Biomedical subjects

J S Stevenson

Publications and source records attributed to J S Stevenson.

At least 37 records · Page 2Linked to original sources

PubMed2000

Prolonging the MGA-prostaglandin F2 alpha interval from 17 to 19 days in an estrus synchronization system for heifers.

Our objective was to determine whether extending the interval from 17 to 19 d between removal of melengestrol acetate (MGA) feed and administration of PGF2 alpha would alter conception rates, pregnancy rates and the degree of synchrony in replacement beef heifers. A commercial heifer operation in north-central Kansas purchased 591 Angus x Hereford heifers from 12 sources. Prior to the spring breeding season, 14% of the heifers were culled. The remaining heifers were assigned randomly to 2 MGA-PGF2 alpha synchronization systems. All heifers were fed MGA (0.5 mg/head/d) for 14 d, and PGF2 alpha was administered either 17 or 19 d after the completion of MGA feeding. Heifers were inseminated artificially for 30 d followed by 30 d of natural mating. Based on each source, first-service conception rates ranged from 66 to 90%, whereas overall pregnancy rates ranged from 91 to 100%. Heifers given PGF2 alpha on Day 17 after MGA had first-service conception rates of 75.9% compared with 81.4% for heifers receiving PGF2 alpha on Day 19. In response to the PGF2 alpha injection, 99% of the Day 19 heifers that were detected in estrus were inseminated artificially by 72 h after the PGF2 alpha injection, whereas 74% of the heifers in the Day 17 treatment were inseminated by that time. Average interval to artificial insemination (AI) after PGF2 alpha was greater (P < 0.01) for the Day 17 heifers (73.1 +/- 1.1 h) than for the Day 19 heifers (56.2 +/- 1.1 h). No differences in conception rates or overall pregnancy rates occurred; however, heifers receiving PGF2 alpha on Day 19 after MGA had shorter intervals to estrus, and a greater proportion was inseminated within 72 h after PGF2 alpha, thus possibly facilitating successful timed insemination of the remaining heifers not yet inseminated by that time.

Animals↗

PubMed2000

Synchronizing estrus and(or) ovulation in beef cows after combinations of GnRH, norgestomet, and prostaglandin F2alpha with or without timed insemination.

Three experiments were conducted to induce estrus and(or) ovulation in 1,590 suckled beef cows at the beginning of a spring breeding season. In Exp. 1, 890 cows at three locations were allotted to three treatments: 1) GnRH on d -7 + prostaglandin F2alpha (PGF2alpha) on d 0 (Select Synch); 2) GnRH on d -7 + PGF2alpha on d 0 (first day of the breeding season) plus a norgestomet implant (NORG) between d -7 and 0 (Select Synch + NORG); or 3) two injections of PGF2alpha given 14 d apart (2xPGF2alpha). More (P < 0.05) cycling cows were detected to have been in estrus after both treatments that included GnRH, whereas, among noncycling cows, the addition of norgestomet further increased (P < 0.05) the proportion in estrus. Pregnancy rates were greater (P < 0.01) among noncycling cows after treatments that included GnRH. For cows that calved >60 d before the onset of the breeding season, conception rates were greater (P < 0.01) than those that calved < or =60 d regardless of treatment, whereas days postpartum had no effect on rates of detected estrus. When body condition scores were < or =4 compared with >4, rates of detected estrus (P < 0.05) and conception (P = 0.07) were increased. In Exp. 2, 164 cows were treated with the Select Synch + NORG treatment and were inseminated either after estrus or at 16 h after a second GnRH injection (given 48 h after PGF2alpha). Conception and pregnancy rates tended (P = 0.08) to be or were less (P < 0.05), respectively, for noncycling cows inseminated by appointment, but pregnancy rates exceeded 53% in both protocols. In Exp. 3, 536 cows at three locations were treated with the Select Synch protocol as in Exp. 1 and inseminated either: 1) after detected estrus (Select Synch); 2) at 54 h after PGF2alpha when a second GnRH injection also was administered (Cosynch); or 3) after detected estrus until 54 h, or in the absence of estrus, at 54 h plus a second GnRH injection (Select Synch + Cosynch). Conception rates were reduced (P < 0.01) in cows that were inseminated by appointment. An interaction of AI protocol and cycling status occurred (P = 0.05) for pregnancy rates with differing results for cycling and noncycling cows. Across experiments, variable proportions of cows at various locations (21 to 78%) were cycling before the breeding season. With the GnRH or GnRH + NORG treatments, ovulation was induced in some noncycling cows. Conception rates were normal and pregnancy rates were greater than those after a PGF2alpha program, particularly when inseminations occurred after detected estrus.

