginal fluid of dairy cows at estrus

The present study was conducted to evaluate rheological properties of the vaginal fluid in dairy cows. Thixotropy and flow behavior were evaluated. Vaginal fluid samples were collected in 8 cows at the beginning of a natural estrus and then every 8 h for 24 h. Vaginal samples were also collected from 208 cows at the time of insemination within 12 to 24 h interval after the onset of a natural estrus.Time-dependent variations were registered during the estrus. The limit shear stress for flow production (T_o), the shear stress of equilibrium (T_e) and the consistency index (K) decreased at 8 and 16 h and markedly increased 24 h after the beginning of estrus. At the time of insemination, structural variation was registered and the fluids were considered to be thixotropic in samples of 181 cows (87%); in the remaining samples (27 cows), structural variation was not registered and the fluids were considered to be nonthixotropic. For flow behavior values, 178 samples (85.6%) presented non-Newtonian behavior, while 30 behaved as Newtonian fluids. The mean values of the T_O and the T_e were 6.1 ± 0.69 and 1.9 ± 0.69 pascals, respectively. Consistency index (K) mean was 364.9 ± 41.4 milipascals per secondⁿ Our data show an increase of fluidity at the middle of the estrus period in the cow and a wide variation of rheological measurements of vaginal fluid at the time of insemination.     

Rheological properties of the anterior vaginal fluid from superovulated dairy heifers at estrus

Anterior vaginal fluid samples were collected from 25 dairy heifers induced to superovulation at 12 to 20 hours after estrus detection. Thixotropy and flow behavior were evaluated. In samples from 19 heifers, structural variation was registered and the fluids were considered to be thixotropic; in the remaining samples (6 heifers), structural variation was not registered and the fluids were considered to be nonthixotropic. The mean estradiol concentration of the thixotropic fluids (20.8 pg/ml) was lower (P=0.0002) than of the nonthixotropic samples (56.7 pg/ml). All the nonthixotropic samples of anterior vaginal fluid exhibited Newtonian behavior. Of the 25 thixotropic anterior vaginal fluid samples, 10 exhibited Newtonian behavior while 9 exhibited non-Newtonian behavior. Heifers in which samples exhibited Newtonian behavior had a higher mean estradiol concentration (38.8 pg/ml; P=0.003) than heifers in which samples exhibited non-Newtonian behavior (12.8 pg/ml). Estradiol concentrations were correlated negatively (P=0.02) with the index of consistency (r = -0.46) and were not related to structural variation (P=0.08), although a certain tendency was shown. These results have shown that thixotropic and flow behavior measurements in the anterior vaginal fluid of superovulated estrous heifers vary over a wide range and even qualitatively. This variation is related to estrogen levels: Fluidity increases with increased plasma estrogen values, and the integrity of the gel structure tends toward elimination.     

Numerical study of the impact of non-Newtonian blood behavior on flow over a two-dimensional backward facing step

Endothelial cell (EC) responsiveness to shear stress is essential for vasoregulation and plays a role in atherogenesis. Although blood is a non-Newtonian fluid, EC flow studies in vitro are typically performed using Newtonian fluids. The goal of the present study was to determine the impact of non-Newtonian behavior on the flow field within a model flow chamber capable of producing flow disturbance and whose dimensions permit Reynolds and Womersley numbers comparable to those present in vivo. We performed two-dimensional computational fluid dynamic simulations of steady and pulsatile laminar flow of Newtonian and non-Newtonian fluids over a backward facing step. In the non-Newtonian simulations, the fluid was modeled as a shear-thinning Carreau fluid. Steady flow results demonstrate that for Re in the range 50-400, the flow recirculation zone downstream of the step is 22-63% larger for the Newtonian fluid than for the non-Newtonian fluid, while spatial gradients of shear stress are larger for the non-Newtonian fluid. In pulsatile flow, the temporal gradients of shear stress within the flow recirculation zone are significantly larger for the Newtonian fluid than for the non-Newtonian fluid. These findings raise the possibility that in regions of flow disturbance, EC mechanotransduction pathways stimulated by Newtonian and non-Newtonian fluids may be different.     

