Testosterone concentrations in plasma of dairy cows with ovarian cysts.

Testosterone in plasma was measured by radioimmunoassay in cows with ovarian cysts and in cows during the estrous cycle. Concentrations of testosterone in plasma (60.8 +/- 2.7 pg/ml; mean +/- standard error) in cows with ovarian cysts were variable but within the range in cows during the estrous cycle. Mean concentrations of testosterone in plasma increased from 46.3 pg/ml at estrus to 85.1 pg/ml on day 13 of the estrous cycle. In cows with ovarian cysts, concentrations of testosterone in plasma declined within 24 h following prostaglandin F2 alpha and tended to increase by 9 days following gonadotropin releasing hormone. The role of testosterone in estrual behavior and inhibiting resumption of ovarian cycles is likely minimal.     

Conception rates and calving intervals after prostaglandin F2 alpha or prebreeding progesterone in dairy cows

Two experiments were performed in two different herds to determine if utilizing prostaglandin F 2 alpha to induce estrus for first services would be effective in reducing the duration and variability of calving intervals. In Experiment 1, cows were assigned randomly as controls (n = 217) to be inseminated as they were detected in estrus (beginning d 42 to 53 postpartum depending on replicate) or treated with prostaglandin F2 alpha (n = 185). In Experiment 2, the same treatments were utilized, except control cows (n = 124) were inseminated at their first detected estrus after d 40 postpartum, and treated cows received either one injection of prostaglandin F2 alpha between d 54 and 63 (n = 116) or were given progesterone (via a progesterone-releasing intravaginal device) for 7 d, with the device removed 24 h after prostaglandin F2 alpha (n = 116). More cows were inseminated and pregnancy rates were higher within 5 d after treatment with prostaglandin F2 alpha, and interval from prostaglandin F2 alpha to first service was reduced compared with that of control cows. Duration and variation of calving intervals were unaffected in either experiment, despite the fact the elective waiting period was 6 to 23 d longer for treated cows than for controls. Prebreeding treatment with progesterone failed to improve conception rates, but the efficiency of estrous expression increased from 54% in prostaglandin F2 alpha-treated cows to 71% in those cows also receiving prebreeding progesterone. We conclude that prostaglandin F2 alpha was ineffective in improving reproductive performance of these herds under good herd management. However, prostaglandin F2 alpha offers the convenience of inseminating small groups of cows, controlling when breedings occur during the work week, and prolonging the elective waiting period without extending the calving interval.     

Controlling first service and calving interval by prostaglandin F2 alpha, gonadotropin-releasing hormone, and timed insemination

Our objective was to determine if calving intervals could be shortened and made less variable by using prostaglandin F2 alpha to control the occurrence of first services. Holstein cows (n = 348) were assigned at calving to four treatment groups. Control cows (n = 88) were inseminated at their first observed estrus after 40 d postpartum. Estrous cycles of the remaining cows were synchronized with prostaglandin F2 alpha to allow insemination (first services) 80 h after the second injection (n = 86), insemination at 80 h preceded by gonadotropin-releasing hormone at 72 h (n = 86), or insemination at 72 and 96 h (n = 88) after the second injection (51 to 57 d postpartum). By design, interval to first service was reduced to 57 d for treated cows (63 d for controls) and was less variable (12% of that for controls). Conception rate at first service was lower after timed inseminations than that of controls. Intervals to conception and subsequent calving were similar in all treated cows and controls. Of cows sampled, 23 of 176 (13%) failed to respond with luteolysis when progesterone in serum exceeded 1 ng/ml, and 26 of 176 (15%) had low concentrations of progesterone in serum and could not respond to prostaglandin F2 alpha. Poor response to timed inseminations may have occurred because only 72% of 176 cows sampled responded with luteolysis. When only cows observed in estrus were considered, conception rate approached that of controls (51%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadotropin-releasing hormone and prostaglandin F2 alpha for postpartum dairy cows: estrous, ovulation, and fertility traits