Animal Husbandry↗

PubMed2000

Reproductive outcomes for dairy heifers treated with combinations of prostaglandin F2alpha, norgestomet, and gonadotropin-releasing hormone.

We conducted three experiments to test various protocols for synchronizing estrus, ovulation, or both before insemination of heifers. In experiment 1, 23 controls received two PGF2alpha injections; 23 heifers were treated like the controls plus a norgestomet implant for 8 d, with the second PGF2alpha injection 24 h before implant removal; and 23 heifers were treated like the previous group plus 100 microg of GnRH 54 h after the second PGF2alpha injection. Although norgestomet and GnRH altered some estrual characteristics, conception rates in experiment 1 (n = 69) and experiment 2 (278 heifers receiving the same treatments as those in experiment 1) generally were not different among treatments. Reproductive outcomes were not improved by adding norgestomet and GnRH to a standard PGF2alpha protocol. In experiment 3, control heifers received PGF2alpha and were inseminated after detected estrus or at 72 to 80 h after a second injection of PGF2alpha given 14 d after the first injection. Select Synch heifers, treated with GnRH either 6 or 7 d before PGF2alpha were inseminated after detected estrus, whereas Ovsynch heifers were treated like Select Synch heifers but also received a second GnRH injection approximately 36 h after PGF2alpha and were inseminated 18 h later. Estrus detection and pregnancy rates after Ovsynch were less than those of controls, whereas conception and pregnancy rates did not differ between control and Select Synch heifers. Therefore, the Select Synch protocol was equivalent to a standard PGF2alpha protocol, whereas Ovsynch was inferior to both of those protocols.

Age Factors↗

PubMed1999

Follicular, hormonal, and pregnancy responses of early postpartum suckled beef cows to GnRH, norgestomet, and prostaglandin F2alpha.

Cycling (n = 16) and noncycling (n = 24), early postpartum, suckled beef cows of three breeds were assigned randomly to three treatments: 1) 100-microg injection of GnRH plus a 6-mg implant of norgestomet administered on d -7 before 25 mg of PGF2alpha and implant removal on d 0 (GnRH+NORG); 2) 100 microg of GnRH given on d -7 followed by 25 mg of PGF2alpha on d 0 (GnRH); or 3) 2 mL of saline plus a 6-mg implant of norgestomet administered on d -7 followed by 25 mg of PGF2, and implant removal on d 0 (NORG). All cows were given 100 microg of GnRH on d +2 (48 h after PGF2alpha). Blood sera collected daily from d -7 to d +4 were analyzed for progesterone and estradiol-17beta, and ovaries were monitored daily by transrectal ultrasonography to assess changes in ovarian structures. Luteal structures were induced in 75% of noncycling cows in both treatments after GnRH, resulting in elevated (P < .01) progesterone on d 0 for GnRH+NORG-treated cows. Concentrations of estradiol-17beta (P < .01) and LH (P < .05) were greater on d +2 after GnRH for cows previously receiving norgestomet implants. Pregnancy rates after one fixed-time AI at 16 h after GnRH (d +2) were greater (P < .05) in GnRH+NORG (71%) than in GnRH (31%) and NORG (15%) cows. Difference in pregnancy rate was due partly to normal luteal activity after AI in over 87% of GnRH+NORG cows and no incidence of short luteal phases. The GnRH+NORG treatment initially induced ovulation or turnover of the largest follicle, induction of a new follicular wave, followed later by increased concentrations of estradiol-17beta and progesterone. After PGF2alpha, greater GnRH-induced release of LH occurred in GnRH+NORG cows before ovulation, and pregnancy rates were greater after a fixed-time AI.

Animals↗

PubMed1999

Twice daily suckling but not milking with calf presence prolongs postpartum anovulation.

