Pinealectomy and sexual rhythm in female rats.

The role of the pineal gland in inducing and maintaining the persistent estrus of rats exposed to continuous illumination was examined. Under the cyclic illumination, the pinealectomy or sham-operation revealed no effect on the estrous cycle, although weights of the ovaries, adrenals and hypophysis were slightly but definitely greater in the pinealectomized animals. In rats exposed to the continous illumination immediately after pinealectomy or sham-operation, both groups exhibited the persistent estrous states soon after the change of lighting condition. In these rats, neither the degree of persistent estrus nor the organ weights a autopsy showed any significant difference between the groups. Moreover, the pinealectomy could not alter the incidence of estrous in persistent estrous rats which had been established already by the continuous illumination.     

Failure of the orally active progestin, Regu-mate, to overcome confinement-induced delayed puberty in gilts

Thirty-three crossbred gilts that were raised in total confinement were randomly allotted to two adjacent pens in a finishing unit at 144.7 +/- .5 days of age and 58.0 +/- 1.7 kg body weight. At approximately 253 days of age, 16 gilts were group fed a daily dose of 20 mg of Regu-mate per gilt for 18 days and 17 control gilts were group fed the same diet without Regu-mate for 18 days. Ovarian morphology was examined on 11 or 12 days after the last feeding of Regu-mate. Based on estrous behavior and ovarian morphology only one Regu-mate gilt displayed an estrus but did not ovulate and only three of the control gilts displayed estrus and ovulated at least once before the start of treatment. Three of the 16 Regu-mate gilts displayed estrus and ovulated 7.3 +/- .3 days after the last feeding and within the same time period the 3 control gilts, which previously displayed estrus, continued to have estrous cycles. One additional control gilt displayed estrus and ovulated 5 days after the last feeding of the control diet. Therefore, the proportion of gilts that displayed estrus and ovulated by the end of the experimental period were similar for the treated (25.0%) and control (23.5%) groups. Based on these results we conclude that treatment of gilts in a state of confinement-induced delayed puberty with 20 mg Regu-mate daily for 18 days failed to result in a synchronized onset of puberty in a significant proportion of gilts.     

Characteristics of the estrous cycle of the swamp buffalo under temperate conditions

Estrous cycle, duration of estrus and time of ovulation of eight cyclic buffaloes were examined during a period of one year. Animals were kept under loose-housing conditions and fed according to the Japanese Feeding Standards for dairy cattle. All the animals were observed for the occurrence of estrus twice daily by using a vasectomized bull, and ovarian cycles of each animal were monitored by weekly rectal palpation. Duration of estrus and time of ovulation were determined in 32 estrous periods from eight animals. Animals came in estrus throughout the year. The estrous cycles corresponding to single ovarian cycles ranged from 11 to 38 days with a mode interval of 20 days, averaged 21.5 +/- 4.7 days. Percentage of the cycles within a range of a mean +/- 1 SD (17-26 days) was 79.2 %, whereas that of cycles shorter or longer than the expected range was 9.4 % and 11.4 %, respectively. Estrus took place regardless of the time of day and lasted 9 to 27 hr (19.9 +/- 4.4 hr). Ovulation occurred 6 to 21 hr (13.9 +/- 3.4 hr) after the end of estrus, with a mode interval of 12 hr. There were no significant seasonal variations in the estrus characteristics studied.     

Conditions for establishment of reflex ovulation in light estrous rats.

Continual anovulatory state associating with persistent vaginal cornification (light estrus) was induced by placing 4-day cycling rats under continuous lighting (LL). Uterine cervical stimulation was applied at arbitrary solar hours to light estrous rats showing continual vaginal estrus for more than 2 weeks. The ovulation was induced between 14 and 16 hr after the stimulation dissociating entirely with solar hours. Injection of anti-LHRH serum 5 min after the stimulation but not later than 20 min blocked this ovulation. Ovulation thus induced was always followed by pseudopregnancy with continual leucocytic vaginal smear lasting 10.70 days. The change in concentrations of peripheral serum progesterone during this period was almost similar to that of normal pseudopregnancy except extremely low levels observed at the start and end. Effectiveness of the cervical stimulation for induction of ovulation in light estrous rats was related to not only the duration of light estrus but also the time after transfer to LL, suggesting that the neural mechanism of ovulation in light estrous rats shifted from that of the spontaneous to reflex ovulators due to the extinction of environmental photic cue.     

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.     

