同期发情定时输精技术对经产奶牛繁殖力的影响

为了研究同期发情定时输精技术对牛群体繁殖力的影响,试验选取同一牛场内不同单元的经产奶牛,随机分为2个组,分别采用自然发情输精和同期发情定时输精两种方法对奶牛进行人工输精,比较两种方法对奶牛群体繁殖力的影响。研究结果显示:同期发情组和自然发情组的参配率分别为,产后54 d之前为96.3%VS 12.1%,55～90 d为64.6%VS 44.6%,91～130 d为48.1%VS 50.1%,131～170 d为39.9%VS 38.7%,180 d内的总参配率分别为249.1%VS 145.5%;相应时段的同期发情组的受胎率为39.2%、36.7%、36.5%、33.9%、92.6%,自然发情组的受胎率为44.8%、47.3%、46.2%、46.1%、 67.5%;2个组的年繁殖率分别为93.8%VS 84.6%、空怀天数为(91.6±18.3)d VS (131.7±26.8)d、配种次数分别为2.5 VS 1.8、淘汰率分别为29.1%VS 13.4%。以上结果表明,在奶牛生产中,使用同期发情定时输精技术,能显著提高牛群的繁殖力,缩短空怀时间。     

Synchronized estrus and fertility of beef cows after weaning calves for short intervals

In Exp. 1, the objective was to determine if interval of separating calves from cows (24 or 48 h) immediately before insemination affects detection and precision of estrus and pregnancy rates of lactating beef cows implanted with norgestomet. Separation of calves from cows for 24 h (n = 418) lengthened intervals to estrus, did not affect precision of estrus, reduced success of detecting estrus and lowered pregnancy rates relative to positive controls (48 h separation, n = 508). Cows with poor body condition, and not suckled for 24 h, conceived at lower rates than cows with similar condition that were not suckled for 48 h. Adverse effects of separation for only 24 h on fertility are apparently due to inadequate intervals between estrus and insemination at 48 h after removing implants. In Exp. 2, the objective was to determine effects of separating calves from cows for 48 h immediately before insemination on detection and precision of estrus and on pregnancy rate of ovulatory lactating beef cows injected twice with prostaglandin F2 alpha (PGF2 alpha). Weaning increased detection of estrus but overall pregnancy rates did not differ between suckled (n = 256) and nonsuckled (n = 221) cows. But, weaning calves improved pregnancy rates of young (2 to 3 yr) cows and reduced fertility among middle (4 to 6 yr)-aged cows. Increased pregnancy rates after weaning calves for 48 h are due largely to greater detection of estrus and inseminating more cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of estrus synchronization protocols on plasma progesterone profile and fertility in postpartum anestrous Kankrej cows

The study was aimed at induction/synchronization of estrus in postpartum anestrous Kankrej cows of zebu cattle maintained at an organized farm. The study included use of different hormone protocols, viz., Ovsynch, CIDR (controlled internal drug release), Ovsynch plus CIDR, and Heatsynch with estimation of plasma progesterone on days 0, 7, 9/11 (artificial insemination--AI) and on day 20 post-AI following fixed time insemination. Thirty selected anestrous animals were divided into five equal groups (four treatment and one control), and the findings were compared with the normal cyclic control group of six cows. All the protocols were initiated in cows with postpartum anestrous period of more than 4 months, considering the day of first GnRH injection or CIDR insertion as day 0. The animals were bred by fixed time artificial insemination. Pregnancy was confirmed per rectum on day 60 post-AI in non-return cases. The conception rates at induced/first heat in Ovsynch, CIDR, Ovsynch + CIDR, and Heatsynch protocols were 33.33, 66.66, 50.00 and 16.67%, respectively. The corresponding overall conception rates of three cycles post-treatment were 50.00% (3/6), 100.00% (6/6), 66.66% (4/6), and 50.00% (3/6). In normal cyclic and anestrous control groups, the pooled pregnancy rates were 83.33% (5/6) and 16.67% (1/6), respectively. The pooled mean plasma progesterone (nanograms per milliliter) concentrations were significantly (P < 0.05) higher on day 7 in Ovsynch (5.727 ± 1.26), CIDR (4.37 ± 0.66), Ovsynch plus CIDR (3.55 ± 0.34), and Heatsynch (5.92 ± 1.11) protocols as compared with their corresponding values obtained on days 0, 9/11 (AI), and on day 20 post-AI. In anestrous control group, the mean progesterone concentration at the beginning of experiment was 0.67 ± 0.33 ng/ml, which was at par with values of all other groups. The overall plasma progesterone levels on the day of initiating treatment were low in all groups, with smooth small inactive ovaries palpated per rectum twice at 10 days interval, suggesting that most of the animals used in the study were in anestrous phase. Mean (± SE) values of plasma progesterone (nanograms per milliliter) on day 20 post-AI were higher in conceived cows than the non-conceived cows of all the groups, but differed significantly (P < 0.05) only in normal cyclic group. These results suggest that use of different hormone protocols particularly Ovsynch, CIDR, and Ovsynch + CIDR may serve as an excellent tool for induction and synchronization of estrus and improvement of conception rate in postpartum anestrous Kankrej cows.     