Two experiments were conducted to determine whether milking beef cows two or five times daily in the presence or absence of their own nonsuckling calves would alter postpartum interval to first ovulation. Multiparous Angus x Hereford cow-calf pairs were assigned randomly between 13 and 18 d postpartum to treatments for 4 wk. In Exp. 1, pairs were assigned to six treatments: 1) calf was weaned permanently from its dam (CW; n = 9); 2) same as CW, but dam was milked twice daily (CW+2xM; n = 9); 3) calf was present continuously with its dam but restricted from contact with the udder (CR; n = 9); 4) same as CR, but dam was milked twice daily (CR+2xM; n = 9); 5) same as CR, but calf was allowed to suckle twice daily (CR+2xS; n = 8); and 6) calf was present continuously with its dam and suckled ad libitum (CP; n = 9). The interval from onset of treatments to first postpartum ovulation was shorter (P<.05) in the CW (14.1+/-3.1 d), CR (14.2+/-3.1 d), CW+2xM (13.0+/-3.1 d), and CR+2xM (17.2+/-3.1 d) than in the CP (34.7+/-3.1 d) and CR+2xS (33.9+/-3.3 d) treatments. Daily milk yield during treatment was greater (P<.01) for CR+2xM cows (7.1+/-.6 kg) than for CW+2xM cows (3.5+/-.6 kg). In Exp. 2, cow-calf pairs were assigned to three treatments: 1) CR+2xM (n = 10); 2) same as CR+2xM but cows were milked five times daily (CR+5xM; n = 10); or 3) CP (n = 10). The interval to first postpartum ovulation was shorter (P<.05) in the CR+2xM (23.6+/-3.5 d) and CR+5xM (26.1+/-3.7 d) treatments than in the CP (37.7+/-3.7 d) treatment. Daily milk yield during treatment was greater (P<.05) for CR+5xM cows (7.7+/-.6 kg) than for CR+2xM cows (6.4+/-.6 kg) by 17%. We conclude that suckling twice daily was sufficient to prolong postpartum anestrus as much as suckling ad libitum. Furthermore, milk removal by suckling, but not by milking two or five times daily, even in the presence of the cow's own nonsuckling calf, is essential to prolong postpartum anovulation.

Animals↗

PubMed1999

Reproductive performance of dairy cows in various programmed breeding systems including OvSynch and combinations of gonadotropin-releasing hormone and prostaglandin F2 alpha.

In Experiment 1, 308 Holstein cows were assigned randomly to four treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 33 h later, and artificial insemination (AI) 16 to 18 h after the second GnRH injection; 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus; 3) injections of PGF2 alpha 14 d apart, GnRH injection 33 h after the second PGF2 alpha injection, and AI 16 to 18 h later; and 4) injections of PGF2 alpha 14 d apart, AI only after detected estrus following the second PGF2 alpha injection or, in the absence of detected estrus, at 80 h after the second PGF2 alpha injection. In Experiment 2, 227 Holstein cows were assigned randomly to two treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 48 h later, and AI 16 to 18 h after the second GnRH injection; and 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus. Although conception rates in both experiments resulting from AI made after detected estrus either tended to be greater or were consistently greater than those following GnRH injection and one fixed-time AI, pregnancy rates were of greater magnitude after fixed-time AI because of poor expression or detection of estrus.

Animals↗

PubMed1999

Suckling reinitiated milk secretion in beef cows after an early postpartum hiatus of milking or suckling.

We determined whether milk secretion in beef cows could be reinitiated by renewed suckling after a hiatus from milking or suckling. Fifty-three Angus x Hereford cows were suckled ad libitum by their own calves for 13 to 18 d postpartum and then assigned to treatments for 4 wk in which cows were 1) neither milked nor suckled (weaned; n = 18), 2) milked 2 x daily (milked; n = 18), or 3) suckled by their own calves (suckled; n = 17). Thereafter, all calves (including earlier weaned calves) suckled their own dams until permanent weaning at 203 d of age, except when their dams were milked once after receiving (i.m.) 40 IU of oxytocin at reinitiation of suckling (0 wk) and again 1 and 5 wk later. Prolactin was increased in milked and suckled cows during 20 min after milking or suckling at the termination of treatments (0 wk). Concentrations of insulin-like growth factor-I were greater for weaned than suckled cows; milked cows had intermediate concentrations. At 0 wk, milk yield was greater for suckled than milked or weaned treatment cows. After 1 wk of renewed suckling, milk secretion of weaned treatment cows increased, and by 5 wk, composition of milk was normal, but yield was still reduced. We concluded that milk secretion was renewed by suckling in early postpartum cows after they were neither suckled nor milked for 4 wk.