Steroid priming shortens prostaglandin-based estrus synchronization program from 14 to 7 days in cattle

Single injection of estrogen and progesterone before prostaglandin (steroid priming) was used to shorten the prostaglandin-based estrus synchronization program. Sixty-five cyclic Sistani cattle, with parity ranging from 1 to 4 and postpartum period of >80 days were selected at unknown stages of the estrous cycle and assigned to 2 groups according to their age, weight and parity. Females in the control group (n=33; 58.4 +/- 4.3 months; 277 +/- 8 kg LW) received two consecutive injections of prostaglandin F2alpha analogue (500 microg; Cloprostenol, PG) 14 days apart (Day 0 = First PG injection). On Day 7, treated females (n=32; 60 +/- 4.8 months; 292 +/- 9 kg LW) were given an intramuscular injection of 100 mg progesterone and 2 mg estradiol benzoate followed by prostaglandin 7 days later, concurrent with the second PG injection of the control group. Estrus detection was carried out every 6 hours for 7 days, commencing from 24 hours after the last PG injection. Females that allowed to be mounted were identified (standing estrus) and inseminated with frozen semen 12 hours later. Pregnancy was diagnosed on Day 50 after AI through palpation per rectum. Data were analyzed using Chi-squared and t-test. The tightness of estrus synchrony (%), the interval from the end of treatment to estrus (h) and conception rates (%) were similar (P > 0.05) between control (69.6%, 77.7 +/- 5.96 h and 56.5%) and treatment (68.2%, 82.6 +/- 7.64 h and 54.5%) groups. In conclusion, steroid priming is an efficient way to shorten the prostaglandin-based estrus synchronization program from 14 to 7 days without compromising estrous response and fertility.     

The influence of the corpus luteum on ovarian follicular dynamics during estrous synchronization in goats

Ovarian follicular dynamics and fertility are unaffected by the presence or absence of a corpus luteum during synchronization of estrus with progestins in goats. On day 5 of the estrous cycle (estrus= day 0), a gestagen-containing sponge was inserted in the vagina for 11 days. To remove corpora lutea, one group of goats (CL-, n=41) received 7.5 mg of luprostiol on days 7 and 8 of the estrous cycle. The second group of goats retained the CL (CL+, n=38). Growth and development of follicles > or =4 mm in diameter were measured daily from onset of estrus to 2 days after subsequent ovulation in seven goats from each group, using rectal ultrasonography. Estrus was detected by the use of a reproductively sterilized buck and estrous does were subsequently mated. The number of waves of follicular development (CL- =3.57+/-0.2 versus CL+ =3.14+/-0.14; P>0.05) did not differ between groups. The second wave of follicular development was present at the time of progesterone decline in the CL- group and neither its duration (CL- =4.8+/-0.4 versus CL+=5.6+/-0.7 days; P>0.05) nor the day of commencement of the third wave of follicular development (CL -=11.6+/-0.7 versus CL+=11.8+/-0.6; P>0.05) were altered by the concentration of endogenous progesterone. The pregnancy rate was similar between the two groups. (CL-=68.29% versus CL+=65.79%; P>0.05). Thus, in goats, ovarian follicular dynamics and fertility were not altered by the presence or absence of a corpus luteum during estrous synchronization.     

Behavioral, follicular and gonadotropin changes during the estrous cycle in donkeys

Sexual behavior, follicular development and ovulation, and concentrations of circulating gonadotropins during the estrous cycle were studied during the summer in 7 jennies. Mean behavioral estrous length was 6.4 +/- 0.6 days (mean +/- SEM, n=19; 5.6 +/- 0.5 days preovulatory and 0.8 +/- 0.2 days post-ovulatory). Mean diestrous length was 19.3 +/- 0.6 days (n=14). Females in estrus typically showed posturing, mouth clapping, clitoral winking, urinating and tail raising. Mouth clapping began approximately one day sooner and lasted approximately one day longer than winking and tail raising, so that the total duration of clapping was significantly greater than for the other two signs. Follicular changes and concentrations of gonadotropins were determined for 14 estrous cycles (2 per jenny). The follicular end points [diameter of the largest follicle and number of large (>25 mm), medium (20-24 mm), and small follicles (<20 mm)] showed a significant day effect. The diameter of the largest follicle and the number of large follicles began to increase significantly 7 days prior to ovulation with a maximum value the day before ovulation. Medium follicles reached a maximum number 4 days prior to ovulation, and small follicles decreased significantly prior to ovulation. After ovulation, all follicular end points, except the number of small follicles, remained low for the next 12 days. Mean values of FSH were low during estrus and high during diestrus with 2 significant peaks, one 3 days and one 9 days after ovulation. In contrast, mean levels of LH were low during diestrus and high during estrus with a maximum value the day after ovulation. The LH profile showed a more prolonged gradual increase prior to ovulation, than that which has been reported for ponies and horses.     