自絮凝酵母SPSC01悬浮液的流变行为

用旋转黏度计测定了自絮凝颗粒酵母悬浮液的流变特性,并考察了其流变特性的影响因素,如菌体生物量、葡萄糖质量浓度、温度等。结果表明：自絮凝颗粒酵母悬浮液呈假塑性非牛顿流体,其流变特性服从幂律指数模型,随着菌体浓度的增大,稠度系数增大,流动行为指数减小;絮凝悬浮液的表观黏度随着糖浓度的增加有所增加,同一生物量下稠度系数k随着糖浓度的增加而增加,流动行为指数n随着糖浓度的增加变化很小,悬浮液的表观黏度随着温度的升高而降低;相同生物量下的流变指数随温度的升高而升高,而稠度系数随温度升高有所下降。     

Absorption of oxygen in highly viscous newtonian and non-Newtonian fermentation model media in bubble column bioreactors

Summary Mean relative gas holdup, slip velocity, bubble size distribution, mean specific interfacial area, and volumetric mass transfer coefficient of oxygen were estimated in sparged columns 14 cm in diameter and 380 and/or 390 cm high with two different aerator types (porous plate and injector nozzle) in highly viscous Newtonian (glycerol solutions) and non-Newtonian (CMC solutions) fluids.For the Newtonian liquids the above properties were estimated as function of the viscosity of the liquid. For the non-Newtonian liquids they were determined as function of the fluid consistency index and flow behavior index. Significant differences between Newtonian and non-Newtonian systems appear. In Newtonian medium k_L a drops with increasing viscosity and already approaches a constant value at =40 cP. In pseudoplastic medium k_L a varies with the fluid consistency and flow behavior indexes in the entire investigated range.In both of these systems the primary bubble population changes into two or three populations along the reactor: the medium bubbles gradually disappear and small and large bubbles are formed.     

Relationship between peripheral estrogen concentrations at insemination and subsequent fetal loss in cattle

In a survey on pregnancy rate and embryonic losses in dairy cattle on 6 Israeli farms, cows (n = 78) were divided into 3 groups on the basis of ultrasonography at 21 d post insemination; pregnancy diagnosis at 40 to 50 d post insemination and blood progesterone (P4) levels at 21 d. The groups were either pregnant (P4 level > 1.0 ng/ mL); not pregnant (P4 < 0.5 ng/mL), or showed early embryo loss (P4 > 1.0 ng/mL and the presence of an embryonic vesicle on D 21 but later returned to estrus or were found not pregnant on D 40 to 50). On the day of insemination, peripheral estrogen was significantly higher (P < 0.05) in the early embryo loss group (15.3 +/- 1.1 pg/mL, n = 27) than in pregnant (9.4 +/- 0.6 pg/mL, n = 26) or not pregnant (9.6 +/- 0.7 pg/mL, n = 25) group. The cows on 3 farms which were fed 1 to 2 kg/d of vetch (Vicia sativa), an estrogenic legume, had higher estrogen concentrations on the day of insemination than cows (2 farms) fed other legumes (13.7 +/- 0.64, n = 58 vs 10.7 +/- 0.8 pg/mL, n = 42; P < 0.01). On one of the 3 farms, vetch was replaced with alfalfa after the first year. Following the cessation of vetch feeding the estrogen concentrations in the blood decreased from 32 +/- 5 pg/mL to 14 +/- 2 pg/mL (n = 9). These data suggest that high peripheral estrogen on the day of insemination is associated with early embryonic loss. These data also indicate that estrogen concentrations on the day of insemination can be influenced by diet.     