A study of 234 Holstein cows was conducted to determine if early postpartum treatments of gonadotropin-releasing hormone, prostaglandin F2 alpha, or both would alter frequency and occurrence of estrus and ovulation as well as subsequent fertility. Cows in groups 1 and 2 received gonadotropin-releasing hormone (200 micrograms) between 10 and 14 d postpartum, and cows in groups 3 and 4 received saline. Ten days later, cows in groups 2 and 3 received prostaglandin F2 alpha (25 mg), and cows in groups 1 and 4 received saline. Treatment with gonadotropin-releasing hormone reduced intervals to first ovulation and first detected estrus as well as increasing the proportion of cows with three or more ovulations before first service from 57% for saline-treated controls to 83%. Treatment with prostaglandin F2 alpha reduced intervals to second and third ovulation and shortened the first estrous cycle. Treatments for cows in groups 1 and 3 increased the proportion of cows having estrous cycles of normal duration. Interval from calving to conception was reduced by 43 to 48 d for cows with an abnormal puerperium treated with either gonadotropin-releasing hormone or prostaglandin F2 alpha compared with controls (group 4) and by 27 to 29 d overall in all cows in groups 1 and 3. Cows with normal or abnormal puerperium in groups 1 and 3 required 26 to 41% fewer services per conception than controls. We conclude that treatments of gonadotropin releasing hormone or prostaglandin F2 alpha, but not the treatment combination, improved fertility of dairy cows, especially those that experienced puerperal problems.     

Dairy herd reproductive management programs with or without synchronization of estrus

Reproductive efficiencies were compared among herds with (treated, n = 25) or without (visited control, n = 25) routine synchronization of estrus and herds without investigator visits (unvisited control, n = 22). Treatment groups were subdivided based on participation in veterinary herd health programs. Reproductive tracts were palpated rectally at 21-d intervals for 6 mo in two sets of treated and visited control herds. Data were collected during the visitation period and from the 6-mo period before visits. In treated herds, cows more than 40 d postpartum with a corpus luteum received prostaglandin F2 alpha. In visited control herds, cows received prostaglandin F2 alpha after 82 d postpartum if they were not observed in estrus. Routine synchronization of estrus did not enhance herd reproductive efficiency compared with no synchronization of estrus in visited herds. Small changes in reproductive efficiency occurred during visits in herds with an established reproductive health program. However, herds not using a health program had 15.2 fewer d from calving to insemination, and the pregnancy rate at 120 d postpartum was 13.0 percentage units higher than before herd visits. Consequently, reproductive performance of those herds during visits was similar to that of contemporaries under a herd health program.     

Use of prostaglandin F2 alpha or gonadotropin releasing hormone in treating problem breeding cows

Ten veterinarians diagnosed and treated 296 cows for reproductive irregularities on 28 dairy farms. Average interval from treatment with 25 mg of prostaglandin F2 alpha (137 cows) to estrus for cows with a corpus luteum (14.6 days) was reduced compared to saline (52 cows) (21.8 days), and a greater percentage (41.6 versus 17.3%) showed estrus within 6 days of treatment. Cows with a cystic corpus luteum (28) were detected in estrus at comparable intervals after prostaglandin F2 alpha or saline (21.8 versus 21.2 days), and similar proportions of cows were detected in estrus within 6 days of treatment (16.7 versus 10.0%). Intervals to estrus among cows with cystic follicles (40 cows) or anestrous cows with follicular ovaries (39 cows) did not differ after treatment with saline or 100 or 200 micrograms of gonadotropin releasing hormone. Within 25 days after treatment, 47.5% of cows with cystic ovaries and 64.1% of anestrous cows showed estrus. Number of cows pregnant after as many as three artificial inseminations of the number examined was 46%, whereas average number of conceptions per service was .32. The long interval from parturition to examination (112 days), the low rate of estrous response after treatment, and the long interval (1.6 estrous cycles) between estruses are consonant with inadequate estrous detection.     