Influence of exogenous gonadotropin-releasing hormone on ovarian function in beef cows after short- and long-term nutritionally induced anovulation

The effect of pulsatile infusion of gonadotropin-releasing hormone (GnRH) on follicular function was evaluated in nutritionally induced anovulatory beef cows. After 4 (short; n = 12) or 18 wk (long; n = 12) of anovulation, cows were randomly assigned within anovulatory group to either 2 microg of GnRH treatment or saline (control; i.v.) every hour for 5 d. Ovarian structures were monitored by daily ultrasonography. Growth rate of the largest follicle (P < 0.01) and maximal size of the largest follicle during treatment were greater (P < 0.01) for GnRH vs control cows. At exsanguination after 5 d of GnRH treatment, the size of the second-largest follicle was greater (P < 0.05) in short (i.e., 4 wk) anovulatory cows than in long (i.e., 18 wk) anovulatory cows and the largest follicle tended (P < 0.10) to be larger in long vs short anovulatory cows. Short anovulatory GnRH-treated cows had more small follicles than short anovulatory control cows or long anovulatory GnRH-treated or control cows (anovulation x GnRH; P < 0.10). Follicular fluid (FFL) concentrations of estradiol (P < 0.01) and androstenedione (P < 0.05) were greater in GnRH vs control cows. Concentrations of insulin-like growth factor-I were greater (P < 0.10) in large vs small follicles in cows that were anovulatory for 4 wk, but not in cows that were anovulatory for 18 wk. The amount of insulin-like growth factor-binding protein (IGFBP)-3 in FFL was greater (P < 0.05) in 4- vs 18-wk anovulatory cows. Amounts of IGFBP-2, -4, and -5 were greater (P < 0.001) in FFL of small (< 5 mm) vs large (> or = 5 mm) follicles regardless of treatment. We conclude that pulsatile treatment with GnRH for 5 d stimulates similar growth of the largest follicles in short- and long-term anovulatory beef cows, and that the duration of anovulation is not a major factor that limits follicular growth w hen anovulatory cowsare treated with GnRH. The primary intrafollicular factors associated with increased follicular size were increased concentrations of estradiol, progesterone, and insulin-like growth factor-I,and decreased concentrations of IGFBP-2, -4, and -5. Increased duration of anovulation was associated with decreased concentrations of IGF-I and IGFBP-3 in FFL.     

Luteinizing hormone release after administration of the gonadotropin-releasing hormone agonist Fertilan (goserelin) for synchronization of ovulation in pigs