Animals↗

PubMed1998

Luteolysis during two stages of the estrous cycle: subsequent endocrine profiles associated with radiotelemetrically detected estrus in heifers.

Our objective was to correlate hormonal changes with the timing and onset of estrus in heifers before and after luteolysis was induced with PGF2 alpha at two stages of the estrous cycle: d 6 to 9 (early; n = 10) or d 14 to 15 (late; n = 10). Blood was collected at intervals of 2 or 12 h to quantify serum concentrations of progesterone, estradiol-17 beta, and LH while heifers were observed visually for estrus and monitored for standing activity by pressure-sensitive, radiotelemetric devices. Although the concentrations of estradiol-17 beta that were associated with the putative appearance of the first dominant follicle declined before luteolysis was induced early in the cycle, some heifers that were given PGF2 alpha were in estrus as early as 35 h. Compared with heifers treated late in the estrous cycle, heifers that were treated early in the cycle produced less progesterone before PGF2 alpha treatment and had greater peak concentrations of estradiol-17 beta at estrus. In addition, heifers that were treated early in the cycle had shorter intervals from PGF2 alpha treatment to estrus, to peak estradiol-17 beta, and to peak LH and to initiation of estrus after the peak in estradiol-17 beta than did heifers treated later in the cycle. The increase in estradiol-17 beta associated with the putative first-wave follicle of the subsequent cycle and the duration of that cycle in early cycle heifers was less than after late cycle luteolysis. Results indicated that greater concentrations of estradiol-17 beta during estrus may be related to the durations of previous cycles and less progesterone exposure before luteolysis. The onset of estrus corresponded closely to, but preceded, the preovulatory LH surge by approximately 3 h.

Animals↗

PubMed1997

Luteinizing hormone release and reproductive traits in anestrous, estrus-cycling, and ovariectomized cattle after tyrosine supplementation.

The role of rumen-protected L-tyrosine as a nutritional signal altering LH release and other reproductive traits in cattle was studied. In Exp. 1, 28 suckled crossbred cows were assigned randomly to five treatments (0 or 40 g of tyrosine daily in feed for 3 d followed by a single i.v. injection of 200 micrograms of GnRH or 1 mg/kg of naloxone on d 26 +/- 1 postpartum; no tyrosine plus an injection of saline was the control). Peak LH after GnRH was greater (P < .001) in GnRH-treated cows regardless of tyrosine supplementation. Compared to cows receiving saline, days to first postpartum ovulation were reduced (P < .05) by naloxone, tyrosine, and GnRH. In Exp. 2, 47 suckled crossbred cows were assigned randomly to six treatments (0, 20, or 40 g of tyrosine daily for 3 d before GnRH or saline was injected i.m. on d 23 +/- 1 postpartum). Injection of GnRH increased (P < .001) LH. An interaction (P = .08) of tyrosine and GnRH tended to reduce days to first postpartum ovulation. In Exp. 3, tyrosine (40 g) administered once daily for 3 d to ovariectomized cows (six cows per treatment) had no effect on any characteristic of LH before or after estradiol-17 beta. In Exp. 4, suckled cows (n = 136) were allotted randomly to two treatments (0 or 30 g of tyrosine daily for 3 d before a PGF2 alpha-synchronized estrus). Tyrosine increased (P = .05) the percentage of cows in estrus after PGF2 alpha but reduced (P = .05) AI conception rate. These results fail to support the thesis that tyrosine alters LH release in cattle. Supplemental tyrosine increased expression of estrus in suckled cows after PGF2 alpha and tended to reduce intervals to first postpartum ovulation.

Analysis of Variance↗

PubMed1997

Ad libitum suckling by an unrelated calf in the presence or absence of a cow's own calf prolongs postpartum anovulation.