Endocrine events during the periestrous period and the subsequent estrous cycle in ewes after estrus synchronization

The aim of the present study was to investigate the endocrinology of the periestrus period and that of the subsequent estrous cycle in ewes synchronized during the breeding season. Animals were treated for 14 days with either MAP intravaginal sponges or subcutaneous progesterone implants, followed by administration of 500 IU PMSG at the time of withdrawal. The time to estrus occurrence following progestagen withdrawal differed significantly between groups (45.3+/-2.7h for the MAP and 21.5+/-1.2h for the implant group, P<0.001). Estradiol levels around estrus did not differ between groups, but a significant difference was detected for the interval from peak estradiol to estrus, with a shorter interval for the implant group (26.7+/-0.7 and 2.7+/-0.9h, P<0.001). Progesterone implants shortened the interval from removal to LH surge, compared to the MAP group (31.2+/-4.4 and 56.5+/-3.6h, respectively, P<0.05). An earlier response was also observed for the interval from estradiol peak to LH peak in the implant group (12.1+/-3.3 and 37+/-2h, respectively, P<0.005), but no difference was observed for the interval from estrus to LH surge. Progesterone levels, particularly during the Days 6 to 10 of the subsequent estrous cycle were significantly higher (P<0.05) in the implant group. It is concluded that the kind of progesterone treatment may affect the time of estrus and the LH peak as well as the progesterone levels of the subsequent cycle.     

Concentrations of 13, 14-dihydro-15-keto-prostaglandin F(2)alpha, estradiol-17beta and progesterone during the peripubertal period in heifers

Twenty prepubertal Holstein heifers were utilized to assess plasma 13, 14-dihydro-15-keto-prostaglandin F(2)alpha (PGFM), serum progesterone (P(4)) and estradiol-17beta (E(2)) concentrations as well as the E(2):P(4) ratio during the onset of puberty in cattle. All animals were maintained as a group along with a sterile marker bull to assist in the detection of estrus. Upon detection of the first estrus (Day=O), daily blood samples were collected from a jugular vein until the heifers had completed 3 estrous cycles. The average body weight and age at first estrus were 247.6+/-4.8 kg and 304.0+/-7.5 days, respectively. Frequency of abnormal length estrous cycles was greater (P<0.02) during the first (40%) and second (35%) cycles than during the third estrous cycle (0%). All heifers had normal cycle lengths (18 to 24 days) by the third estrous cycle. Serum P(4) was greater during the third cycle (P<0.05) from Day 10 to Day 4 before the next estrus compared with the same period of the first estrous cycle. Serum E(2) did not peak until the day of estrus in the first cycle, whereas E(2) reached a maximal level 2 days before estrus in the third estrous cycle. Serum E(2) was higher (P<0.0001) 2 days before estrus in the third cycle than in the first estrous cycle. Plasma PGFM reached maximum concentrations 3 days before estrus in the third cycle compared with 1 day before estrus at the end of first estrous cycle. As estrus approached during the third cycle, PGFM rose 1 day before E(2) rose and P(4) declined, while the rise in PGFM and E(2) occurred simultaneously, with P(4) declining at the end of the first estrous cycle. During diestrus, the E(2):P(4) ratio was lower (P<0.07) in the third cycle than in the first, but it was higher (P<0.04) at estrus and 1 day before in the third estrous cycle. These data reveal a high incidence of abnormal length estrous cycles during the first two estrous cycles of the peripubertal period, and demonstrate anomalies in uterine and ovarian endocrine activity during the peripubertal period in cattle.     