Fertility of postpartum dairy cows after administration of gonadotropin-releasing hormone and prostaglandin F2 alpha: a field trial

Our objective was to examine further the potential profertility effects of gonadotropin-releasing hormone and prostaglandin F2 alpha in postpartum Holstein cows. Reproductive performance was monitored in 843 cows milked thrice daily. One group of cows (n = 218) was untreated, while three groups received either 100 micrograms gonadotropin-releasing hormone administered once between d 11 and 25 (n = 211); 25 mg prostaglandin F2 alpha given once between d 11 and 25 (n = 215); or 25 mg prostaglandin F2 alpha given once between d 25 and 40 postpartum (n = 190). No profertility effects were detected in cows, regardless of their health status during the periparturient period, except cows given gonadotropin-releasing hormone between d 11 and 18 had shorter intervals to first estrus and to first service than controls. Cows with reproductive disorders (abnormal health status) in the concurrent lactation had longer intervals from calving to conception after receiving gonadotropin-releasing hormone between d 18 and 25 or prostaglandin F2 alpha between d 33 and 40. Abnormal health status adversely affected every reproductive trait measured. Early postpartum treatments with either hormone failed to improve reproductive performance of dairy cows, in contrast to several reports of profertility effects for gonadotropin-releasing hormone, and a few reports for prostaglandin F2 alpha.     

Synchronization of estrus in dairy cows with prostaglandin F2 alpha and estradiol benzoate

A field study using 322 lactating dairy cows in seven commercial and two university herds was conducted to determine if treatment with estradiol benzoate 40 to 48 h after treatment with prostaglandin F2 alpha would enhance synchronization of estrus. Estrogen treatment tended to increase the proportion of cows in estrus within 5 d (synchronized) after prostaglandin treatment (66.9% versus 58.9%). Of synchronized cows, a greater proportion treated with estrogen (66.9%) were in estrus on d 3 than those not receiving estrogen (48.2%). First service conception rate (31.9%) and interval to second service (35.6 d) were not affected by treatment with estrogen. Milk progesterone was measured in university herds. More cows with milk progesterone concentrations greater than or equal to 8 ng/ml were synchronized (75.4%) than those with less than 8 ng/ml (63.3%). Treatment with estrogen increased synchrony of cows with high progesterone (90.3%) more than prostaglandin alone (60.0%). Based on progesterone concentrations at breeding and 22 to 24 d later, estimated conception rate was 58.7%, and net conception rate based on palpation was 41.3%. Tighter synchrony of estrus can be achieved by using estradiol benzoate 40 to 48 h after prostaglandin. Concentrations of milk progesterone might predict success of treatment.     

Changes throughout estrous cycles of variables that might indicate estrus in dairy cows

Two experiments examined physiological changes throughout estrous cycles of Holstein cows. In experiment one, changes were characterized for physical activity, vaginal pH, vaginal temperature, milk yield, heart rate, and concentration in blood plasma of progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha. Variables were measured daily in 11 cows through a total of 28 estrous cycles. Cows in estrus at least once postpartum were used. Observations for estrus were at least twice daily. Variables changed significantly with day of estrous cycle. Changes of progesterone, physical activity, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were more marked around estrus than were changes of the other variables. Peaks of physical activity coincided with estrus in 75% of the cases. Experiment two was to determine if increased physical activity, measured with pedometers, coincided with estrus in commercial dairy herds. Cows on 14 farms in New York were fitted with mechanical pedometers, and the pedometers were read at each milking. Readings from 3 days before until 3 days after estrus were used from 55 estrous periods identified by the producers. Physical activity was maximal on day of estrus in 73% of the estrous periods. Increased physical activity of commercial dairy cows agreed well with the producers' diagnoses of estrus. Pedometers could be a valuable component of an estrous detection program.     