Our objective was to determine whether onset of first postpartum ovulation would be altered in suckled cows nursing an unrelated calf in the presence or absence of their own nonsuckling calf. In a 2-yr study, Angus x Hereford cows were assigned randomly to five treatments between d 13 and 18 postpartum for 4 wk: 1) own calf was weaned (OCW, n = 9); 2) own calf was present continuously (OCP, n = 12); 3) own calf was present continuously but restricted from udder contact (OCR, n = 9); 4) unrelated calf was present continuously after own calf was removed (UCP, n = 10); and 5) unrelated calf was present continuously and own calf was present but restricted as in the OCR treatment (OCR + UCP, n = 10). Interval to the first increase in progesterone (ovulation) was less (P < .05) in OCW (14.7 +/- 3.4 d) and OCR (19.9 +/- 3.4 d) than in the OCP (35.0 +/- 2.9 d), UCP (38.0 +/- 3.4 d), and OCR + UCP (37.6 +/- 3.4 d) treatments. The OCW cows showed no maternal bond with their own calves after 4 wk of treatment, whereas OCR, OCP, and OCR + UCP cows were bonded to their own natural calves. Cows in the UCP treatment, suckled by unrelated calves, formed new maternal bonds with those calves, resulting in prolonged anovulation. Further, OCR + UCP cows had prolonged anovulation because maternal bonds were maintained with their own restricted calves while milk was removed by unrelated calves. We conclude that milk removal preceded by a continuously reinforced cow-calf bond (original or reestablished) is essential to prolong anovulation in beef cows.

Analysis of Variance↗

PubMed1997

Fertility in estrus-cycling and noncycling virgin heifers and suckled beef cows after induced ovulation.

A procedure was developed to either induce or synchronize ovulation in heifers and suckled cows. Beef females were assigned to two breeding programs: 1) two injections of prostaglandin F2alpha (PGF2alpha) given 14 d apart to synchronize estrus (PGF2alpha control; n = 179), with inseminations 12 to 16 h after detected estrus or at 80 h in the absence of estrus, or 2) two injections of PGF2alpha (d -14 and 0) plus 100 microg of GnRH on d -7 when 6 mg of norgestomet was implanted (PGF2alpha/NORG/GnRH treatment; n = 173). Implants were removed 24 h after the second PGF2alpha injection (d +1) and females were inseminated 12 to 16 h after detected estrus until 54 h after PGF2alpha. The remaining cattle were given a second 100-microg GnRH injection 54 h after PGF2alpha and inseminated 18 to 20 h later. Percentages of noncycling females with subsequently elevated progesterone (P4) on d 0 or +1 were not different between treatment groups (20.4 vs 25%), but conception rate was greater (P < .05) in noncycling treated females than in noncycling controls (55 vs 12.8%). Conception rates in cycling (59.2%) and noncycling (62.2%) treated females were similar to those in cycling controls (56.2%) but greater (P = .06) than those in noncycling controls (26.5%). Conception rates in treated females inseminated 12 to 16 h after detected estrus (63.1%) or at one fixed time (58.3%) were similar to those in controls inseminated 12 to 16 h after detected estrus (68.7%). This treatment procedure produced fertility after one timed insemination that was equal to controls inseminated after detected estrus and induced equally fertile ovulations in noncycling heifers and cows.

Aging↗

PubMed1997

Body temperature and endocrine interactions before and after calving in beef cows.

Multiparous beef cows (n = 7) were used to evaluate peripartum changes and interactions among body temperature (BT) and circulating progesterone (P4), estradiol-17beta (E2), triiodothyronine (T3), cortisol, thyroxine (T4), and 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) concentrations. Electronic temperature monitors were placed under the obliquus abdominis internus muscle of the left flank, and BT was measured using radiotelemetry every 3 min for 10-s periods from 144 h before to 24 h after calving. Environmental temperatures (ET) were recorded hourly. Body and environmental temperatures were averaged, separately, within 8-h periods. Blood samples were collected every 8 h, and hormone concentrations were measured. Time of day affected BT (P < .01), at 0300 cows had the lowest BT, at 1900 the highest, and at 1100 values were intermediate. Body temperature remained relatively constant (P > .10) from 144 to 56 h before calving and from 8 to 24 h after calving but decreased (P < .01) from 48 to 8 h before calving. Precalving BT was affected (P < .01) by ET, but hour-before-calving (time) had the greatest effect on BT during the 48 to 8 h immediately preceding parturition (b' = .41, P < .01) and was independent of ET effects. Before the BT decrease, cows gestating heifers had lower (P < .01) BT than cows gestating bulls. Plasma E2, PGFM, T3, and T4 concentrations before the precalving decrease in body temperature were greater (P < .03) in cows gestating bull rather than heifer calves. Approximately 30% of the variation (R2) during the temperature decrease was explained by plasma hormone concentrations; PGFM (b' = -.30, P < .05) and T3 (b' = -.22, P < .10) had the most significant effects. In conclusion, BT of the cow before the precalving decrease was affected by ET and sex of calf. However, the prepartum BT decrease was independent of these variables, and seemed partially endocrine-induced.