Effect of presence of the male on initiation of estrous cycle activity of goats

Serum progesterone concentrations and behavioral estrus were determined in two groups of 17 mixed breed dairy does at the beginning of the breeding season. The treatment group was pastured adjacent to two mature bucks while two teaser bucks ran with the group. The control group was pastured without exposure to bucks. Goats were observed for estrus daily for 35 days and samples of jugular blood were collected every other day for radioimmunoassay of progesterone. Signs of estrus were observed in 16 of 17 does in the treatment group within a mean +/- S.E. of 5.5 +/- 1.3 days after introduction of the bucks. Thirteen does demonstrated a progesterone profile characteristic of a normal estrous cycle with peak progesterone concentrations of 5.9 +/- 0.5 ng/ml. Signs of behavioral estrus were not observed in the control group. One control doe demonstrated a progesterone profile characteristic of a normal estrous cycle attaining a peak progesterone concentration of 3.9 ng/ml. Progesterone concentrations in the remaining 16 control does were at or near the lower limits of sensitivity of the assay for the duration of the experiment. Fifteen of the control does exhibited estrus within 7 +/- 1.5 days after exposure to bucks at the end of the experiment. These results clearly demonstrated a profound influence of the male on estrous cycle activity during the beginning of the breeding season.     

Mating of captive thirteen-lined ground squirrels and the annual timing of estrus

Thirteen-lined ground squirrels (Spermophilus tridecemlineatus) have a single annual mating season in Michigan, beginning shortly after their spring emergence from hibernation. Captive females were studied during a 3-year period to determine relations among time of removal from the coldroom, vaginal estrus, and mating behavior. Following a 7-month period females spent in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females removed from the coldroom about when free-living animals emerge from hibernation were in vaginal estrus within 24-48 hr and had an initial period of persistent estrus (ca. 3 weeks), followed by briefer (less than 1 week) and more sporadic estrous periods. Females left in the coldroom 3 weeks longer than normal had significantly briefer initial periods of vaginal estrus after being removed from the coldroom. Similarly, virgin Yearlings and virgin 2-Year-Olds had significantly briefer initial periods of estrus than nonvirgin Adults (greater than or equal to 2 years old). In 1985, eight of eight females paired with males mated within the first week after removal from the coldroom and subsequently produced litters. Mated females remained in vaginal diestrus from within a few days of mating until after parturition. In contrast, unmated females remained in prolonged vaginal estrus during this period. Females first paired with males 3 weeks after being taken from the coldroom failed to mate. In 1986, five of six females first paired with males 2 weeks after being removed from the coldroom similarly failed to mate. However, five of six females did mate that were removed from the coldroom 10 days after those in the previously described group and paired with a male 4 days after removal. This first report of reliable mating behavior in captive thirteen-lined ground squirrels should facilitate subsequent analysis of reproductive patterns in this species.     

Induction of estrus in non-lactating dairy goats with different estrous synchrony protocols

The objective of this study was to evaluate two protocols of estrous synchronization in non-lactating Toggenburg goats. Nineteen goats were allocated, according to body condition score and weight, into two groups (A and B) and evaluated utilizing two treatments (T1 and T2). Animals in the T1 and T2 groups received an intravaginal sponge (day 0) containing 60 mg medroxyprogesterone acetate for 6 and 9 days, respectively, plus 200 IU equine chorionic gonadotrophin (eCG) and 22.5 microg cloprostenol 24 h before sponge removal. Females were bred only at the second estrus and received 22.5 microg cloprostenol 7 days later to prevent pregnancy. Percentages of animals in estrus did not differ (P > 0.05) between T1 (89.5%) and T2 (84.2%). From 33 females in estrus (T1 + T2), 28 (84.8%), 2 (6.1%), and 3 (9.1%) were identified in estrus at 06:00, 12:00 and 18:00 h, respectively. Additionally, 6 (18.2%), 0 (0.0%) and 27 (81.8%) were no longer detected to be on estrus at 06:00, 12:00 and 18:00 h, respectively. Interval from sponge removal and the onset of estrus (IE) did not differ (P > 0.05) between T1 (46.1 +/- 15.0 h) and T2 (53.6 +/- 16.1 h). Duration of estrus did not differ (P > 0.05) between T1 (30.0 +/- 12.0 h) and T2 (27.2 +/- 11.2 h). Both protocols were effective in inducing estrus in non-lactating goats. The onset and end of the estrus relative to hour of the day should be considered in estrous detection, natural breeding, and artificial insemination in goats.     