Comparison of pregnancy rates of repeat-breeder dairy cows given gonadotropin releasing hormone at or prior to the time of insemination

A total of 585 repeat-breeder dairy cows was used to study the effect of GnRH treatment, either at or prior to insemination, on the pregnancy rate. The cows were divided into 6 treatment groups. Cows in Group 1 (n = 142) were observed in estrus, and 11 +/- 0.42 hours (mean +/- SEM) later they were given 100 ug, i.m. gonadotropin releasing hormone (GnRH) and were inseminated. Cows in Group 2 (n = 139) were observed in estrus and were inseminated 11.4 +/- 0.43 hours later. Cows in Group 3 (n = 33) were monitored for estrus with an activated heatmount detector but were not observed in estrus; they were inseminated 1.5 +/- 0.87 hours later and were given 100 ug, i.m. GnRH. Cows in Group 4 (n = 35) were not observed in estrus, but they did activate the heatmount detector and were inseminated 2.2 +/- 0.87 hours later. Cows in Group 5 (n = 107) were observed in estrus, given 100 ug, i.m. GnRH 2.0 +/- 0.40 hours later, and were inseminated 9 +/- 0.60 hours after GnRH treatment. Cows in Group 6 (n = 129) were observed in estrus and were inseminated 10 +/- 0.50 hours later. Pregnancy rates were analyzed by Chi-square. Interactions between pregnancy rate, treatment and time of insemination were evaluated using ANOVA and LSM (P < 0.05). There was no effect on pregnancy rate when GnRH was given at or prior to insemination. Cows inseminated on the basis of observed estrus had a higher pregnancy rate (P < 0.05) than cows inseminated on the observation of an activated heatmount detector. From the results of this study, it is concluded that treatment with GnRH at or prior to insemination did not improve the pregnancy rate of repeat-breeder dairy cows.     

Reproductive performance of lactating dairy cows treated with cloprostenol at the time of insemination

The effect of intravenous cloprostenol treatment at the time of insemination on reproductive performance was consecutively evaluated in three different subpopulations of high producing lactating dairy cows: Study (1) early postpartum synchronized and fixed-time inseminated (about 50 days in milk) cows (n = 379: 187 control and 192 treated cows); Study (2) presumed high fertility cows first inseminated between 90 and 120 days postpartum (n = 248: 124 control and 124 treated cows); and Study (3) heat stressed repeat breeder cows (n = 183: 93 control and 90 treated cows). Data were analyzed using multiple regression methods. Study 1: Parity (primiparous versus multiparous), milk production, body condition score at AI, insemination season (cool versus warm period) and treatment were included in the analysis as potential factors affecting ovulation, double ovulation, return to estrus, and pregnancy to first AI and to second AI (first AI plus return AI) rates. Logistic regression analysis indicated that the final model for ovulation rate only included the interaction (P = 0.002) between insemination season and treatment. Cloprostenol treatment at insemination led to a 4.2-fold increase in the ovulation rate in cows inseminated during the warm period. There were no significant effects of treatment, parity, milk production, body score or the insemination season on the return to estrus rate. The only variables included in the final logistic model for double ovulation and pregnancy to first AI rates were treatment and season, respectively. Treatment led to a 2.6-fold increase (P = 0.001) in the double ovulation rate, whereas cows inseminated in the warm period were 2.1 times less likely (P = 0.007) to become pregnant at first AI compared to those inseminated in the cool season. The variables included in the final logistic model for the pregnancy rate to second AI were treatment and season. Cloprostenol given at AI increased the risk of pregnancy 1.9 times (P = 0.002), and cows inseminated during the warm season were two times less likely to become pregnant (P = 0.003). No significant interactions were found among these three dependent variables (double ovulation and pregnancy to first and to second AI rates). Study 2: Logistic regression analysis of all the dependent variables: return to estrus, and pregnancy to first and to second AI (first AI plus return to AI) rates indicated no significant effects of treatment, parity, days in milk, milk production or body score at AI. No significant interactions were found. Study 3: The final model for the pregnancy rate only included the interaction between parity (primiparous versus multiparous) and treatment. Days in milk, milk production and insemination number showed no significant effect on pregnancy rate. Cloprostenol treatment at insemination increased the pregnancy rate in primiparous repeat breeder cows (odds ratio: 3.6). The treatment group and parity showed significant (P < 0.0001) interaction. This interaction suggests that cloprostenol treatment of primiparous cows at insemination might enhance pregnancy yet have no effect in multiparous cows. Our findings indicate that cloprostenol administered at insemination promotes ovulation and double ovulation in lactating dairy cows. Cloprostenol treatment showed no benefit in cows with acceptable reproductive performance, suggesting that cloprostenol treatment at AI may only be useful in cows in which stress factors affect ovulation and in repeat breeder cows.     