The generic GnRH agonist, Fertilan (goserelin), was tested for the ability to induce an LH surge and ovulation in estrus-synchronized gilts. Three experiments were performed to 1) examine the effect of various doses of Fertilan on secretion of LH in barrows, to select doses to investigate in gilts (Exp. 1); 2) determine doses of Fertilan that would induce a preovulatory-like rise of LH in gilts (Exp. 2); and 3) determine the time of ovulation after Fertilan treatment (Exp. 3). In Exp. 1, 10 barrows were injected on d 1, 4, 7, 10, and 13 with 10, 20, or 40 microg of Fertilan; 50 microg of Gonavet (depherelin; GnRH control) or saline (negative control); and sequential blood samples were collected for 480 min. There was a dose-dependent stimulation (P < 0.05) of LH release. Maximal plasma concentrations of LH (LH(MAX)) were 2.1 +/- 0.2, 4.1 +/- 0.3, 2.6 +/- 0.4, and 3.4 +/- 0.3 ng/mL after 10, 20, and 40 microg of Fertilan and 50 microg of Gonavet, respectively, and duration of release was 78 +/- 9, 177 +/- 12, 138 +/- 7, and 180 +/- 11 min, respectively. Fertilan doses of 10 and 20 microg were deemed to be the most suitable for testing in gilts. In Exp. 2, 12 gilts received (after estrus synchronization with Regumate and eCG) injections of 10 or 20 microg of Fertilan or 50 microg of Gonavet 80 h after eCG to stimulate a preovulatory-like LH surge and ovulation. An LH surge was induced in 3 of the 4 gilts in both of the Fertilan groups and in all of the Gonavet-treated gilts. Characteristics of induced release of LH did not differ among groups: LH(MAX), 5.0 +/- 0.9 vs. 4.6 +/- 1.8 vs. 6.6 +/- 1.1 ng/mL; duration, 11.7 +/- 2.0 vs. 12.3 +/- 2.2 vs. 14.3 +/- 0.5 h; interval from GnRH injection to LH(MAX), 4.0 +/- 2.0 vs. 6.7 +/- 1.3 vs. 5.8 +/- 1.6 h. In Exp. 3, estrus-synchronized gilts were injected with 20 microg of Fertilan (n = 8) or 50 microg of Gonavet (n = 4), and the time of ovulation was determined by repeated endoscopic examination. Time of ovulation ranged from 34 to 42 h postGnRH; however, ovulation occurred earlier in the Gonavet compared with the other groups (P < 0.05). Results of these experiments indicate that 1) barrows are an appropriate model for determining GnRH doses that can be effective in inducing a preovulatory-like LH surge in females; 2) the generic GnRH agonist Fertilan, at doses of 10 to 20 microg, can stimulate an LH surge in gilts, with subsequent ovulation; and 3) Fertilan at doses of 10 and 20 microg should be examined further for use in fixed-time insemination protocols.     

Synchronization of estrus in suckled beef cows for detected estrus and artificial insemination and timed artificial insemination using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone

We determined whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or estrous detection plus TAI, and whether adding a controlled internal device release (CIDR) to GnRH-based protocols would enhance fertility. Estrus was synchronized in 2,598 suckled beef cows at 14 locations, and AI was preceded by 1 of 5 treatments: 1) a CIDR for 7 d with 25 mg of PG F(2alpha) (PGF) at CIDR removal, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received 100 mug of GnRH and TAI at 84 h (control; n = 506); 2) GnRH administration, followed in 7 d with PGF, followed in 60 h by a second injection of GnRH and TAI (CO-Synch; n = 548); 3) CO-Synch plus a CIDR during the 7 d between the first injection of GnRH and PGF (CO-Synch + CIDR; n = 539); 4) GnRH administration, followed in 7 d with PGF, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received GnRH and TAI at 84 h (Select Synch & TAI; n = 507); and 5) Select Synch & TAI plus a CIDR during the 7 d between the first injection of GnRH and PGF (Select Synch + CIDR & TAI; n = 498). Blood samples were collected (d -17 and -7, relative to PGF) to determine estrous cycle status. For the control, Select Synch & TAI, and Select Synch + CIDR & TAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed using the AM/PM rule. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of cows cycling at the initiation of treatments was 66%. Pregnancy rates (proportion of cows pregnant to AI of all cows synchronized during the synchronization period) among locations across treatments ranged from 37% to 67%. Pregnancy rates were greater (P < 0.05) for the Select Synch + CIDR & TAI (58%), CO-Synch + CIDR (54%), Select Synch & TAI (53%), or control (53%) treatments than the CO-Synch (44%) treatment. Among the 3 protocols in which estrus was detected, conception rates (proportion of cows that became pregnant to AI of those exhibiting estrus during the synchronization period) were greater (P < 0.05) for Select Synch & TAI (70%; 217 of 309) and Select Synch + CIDR & TAI (67%; 230 of 345) cows than for control cows (61%; 197 of 325). We conclude that the CO-Synch + CIDR protocol yielded similar pregnancy rates to estrous detection protocols and is a reliable TAI protocol that eliminates detection of estrus when inseminating beef cows.     