Prostaglandin F2alpha-induced estrus in ewes exhibiting estrous cycles of different duration

Effects of prostaglandin F(2alpha) (PGF(2alpha)), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (< or =16.5 days, short-cycle ewes, n = 10) or long (> or =18 days, long-cycle ewes, n = 9) based on the durations of two estrous cycles (cycles -2 and -1) before treatment. The ewes received (i.m.) 20mg of PGF(2alpha) on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 microg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF(2alpha) and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF(2alpha) and GnRH treatment on cycle 0 was not different (P > 0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner (P < 0.05) after PGF(2alpha) injection in short-cycle ewes than in long-cycle ewes (1.9 +/- 0.1 days and 2.3 +/- 0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer (P < 0.01) than cycle -1 in short-cycle ewes. However, duration of estrous cycle +1 did not change (P > 0.05) after PGF(2alpha) and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ (P > 0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17beta in follicular fluid between short- and long-cycle ewes after PGF(2alpha) and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF(2alpha) and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.     

Estrus induction in Beagle bitches with the GnRH-agonist implant containing 4.7 mg Deslorelin

Estrogens, gonadotrophins, dopamine agonists, gonadotrophin releasing hormone (GnRH) and its agonists have been used for estrus induction in bitches. A long acting GnRH agonist implant (4.7 mg Deslorelin; Suprelorin®, Virbac) with a continuous hormone release has been developed for suppression of sexual function in male dogs. In this study we administered the Deslorelin implant placed subcutaneously on the medial side of the leg to induce estrus in 11 anestrous Beagle bitches (group A). 6 Beagle bitches (group B) with a spontaneous estrous cycle were used as controls. The progress of pre-estrus and estrus was documented by behaviour, vaginoscopy, vaginal cytology and progesterone concentration. In group A a bloody vaginal discharge was detected on average 4.8 (range 3-10) d after application of the implant. At this moment implants were removed under local anaesthesia. Pre-estrus lasted for an average of 4.5 d (range 1-12). All bitches showed estrous signs and ovulated. The ovulation took place on day 8.2 (range 4-15) after start of pre-estrus. In group B pre-estrus lasted for 7.5 d (range 6-9), and the mean day of ovulation was day 11 (range 9-13). As a consequence of ovulation, progesterone serum concentrations exceeded 10 ng/ml during or after the time of ovulation in all bitches. All bitches were bred to fertile Beagle stud dogs or inseminated with fresh semen intravaginally. Between days nine and 19 after ovulation all bitches underwent ovariohysterectomy. The uterine horns were flushed and flushes were examined for ova or embryos. The pregnancy rate in group A was 63.6% and in group B 66.7%. Despite the significantly shorter period of pre-estrus a fertile estrus could be induced in 7 out of 11 treated bitches. Induction of a fertile estrus can be achieved with a GnRH-implant—already registered for the use in male dogs—placed subcutaneously on the medial side of the leg.     

Superovulatory response of Sistani cattle to three different doses of FSH during winter and summer

Objective of the present study was to investigate the effect of season and dose of FSH on superovulatory responses in Iranian Bos indicus beef cattle (Sistani). Cyclic cows, in summer (n=16) and winter (n=16), were assigned randomly to three dose-treatment groups of 120 (n=10), 160 (n=12) and 200 (n=10) total mg of Folltropin-V with injections given twice daily for 4 days in decreasing doses. Estrous cycles were synchronized with two prostaglandin F2alpha injections given 14 days apart. From day 5 after the ensuing cycle, daily ovarian ultrasonography was conducted to determine emergence of the second follicular wave at which time superovulation was initiated. Relative humidity, environmental and rectal temperatures were measured at 08:00, 14:00 and 20:00 h for the 3 days before and 2 days after the estrus of superovulation. Non-surgical embryo recovery was performed on day 7 after estrus. The effects of season, dose, time of estrous expression and all two-way interactions were evaluated on superovulatory responses: total numbers of CL, unovulated follicles (10 mm), ova/embryo, transferable and non-transferable embryos. Season (summer or winter), doses of Folltropin-V (120, 160 or 200 mg NIH) and time of estrous expression (08:00, 14:00 or 20:00 h) did not affect the number of transferable embryos (3.1+/-0.58). When superovulatory estrus was detected at 08:00, a FSH dose effect was detected with the greatest numbers of CL (12.2+/-0.87) and total ova/embryos (12.2+/-1.46) occurring with 200 mg FSH (dosextime of estrous expression; P<0.01).     

Delayed persistent estrus induced by continuous lighting after inadequate acclimation in rats.

While the normal estrous cycle of adequately acclimated female rats was replaced by a persistent estrus (PE) under continuous lighting, the onset of PE was delayed following several irregular cycles without acclimation or after acclimation for one week, suggesting that transportation induces a significant critical stress.     