Effect of human chorionic gonadotropin administered at specific times following breeding on milk progesterone and pregnancy in cows

Two trials were conducted to investigate the efficiency of human chorionic gonadotropin (hCG) following breeding to increase progesterone (P(4)) secretion and pregnancy rates in cows. In Trial 1, 79 lactating Holstein cows were randomly allocated to four groups to receive hCG either at breeding (Day 0, n=20), Day 7 (n=20) or Day 14 (n=20), or to receive no hCG treatment (control n=19). Whole milk samples were collected every other day from breeding until Day 21 and, thereafter, at weekly intervals until Day 42 or until the return to estrus for determination of P(4) concentrations. Similar treatments were employed in Trial 2, and 121 lactating Holstein cows were randomly assigned to treatment at Day 0 (n=29), Day 7 (n=32), or Day 14 (n=29), or to receive no treatment and serve as a control group (n=31). Milk samples were obtained at weekly intervals from breeding until Day 42, or the return to estrus for determination of P(4) concentrations. Pregnancy diagnosis was made by palpation per rectum at approximately 60 days post breeding. Significant increases in P(4) concentrations were observed in Day-7 and Day-14 treated cows from Days 18 to 42 after breeding compared with the Day 0 or the control cows. A slight decrease in P(4) concentration throughout the sampling period was observed in the Day-0 treated cows. Significant increases in pregnancy rates were observed in hCG-treated cows compared with that of the controls, with the highest rate observed in the Day-7 treated group. The overall pregnancy rates were 47, 62, 55 and 40% for the Day 0, 7 and 14 groups and for the control groups, respectively. In nonpregnant cows the mean (+/- SEM) numbers of days to basal P(4) concentrations were 21.6 +/- 1.3, 24.1 +/- 1.6, 24.6 +/- 1.3 and 23.2 +/- 1.3 for cows treated on Days 0, 7 and 14 and for the control group, respectively. It is concluded that the administration of hCG at Day 7 or Day 14 after insemination could be used as a management tool to improve pregnancy rates in postpartum cows.     

Effect of injection of beta-carotene or vitamin E and selenium on fertility of lactating dairy cows

Experiments tested whether supplemental antioxidants improved fertility. To test effects of beta-carotene, cows in a hot environment were injected with prostaglandin F2 alpha (PGF2 alpha) and were given 3 injections, i.m., of 800 mg beta-carotene or saline at Days -6 and -3 before the anticipated date of insemination and at insemination (n = 37-41 inseminated cows/group). There was no effect of beta-carotene on the proportion of cows detected in estrus following PGF2 alpha, timing of estrus after PGF2 alpha injection or pregnancy rate in inseminated cows. In a second trial, cows in a temperate climate received intramuscular injections of vitamin E (500 mg) and selenium (50 mg) at 30 d post partum (n = 97) or were untreated controls (n = 89). Treatment did not affect interval from calving to first insemination or the proportion of cows pregnant at first service, but it increased the pregnancy rate at second service (69.8 vs 52.1%; P = 0.07) and reduced services per conception (1.7 vs 2.0; P < 0.05) and interval from calving to conception (84.6 vs 98.1; P < 0.05). Thus, injection of vitamin E and selenium increased fertility in cattle that did not become pregnant at first service.     