Luteal lifespan and fertility after estrus synchronization in goats

The present experiment aims to examine the efficiency of estrus synchronization using progesterone and equine chorionic gonadotrophin (eCG) and to look at luteal function. During the non-breeding and breeding season, 5 adult female Korean native goats were injected intramuscularly with 2.5 ml of physiological saline as the control. A progesterone impregnated intravaginal sponge was then kept in the same goats for 10 days followed, after a week, by an intramuscular injection of 500 IU eCG. Five adult female Nubian goats were mated with a fertile buck during the non-breeding season. During the non-breeding season 2 of the 5 goats showed a normal estrous cycle (ranging from 18 to 21 days) and 3 a short estrous cycle (ranging from 3 to 6 days). During the breeding season the equivalent figures were 1 and 2. The major axes of the corpus luteum (CL) were measured by means of calipers built into the ultrasonography system, and the concentrations of plasma progesterone (P₄) were determined by double antibody radioimmunoassay. The mean major axes of the CL in goats showing the short cycle (6.1 ± 0.5 mm) was significantly smaller than in those showing the normal cycle (8.9 ± 0.5 mm; p < 0.01) and also the value of P₄ in goats showing the short cycle (4.2 ± 2.1 ng/ml) was significantly lower than for those showing the normal cycle (10.3 ± 4.3 ng/ml; p < 0.05) at day 3 following ovulation. Three out of 5 Nubian goats became pregnant but only one goat carried to full term. The present experiment indicated that a combination of progesterone and eCG was effective in inducing estrus, although it resulted in a high incidence of short luteal lifespan. The low kidding rate and high incidence of embryonic loss may be due to the instability of the luteal lifespan.     

The effect of intramuscular injection of dinoprost or gonadotropin-releasing hormone in dairy cows on beef quality

Intramuscular injections of drugs and vaccines cause tissue damage and subsequent effects on tenderness and consumer acceptability of beef. In the 2007 National Market Cow and Bull Beef Quality Audit, 100% of plants reported fabricating subprimal cuts such as rib eyes and tenderloins from cow and bull carcasses. Dairy beef quality should therefore be a consideration when injections are given to dairy animals. The discussion about injection site reactions and tenderness has focused on vaccines and antimicrobial drugs with little concern for the effects of reproductive hormones. The objective of this study was to quantify antemortem the effects of semimembranosis/semitendinosis muscle injection of dinoprost and GnRH in lactating dairy cows by estimating the weight of tissue damaged and comparing that with a drug known to cause extensive tissue damage, flunixin meglumine. Tissue damage was estimated from previously reported equations for grams of muscle tissue damage based on area under the curve of serum concentrations of the muscle enzyme creatine kinase over time. Dinoprost and flunixin injection both caused a significantly increased estimate of muscle tissue damaged compared with needle only (P = 0.0351 and 0.0355, respectively). Dinoprost and flunixin caused a marginally significant increased muscle tissue damage compared with GnRH (P = 0.1394 and 0.1475, respectively). No statistically significant difference was found between the estimated weight of muscle tissue damaged by flunixin compared with dinoprost (P = 1.0000), or by saline compared with GnRH (P = 0.7736) or needle only (P = 0.4902). The assumption that reproductive hormones are less damaging than vaccines and antimicrobial drugs should be examined more closely, including postmortem evaluation of injection site lesions and effects on tenderness.     

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: replacement of gonadotropin-releasing hormone with human chorionic gonadotropin

Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 μg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.     