Animals↗

PubMed1997

Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus.

Two synchronization protocols were tested for lactating dairy cows and heifers. Nulliparous dairy heifers (13 to 23 mo; n = 155) and primiparous and multiparous dairy cows (60 to 289 d postpartum; n = 310) were assigned randomly to two treatments. Controls received 25 mg of PGF2 alpha and were artificially inseminated according to the a.m.-p.m. rule following detected estrus. All controls that were not detected in estrus were injected with 25 mg of PGF2 alpha at 14-d intervals until artificial insemination (AI) at a detected estrus or until timed AI at 72 to 80 h after a third sequential injection of PGF2 alpha. Treated cows and heifers received a protocol that used GnRH and PGF2 alpha to synchronize ovulation (Ovsynch). Cows and heifers that were treated with Ovsynch were injected i.m. with 100 micrograms of GnRH at a random stage of the estrous cycle. Seven days later, cows and heifers in this group received 25 mg of PGF2 alpha followed by a second injection of 100 micrograms of GnRH 30 to 36 h later. Subsequently, the treated cows and heifers received AI 16 to 20 h after the second injection of GnRH. Pregnancy rates per AI were similar (38.9% vs. 37.8%) for control cows and cows treated with the Ovsynch protocol, respectively. However, pregnancy rate per AI was greater for control heifers (74.4%) than for heifers treated with Ovsynch (35.1%). Evaluation of serum progesterone concentrations at each hormonal injection indicated that the first injection of GnRH synchronized luteal function of lactating dairy cows but not of heifers. In summary, one fixed-time AI at a synchronized ovulation provided similar pregnancy rates per AI as did AI following the a.m-p.m. rule after estrus had been induced by PGF2 alpha in lactating cows, but the fixed-time AI was not effective for heifers because of the lack of synchronization.

Animals↗

PubMed1996

The relationship between binge eating severity and body fat in nonpurge binge eating women.

The relationship between binge eating severity, measured by caloric intake, and amount of body fat, measured by percent of body fat and body mass index (BMI) was examined in nonpurge binge eating women. Although there was a low, but significant, relationship between binge eating severity and BMI, the relationship was not significant between binge eating severity and percent of body fat. Age and weight cycling were the best predictors for percent of body fat, while weight cycling alone was the best predictor for BMI. It cannot be assumed that caloric intake during binge eating is the central cause of obesity in nonpurge binge eating women.

Adult↗

PubMed1996

Restricting calf presence without suckling compared with weaning prolongs postpartum anovulation in beef cattle.

To determine how continued presence of a calf affected duration of postpartum anovulation, 23 udder-intact cows and their calves were assigned to three treatments on d 4 to 9 postpartum (experimental d 0). The treatments were 1) calf present with unlimited contact with its dam (n = 8), 2) calf restricted to noninguinal contact with its dam (n = 8), and 3) calf weaned from its dam (n = 7). Calves in the calf-present and calf-restricted treatments were weaned after 5 wk. Based on daily measurements of blood progesterone, days to first ovulation after onset of treatments were 35.4 +/- 2.2, 22.5 +/- 2.2, and 14.3 +/- 2.2 for the calf-present, calf-restricted, and calf-weaned treatments, respectively; each one differed (P < .01) from the others. Mean concentrations of LH were greater (P < .05) in the calf-restricted treatment and tended (P = .13) to be greater in the calf-weaned treatment than in the calf-present treatment on d 7 after the onset of treatments. On d 7 and 21, calves in the calf-present and calf-restricted (calves could not suckle) treatments were returned to their dams after overnight separation. Blood samples were collected to assess changes in cortisol, ACTH, prolactin, and oxytocin. No treatment effects were detected on d 7, but on d 21, the calf-present and calf-restricted cows had a greater (P < .05) increase in cortisol after calf return than the calf-weaned cows (calves were not returned), whereas prolactin was increased (P < .05) after calf return in the calf-present cows only. We conclude that calf presence is associated with an increase in cortisol and calf presence without suckling is one factor that delays the onset of first postpartum ovulation in beef cows.