Prevention of continuous light-induced anovulation in rats by early exposure to continuous light

Continuous illumination (LL) beginning at 22 days of age caused precocious puberty followed by persistent estrus with anovulation in female offspring originating from mother rats exposed to a 14L:10D light-dark cycle prior to and during pregnancy. However, LL had no deleterious effect on reproductive cycles of offspring reared in LL and originating from mothers exposed to LL prior to and during pregnancy. These rats had a normal onset of puberty in LL, a normal 4-day estrous cycle, a periodic rise of plasma estrogen prior to the periodic appearance of the preovulatory luteinizing hormone (LH) surge, and spontaneous ovulation in LL continued until at least 300 days of age. Also, the female offspring of these rats showed a similar resistance to the deleterious effects of LL on cyclic ovulation. These results support the following interpretation: 1) offspring from mother rats exposed to LL prior to and during pregnancy become insensitive to the deleterious effects of LL on cyclic ovulation, 2) neural elements controlling cyclic release of LH are not totally photoperiod (14L:10D)-dependent, and 3) in the absence of daily 14L:10D signals, an endogenous clock, possibly timed by daily laboratory signals (temperature, noise, taking of vaginal smears), may provide time cues for cyclic LH release.     

Effect of dietary phosphorus concentration on estrous behavior of lactating dairy cows

The objective of this study was to determine the effect of dietary phosphorus (P) concentrations of 0.38 (adequate) or 0.48% (excess) of the total mixed ration (TMR) (dry matter basis) on estrous behavior of lactating cows as measured by a radiotelemetric system (HeatWatch; De Forest, WI, USA). At calving, 42 Holstein cows (n=21 per treatment) were randomly assigned to one of two dietary P treatments. Cows were milked twice daily and milk weights were recorded. Cows were housed in a free-stall barn and were fitted with a radiotelemetric transmitter 40 days postpartum to record estrous mounting activity. The total number of estruses recorded for the 42 cows were 72 (37 and 35 for cows in the adequate and excess P groups, respectively). The mean duration of estrous cycles was 22 +/- 0.6 days and 21 +/- 0.4 days for cows fed the adequate and excess P diets, respectively (P=0.14). The mean duration of estrus was 8.9 +/- 1.1 h and 8.6 +/- 1.2 h (P=0.86), the average number of mounts during estrus was 7.0 +/- 1.2 and 8.2 +/- 1.7 (P=0.57), and the total mounting time was 27.1 +/- 4.3 s and 30.8 +/- 6.5 s (P=0.64) for cows fed the adequate and excess P diets, respectively. Phosphorus treatment had no significant effect on intensity or duration of estrus.     

Various behavioral signs of estrous and their relationship with time of ovulation in dairy cattle

The objective of this study was to investigate the relationship between various behavioral signs of estrous and time of ovulation and, determine which behavioral estrous sign(s) best predicted time of ovulation. In total, 94 ovulations were observed in 67 Holstein-Friesian dairy cows. Different behavioral estrous signs were observed at 3-h intervals and their relation with time of ovulation (ultrasound examinations at 3-h intervals) was investigated. In all estrous periods, sniffing and chin resting was displayed, while mounting was displayed in 90% and standing heat in 58% of estrous periods. Estrus was more intense in primiparous cows compared to multiparous cows and when more animals were in estrus at the same time. Although, these factors influenced intensity of estrous behavioral signs, they did not influence time of ovulation. Ovulation occurred 30.0 +/- 5.1 h after onset of estrus (ranging between 18.5 and 48.5 h) and 18.8 +/- 4.4 h after end of estrus (ranging between 9.5 and 33.5 h). Although informative, these predictors are highly variable between individuals and the method used to determine the onset and end of estrus is time consuming this, therefore limits in their use as a practical predictor of ovulation. Sniffing and chin resting were displayed during the non-estrous period and are therefore, not useful predictors of ovulation time. For animals that displayed standing heat, onset of standing heat was a good predictor for ovulation time (occurring 26.4 +/- 5.2 h before ovulation). However, standing heat was only displayed in a limited number of cows, especially when only one cow was in estrus at a time. Onset of mounting was the best predictor for time of ovulation (occurring 28.7 +/- 5.3 h before ovulation), and it was displayed in 90% of the estrous periods. However, mounting cannot yet be assessed automatically, which limits its practical use as ovulation predictor.