Effect of dietary energy, body condition and calf removal on pituitary gonadotropins, gonadotropin-releasing hormone (GnRH) and hypothalamic opioids in beef cows

Beef cows (n = 64) were slaughtered to evaluate effects of dietary energy and calf removal (CR) on hypothalamic and adenohypophysial endocrine characteristics. From d 190 of gestation until parturition, cows received maintenance (ME; n = 32) or low (LE; n = 32) energy diets (ME = 100%, LE = 70% NRC recommendations). After parturition, half (n = 16) of each prepartum diet group received low (LE; n = 32) or high (HE = 130% NRC; n = 32) energy diets. At 30 d postpartum, cows were slaughtered 0 or 48 hr after CR. Hypothalami [preoptic area (POA), hypothalamus (HYP), stalk-median eminence (SME)] and pituitaries were collected. Basal and K(+)-induced release of GnRH from SME, and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not differ among groups (P greater than .05). Hypophyseal LH was correlated (P less than .01) with body condition score (BCS) at parturition and slaughter (r = .36 and .47, respectively). Prepartum LE diet increased (P less than .05) met-enkephalin in POA compared to prepartum ME (.59 +/- .05 vs. .44 +/- .04 pmol/mg) regardless of postpartum diet or suckling status. Concentrations of beta-endorphin in combined HYP + POA were decreased (P less than .05) by 48 hr CR (15.1 +/- 1.1 vs. 18.1 +/- 0.7 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of megesterol acetate for synchronization of estrus in cows]

Megestrol acetate has proved to be of positive impact upon synchronisation of oestrus in beef cows. Fodder-borne administration of 35-45 mg megestrol acetate caused oestrus in nursing cows, accompanied by disorders in ovarian function. The physiological condition of the animal at the date of treatment was found to be of major relevance to success. Evidence was produced to the strong action of serum obtained from pregnant mares in which the ratio of total gonadotrophic activity to luteinising activity was between 3:1 and 2.5:1. The use of megestrol acetate is recommended as a method by which to activate sexual function in the context of beef cattle breeding.     

Effect of GnRH pretreatment on reproductive performance of postpartum suckled beef cows following synchronization of estrus using GnRH and PGF2alpha

The effect of GnRH pretreatment on estrus detection rate, precision of estrus, and reproductive performance of postpartum beef cows synchronized to estrus using GnRH and PGF2alpha was evaluated. In Exp. 1, Angus cows (n = 87) were randomly assigned by parity, postpartum interval, and body condition score (BCS) to receive either 1) GnRH on d -7 and PGF2alpha on d 0 (GP) or 2) the GP treatment and an additional injection of GnRH on d -16 (GGP). Estrus detection and AI were conducted twice daily from d -3 to d 3. At 72 h after PGF2alpha, all animals not previously detected in estrus were bred by AI and received a concurrent injection of GnRH (TAI). Synchronized pregnancy rates were numerically increased (P = 0.15) in cows treated with GGP (55%) compared with those on the GP treatment (44%). In Exp. 2, 1,276 spring-calving, suckled beef cows in nine herds were randomized to treatments as described for Exp. 1, except that the initial GnRH injection for the GGP treatment was administered on d -14. Herd affected all indicators of reproductive performance (P < 0.05). The percentage of animals detected in estrus prematurely (d -3 to d 0; 7%) was not affected by treatment. Estrus response rate was influenced by postpartum interval (< 60 vs > or = 60; 61 vs 73%; P < 0.01) and a three-way interaction of parity, BCS, and treatment (P < 0.01). Within animals with a BCS > or = 5.5, the GGP treatment tended to increase the detection of estrus in primiparous cows (GP vs GGP; 76 vs 91%; P = 0.11) and decrease detection in multiparous cows (GP vs GGP; 78 vs 72%; P < 0.10). However, because conception rate to TAI in animals with a BCS > or = 5.5 was greater (P < 0.05) in the GGP than in the GP group (28 vs 8%, respectively), this interaction was interpreted to represent a shift in interval to estrus induced by the GGP treatment, rather than a reduction in the synchronization of ovarian function. Conception rates of animals inseminated to an observed estrus did not differ among treatments (P = 0.15). Synchronized pregnancy rate tended (P = 0.06) to be greater in GGP- (53%) than in GP-treated animals (47%). In conclusion, pretreatment with GnRH tended to increase pregnancy rates during a 6-d synchronization period, primarily through enhanced conception rates of cows bred by TAI. In contrast to our hypothesis, GnRH pretreatment did not increase the percentage of animals detected in estrus or the precision of estrus expression.     