Duration of estrous cycles subsequent to two injections of prostaglandin F2 alpha given at a 14-day interval in nonlactating Holstein cows

Data from previous experiments in our laboratory indicated that estrous cycles following synchronization with two injections of prostaglandin F2 alpha often averaged more than 21 d. To investigate whether this could be an effect of prostaglandin F2 alpha, 54 mature heifers and nonlactating Holstein cows were used in a crossover experiment in which estrous cycles either occurred spontaneously or followed two injections of prostaglandin F2 alpha at a 14-d interval (induced estrus). One estrous cycle of each type was recorded for each animal. Blood samples were collected twice weekly for analysis of progesterone. Cattle were observed twice daily for estrus with the aid of tail chalking and an androgenized cow. Estrous cycles following induced estrus were longer than those following spontaneous estrus (24.2 vs. 22.7 d). Ninety-two percent of the cycles following spontaneous estrus were 17 to 25 d in duration compared with 71% of the cycles following induced estrus. If the first prostaglandin F2 alpha was given when progesterone was greater than 1 ng/ml, the estrous cycle following treatment was longer than if the first prostaglandin F2 alpha was given when progesterone was less than 1 ng/ml (26.0 vs. 22.6 d). This experiment demonstrates that two injections of prostaglandin F2 alpha increase the incidence of estrous cycles greater than 25 d. Stage of the estrous cycle at time of the first injection of prostaglandin F2 alpha may contribute to this effect.     

Comparison of methods for the synchronization of estrous cycles in dairy cows. 1. Effects on plasma progesterone and manifestation of estrus

Dairy cows (n = 571) were treated with 1) one or two injections of prostaglandin F2 alpha given 11 or 14 d apart, 2) two injections given 14 d apart and a progesterone coil inserted 8 d after the first injection for a 7-d period; or 3) a coil inserted for 7 d and prostaglandin injected 1 d before its removal. Cows given two prostaglandin injections that conceived had higher progesterone concentrations during the luteal phase preceding AI than did cows that did not conceive. Cows with progesterone coils that conceived did not have higher progesterone concentrations than did cows that did not conceive. Older cows had lower progesterone concentrations than younger ones, and they appeared in estrus earlier after treatment. In four daily observations, 75% of cows were seen in estrus within 7 d after treatment. Cows mounting two or more times had a conception rate (62%) similar to that of cows that stood to mount. Fewer cows (56%) treated with prostaglandin that had low concentrations of progesterone appeared in estrus than did cows with high progesterone (84%). Cows treated with prostaglandin differ from cows treated with progesterone coils in respect to manifestation of estrus and to the relationship between plasma progesterone and conception.     

Use of bovine somatotropin in lactating dairy cows receiving timed artificial insemination

Objectives of the research were to examine the effect of bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol and to test a resynchronization system with two consecutive synchronized services. Lactating Holstein cows (n = 403) were assigned to the following treatments: bST treatment (500 mg) was initiated at 63 +/- 3 d postpartum concomitantly with initiation of the timed artificial insemination protocol or bST treatment was initiated at 105 +/- 3 d postpartum. At 63 +/- 3 d postpartum, all cows received GnRH (100 microg), an injection of PGF2alpha (25 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were reinseminated at detected estrus or resynchronized with a GnRH injection at 20 d after insemination. At 27 d after insemination, cows were examined for pregnancy. Resynchronized cows diagnosed nonpregnant received an injection of PGF2alpha and were inseminated at detected estrus or received an injection of GnRH at 48 h after PGF2alpha and inseminated 16 to 20 h later. Cows pregnant at d 27 were reexamined for pregnancy at 45 d after insemination. First-service pregnancy rates at d 45 were increased in cows not resynchronized that initiated bST treatment at 63 +/- 3 d postpartum, compared with cows initiating bST treatment at 105 +/- 3 d postpartum (37.7 +/- 5.8% and 22.1 +/- 4.2%, respectively), but the effect of bST treatment was not observed when cows were resynchronized (25.6 +/- 4.3% and 25.8 +/- 5.5%, respectively). Thus, bST increased pregnancy rates to a timed artificial insemination protocol.     

Bovine immunoglobulin G, beta-lactoglobulin, alpha-lactalbumin and serum albumin in colostrum and milk during the early post partum period.

