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.     

Pour-on method of administering chlormadinone acetate for estrus synchronization in heifers

Experiments with chlormadinone (Bovisynchron) on 380 heifers and 60 cows showed that the drug was absorbed following pour-on application. A volume of 2 ml was rubbed into the skin of the back anterior to the sacrum, once daily for 15 days. Residual amounts were removed 24 hours after the final application by washing the hair coat with dimethyl sulphoxide solution. Insemination was performed at the same time as after oral administration. The pour-on method was particularly suitable for heifers and cows out at pasture.     

Insertion and removal of intravaginal tampons during estrus synchronization in heifers]

In eight trials, 197 heifers were synchronized with gestagen chlorsuperlutin (CSL). The intravaginal tampons soaked with chlorsuperlutin were introduced in the vagina by means of an applier by a vaginal speculum. Silon threads were attached to the tampons, by which they were pulled out after treatment. The mentioned method of application removes the great physical exertion needed for manual application and increases labour productivity in tampon application by about 200%. The hazard of tampon contamination is reduced to the minimum. Of the two tampon types tested (ester and ether type) the ester type was found to be better for not needing sterilization if the disinfectant Aseptin is dropped upon it prior to application. The retention of the tampons was 94.9%. Eighty-four per cent of the retained tampons could be removed by pulling the silon threads. About 40 to 60% of CSL is excreted from the tampons during the treatment. If the initial content of CSL is increased, its excretion is raised as well.     

Physiology and Endocrinology Symposium: Harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers

The development of replacement heifers is a major economic investment for all beef and dairy operations. The costs associated with heifer development cannot be recovered if heifers do not conceive and remain productive in the herd; therefore, heifers need to conceive early in the breeding season or risk being culled. Previous research has reported up to a 21% increase in fertility from pubertal estrus to the third estrus of a heifer. The use of reproductive tract scores to determine pubertal status has demonstrated that peripubertal and pubertal heifers have increased pregnancy success to estrous synchronization compared with heifers that were prepubertal. The development of RIA has allowed accurate measurement of peripheral blood hormone concentrations associated with the pubertal process and luteal formation. This basic knowledge has increased our understanding of the mechanisms that control puberty in heifers. In addition, understanding the hormonal changes that occur during the estrous cycle has allowed for the development of estrous synchronization protocols that result in increased control of follicular growth, regression of luteal tissue, and ovulation. Transrectal ultrasonography has increased our understanding of follicular waves; this understanding led to research investigating the endocrine regulation of follicular waves and development of methods to synchronize follicular waves for purposes of fixed-time AI. Current topics of research include the effect of antral follicle count on fertility and the effect of maternal nutrition (on the fetus in utero) on subsequent reproductive potential of a heifer (i.e., fetal programming). Advancements in genomic technologies will likely provide a powerful tool for selecting heifers at birth that will have a greater probability of being reproductively successful if managed correctly. Therefore, knowledge gained through basic research on factors that control puberty has improved and will continue to improve heifer development and fertility.     

Studies on the use of megestrol acetate for estrus synchronization in heifers

Megestrol acetate has been tested for its applicability to synchronisation of oestrus in 463 mature heifers in the framework of preclinical and clinical experiments. Clinical tests and studies in the context of laboratory diagnostics have shown that 40 mg/die megestrol acetate, administered in two applications with twelve hours in-between and over 15 days, are necessary for maximum synchronisation effect. The resulting oestrus was found to be prolonged, with ovulations taking place within two or three days. Technological requirements in this context are discussed. Megestrol acetate is found to be suitable for oestrus synchronisation in heifer. Tests conducted under industrialised conditions have shown conception rates to be identical with those obtained by administration of chloromadinone acetate.     