Progesterone in bovine milk fat

The progesterone (P(4)) concentration (ng/5 mul) in the fat portion of cow's milk was measured on days 0, 12, 20, 24, and 30 after insemination in an effort to assess the ability of this analysis to judge the reproductive status of dairy cows. Pregnancy was determined by rectal palpation at approximately 40 days after insemination. The mean P(4) concentration (ng/5 mul) +/- SD in the pregnant cows (n=17) was 0.14+/-.07, 1.31+/-.36, 1.41+/-.52, 1.22+/-.21, and 1.30+/-.43 on post-insemination days 0, 12, 20, 24, and 30 respectively. At these same intervals the P(4) concentration in the non-pregnant (NP) cows (n=18) was 0.14+/-.06, 1.26+/-.37, 0.56+/-.52, 0.57+/-.42, and 1.08+/-.59. On days 20 and 24 after insemination, mean P(4) levels were significantly (P<.001) elevated in the pregnant cows. It was concluded that an accurate assessment of the reproductive status of a cow, milk samples from days 0, 20, and 24 post-insemination would have to be analyzed for milkfat P(4) concentrations. In order to determine the percentage of cows inseminated out of the periestrual period, milkfat P(4) concentrations were ascertained in milk collected from 165 cows at the time of insemination. Cows that conceived (n=38) had a mean milkfat P(4) concentration at the time of insemination of 0.16+/-.09. The upper limit for P(4) in the milkfat at the time of insemination in cows that conceived was calculated to be 0.43 ng/5 mul milkfat. Subsequently, it was found that of the 14 cows that had P(4) levels above this upper limit at time of insemination, nine were inseminated at a period other than in the periestrual period and five were inseminated while already pregnant.     

The influence of the non-Newtonian properties of blood on the flow in large arteries: unsteady flow in a 90 degrees curved tube.

A numerical and experimental investigation of unsteady entry flow in a 90 degrees curved tube is presented to study the impact of the non-Newtonian properties of blood on the velocity distribution. The time-dependent flow rate for the Newtonian and the non-Newtonian blood analog fluid were identical. For the numerical computation, a Carreau-Yasuda model was employed to accommodate the shear thinning behavior of the Xanthan gum solution. The viscoelastic properties were not taken into account. The experimental results indicate that significant differences between the Newtonian and non-Newtonian fluid are present. The numerical results for both the Newtonian and the non-Newtonian fluid agree well with the experimental results. Since viscoelasticity was not included in the numerical code, shear thinning behavior of the blood analog fluid seems to be the dominant non-Newtonian property, even under unsteady flow conditions. Finally, a comparison between the non-Newtonian fluid model and a Newtonian fluid at a rescaled Reynolds number is presented. The rescaled Reynolds number, based on a characteristic rather than the high-shear rate viscosity of the Xanthan gum solution, was about three times as low as the original Reynolds number. Comparison reveals that the character of flow of the non-Newtonian fluid is simulated quite well by using the appropriate Reynolds number.     

Temporal relationships among estrus, body temperature, milk yield, progesterone and luteinizing hormone levels, and ovulation in dairy cows