Colostrum and milk samples from 60 Holstein-Friesian cows were analysed for concentrations and yields of immunoglobulin G (IgG), beta-lactoglobulin (beta-lg), alpha-lactalbumin (alpha-la) and serum albumin (BSA) throughout the first 16 milkings post partum (8 d of lactation) using a single radial immunodiffusion assay. Concentrations (mg/ml, means +/- SD) at first milking were IgG 59.8 +/- 28.5, beta-lg 14.3 +/- 4.6, alpha-la 2.04 +/- 0.6, BSA 1.21 +/- 0.44. Large variations were recorded for IgG concentrations (15.3-176.2 mg/ml) and yields (0.2-925 g). Cows in their first lactation produced significantly lower concentrations and yields of colostral IgG than cows in later lactations. A colostral yield of IgG below the 100 g required to prevent calf hypo-gamma-globulinaemia was found in 18.3% of the cows. The concentrations of IgG, beta-lg and BSA dropped abruptly in subsequent milkings and alpha-la concentration decreased slowly. The mean IgG concentration was < 2 mg/ml after eight milkings and < 1 mg/ml after fifteen milkings. However, IgG concentration did not differ significantly, at the 1% level, during milkings 11-15. The results were tabulated to make it possible to calculate the excess of whey proteins that would be obtained if early milks were illegally added to the milk supply.     

Comparison of methods for the synchronization of estrous cycles in dairy cows. 2. Effects of progesterone and parity on conception

Three experiments with 571 dairy cows indicated that significantly more primiparous cows given two prostaglandin F2 alpha injections 14 d apart conceived within 30 d of first AI than did cows given two injections 11 d apart (84 vs. 62%). Fewer multiparous cows given two injections 14 d apart and inseminated after estrus conceived than did cows given two injections and a progesterone intravaginal coil inserted 8 d after the first injection (42 vs. 66%). Fewer cows given one injection of prostaglandin and inseminated at estrus conceived than did cows given two injections 14 d apart and a progesterone coil (39 vs. 66%). Conception rates of cows given two prostaglandin injections were positively related to plasma progesterone concentrations 2 and 4 d before the second injection (r = .81 and .86). Cows with progesterone concentrations below 5 ng/ml, 2 d before the second prostaglandin injection, and synchronized by two prostaglandin injections or by two injections and a progesterone coil had conception rates of 36 and 63%, respectively. Cows with progesterone concentrations above 5 ng/ml had a conception rate of 75 and 46% in the two treatments, respectively. Conception after estrus synchronization depends on the method and on the plasma concentrations of progesterone. Progesterone coils may be used before AI to enhance fertility in cows with low progesterone concentrations.     

Hormonal induction of lactation: estrogen and progesterone in milk

Estrogen and progesterone in milk during the first 21 days of induced and postpartum lactation in Holstein cows and heifers were estimated by assay procedures. Lactation was induced with estradiol-17 beta and progesterone treatment for 7 days. Estrogen and progesterone in induced lactations differed from concentrations in postpartum lactations. In early lactation estrogen was higher in postpartum milk (521 +/- 103 pg/ml on day 1) than in induced milk (336 +/- 46 pg/ml on day 1), but after day 7 the reverse was true (192 +/- 33 pg/ml and 233 +/- 32 pg/ml on day 7). Progesterone remained higher in induced lactation through the first 21 days than in postpartum lactation with the exception of day 19. Progesterone in postpartum milk increased from 4 +/- 1 ng/ml on day 1 to 11 +/- 2 ng/ml on day 21. Progesterone in induced milk showed greater fluctuation (11 +/- 3 ng/ml on day 1 and 22 +/- 9 ng/ml on day 3) but gradually decreased to 12 +/- 2 ng/ml on day 21 (11 +/- 2 ng/ml on day 21 of postpartum lactation).     

