Conception rates to artificial insemination in primiparous, suckled cows exposed to the biostimulatory effect of bulls before and during a gonadotropin-releasing hormone-based estrus synchronization protocol

The objective of these studies was to evaluate whether exposing primiparous, suckled beef cows to the biostimulatory effect of bulls alters breeding performance associated with an estrus synchronization protocol that included GnRH followed 7 d later by PGF(2alpha) and fixed-time AI (TAI). This was a composite analysis of 3 experiments that evaluated (1) the effects of bull exposure at different days after calving (yr 1); (2) the biostimulatory effects of bull excretory products (yr 2); and (3) the biostimulatory effects of familiar and unfamiliar bulls (yr 3) on the resumption of ovarian cycling activity. In all studies, cows were exposed (biostimulated; n = 94) or not exposed (nonbiostimulated; n = 67) to bulls or excretory products of bulls for at least 60 d before the beginning of the estrus synchronization protocol. Average calving day did not differ among years and was 52 +/- 5 d. Year did not affect the proportions of biostimulated and nonbiostimulated cows that were cycling at the beginning of the estrus synchronization protocol; however, a greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows were cycling at this time. In each year, cows were given GnRH followed by PGF(2alpha) 7 d later. Cows were observed for estrus twice daily (am and pm) after PGF(2alpha). Cows that exhibited estrus before 54, 60, and 64 h after PGF(2alpha) were inseminated by AI 12 h later in yr 1, 2, and 3, respectively. Cows that failed to show estrus were given GnRH and TAI at 62, 72, and 72 h after PGF(2alpha) in yr 1, 2, and 3, respectively. Conception rates were determined by transrectal ultrasonography 35 d after TAI in each year. The percentages of cows that exhibited estrus after PGF(2alpha) and before TAI, the interval from PGF(2alpha) to estrus, and the percentages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows and were 51%, 54.7 +/- 7.3 h, 35%, and 65%, respectively. Conception rates for cows bred by AI 12 h after estrus did not differ between biostimulated and nonbiostimulated cows; however, the TAI conception rate was greater (P < 0.05) for biostimulated cows (57.6%) than for nonbiostimulated cows (35.6%). We conclude that TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF(2alpha) may be improved by the biostimulatory effect of bulls in postpartum, primiparous cows.     

Follicular dynamics and steroid profiles in cows during and after treatment with progestin-based protocols for synchronization of estrus

Two progestin-based protocols for the synchronization of estrus in beef cows were compared. Cyclic, nonlactating, crossbred, beef cows were assigned by age and body condition score to one of two treatments. Cows assigned to the MGA Select protocol were fed melengestrol acetate (MGA; 0.5 mg x cow(-1) x (-1)) for 14 d, GnRH was administered (100 microg i.m. of Cystorelin) 12 d after MGA withdrawal, and PGF2alpha (25 mg of i.m. Lutalyse) was administered 7 d after GnRH. Cows assigned to the 7-11 Synch protocol were fed MGA for 7 d and were injected with PG on d 7 of MGA, GnRH on d 11, and PG on d 18. Transrectal ultrasonography was performed daily to monitor follicular dynamics from the beginning of MGA feeding through ovulation after the synchronized estrus. All cows exhibited estrus in response to PG. Mean interval to estrus was shorter (P < 0.01) for 7-11 Synch-treated cows (56 +/- 1.5 h) than for cows assigned to the MGA Select protocol (73 +/- 4.7 h). Mean interval from estrus to ovulation did not differ between treatments (P > 0.10). Variances for interval to estrus differed (P < 0.01) between treatments. Mean follicular diameter at GnRH injection, PG injection, and estrus did not differ (P > 0.10) between treatments. Relative to MGA Select, serum estradiol-17beta concentrations were higher (P < 0.01) for 7-11 Synch 2 d and 1 d before, on the day of GnRH injection, in addition to 4 d after GnRH, and 24 h after PG. Mean progesterone concentrations were greater (P < 0.01) for MGA Select cows from 4 d before to 7 d after GnRH. Forty-four percent of the variation in interval to estrus between treatments was explained by differences in estradiol-17beta concentrations 24 h after PG. This study suggests that follicular competence is likely related to steroidogenic capacity of the follicle and the endocrine environment under which growth and subsequent ovulation of the dominant follicle occurs.     

