Increased testosterone secretion in bulls treated with a luteinizing hormone releasing hormone (LHRH) agonist requires endogenous LH but not LHRH

The requirement for endogenous LHRH and LH action in the maintenance of elevated plasma concentrations of testosterone in bulls receiving the LHRH agonist deslorelin was examined. In Experiment 1, bulls were either (i) left untreated (control); (ii) implanted with deslorelin; (iii) actively immunized against LHRH; or (iv) implanted with deslorelin and immunized against LHRH. Experiment 2 was of similar design to Experiment 1, except that bulls were immunized against LH in place of LHRH. In Experiment 1, plasma LH declined in bulls immunized against LHRH, but not in the bulls immunized against LHRH and implanted with deslorelin. Also in Experiment 1, plasma testosterone declined in bulls immunized against LHRH but was elevated in bulls treated with deslorelin and bulls treated with deslorelin and immunized against LHRH. In Experiment 2, bulls immunized against LH and treated with deslorelin had plasma concentrations of testosterone similar to controls, whereas bulls treated only with deslorelin had elevated plasma testosterone. It was concluded from these experiments that endogenous LHRH action was not required for increased steroidogenic activity in bulls treated with a LHRH agonist. However, circulating LH was necessary for increased plasma testosterone in bulls implanted with deslorelin. LH is therefore involved in mediating the response of bulls to treatment with deslorelin, either by acting directly at the testes or through a permissive role that allows a direct action of deslorelin at the testes.     

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)     

Insemination of Holstein heifers at a preset time after estrous cycle synchronization using progesterone and prostaglandin

Two experiments were conducted to study estrous cycle control regimens that combine progesterone administration via an intravaginal device ( PRID ) with a single injection of prostaglandin F2 alpha (PG). In Exp. I, 242 Holstein heifers were assigned randomly to one of three treatment groups at 14 to 18 mo of age. Treatments were: 1) control, 2) PRID -6 + PG-6 ( PRID in place for 6 d plus PG on the day of PRID removal) and 3) PRID -7 + PG-6 ( PRID in place for 7 d plus PG on the day before PRID removal). Heifers were observed for estrous activity and were inseminated at 8 to 20 h after estrus was detected. Estrus and ovulation were effectively synchronized after both PRID + PG treatments. Ninety-nine percent of the heifers in each group were in estrus within 168 h after PG injection. However, the interval from PG administration to the onset of estrus was longer after PRID -7 + PG-6 (75 +/- 2 h) than after PRID -6 + PG-6 (66 +/- 2 h). A lower variance in the interval from PG treatment to estrus was observed after PRID -7 + PG-6, suggesting that the 24 h delay in PRID withdrawal improved the synchrony of the onset of estrus. Pregnancy rates (72 to 82%) did not vary across treatment groups. Two-hundred seventy-four heifers were assigned to Exp. II. Treatments were 1) control, 2) 2 X PG (two injections of PG at an 11 d interval) and 3) PRID -7 + PG-6.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute Insulin-induced Hypoglycaemia does not alter IGF-1 and LH Release in Cyclic Mares

Lactation in the mare is associated with changes in the release of metabolic as well as reproductive hormones. Plasma glucose concentration is constantly reduced in lactating compared with non-lactating mares. Several metabolic signals have been proposed to link nutrition and somatic metabolism with reproductive function. The following experiment was performed to study the effect of acute hypoglycaemia on the release of insulin-like growth factor-1 (IGF-1) and luteinizing hormone (LH) in cyclic mares. Different doses of insulin (0.1 and 0.2 IU/kg body weight) were given to induce a decrease in plasma glucose concentration, as existent in lactating mares. All horses treated with insulin developed a hypoglycaemia over a time period of nearly 10 h. The IGF-1 and LH were analysed before and after insulin administration. At no point of time, a significant difference between the two insulin treatments and the control treatment was observed. Therefore, the hypoglycaemic horse is apparently able to provide the brain with sufficient glucose. Short-term hypoglycaemia does not affect the hypothalamo-pituitary-ovarian axis, and concentrations of IGF-1 and LH remained stable during insulin-induced hypoglycaemia. An acute change in plasma glucose concentration is thus not or at least not the only metabolic signal that links nutrition and somatic metabolism with reproductive function in the horse mare.     