Estrous cycles of 10 postpartum cyclic Holstein cows were synchronized using prostaglandin f(2alpha) (PGF(2alpha)) given twice 12 d apart to study the relationship of the onset of estrus, body temperature, milk yield, luteinizing hormone (LH) and progesterone concentration to ovulation. Blood samples and body temperatures (vaginal and rectal) were taken every 4 h until ovulation, starting 4 h prior to the second PGF(2alpha) treatment. All cows were observed for estrus following the second administration of PGF(2alpha). Ultrasound scanning of the ovaries commenced at standing estrus and thereafter every 2 h until the disappearance of the fluid filled preovulatory follicle (ovulation). Two cows failed to ovulate and became cystic following the second PGF(2alpha) treatment. The remaining eight cows exhibited a decline in progesterone to <1.0 ng/ml within 28 h, standing estrus and a measurable rise (> 1.0 degrees C) in vaginal but not rectal temperature, and ovulated 90 +/- 10 h after the second PGF(2alpha) treatment. Onset of standing estrus, LH peak and vaginal temperature were highly correlated (P<0.05) with time of ovulation (0.82, 0.81 and 0.74, respectively). Intervals to ovulation tended to depend upon parity. Pluriparous (n = 4) and biparous (n = 4) cows ovulated within 24 and 30 +/- 3 h from the onset of standing estrus; 22 and 31 +/- 2 h from the LH peak; and 22 and 27 +/- 3 h from peak vaginal temperature (mean +/- standard error of the mean), respectively. The results indicated that the onset of standing estrus and rise in vaginal temperature are good practical parameters for predicting ovulation time in dairy cattle.     

Effect of climate on the response to three oestrous synchronisation techniques in lactating dairy cows

The reproductive efficiency of Friesian dairy cows was investigated in a three (oestrous synchronisation technique) x two (seasons of the year) factorial design. The 90 primiparous and multiparous cows (winter, n=42; summer, n=48) were allocated at random to three synchronisation treatments (n=30 cows per treatment). In treatment 1 (GPG), the cows were administered 15 mg PGF(2alpha) i.m. at 30 +/- 3 days postpartum, 100 microg GnRH i.m. at 51 +/- 3 days and 15 mg PGF(2alpha) 7 days later. A second 100 microg dose of GnRH was given after, further 2 days and fixed time AI occurred 16-20 h later. In treatment 2 (PG-PG), 15 mg PGF(2alpha) was administered i.m. to each cow on three occasions at successive 14 days interval starting at 30 +/- 3 days postpartum and the cows were inseminated at observed oestrus following the third dose of PGF(2alpha). Cows in treatment 3 (PG) had a single administration of 15 mg PGF(2alpha) i.m. at 57+/-3days postpartum and were inseminated as in treatment 2. Mean daily ambient temperature was 10.9 degrees C in winter (November-March) and 20.2 degrees C in summer (June-October). The cows were confined in an open-fronted shed and had ad libitum access to a complete diet with a 37:63 forage to concentrate ratio. Body condition score was assessed at 57 +/- 3 days postpartum. Cow rectal temperature at insemination, milk yield, reproductive data and climatic variables were recorded. Blood samples were collected for progesterone assay on days 4, 11, 18, 25, 32, 39 and 46 post-AI from 54 of the cows (19 GPG; 17 PG-PG; 18 PG). Pregnancy rate to first AI was 36.7% (11/30) for GPG and 16.7% (5/30) for both PG-PG and PG treatments. The difference was not significant. The cumulative pregnancy rate after third AI were GPG 83.3% (25/30), PG-PG 60.0% (18/30) and PG 60.0% (18/30; P<0.057). The cumulative pregnancy rate for cows inseminated in the winter (81.0%; 34/42) was higher (P<0.01) than for those inseminated in the summer (56.3%; 27/48). The interval from calving to first service was shorter (P<0.05) in treatment PG-PG (65.4+/-1.3 days) than in PG (69.2+/-1.3 days). Mean plasma progesterone concentrations post-AI of pregnant cows were higher (P<0.001) for GPG cows than those for PG-PG and PG cows. Plasma progesterone levels of pregnant cows tended to be higher (P=0.087) in winter than in summer. In conclusion, although the cumulative pregnancy rate was higher for GPG cows, it may be appropriate to correct the nutrition and management of the herd before resorting to synchronisation techniques to improve animal reproductive performances.     

Effect of a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.     

The influence of the non-Newtonian properties of blood on the flow in large arteries: steady flow in a carotid bifurcation model.