Effects of standing estrus and supplemental estradiol on changes in uterine pH during a fixed-time artificial insemination protocol

Cows that exhibit estrus within 24 h of fixed-time AI have elevated concentrations of estradiol and greater pregnancy rates compared with cows not in estrus. Our objective was to determine whether estradiol, estrus, or both had an effect on uterine pH during a fixed-time AI protocol. Beef cows were treated with the CO-Synch protocol (100 mircog of GnRH on d -9; 25 mg of PGF(2alpha) on d -2; and 100 mircog of GnRH on d 0). One-half of the cows received an injection of estradiol cypionate (ECP; 1 mg) 12 h after PGF(2alpha). Cows detected in standing estrus within 24 h of the second GnRH injection were considered to be in standing estrus. Uterine pH was determined in all animals 12, 24, and 48 h after the PGF(2alpha) injection. For Exp. 1, pH was also determined 72 and 96 h after the PGF(2alpha) injection; in Exp. 2, pH was also determined at 54, 60, 66, 72, 78, 84, 90, and 96 h after the PGF(2alpha) injection or until ovulation. A treatment x time interaction (P < 0.01) influenced concentrations of estradiol. All cows had similar (P > 0.15) concentrations of estradiol at the time of ECP administration, but after ECP treatment all cows treated with ECP and control cows that exhibited estrus had greater (P < 0.01) concentrations of estradiol compared with nontreated cows that did not exhibit estrus. In all animals, estradiol diminished 48 h after the PGF(2alpha) (time of the second GnRH injection), but ECP-treated cows, regardless of estrus, had elevated (P < 0.02) concentrations of estradiol compared with control cows. There was a treatment x time interaction (P < 0.001) on uterine pH. All cows had similar uterine pH (P > 0.19) 24 h after the PGF(2alpha) injection. Control cows that did not exhibit estrus had a greater uterine pH compared with control cows that exhibited estrus (P < 0.01) and ECP cows that exhibited estrus (P = 0.05) 48 h after the PGF(2alpha) injection (7.0 +/- 0.1 vs. 6.7 +/- 0.1 and 6.8 +/- 0.1, respectively). Estradiol cypionate-treated cows not exhibiting estrus were intermediate (6.8 +/- 0.1; P > 0.05). All cows had similar uterine pH 72 h after the PGF(2alpha) injection through ovulation (P > 0.06). In summary, uterine pH was similar among all animals that exhibited estrus, regardless of treatment with ECP.     

Effect of the uterus on subnormal luteal function in anestrous beef cows

The effect of the uterus on luteal lifespan and pattern of secretion of progesterone following early weaning of calves from anestrous beef cows was studied. Calves were weaned from 15 anestrous beef cows 23 to 33 d postpartum, and cows were allotted to a control (sham surgery, n = 8) or a hysterectomy (n = 7) group, with surgery performed at weaning. Cows in the hysterectomy group were injected (im) with 25 mg prostaglandin F2 alpha (PGF2 alpha) approximately 20 d after first estrus (d 0). The interval from weaning to estrus was longer (P less than .05) for the hysterectomy group (10.4 +/- 1.6 d) than the control group (6.2 +/- .5 d). In the control group, the first estrous cycle (8.8 +/- .3 d) was shorter (P less than .01) than the second estrous cycle (20.2 +/- .5 d). Following first estrus in the hysterectomy group, cows were not detected in estrus until after injection of PGF2 alpha and did not return to estrus. From d 0 to 5, mean concentrations of plasma progesterone were similar (P greater than .05) between groups for both estrous cycles; after d 5 of estrous cycle 1, concentrations of plasma progesterone decreased in the control group. Within the hysterectomy group, the pattern of secretion of progesterone from d 0 to 16 was similar after the first and second estrus. Furthermore, there was no difference in the pattern of secretion of progesterone from d 0 to 16 between hysterectomy (first or second estrous cycles) and control (second estrous cycle) groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prostaglandin F2 alpha-induced luteolysis on in vivo and in vitro progesterone production by individual placentomes of cows

This study investigated placental progesterone production by bovine placentomes. Catheters were placed in the femoral artery (FA) and in the caruncular artery (CA), caruncular vein (CV) and lymphatic vessel of a prominent placentome of 13 cows at 200 d of gestation. Four of the 13 cows were given prostaglandin F2 alpha (PGF2 alpha) after surgery, and blood and lymph were collected for progesterone determination. After 24 h, progesterone was higher (P less than .01) in FA and CA plasma from control cows that FA and CA plasma from PGF2 alpha-treated cows (5.11 +/- .29 and 5.17 +/- .64 vs 1.41 +/- .08 and 1.15 +/- .08 ng/ml, respectively), but CV concentrations were similar (3.38 +/- .30 vs 2.56 +/- .24, respectively). There was a net uptake of progesterone by placentomes from control cows (P less than .01) but a net secretion in PGF2 alpha-treated cows (P less than .05). Lymph contained low progesterone concentrations regardless of treatment. Cows were slaughtered at 240 d of gestation. Placentomes were removed and perfused with pregnenolone through the maternal and fetal arteries. Fetal venous effluent contained more progesterone than maternal venous effluent (P less than .001) in both groups, and fetal venous effluent of placentomes from PGF2 alpha-treated cows contained more progesterone than that from control cows (P less than .05). Maternal and fetal components of other placentomes were cultured alone or in co-culture along with pregnenolone and (or) epostane. Fetal tissue produced more progesterone (P less than .001) than maternal tissue when each was cultured alone, but fetal tissue production declined when co-cultured with maternal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of an agonist of gonadotropin-releasing hormone (buserelin) on estrus synchronization and fertility in beef cows.