Evaluation of reproductive performance in lactating dairy cows with prostaglandin F2alpha, gonadotropin-releasing hormone, and timed artificial insemination

Nine hundred and twenty Holstein cows from 16 commercial dairy herds to evaluate three systematic breeding protocols: 14-d PGF2alpha, timed artificial insemination (AI), and GnRH-PGF2alpha, relative to AI following estrus detection without hormone intervention. The timed AI protocol involved GnRH, followed by PGF2alpha 7 d later and GnRH again 2 d after PGF2alpha, with AI 6 to 18 h after the second GnRH. The GnRH-PGF2alpha protocol consisted of GnRH followed by PGF2alpha 7 d later. Eight herds relied on visual observation to detect estrus, and eight herds utilized the HeatWatch estrus detection system. The average interval to first postpartum AI was shortest for the timed AI protocol (77.1 d) followed by the 14-d PGF2alpha protocol (81.6 d). There was no difference in days to first AI between the control (86.1 d) and GnRH-PGF2alpha (89.5 d) protocols. Percent pregnant per first AI did not differ among control (45.6%), 14-d PGF2alpha (43.7%), or GnRH-PGF2alpha (44.0%) protocols, but all protocols had a higher percent pregnant per first AI than the timed AI protocol (30.1%). Response to the GnRH-PGF2alpha protocol was limited because 44.0% of the cows submitted to the protocol were not detected in estrus < or = 10 d post-PGF2, administration and had an interval to first AI of 103.8 d. Cumulative percent pregnant by 120 d postpartum did not differ between control cows (53.1%) and hormonally treated cows (50.6%). Visual observation herds had a shorter interval to first postpartum AI (82.8 d) than the HeatWatch herds (84.8 d), with a higher overall rate of estrus detection across all protocols (75.3 and 67.6%, respectively).     

Routine postpartum treatment of dairy cattle with intrauterine neomycin sulfate boluses.

Within location, 119 dairy cattle from two experiment station herds, which had no problems associated with parturition, were randomly either treated by insertion of two intrauterine boluses containing a total of 1000 mg neomycin sulfate 24 h postpartum or maintained as a control. Uteri and ovaries of all cows were palpated 17 to 24 days postpartum and at 14 day intervals thereafter until inovulation of the uterus was judged complete and an estrus had been observed. All cows were inseminated at the first estrus after 60 days postpartum and at each estrus thereafter until conception. Cows treated with neomycin sulfate required more services per conception (1.7 to 1.4) and were open more days before conception (100.5 to 88.5) than the controls. The probable cause of the lowered reproductive efficiency is discussed. Treatment did not later significantly days to ovulation, estrus, involution, or first service. Three treated and five control animals needed additional uterine treatment. Routine intrauterine treatment of all cows with neomycin sulfate boluses should not be recommended.     

Induction of persistent ovarian follicular structures following administration of progesterone near the onset of estrus in dairy cattle

The objective of this study was to determine if progesterone administered near the onset of estrus in dairy cows would block the preovulatory surge of LH and result in subsequent persistence of ovarian follicular structures. Following synchronization of estrus with prostaglandin F2 alpha, 20 multiparous, non-lactating Holstein cows were randomly assigned into three groups: 1 ml ethanol administered i.m. at 12-h intervals for 24 h (n = 6; group 1); 1 mg progesterone administered i.m. at 12-h intervals for 24 h (n = 7; group 2); 2.5 mg progesterone administered i.v. at the onset of standing estrus (n = 7; group 3). Ovarian structures were palpated per rectum on the day of estrus and twice weekly for 14 d. Blood was collected every 2 h from onset of standing estrus for 30 h, and concentrations of LH and progesterone were determined. Numbers of cows diagnosed with persistent follicles 10 d after estrus were 1 of 6 (group 1), 2 of 7 (group 2), and 5 of 7 (group 3). The preovulatory surge of LH did not occur during the sampling period (30 h) for 1 of 6, 7 of 7 and 5 of 7 cows, for groups 1, 2, and 3, respectively, and mean serum concentrations of LH were higher in group 1 than in groups 2 and 3. Serum concentration of progesterone (ng/ml) was higher in group 1 (1.9 +/- .4) than in groups 2 (.9 +/- .4) and 3 (.9 +/- .4) 10 d following estrus. Blocking the preovulatory surge of LH with exogenous progesterone resulted in persistence of ovarian follicles.     