Laser Doppler anemometry experiments and finite element simulations of steady flow in a three dimensional model of the carotid bifurcation were performed to investigate the influence of non-Newtonian properties of blood on the velocity distribution. The axial velocity distribution was measured for two fluids: a non-Newtonian blood analog fluid and a Newtonian reference fluid. Striking differences between the measured flow fields were found. The axial velocity field of the non-Newtonian fluid was flattened, had lower velocity gradients at the divider wall, and higher velocity gradients at the non-divider wall. The flow separation, as found with the Newtonian fluid, was absent. In the computations, the shear thinning behavior of the analog blood fluid was incorporated through the Carreau-Yasuda model. The viscoelastic properties of the fluid were not included. A comparison between the experimental and numerical results showed good agreement, both for the Newtonian and the non-Newtonian fluid. Since only shear thinning was included, this seems to be the dominant non-Newtonian property of the blood analog fluid under steady flow conditions.     

Low dose insemination in cattle with the Ghent device

A new artificial insemination device for semen deposition near the uterotubal junction (UTJ) in cattle (Ghent device) was developed at Ghent University (Belgium). In this study, UTJ insemination of dairy cows with the Ghent device was compared with the conventional insemination technique to evaluate the effect on pregnancy rates after insemination with different doses of semen. In each of three field trials, the cows (n=795, 659, 360) and heifers (n=253, 182, 231) were randomly assigned to receive 12 million sperm deposited in the uterine body using conventional techniques (control) or a reduced sperm dose (RSD) deposited in the same manner as the control or bilateral deposition near the uterotubal junction using the Ghent device (Ghent). Sperm dosages for RSD and Ghent inseminations were 8, 4, and 2 million sperm for field trials 1-3, respectively. In the multivariable analysis, the pregnancy rates were significantly affected by the parity of the cow (p相似文献   

Dose dependent effect of GnRH analogue on pregnancy rate of repeat breeder crossbred cows

The aim of this study was to investigate the effect of treating repeat breeder dairy crossbred cows with different doses of GnRH analogue through i.m. at the time of artificial insemination, on pregnancy rates from their first service after treatment and overall pregnancy rates. One hundred and thirty seven crossbred dairy cows with a history of repeat breeding and eligible after 6-8 infertile services but clinically free of diseases were selected for the study. The animals were randomly divided into three groups. Group 1 (n = 55) cows were treated intramuscularly with each 20 microg Buserelin-acetate (Receptal, Hoechst Roussel Vet GmbH) at the time of artificial insemination. Group 2 (n = 40) cows were treated intramuscularly with each 10 microg Buserelin-acetate at the time of artificial insemination. Group 3 (n = 42) cows were treated intramuscularly with saline as control at the time of artificial insemination. The first service pregnancy rates in Groups 1-3 were 45, 25 and 17%, respectively. Similarly, the overall conception rates in Groups 1-3 were 87, 58 and 48%, respectively. The results indicated that the pregnancy rate in crossbred cows could be improved by the GnRH treatment. The higher dose of GnRH significantly increased (P < 0.05) the first service as well as overall pregnancy rate in a dose dependent manner in repeat breeder crossbred cow bred previously 6-8 times unsuccessfully.     

Effect on pregnancy rate of nonestrus insemination in previously inseminated dairy cows

Lactating dairy cows (n = 157) designated for slaughter under the 1986 U.S. Dairy Termination Program were utilized in two trials to determine the effects of a second insemination on fertility. Cows that had been previously inseminated at estrus were inseminated again at 12-24 d later, when not in estrus. Cows that were reinseminated into the uterine body had significantly lower pregnancy rates (4% vs 40.6% for controls). Differences in pregnancy rates when the reinsemination was performed in the mid-cervical region were not significant (34.8% vs 50% for controls). Based upon these studies, intrauterine insemination of cows displaying questionable signs of estrus should be avoided in previously inseminated cows.