The objective of this experiment was to determine the effect of sequential treatment with buserelin (a GnRH agonist) and cloprostenol (a prostaglandin F2 alpha analog) on estrous response and fertility in beef cattle with different ovarian conditions. On d 0 (1st d of treatment), the control group (n = 52, 10 heifers and 42 cows) and the GnRH group (n = 48, 10 heifers and 38 cows) received 2 mL of saline or 2 mL of Receptal (8 micrograms of buserelin), respectively. On d 6, all cows that had not exhibited spontaneous estrus were given i.m. 500 micrograms of cloprostenol (PGF). Ultrasonography on d 0 and assays of progesterone in blood on d -11, 0, and 6 were used to identify follicular and luteal status of animals. Cattle were observed for estrus from d 0 to 10. Cows showing estrus were bred artificially 12 h after onset of estrus. Over the 10-d period, the number of cows detected in estrus and pregnancy and conception rates were identical for the two groups. However, between d 0 and 6, the proportion of cows exhibiting estrus was lower (P less than .01) in the GnRH group than in the control group. Between d 6 and 10, the synchronization rate and precision of estrus were greater (P less than .01) in the buserelin-treated group than in the control group. Conception rate and interval from PGF injection to onset of estrus were not different between the two treatment groups. Presence of a large (greater than 10 mm) follicle on d 0 enhanced synchronization rate and precision of estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estrous behavior and initiation of estrous cycles in postpartum Brahman-influenced cows after treatment with progesterone and prostaglandin F2alpha

Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.     

Effect of age and norgestomet on endocrine parameters and production of embryos in superovulated beef cows

Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses to induction of superovulation were studied in old (greater than 12 yr) and young (5 to 7 yr) lactating beef cows. Seventeen cows (8 old and 9 young) received a 6-mg N ear implant on d 4 or 5 of the cycle (d 0 = estrus); the remaining 17 cows (9 old and 8 young) served as untreated controls (C). All animals were treated with 38 mg of porcine follicle-stimulating hormone (FSH-P) in decreasing dosages over a 4.5-d period beginning on d 10 or 11. Regression of the corpus luteum was induced with injections of PGF2 alpha at 0800 and 2000 on d 4 of FSH-P treatment; implants were removed at the second injection of PGF2 alpha. Cows were inseminated artificially 12 and 24 h after onset of estrus. Embryos were collected on d 7 or 8 postinsemination. Blood samples were obtained daily at 0800 from 2 d prior to initiation of treatment with FSH-P until collection of embryos. An additional sample was collected each day at 2000, from the first injection of PGF2 alpha to 1 d after onset of estrus. Samples were assayed for luteinizing hormone (LH), progesterone (P4), follicle stimulating hormone (FSH) and estradiol-17 beta (E2). Total number of embryos plus ova recovered was lower (P less than .01) in N-treated (5.2 +/- 1.1) than in C-treated (10.6 +/- 1.6) cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of preovulatory concentrations of estradiol and initiation of standing estrus on uterine pH in beef cows

Previous studies have indicated that initiation of standing estrus within 24h of fixed-time AI influenced pregnancy rates. Furthermore, uterine environment at time of insemination can influence sperm transport. We hypothesized that preovulatory concentrations of estradiol would influence uterine pH at time of insemination. The objective of this study was to determine the influence of elevated preovulatory concentrations of estradiol on uterine pH following a fixed-time AI protocol. Cows were synchronized with the CO-Synch (n=57) protocol, and 29 cows were treated with an injection of estradiol cypionate (ECP; 1mg) 36h before the second injection of GnRH. Cows that exhibited standing estrus or were treated with ECP had increased (P<0.05) concentrations of estradiol compared to cows not in estrus and not administered ECP, respectively. There was an ECP by standing estrus interaction on uterine pH (P=0.01). Control cows that exhibited estrus had a reduced uterine pH (6.72+/-0.10; P=0.05) compared to control cows not exhibiting estrus (7.0+/-0.06). Cows treated with ECP and detected in standing estrus had a greater uterine pH (7.0+/-0.07) compared to control cows in estrus (P=0.02) and ECP cows not in estrus (6.81+/-0.09; P=0.06). The interval between the initiation of standing estrus and when pH was determined also influenced uterine pH. Cows that initiated standing estrus within 4h of pH determination had a lower uterine pH (6.74+/-0.12) compared to cows that initiated estrus 4-8h (7.09+/-0.08; P=0.07) or 8-12h (7.10+/-0.15; P=0.03) after pH determination. In summary, elevated concentrations of estradiol influenced standing estrus but only influenced uterine pH when pH was determined within 4h of the initiation of standing estrus.     

Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d -10), PGF(2alpha) (d -3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF(2alpha) were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF(2alpha) were TAI at 72 h and given GnRH (100 mug). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF(2alpha) did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF(2alpha) than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.     

Ovsynch plus CIDR protocol for timed embryo transfer in suckled postpartum Japanese Black beef cows

We compared synchronization and pregnancy rates, and the increase in blood progesterone concentrations during luteal development, between (1) Ovsynch plus an intravaginal controlled internal drug release (CIDR) device protocol followed by timed embryo transfer (timed ET), and (2) a conventional estrus synchronization method using PGF(2 alpha) and ET in suckled postpartum Japanese Black beef cows. Cows in the PGF group (n=18) received a PGF(2 alpha) analogue when a CL was first palpated per rectum at 10-d intervals after 1 to 2 month postpartum. Cows (n=11), which showed estrus (Day 0) within 5 d of the PGF(2 alpha), and had a CL on Day 7, received ET. Cows in the Ovsynch+CIDR group (n=19) underwent the Ovsynch protocol plus a CIDR for 7 d (GnRH analogue and CIDR on Day-9, PGF(2alpha) analogue with CIDR removal on Day-2, and GnRH analogue on Day 0), with ET on Day 7. The ovulation synchronization (100%) and embryo transfer (100%) rates in the Ovsynch+CIDR group were greater (P<0.01) than the estrus synchronization (66.7%) and the embryo transfer (61.1%) rates in the PGF group. The postpartum interval at ET in the Ovsynch+CIDR group (62.5 +/- 2.5 d) was shorter (P<0.01) than in the PGF group (74.9 +/- 3.9 d). The pregnancy rate in the Ovsynch+CIDR group (57.9%) did not differ significantly from that in the PGF group (50.0%). Plasma progesterone concentrations were not significantly different in the two groups on Days 0, 1, 2, 5, 7, 14 and 21. In summary, higher synchronization and transfer rates, and shorter postpartum interval to ET, can be achieved with timed ET following the Ovsynch plus CIDR protocol than after estrus with the single PGF(2 alpha) treatment followed by ET in suckled postpartum recipient beef cows. Pregnancy rates were similar. Also, the increase in blood progesterone concentrations during luteal development following ovulation synchronized by the Ovsynch plus CIDR protocol was similar to that after estrus induced by the PGF(2 alpha) treatment.     

Effect of termination of pregnancy or long-term progestogen exposure on subsequent estrous cycle length and concentration of progesterone in plasma of heifers

An experiment was conducted to determine whether short estrous cycles following abortion of heifers between 70 and 75 d of gestation are due to factors associated with the previous presence of a conceptus or long-term exposure of the uterus and(or) ovaries to a progestogen. Fifty crossbred heifers were randomly allotted at estrus (d 0) to five groups: control (n = 10), pregnant (Preg.; n = 14), progestogen (norgestomet) implant (Norg.; n = 9), progesterone-releasing intravaginal device (PRID; n = 9), or hysterectomy (Hyst.; n = 8). Control heifers were injected during the mid-luteal phase of an estrous cycle with 25 mg prostaglandin F2 alpha (PGF2 alpha) and length of the subsequent estrous cycle was determined. Beginning 6 to 8 d after estrus, heifers in the Norg. or PRID groups were given norgestomet ear implants or intravaginal coils, respectively, every 10 d for 70 d. Heifers were hysterectomized 5 to 8 d after estrus. Seventy to 75 d after conception, progestogen treatment or hysterectomy, heifers were injected (i.m.) with 25 mg PGF2 alpha and the last norgestomet ear implants or PRIDs were removed. Interval from PGF2 alpha injection to first estrus (means +/- SE) ranged from 2.5 +/- .2 to 4.4 +/- .7 d (P greater than .05). Length of the first estrous cycle means +/- SE) following PGF2 alpha-induced luteolysis or progestogen withdrawal was shorter (P less than .01) for the Preg. group (8.2 +/- .4 d) than for the control, Norg. and PRID groups (21.5 +/- .6 d; 19.3 +/- 1.4 d; and 18.2 +/- 1.3 d, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal effects on estrous behavior and time of ovulation in nonlactating beef cows