Plasma steroid profiles following follicle-stimulating hormone or equine chorionic gonadotropin injection in cows chronically treated with gonadotropin-releasing hormone agonist

Plasma steroid profiles following follicle-stimulating hormone (FSH) or equine chorionic gonadotropin (eCG) injection were studied in chronically gonadotropin releasing hormone agonist (GnRH-A)-treated cows. Follicular development and irINH secretion were stimulated by FSH or eCG injection. The plasma concentrations of estradiol-17 beta (E(2)) and testosterone (T) were markedly increased following eCG injection. However, significant increases of the plasma E(2) and T concentrations were not detected in FSH-treated cows. Ovulation of developed follicles were depended on the hCG injection in both groups. These results show: 1) Follicular response to an exogenous gonadotropin is still remained, 2) Ovulation of developed follicles is induced by hCG injection and 3) FSH and eCG cause disparate plasma steroid profiles, under the influence of repeated GnRH-A treatment.     

Effect of copper status, supplementation, and source on pituitary responsiveness to exogenous gonadotropin-releasing hormone in ovariectomized beef cows

The effect of Cu status, supplementation, and source on pituitary responsiveness to exogenous GnRH was evaluated using nine multiparous, nonpregnant, nonsuckling, ovariectomized Angus cows (7.1 +/- 3.3 yr; 622.9 +/- 49.8 kg; BCS = 6.0 +/- 0.5). Cows were considered Cu-deficient based on liver Cu concentrations (< 30 mg of Cu/kg of DM) after receiving a low-Cu, forage-based diet supplemented (DM basis) with 5 mg of Mo/kg and 0.3% S for 216 d. Copper-deficient cows were stratified based on age, BW, BCS, and liver Cu concentration and assigned randomly to repletion-phase treatments. Treatments included 1) control (no supplemental Cu); 2) organic (ORG; 100% organic Cu); and 3) inorganic (ING; 100% inorganic CuSO4). Treatments were formulated to meet all NRC recommendations, except for Cu, which was supplemented to ORG and ING cows at 10 mg of Cu/kg of dietary DM. During the 159-d repletion phase, Cu status was monitored via liver biopsy samples, and all cows received exogenous progesterone. A controlled intravaginal drug-release device (replaced every 14 d) was used to maintain luteal phase progesterone as a means to provide negative feedback on the hypothalamic-pituitary axis. During the repletion phase, liver Cu concentrations did not differ between ORG and ING cows at any time. By d 77 of the repletion phase, all supplemented cows were considered adequate in Cu, and liver Cu concentrations were greater in supplemented than in nonsupplemented control cows on d 77 (P < 0.05) and throughout (P < 0.01) the repletion phase. Beginning on d 99, exogenous GnRH was administered to all cows at low (0, 3, and 9 microg; Exp. 1) and high doses (0, 27, and 81 microg; Exp. 2) at six different times. Cows were catheterized every fifth day, and blood samples were collected every 15 min for 1 h before and 4 h after GnRH administration and analyzed for LH concentration. In Exp. 1, Cu status and supplementation did not affect basal or peak LH concentrations, but total LH released tended (P < 0.07) to be greater in Cu-supplemented vs. control cows when 3 microg of GnRH was administered. In Exp. 2, there was no effect of Cu supplementation or source on basal, peak, or total LH released, regardless of GnRH dose. Pituitary LH concentrations did not differ across treatments. In conclusion, Cu status, supplementation, and source did not affect GnRH-induced LH secretion or pituitary LH stores in ovariectomized, progesterone-supplemented cows in this experiment.     

Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone

We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F2alpha (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 microg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 microg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 microg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.     

Effects of chronic gonadotropin-releasing hormone agonist treatment on serum luteinizing hormone and testosterone concentrations in boars.

Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH210), and serum luteinizing hormone (LH) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days -2 and -1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days -1, 0, 4, and 8. Serum testosterone and LH concentrations were determined by radioimmunoassay. Maximal LH (7 +/- 1 ng/ml) and testosterone (26 +/- 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, LH and testosterone concentrations decreased to pretreatment values (0.3 +/- 0.1 ng/ml and 1.8 +/- 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile LH release were observed between the groups. Testosterone and LH concentrations in samples collected at 6- and 12-hour intervals and pulsatile LH release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum LH and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in LH and testosterone concentrations in mature boars.     