Systemic progesterone concentration following human chorionic gonadotropin administration at various times during the estrous cycle in beef heifers

In Trial 1, 26 heifers were allotted randomly to a control group or one of four groups to receive a single injection of 3,000 IU hCG on d 1, 4, 7 or 10 of an estrous cycle. Heifers next completed a nontreated cycle, and at their third estrus were reallotted to one of the five groups described previously. Estrous cycle length was extended in cycle 1 but was not altered during the nontreated cycle or in cycle 3. Administration of hCG on d 4 or 7 increased (P less than .05) mean serum progesterone (P4) over the first 16 d of the estrous cycle by .9 and .8 ng/ml, respectively. In Trial 2, 23 heifers were allotted randomly to one of two groups to receive a placebo or a single injection of 3,000 IU hCG on d 4 of an estrous cycle. Heifers were inseminated artificially at subsequent estrus. On d 4 postbreeding, treatments were repeated. Administration of hCG on d 4 of the prebreeding estrous cycle increased (P less than .05) mean P4 over the first 16 d by .9 ng/ml, whereas mean P4 over the first 16 d postbreeding was not affected by a second injection of hCG on d 4 postbreeding. Administration of hCG increased (P less than .05) first-service pregnancy rate (92 vs 55%). In conclusion, progesterone concentrations were enhanced by hCG given on d 4 or 7 of the estrous cycle, and pregnancy rate was increased when hCG was administered both on d 4 of the prebreeding cycle and d 4 postmating.     

Copper deficiency in the young bovine results in dramatic decreases in brain copper concentration but does not alter brain prion protein biology

An Mn for Cu substitution on cellular prion proteins (PrP(c)) in the brain that results in biochemical changes to PrP(c) has been implicated in the pathogenesis of transmissible spongiform encephalopathies. Recent research in the mature bovine does not support this theory. The present study tested this hypothesis by using progeny from gestating cows receiving Cu-deficient diets or Cu-deficient diets coupled with high dietary Mn. Copper-adequate cows (n = 39) were assigned randomly to 1 of 3 treatments: 1) control (adequate in Cu and Mn), 2) Cu deficient (-Cu), or 3) Cu deficient plus high dietary Mn (-Cu+Mn). Cows assigned to treatments -Cu and -Cu+Mn received no supplemental Cu and were supplemented with Mo to further induce Cu deficiency. The -Cu+Mn treatment also received 500 mg of supplemental Mn/kg of dietary DM. Calves were weaned at 180 d and maintained on the same treatments as their respective dams for 260 d. Copper-deficient calves (-Cu and -Cu+Mn) had decreased (P = 0.001) brain (obex) Cu and tended to have increased (P = 0.09) obex Mn relative to control calves. Obex Mn:Cu ratios were substantially increased (P < 0.001) in calves receiving -Cu and -Cu+Mn treatments compared with control calves and were greater (P < 0.001) in -Cu+Mn calves than in -Cu calves. Obex prion protein characteristics, including proteinase K degradability, superoxide dismutase (SOD)-like activity, and glycoform distributions, were largely unaffected. Obex tissue antioxidant capacity was not compromised by perturbations in brain metals, but Cu-deficient calves tended to have decreased (P = 0.06) Cu:Zn SOD activity and increased (P = 0.06) Mn SOD activity. Although obex Cu was decreased because of Cu deficiency and Mn increased because of exposure to high dietary Mn, the obex metal imbalance had minimal effects on PrP(c) functional characteristics in the calves.     

LHRH receptor, LH and FSH concentrations in anterior pituitaries of cycling, noncycling and early pregnant heifers

In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytoplasmic estrogen and progesterone receptors in canine endometrium during the estrous cycle