Estrous behavior and time of ovulation relative to the onset of estrus were determined in mature Angus x Hereford cows (n = 17 to 21 each season) during summer, winter, and spring for 2 yr. Estrous behavior was evaluated during the first of two consecutive estrous periods, and time of ovulation was determined during the second estrus. Concentrations of progesterone were quantified in twice weekly blood samples to ensure all cows had normal estrous cycles. The HeatWatch system was used to measure the duration of estrus, number of mounts received per estrus, and duration of the longest interval between mounts received. Commencing 16 h after the onset of the second estrus, transrectal ultrasonography was performed every 4 h until the dominant follicle was no longer present on the ovary, and time of ovulation was defined as 2 h preceding the absence of the dominant follicle. There was a seasonal effect on the duration of estrus; cows were estrus longer in summer (17.6 +/- 0.8 h) than in winter (15.5 +/- 0.8 h; P = 0.07) or spring (13.9 +/- 0.9 h; P < 0.05). Cows were mounted more times per estrus (P < 0.05) in winter (59.0 +/- 5.3) than in summer (43.6 +/- 5.3) or spring (38.2 +/- 5.8). Intervals between mounts of estrous cows were longer (P < 0.05) in summer (4.1 +/- 0.4 h) than in spring or winter (2.7 +/- 0.4 h). During all seasons, cows were mounted more times (P < 0.01) between 0600 to 1200 (3.2 +/- 0.2 mounts received/h of estrus) than during other times of the day (2.1 +/- 0.2 mounts received/h of estrus). Cows ovulated 31.1 +/- 0.6 h after the onset of estrus, and time of ovulation was not influenced by season. We conclude that season influences estrous behavior of beef cows; cows are mounted more times per estrus in winter than in summer or spring. Time of ovulation relative to the onset of estrus is constant during all seasons and averages 31.1 h.     

GnRH in the infundibular stalk-median eminence is related to percentage body fat in carcasses of beef cows.

Mature Hereford cows (n = 28) were used to determine the effect of percentage body fat on secretion of LH and content of GnRH in the infundibular stalk-median eminence (ISME). Cows were fed to maintain, lose, or gain weight to achieve body condition scores (BCS; 1 = emaciated; 9 = obese) of 3 to 7. Then cows were fed to maintain weight and body condition. Before slaughter, estrus was synchronized using two injections of prostaglandin F2 alpha(PGF) 11 d apart. Five d after the second PGF injection, cows were given 100 micrograms of GnRH (im) and serum samples were obtained. LH was quantified using RIA. The anterior pituitary and ISME were obtained within 45 min of death. Anterior pituitary weight and LH concentration, total GnRH in the ISME, total carcass fat, and percentage carcass fat were determined. BCS of cows at the time of slaughter influenced percentage carcass fat (P less than .001), total GnRH in the ISME (P less than .02), and maximum LH after GnRH treatment (P less than .09), but did not influence pituitary weight or concentration of LH in the pituitary. Content of GnRH in the ISME averaged 76 +/- 12, 32 +/- 14, 27 +/- 13, and 24 +/- 13 ng for cows with BCS of 3, 5, 6, and 7, respectively. BCS was correlated (P less than .001) with percentage carcass fat (r = .94) and total fat in the carcass (r = .92). Total GnRH in the ISME was negatively correlated (P less than .005) with BCS (r = -.54), percentage carcass fat (r = -.55), and total carcass fat (r = -.49).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows

The influences of body condition score (BCS) at calving and postpartum nutrition on endocrine and ovarian functions, and reproductive performance, were determined by randomly allocating thin (mean BCS = 4.4 +/- 0.1) or moderate condition (mean BCS = 5.1 +/- 0.1) Angus x Hereford primiparous cows to receive one of two nutritional treatments after calving. Cows were fed to gain either 0.45 kg/d (M, n = 17) or 0.90 kg/d (H, n = 17) for the first 71 +/- 3 d postpartum. All cows were then fed the M diet until 21 d after the first estrus. A replication (yr 2; M, n = 25; H, n = 23) was also used to evaluate reproductive characteristics. Concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were quantified in plasma samples collected weekly during treatment and during 7 wk before the first estrus. Estrous behavior was detected by radiotelemetry, and luteal activity was determined based on concentrations of progesterone in plasma. All cows were bred by AI between 14 and 20 h after onset of estrus, and pregnancy was assessed at 35 to 55 d after AI by ultrasonography. Cows that calved with a BCS of 4 or 5 had similar endocrine function and reproductive performance at the first estrus. During treatment, H cows gained BW and increased BCS (P < 0.01), and had greater (P < 0.05) concentrations of IGF-I, leptin, insulin, glucose, and thyroxine in plasma than M cows. However, during the 7 wk before the first estrus, plasma concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were not affected by time. Cows previously on the H treatment had a shorter (P < 0.01) interval to first postpartum estrus and ovulation, and a larger dominant follicle (P < 0.01) at first estrus, than M cows, but duration of estrus and the number of mounts received were not influenced by nutrient intake. Pregnancy rate at the first estrus was greater (P < 0.03) for H (76%, n = 38) than for M (58%, n = 33) cows. Increased nutrient intake after calving stimulated secretion of anabolic hormones, promoted fat deposition, shortened the postpartum interval to estrus, and increased pregnancy rate at the first estrus. Concentrations of IGF-I and leptin in plasma were constant during 7 wk before the first estrus, indicating that acute changes in these hormones are not associated with the resumption of ovarian function in primiparous beef cows.     

Effects of body condition score at parturition and postpartum protein supplementation on estrous behavior and size of the dominant follicle in beef cows

The objective of this study was to determine the effects of BCS at calving and the amount of postpartum protein supplementation on the dominant follicle (DF) and behavioral characteristics at the first postpartum estrus of mature beef cows. Multiparous Angus x Hereford cows (n = 45) were fed to calve in thin (T; < 5) or moderate (M; >or=5) BCS. Cows were stratified by BCS and calving date, and randomly assigned to receive lesser (L; 1.2 kg/d) or greater (G; 2.5 kg/d) amounts of a 42% CP supplement. All cows grazed the same native grass pasture and were fed in individual stalls for 49 +/- 2 d. Beginning 20 d after calving, blood samples were collected from each cow thrice weekly, and estrous behavior was monitored continuously with a radiotelemetry system. At 4 to 16 h after the onset of estrus, size of the DF was determined by ultrasonography. Body condition score of T cows was less (P < 0.01) at calving than M cows; L and G cows had similar BCS at calving and at the end of the feeding period. Body weight gains during treatment did not differ for L or G cows. Duration from calving to first estrus was greater (P < 0.01) for T than M cows. The incidence of a short luteal phase before first estrus was not influenced by BCS or protein supplement. Concentrations of IGF-I in plasma tended (P < 0.07) to be greater and size of the DF was greater (P < 0.01) for M than T cows. Size of the DF tended (P < 0.06) to be greater for G than L cows. Duration and number of mounts received at the first estrus were not influenced by BCS or supplement. Pregnancy rate of M cows during the breeding season was greater (P < 0.05) than T cows. Postpartum protein intake and BCS at calving influenced the size of the DF at the first postpartum estrus in mature suckled beef cows. Cows should be managed to calve in moderate BCS and maintain BW after parturition to decrease the interval to first estrus, increase follicular development, and maximize pregnancy rate.     

Influence of premature induction of a luteinizing hormone surge with gonadotropin-releasing hormone on ovulation, luteal function, and fertility in cattle

We tested the hypothesis that luteal function and fertility would be reduced in cattle induced to ovulate prematurely compared with those ovulating spontaneously. Estrus was synchronized in 56 beef cows (24 that were nonlactating and 32 that were nursing calves). At 6.4 +/- 0.1 d after estrus, all follicles > or = 5 mm were aspirated (day of aspiration = d 0) with a 17-gauge needle using the ultrasound-guided transvaginal approach. On d 1.5 and 2, cows were administered 2 luteolytic doses of PGF2alpha. Ovarian structures were monitored by transrectal ultrasonography from d -2 to 12, or ovulation. Emergence of a new follicular wave occurred on d 1.7 +/- 0.1. When the largest follicle of the newly emerged wave was 10 mm in diameter (d 4.8 +/- 0.1), cows were assigned on an alternating basis to receive 100 microg of GnRH (GnRH-10; n = 29) to induce ovulation or, upon detection of spontaneous estrus, to the spontaneous (SPON) treatment (n = 24). Cows were bred by AI at 12 h after GnRH (GnRH-10) or 12 h after the onset of estrus (SPON) as detected using an electronic surveillance system. Blood samples were collected every other day beginning 2 d after ovulation until pregnancy diagnosis 30 d after AI. Ovulation and AI occurred in 29/29 cows in the GnRH-10 and in 24/24 cows in the SPON treatment. Ovulation occurred later (P < 0.05) in the SPON (d 7.7 +/- 0.1) than GnRH-10 (d 6.8 +/- 0.1) treatment. Double ovulations were detected in 47% of cows, resulting in 1.5 +/- 0.1 ovulations per cow. Diameters of the ovulatory and the second ovulatory (in cows with 2 ovulations) follicles were greater (P < 0.05) in the SPON (12.0 +/- 0.3 mm and 10.5 +/- 0.4 mm, respectively) than in the GnRH-10 (10.7 +/- 0.1 mm and 9.2 +/- 0.3 mm) treatment. Cross-sectional areas of luteal tissue and plasma concentrations of progesterone during the midluteal phase were greater (P < 0.05) in the SPON (3.62 +/- 0.2 cm2 and 6.4 +/- 0.3 ng/mL) than in the GnRH-10 (3.0 +/- 0.2 cm2 and 5.4 +/- 0.2 ng/mL) treatment. The conception rate to AI in the SPON (100%) treatment was greater (P < 0.05) than in the GnRH-10 (76%) treatment. The animal model used in this study resulted in unusually high conception rates and double ovulations. In conclusion, premature induction of the LH surge reduced the diameter of ovulatory follicle(s), the luteal function, and the conception rate to AI.     