A comparison of progestin-based protocols to synchronize estrus in postpartum beef cows

Two progestin-based protocols for estrus synchronization in postpartum beef cows were compared following treatment administration on the basis of estrous response, interval to and synchrony of estrus, and pregnancy. Cows were assigned to one of the two treatment protocols by age, body condition score (BCS), and days postpartum (DPP). The MGA Select-treated cows (MGA Select; n = 109) were fed melengestrol acetate (MGA; 0.5mg x cow-1 x d(-1)) for 14 d, fed carrier for 8 d, GnRH (100 microg of Cystorelin) was injected i.m. 12 d after MGA withdrawal, and PG (25 mg of Lutalyse) was administered i.m. 7 d after GnRH. Cows assigned to the 7-11 Synch protocol (7-11 Synch; n = 111) were fed carrier for 15 d, fed MGA for 7 d, injected with PG on d 22 (d 7 of MGA), injected with GnRH on d 26, and injected with PG on d 33. Mean BCS (4.8 +/- 0.1, MGA Select; 4.7 +/- 0.1, 7-11 Synch) and DPP (40 +/- 1, MGA Select; 40 +/- 1, 7-11 Synch) did not differ between treatments. Blood samples were collected 8 d and 1 d before feeding of MGA or carrier to determine the pretreatment estrous cyclicity (progesterone > or = 1 ng/mL; 10/109 [9%], MGA Select; 12/111 [11%], 7-11 Synch), and again at PG on d 33 to evaluate treatment response (81/109 [74%], MGA Select; 84/111 (76%), 7-11 Synch). Serum concentrations of progesterone at PG on d 33 differed (P < 0.01) between treatments (3.3 +/- 0.3 ng/mL [MGA Select] vs. 1.7 +/- 0.1 ng/mL [7-11 Synch]). HeatWatch was used for 6 d after PG on d 33 to detect estrus, and AI was performed 12 h after the onset of estrus. Estrous response did not differ between treatments (100/109 [92%], MGA Select; 101/111 [91%], 7-11 Synch). Mean interval to estrus (65 +/- 2.7 h, MGA Select; 52 +/- 1.8 h, 7-11 Synch) and synchrony of estrus differed (P < 0.01) between treatments. Synchronized conception and pregnancy rates (61/100 [61%], 61/109 [56%], MGA Select; 71/101 [70%], 71/111 [64%], 7-11 Synch), and final pregnancy rates (94/109 [86%], MGA Select; 99/110 [90%], 7-11 Synch) did not differ between treatments. In summary, estrous response and fertility did not differ among cows assigned to the MGA Select or 7-11 Synch protocols. Synchrony of estrus, defined as the variance in the interval to estrus from PG, however, was improved following treatment with the 7-11 Synch protocol.     

Effect of ovulatory follicle size and expression of estrus on progesterone secretion in beef cows