Estradiol and progesterone receptors (ER, PR) were characterized and measured in cytosols from canine endometrium, using saturation and sucrose-gradient centrifugation radioassays. Both receptors were demonstrated to be steroid- and tissue-specific saturable proteins, which bound the respective steroids with high affinity (dissociation constant [Kd] approximately 10(-9)M). Serum estradiol, progesterone, and endometrial cytosol receptor concentrations and receptor-binding affinity were measured for 25 bitches from which samples were obtained at 5 stages of the estrous cycle (5 bitches each): anestrus (A), the 3rd day of proestrus (P3), the 3rd day of estrus (E3), the 12th day after onset of estrus (E12), and the 28th day after onset of estrus (E28). Mean (+/- SEM) serum estradiol concentrations were 17.0 +/- 2.2 (A), 55.4 +/- 5.0 (P3), 89.4 +/- 24.9 (E3), 41.0 +/- 5.9 (E12), and 50.6 +/- 3.9 (E28) pg/ml. Mean (+/- SEM) serum progesterone concentrations were 0.4 +/- 0.1 (A), 1.5 +/- 0.2 (P3), 17.3 +/- 7.5 (E3), 41.6 +/- 9.5 (E12), and 25.8 +/- 3.2 (E28) ng/ml. Concentrations of ER increased significantly from 1.06 pmol/g of uterus during stage A to a peak concentration of 6.18 pmol/g of uterus at E12, followed by a gradual decrease to 0.69 pmol/g of uterus by E28. The PR concentrations increased from 3.01 pmol/g of uterus in stage A to 17.32 pmol/g of uterus at P3; PR concentrations, thereafter, decreased gradually to 1.85 pmol/g of uterus by E28. Dissociation constants were significantly higher at E12 for the ER (Kd = 2.6645 X 10(-9)M) and at P3 for the PR (Kd = 5.8282 X 10(-9)M) than at the other stages examined, indicating a decrease in receptor affinity during the periods of high receptor concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of progesterone and oestrogen treatment in heifers on oestrous cycle control and plasma progesterone levels

Data are presented on the effects of a short-term progesterone treatment for oestrous cycle control in cattle. Progesterone was administered by intravaginal sponge pessaries inserted for a 10-day period. Progesterone pessaries alone did not affect oestrous cycle length or corpus luteum function at either early (day 2) or midluteal (day 12) cycle stages. However, when progesterone (250 mg) and oestradiol benzoate (7-5 mg) were given intramuscularly on the day of pessary insertion corpus luteum development was inhibited in animals treated at day 2 and was regressed in animals at day 12. This combined oestrogen-progesterone treatment efficiently controlled oestrous cycle length.     

富铜酵母对西门塔尔牛发情周期生殖激素分泌的影响

选用16头18月龄、体况良好、体质量390 kg的西门塔尔牛育成母牛,采用完全随机分组设计分为4组,研究富铜酵母(0、8、16、24 mg/kg)对发情周期外周血清促黄体素、促卵泡素、孕酮和雌二醇分泌规律的影响.结果显示,8 mg/kg组和16 mg/kg组显著提高了发情周期促黄体素、促卵泡素、孕酮和雌二醇水平(P<0.05);24 mg/kg组有提高趋势,但与对照组比差异不显著(P>0.05).结果表明,添加富铜酵母以8～16 mg/kg对发情周期生殖激素分泌有促进作用,以8 mg/kg为佳,兼顾基础日粮的含铜量,建议日粮铜水平为13.87 mg/kg.     

Influence of nutrition on serum concentrations of progesterone, luteinizing hormone and estrous behavior in dairy heifers

Thirty postpubertal Holstein heifers were used to investigate the influence of dietary intake on 1) serum concentrations of progesterone (P4) and luteinizing hormone (LH) during diestrus and 2) estrous behavior. Heifers were randomly allotted to receive either 80, 100 or 120% of the National Research Council (NRC) requirements for energy, protein and dry matter intake for 139 d. Heifers were fed their respective diets in groups in outdoor lots for 114 d at which time individual feeding of diets was initiated in a stanchion barn. Estrus was synchronized with two injections of prostaglandin (PG) so that on d 138 of dietary treatment the heifers were in diestrus (means = d 8 of estrous cycle). Also, on d 138, blood samples were collected via jugular cannula at 20-min intervals for 12 h beginning at 0630. After collection of the 37th blood sample, all heifers were treated with PG and additional blood samples were collected at 1-h intervals for 24 h. Immediately thereafter, all heifers were moved to a common outdoor lot for 72 h of continuous observation for estrous behavior. Weight gains during the experimental period differed among groups and were 46 +/- 5, 83 +/- 5 and 113 +/- 4 kg for the heifers fed 80, 100 and 120% of the NRC requirements, respectively. Mean serum concentrations of P4 for the 80% NRC group (4.6 +/- .6 ng/ml) tended to be lower than both the 100% (5.9 +/- .6 ng/ml) and 120% (6.0 +/- .5 ng/ml) NRC groups, respectively. Mean serum concentrations of LH, number of LH secretory peaks/12 h and LH peak amplitude were similar among all NRC groups. Rate of decline in serum P4 after PG was also similar among all NRC groups.(ABSTRACT TRUNCATED AT 250 WORDS)