Effect of addition of a progesterone intravaginal insert to a timed insemination protocol using estradiol cypionate on ovulation rate, pregnancy rate, and late embryonic loss in lactating dairy cows

The objectives of this study were to determine the effects of incorporating a progesterone intravaginal insert (CIDR) between the day of GnRH and PGF2alpha treatments of a timed AI protocol using estradiol cypionate (ECP) to synchronize ovulation on display of estrus, ovulation rate, pregnancy rate, and late embryonic loss in lactating cows. Holstein cows, 227 from Site 1 and 458 from Site 2, were presynchronized with two injections of PGF2alpha on study d 0 and 14, and subjected to a timed AI protocol (100 mixrog of GnRH on study d 28, 25 mg of PGF2alpha on study d 35, 1 mg of ECP on study d 36, and timed AI on study d 38) with or without a CIDR insert. Blood was collected on study d 14 and 28 for progesterone measurements to determine cyclicity. Ovaries were scanned on d 35, 37, and 42, and pregnancy diagnosed on d 65 and 79, which corresponded to 27 and 41 d after AI. Cows receiving a CIDR had similar rates of detected estrus (77.2 vs. 73.8%), ovulation (85.6 vs. 86.6%), and pregnancy at 27 (35.8 vs. 38.8%) and 41 d (29.3 vs. 32.3%) after AI, and late embryonic loss between 27 and 41 d after AI (18.3 vs. 16.8%) compared with control cows. The CIDR eliminated cows in estrus before the last PGF2alpha injection and decreased (P < 0.001) the proportion of cows bearing a corpus luteum (CL) at the last PGF2alpha injection because of less ovulation in response to the GnRH and greater spontaneous CL regression. Cyclic cows had greater (P = 0.03) pregnancy rates than anovulatory cows at 41 d after AI (33.8 vs. 20.4%) because of decreased (P = 0.06) late embryonic loss (16.0 vs. 30.3%). The ovulatory follicle was larger (P < 0.001) in cows in estrus, and a greater proportion of cows with follicles > or = 15 mm displayed estrus (P < 0.001) and ovulated (P = 0.05) compared with cows with follicles <15 mm. Pregnancy rates were greater (P < 0.001) for cows displaying estrus, which were related to the greater (P < 0.001) ovulation rate and decreased (P = 0.08) late embryonic loss for cows in estrus at AI. Cows that were cyclic and responded to the presynchronization protocol (high progesterone at GnRH and CL at PGF2alpha) had the highest pregnancy rates. Incorporation of a CIDR insert into a presynchronized timed AI protocol using ECP to induce estrus and ovulation did not improve pregnancy rates in lactating dairy cows. Improvements in pregnancy rates in cows treated with ECP to induce ovulation in a timed AI protocol are expected when more cows display estrus, thereby increasing ovulation rate.     

Effect of estrus synchronization with norgestomet on the integrity of oocytes from persistent follicles in beef cattle.