Comparison of protocols to synchronize estrus and ovulation in estrous-cycling and prepubertal beef heifers

The objective of the experiment was to compare follicular dynamics, ovulatory response to GnRH, and synchrony of estrus and ovulation among estrous-cycling and prepubertal beef heifers synchronized with a controlled internal drug-release (CIDR)- based or GnRH-PGF(2alpha) (PG) protocol. Estrous-cycling beef heifers were randomly assigned to 1 of 4 treatments (C1, C2, C3, C4), and prepubertal beef heifers were randomly assigned to 1 of 2 treatments (P1, P2) by age and BW. Blood samples were taken 10 and 1 d before treatment to confirm estrous cyclicity status (progesterone > or =0.5 ng/mL estrous cycling). The CIDR Select (C1, n = 12; P1, n = 14)-treated heifers received a CIDR insert (1.38 g of progesterone) from d 0 to 14, GnRH (100 microg, i.m.) on d 23, and PG (25 mg, i.m.) on d 30. Select Synch + CIDR (C2, n = 12; P2, n = 11)-treated heifers received a CIDR insert and GnRH on d 23 and PG at CIDR removal on d 30. The CIDR-PG (C3, n = 12)-treated heifers received a CIDR insert on d 23 and PG at CIDR removal on d 30. Select Synch (C4, n = 12)-treated heifers received GnRH on d 23 and PG on d 30. HeatWatch transmitters were fitted at CIDR removal (C1, C2, C3, P1, and P2) or at GnRH administration (C4) for estrus detection. Ultrasound was used to determine the response to GnRH and the timing of ovulation after estrus. Among the estrous-cycling heifers, ovulatory response to GnRH and estrous response did not differ (P > 0.05). Among the prepubertal heifers, more (P = 0.02) P1 heifers responded to GnRH than P2 heifers, but estrous response did not differ (P > 0.05). Among the estrous-cycling heifers, variance for interval to estrus after PG was reduced (P < 0.05) for C1 compared with each of the other treatments, and C3 [corrected] was reduced (P < 0.05) compared with C2 [corrected] Variance for interval to ovulation after PG was reduced (P < 0.05) for C1 compared with each of the other treatments. Among the prepubertal heifers, there was no difference (P > 0.05) in variance for interval to estrus or ovulation. Results from C1 and P1 (T1) and C2 and P2 (T2) were combined to compare T1 and T2 among mixed groups of estrous-cycling and prepubertal heifers. Response to GnRH was greater (P < 0.01; 81% T1 and 39% T2), and variances for interval to estrus and ovulation for T1 were reduced (P < 0.01) compared with T2. In summary, CIDR Select improved (P < 0.01) the synchrony of estrus and ovulation compared with Select Synch + CIDR.     

Improved synchrony of estrus and ovulation with the addition of GnRH to a melengestrol acetate-prostaglandin F2alpha synchronization treatment in beef heifers

The objective of this experiment was to determine the effect of a GnRH injection within a melengestrol acetate (MGA)-PGF2alpha (PGF) estrus synchronization protocol on follicular dynamics and synchronization of estrus. Pubertal crossbred beef heifers (n = 34) were randomly assigned to one of two treatments. Both treatment groups were fed MGA (0.5 mg x hd(-1) x d(-1)) for 14 d and injected (i.m.) with PGF (25 mg of Lutalyse) 19 d after MGA withdrawal. Melengestrol acetate was delivered in a feed supplement of 1.8 kg x hd(-1) x d(-1). Seventeen heifers received an injection of GnRH (100 microg Cystorelin) 12 d after MGA withdrawal and 7 d before PGF. The control group (n = 17) received only MGA-PGF. Estrus was detected four times/d for 7 d beginning on the day PGF was injected. Transrectal ultrasonography was performed daily on eight heifers from each treatment to monitor ovarian activity and characterize changes in follicular dynamics after MGA withdrawal and until ovulation after PGF. Each of the GnRH-treated heifers either ovulated or had a luteinized dominant follicle following GnRH and subsequently initiated a new follicular wave (8/8, 100%). All GnRH-treated heifers (17/17, 100%) and 94% of controls (16/17) exhibited estrus after PGF. Estrus was exhibited over a 132-h period (12 to 144 h) for control heifers compared with 60 h (48 to 108 h) for GnRH-treated heifers. The peak synchronized period for both treatments was between 48 and 72 h after PGF, during which time 76% (13/17) of the GnRH-treated heifers exhibited estrus compared with 63% (10/16) for controls. Seventy-one percent (12/17) of the GnRH-treated heifers exhibited estrus from 48 to 60 h after PGF, compared with 38% (6/16) for controls (P < 0.05). In summary, injection of GnRH within a 14- to 19-d MGA-PGF protocol increased the synchrony of estrus during the synchronized period and concentrated the period of detected estrus. This protocol may offer potential for the fixed-time insemination of replacement beef heifers.     