Follicular cysts occur after a normal estradiol-induced GnRH/LH surge if the corpus hemorrhagicum is removed

The pathophysiology underlying follicular cysts appears to be lack of an estradiol (E2)-induced GnRH/LH surge due to hypothalamic insensitivity to E2. In addition, progesterone (P4) can cause animals with follicular cysts to resume normal cyclicity and normal hypothalamic responsiveness to E2. We postulated that follicular cysts may be a pathological manifestation of a physiological state that cows, and possibly other species, go through during the normal estrous cycle but the rise in P4 following ovulation induces them back to normal hypothalamic responsiveness to E2. Based on this hypothesis, we expected that removal of the ovary containing the corpus hemorrhagicum would prevent the normal rise in P4 following ovulation and induce development of follicular cysts. Cows (n = 24) on day 7 of the estrous cycle were treated with prostaglandin F2alpha (PGF2alpha) and time of ovulation was detected by ovarian ultrasonography every 8 h. Immediately following detection of ovulation, cows were randomly but unequally assigned to have the ovary containing the corpus hemorrhagicum removed (TRT; n = 16) or the ovary opposite to the corpus hemorrhagicum removed (CON; n = 8). Cows were subsequently evaluated by daily ultrasound and blood sampling to determine follicular dynamics. Ovulation was detected at 93.7 +/- 4.5 h after PGF2alpha injection. All CON cows had a normal estrous cycle length (22.0 +/- 0.6 days) after ovariectomy (OVX). Half of the TRT cows became anovular (TRT-ANO; n = 8) after OVX with large anovular follicles developing on the ovary (maximal size, 25.4 +/- 1.4 mm; range, 20-32 mm). However, eight TRT cows ovulated (TRT-OV; n = 8) 7.3 +/- 0.6 days after OVX. Control cows had a normal P4 rise after ovulation. Removal of the newly formed corpus hemorrhagicum prevented the rise in circulating serum P4 in TRT-ANO cows throughout the 25-day experimental period. The TRT-OV cows had a delayed increase in circulating P4 but it was normal in relation to time of ovulation. Serum E2 concentrations were similar among groups (TRT-OV, TRT-ANO and CON cows) until 7 days after OVX. Serum E2 concentrations then decreased in TRT-OV and CON cows but remained elevated (>5 pg/ml) in TRT-ANO cows. Thus, the endogenous increase in circulating E2 that induces the GnRH/LH surge and estrus is sufficient to induce cows into a physiological state that resembles follicular cysts if it is not followed by increased circulating P4.     

Reproductive performance of dairy cows fed two concentrations of phosphorus

The objective of this study was to determine the effect of dietary P concentrations of 0.37 (recommended) or 0.57% (excess; dry matter basis) on reproductive performance. At calving, Holstein cows were randomly assigned to 1 of 2 dietary treatments (n = 134 for 0.37% P and n = 133 for 0.57% P). Cows were fitted with a radiotelemetric transmitter (50 d in milk [DIM]) to record mounting activity during estrus and bred to natural estrus from 50 to 100 DIM, then to synchronized estrus (Ovsynch protocol) after 100 DIM. Weekly ultrasonography was performed from 50 DIM until pregnancy was diagnosed (-30 d after artificial insemination). Pregnancy was confirmed approximately 60 d after artificial insemination (artificial insemination). Weekly blood samples were analyzed for progesterone concentrations. Days to first increase (>1 ng/ml) in progesterone, days to first estrus detected by radiotelemetry, days to first service detected by herd personnel, and conception rate at first service did not differ between the recommended and excess P groups, respectively. Similarly, conception rate at 30 d, days open, pregnancies lost from 30 to 60 d, multiple ovulation rate, and the incidence of anovulatory condition at 71 DIM did not differ between these groups. The mean duration of estrus was 8.7 +/- 0.5 and 8.7 +/- 0.7 h, and the average number of mounts per estrus was 7.4 +/- 0.5 and 7.8 +/- 0.5 for a total mounting time during estrus of 25.8 +/- 1.8 and 24.5 +/- 1.6 s for cows fed the recommended and excess P diet, respectively. Phosphorus treatment had no detectable effect on reproductive performance.