Induced ovulation of small dominant follicles (SF, < 12 mm; CO-Synch protocol) in postpartum beef cows resulted in formation of corpora lutea (CL) that exhibited a delayed rise in progesterone (P4) compared with CL from large dominant follicles (LF, > 12 mm). Experiment 1 characterized P4 concentrations from ovulation to subsequent estrus among GnRH-induced or spontaneously ovulated SF (or= 12 mm) to determine if P4 secretion by CL formed from GnRH-induced SF remains lower postovulation in nonlactating beef cows. Nonlactating beef cows were induced to ovulate 48 h after PGF(2alpha) (CO-Synch; GnRH on d - 9, PGF(2alpha) on d - 2, and GnRH on d 0) or exhibited estrus and spontaneously ovulated after PGF(2alpha). Follicle size was measured at the second GnRH in cows induced to ovulate or approximately 3 h after the onset of estrus for cows that ovulated spontaneously. Cows were classified into 1 of 4 groups: 1) GnRH-induced ovulation-SF (or= 12 mm; Ind-LF; n = 16); 3) spontaneous ovulation-SF (or= 12 mm; Spon-LF; n = 22). Serum concentrations of P4 from d 3 to 15 were reduced in the Ind-SF compared with the Ind-LF (P = 0.05), Spon-SF (P = 0.07), and Spon-LF (P = 0.03). Experiment 2 characterized P4 concentrations (0 to 60 d postAI) among GnRH-induced or spontaneously ovulated SF (or= 13 mm) to determine if P4 secretion by CL formed from GnRH-induced SF remained lower during early gestation. Ovulation was induced with GnRH 48 h after PGF(2) (CO-Synch) or occurred spontaneously, and ovulatory follicle size was measured at AI. Lactating cows were classified into 1 of 3 groups: 1) GnRH-induced ovulation-SF (or= 13 mm; Ind-LF; n = 43); or 3) spontaneous ovulation-LF (>or= 13 mm; Spon-LF; n = 27). The increase in P4 concentrations was greater (P = 0.06) in pregnant (d 2 to 12) compared with nonpregnant cows. Also, the increase in P4 from d 2 to 12 was greater (P = 0.01) in the Ind-LF compared with the Ind-SF groups, but there was no difference (P = 0.94) among groups in P4 from d 14 to 60 in pregnant cows. Follicle size at AI influenced the increase in P4 in cows that failed to conceive (P = 0.007), but not among cows that became pregnant (P = 0.32) to AI. In summary, P4 secretion after GnRH-induced ovulation of SF was decreased from d 2 to 12 compared with that of LF, but was similar among pregnant cows from d 14 to 60 postAI (d 0).     

Influence of the ovary and suckling on luteinizing hormone response to naloxone in postpartum beef cows

The influence of the suckling stimulus and ovarian secretions on LH response to naloxone was studied in 16 postpartum anestrous beef cows that were assigned randomly to one of four groups (n = 4/group): intact suckled (IS), intact nonsuckled (IN), ovariectomized suckled (OS) or ovariectomized nonsuckled (ON). Ovariectomy (OS + ON) and calf removal (IN + ON) were performed on d 2, 3 or 4 after parturition. Jugular venous blood was collected at 15-min intervals for 4 h before and 4 h after administration of naloxone (1 mg/kg BW, i.v.) on d 14 and d 28 after parturition. Gonadotropin-releasing hormone (5 micrograms, i.v.) was given 3 h after naloxone. Both IN and OS increased (P less than .05) mean pretreatment LH above IS values (mean +/- SE, ng/ml; IS 1.6 +/- .1 vs IN 2.5 +/- .3 and OS 2.7 +/- .4; P less than .01), whereas ON increased (P less than .01) LH (3.7 +/- .3 ng/ml) even further. Mean LH increased (P less than .05) after naloxone administration in all treatment groups. However, magnitude of this response was variable and dependent on ovarian status. Amplitude of the naloxone-induced LH response was greater (P less than .05) for ovariectomized (5.9 +/- 1.1 ng/ml) than for intact groups (2.7 +/- .5 ng/ml). Gonadotropin-releasing hormone increased mean LH concentrations in all groups. We suggest that ovarian secretions and the suckling stimulus contribute to endogenous opioid inhibition of LH during the postpartum interval.(ABSTRACT TRUNCATED AT 250 WORDS)     

热带牛同期发情-定时输精和胚胎移植效果分析

研究了同期发情-定时输精和胚胎移植以及同期发情方法的效果和影响因素.结果表明,婆罗门牛和BMY牛同期发情率和妊娠率无显著差异( P＞0.05);同期发情后,表观发情牛和表观未发情牛的妊娠率没有显著差异(P＞0.05).结果提示,对没有观察到发情症候的母牛实施定时输精是必要的,可以有效提高情期受胎率;体况(4.5)较肥的繁殖母牛可以获得良好受胎率,情期受胎率高达78.9%,在实际工作中,主要防止体况差影响繁殖率,而不是防止牛体过肥影响繁殖率;同期发情②法比①法能极显著提高胚胎移植受体牛可用率,移植妊娠率差异不显著(P＞0.05);埋栓时存在优势卵泡或发情,对胚胎移植受体牛可用率没有显著影响.