Adrenocorticotropic Hormone↗

PubMed1996

Detection of estrus by visual observation and radiotelemetry in peripubertal, estrus-synchronized beef heifers.

The effectiveness of two estrus-detection methods (visual observation and radiotelemetric, pressure-sensitive, rump-mounted devices) was compared in peripubertal, crossbred yearling beef heifers. Heifers (n = 50) were fitted with a pressure-sensitive device affixed to their rumps to which a battery-operated radio transmitter was connected. Activation of the sensor sent a radiotelemetric signal to a microcomputer via a fixed radio antenna. Heifer identification, date, time, and duration of standing events were recorded. Estrus was synchronized by feeding melengestrol acetate (MGA) for 14 d and then injecting PGF2 alpha 17 d after the last daily dose of MGA. Following the injection of PGF2 alpha, heifers were observed visually for signs of estrus at 0730 and 1630 (45 min each). Estrus was detected in 41 of 49 heifers (one lost the device) by visual observation and(or) the radiotelemetric device. Number of standing events during estrus, determined by the radiotelemetric device, averaged 50.1 +/- 6.4 per heifer, with the duration of estrus ranging from 2.6 to 26.2 h (average = 14 +/- .8 h). Visual observation failed to detect 11 of 41 heifers (37%) that were detected by the radiotelemetric device. Heifers with fewer standing events (19.3 vs 60.5; P < .001) and estrus of shorter duration (8.4 vs 15.6 h; P < .001) were those not identified by visual observation. Based on intervals between the first detected standing event of estrus and time of insemination, a wide window of fertility seems to exist in some heifers. Radiotelemetric devices were useful in identifying a greater (P < .05) proportion (100%) of heifers in estrus (increased efficiency) compared with visual observation (73%). However, accuracy of both methods was similar.

Animals↗

PubMed1996

Altering conception of dairy cattle by gonadotropin-releasing hormone preceding luteolysis induced by prostaglandin F2 alpha.

The objective of these experiments was to determine the effect on fertility of GnRH when used in conjunction with one or two injections of PGF2alpha. In Experiment 1, GnRH was administered 7 d before the second of two injections of PGF2alpha (14 d apart). The control group received two injections of PGF2alpha without GnRH. Conception was reduced from 63.5% for 74 controls to 48.7% for the 79 heifers and cows that had been treated with GnRH, but estrus detection and pregnancy rates were similar. In Experiment 2, 85 heifers and cows received GnRH at a random stage of the estrous cycle, followed in 7 d by PGF2alpha. Thirty to 32 h after PGF2alpha, a second dose of GnRH was given to induce ovulation of the preovulatory follicle, followed by one fixed-time insemination 18 to 19 h later (treatment designated as GnRH, PGF2alpha, and GnRH). Controls (n = 85) were given PGF2alpha and inseminated at estrus. Although conception rate was not different, one fixed-time insemination after the GnRH, PGF2alpha, and GnRH treatment tended (35.3%) to reduce fertility compared with effects of the control (47.1%). It is unclear how an injection of GnRH during the intervening week between two injections of PGF2alpha reduced fertility in Experiment 1. However, in Experiment 2, when GnRH was given 7 d before one injection of PGF2alpha and when ovulation was induced with a second GnRH injection, one fixed-time insemination seemed to produce acceptable fertility in dairy cows but probably less than that when inseminations were based on detected estrus.

Animals↗

PubMed1995

Skin temperature and limb blood flow as predictors of cardiac index.

Thermodilution cardiac output and cardiac index (CI) require inserting a pulmonary artery catheter, an invasive device associated with many iatrogenic complications. The purpose of this study was to establish the concurrent validity of two noninvasive measures of CI (skin temperature and limb blood flow) by determining their correlation with invasive CI. Twenty-one subjects undergoing coronary artery bypass grafting (CABG) were studied every 2 hours for 8 hours in the immediate postoperative period. Neither limb blood flow (LBF) nor skin temperature at five sites correlated significantly (p < .05) with CI at all five data collection times. Ankle temperature and LBF were significantly correlated with CI at one data collection time. On the basis of the findings of this study, neither skin temperature nor LBF can be used as a noninvasive predictor of CI in the immediate postoperative period following CABG.

Adult↗