Steroid hormone levels in follicular fluid of swine with spontaneous estrus and ovulation synchronization

The steroid hormones oestradiol 17 beta, oestrone (E1), testosterone (T), and progesterone (P) were quantitatively determined in follicular fluids in the pre-oestric phase of pigs with spontaneous oestrus and synchronised ovulation. As a whole, mean steroid hormone concentrations exhibited characteristic curves in spite of a relatively wide scatter of individual values. Drastic decline in oestrogen concentration in pigs with spontaneous oestrus and synchronised ovulation was accompanied by rise of P levels, while T values stayed relatively constant. As compared to spontaneous oestrus, treatment for synchronised ovulation caused significantly higher increases in follicular T levels. Positive (P) or negative (E1, T) correlations were found to exist between follicle size and steroid hormone concentration. Conclusions are suggested for further studies.     

Nonpuberal estrus in beef heifers

The frequency of occurrence of behavioral estrus without subsequent development of functional luteal tissue (termed nonpuberal estrus, NPE), was determined in 43 Simmental X Hereford-Brahman heifers. Blood samples were collected weekly from the start of the study to first behavioral estrus and then daily from d 1 (d 0 = estrus) through d 14 following first and subsequently observed estrous behaviors. All blood samples were analyzed for serum progesterone (P4) concentrations by radioimmunoassay. More heifers (62.8%) exhibited NPE than had luteal development after their first behavioral estrus (37.2%). There was a tendency for fewer light-weight heifers (less than or equal to 240 kg at the start of the experiment) to exhibit a puberal first estrus compared with the heavy-weight (greater than 240 kg at the start of the experiment) heifers (31.2% vs 68.8%, respectively; P = .12). Heifers that had a puberal first estrus were older (376 +/- 12 d vs 334 +/- 9 d, P less than .05) compared with heifers that had NPE. Weight at first behavioral estrus was similar between heifers that had a puberal first estrus and those that had NPE (298 +/- 8 kg and 289 +/- 6 kg, respectively). More heifers that had a puberal first estrus also had an elevation in serum P4 concentrations before that first estrus (64.3% vs 20.0%, P less than .05), and the serum P4 elevation was greater (2.5 +/- .4 ng vs 1.2 +/- .1 ng, P less than .05) than heifers that had NPE. We have concluded from these results that NPE is a common occurrence in heifers approaching puberty.(ABSTRACT TRUNCATED AT 250 WORDS)     

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。     

Control of ovulation and fixed time insemination in heifers following cloprostenol.

The time of ovulation was determined in heifers following two injections 11 days apart of 500 microgram of cloprostenol by recovery of reproductive tracts at slaughter. Ovulation had not begun by 72 hours while 31%, 61% and 95% had ovulated by 78, 92 and 96 hours respectively after the second injection of cloprostenol. Injection of synthetic LH-releasing factor (GnRH) given 48 hours after cloprostenol significantly hastened the time of ovulation in animals slaughtered at 78 hours after the second cloprostenol injection. Insemination of heifers at 48, 60 or 72 hours resulted in lower fertility than two inseminations at 60 and 72 hours or at 48 and 72 hours after treatment. Controlling the time of ovulation with GnRH did not increase the fertility following a single insemination 71 hours after the treatment with cloprostenol.