Our objective was to determine whether oocyte integrity is compromised when oocytes are recovered from progestogen-induced persistent follicles. Beef cows were presynchronized using PGF2alpha (PGF). Cows detected in estrus after PGF were assigned to either NOR (one 6-mg norgestomet implant for 10 d starting on d 16 of cycle; day 0 = estrus; n = 112) or CON (control, no implant [n = 128] and presynchronized 8 d later than NOR). All cows received 25 mg of PGF at the end of treatment (NOR, d 26; CON, d 18). Treatments produced persistent preovulatory follicles (NOR) or normal preovulatory-size follicles (CON), which were measured via ultrasonography 1 d before slaughter. Ovaries were collected from all animals (NOR, d 27; CON, d 19) along with random (RAN) ovaries from cattle slaughtered on the same days. Cumulus oocyte complexes (COC) were aspirated from the preovulatory follicles with recovery rates of 63% across treatments. Small follicles (2 to 7 mm diameter) from NOR, CON, and RAN cows were also aspirated to recover COC. Preovulatory follicles were larger (19.5+/-.9 vs. 13.6+/-.4 mm, P<.05), serum P4 was lower (.4+/-.1 vs. 3.9+/-.2 ng/mL, P<.05), and serum E2 was higher (28.7+/-1.6 vs. 7.6+/-.8 pg/mL, P<.05) in NOR than in CON cows. Cumulus oocyte complexes recovered from preovulatory follicles (62 NOR, 64 CON) were matured, fertilized, and cultured in vitro for comparison of embryonic development. A subset (24 NOR, 34 CON) of COC were assigned morphological quality grades. A separate set of recovered COC (10 NOR, 15 CON) was fixed within 1 h after recovery for assessment of the stage of meiosis. Treatments did not differ for oocyte quality grade or stage of meiosis. However, COC from NOR cows had more layers of cumulus cells (P<.05), and more of those COC had undergone cumulus expansion (29.2 vs. 5.9%, P<.05 for NOR vs. CON, respectively). Development of cleaved embryos to the morula and blastocyst stages from preovulatory follicles (22.6% NOR, 18.9% CON) or small follicles (42% NOR, 40% CON, 42% RAN) did not differ with treatment. Oocyte quality and in vitro developmental competence were not compromised for oocytes from induced persistent follicles compared with oocytes from normal preovulatory follicles. Increased expansion of cumulus cells associated with oocytes from progestogen-induced persistent follicles may be relevant to the reduction of in vivo fertility associated with such follicles.     

Factors affecting pregnancy rate to estrous synchronization and fixed-time artificial insemination in beef cattle

Application of AI in extensive beef cattle production would be facilitated by protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI). The objectives were to determine whether use of a controlled internal drug release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI in beef cows. Beef cows (n = 1,240) in 6 locations within the US Meat Animal Research Center received 1 of 2 treatments: 1)?an injection of GnRH [100 μg intramuscularly (i.m.)] followed by PGF(2α) (PGF; 25 mg i.m.) 7 d later (CO-Synch), or 2) CO-Synch plus a CIDR during the 7 d between GnRH and PGF injections (CO-Synch + CIDR). Cows received TAI and GnRH (100 μg i.m.) at 60 h after PGF. Progesterone was measured by RIA in blood samples collected 2 wk before and at initiation of treatment (d 0) and at PGF injection (d 7). Estrous behavior was monitored by Estrotect Heat Detectors. Pregnancy was diagnosed by ultrasonography 72 to 77 d after TAI. Plasma progesterone concentrations did not differ (P > 0.10) between synchronization protocols at first GnRH injection (d 0), but progesterone was greater (P < 0.01) at PGF injection (d 7) in cows receiving CO-Synch + CIDR vs. CO-Synch as a result of fewer CIDR-treated cows having progesterone ≤1 ng/mL at PGF (10.7 vs. 29.6%, respectively). A greater (P < 0.01) proportion of CO-Synch + CIDR vs. CO-Synch cows were detected in estrus within 60 h after PGF (66.7 vs. 57.8 ± 2.6%, respectively) and a greater (P < 0.01) proportion were pregnant to TAI (54.6 vs. 44.3 ± 2.6%, respectively). For both synchronization protocols, cows expressing estrus within 60 h before TAI had a greater pregnancy rate than cows without estrus. For cows with plasma progesterone ≤1 ng/mL at PGF injection, CO-Synch + CIDR increased pregnancy rate (65.2 ± 5.9 vs. 30.8 ± 3.4% with vs. without CIDR), whereas pregnancy rates did not differ (P > 0.10) between protocols (52.1 ± 2.1 vs. 50.0 ± 2.4%, respectively) when progesterone was >1 ng/mL (treatment × progesterone; P < 0.01). Inclusion of a CIDR in the synchronization protocol increased plasma progesterone concentration, proportion of cows detected in estrus, and pregnancy rate; however, the increase in pregnancy rate from inclusion of the CIDR was primarily in cows with decreasing or low endogenous progesterone secretion during treatment.