Korea is facing a significant problem with historically low fertility rates, which is becoming a major social issue affecting the economy, labor force, and national security. This study analyzes the factors contributing to the regional gap in fertility rates and derives policy implications. The government and local authorities are implementing a range of policies to address the issue of low fertility. To establish an effective strategy, it is essential to identify the primary factors that contribute to regional disparities. This study identifies these factors and explores policy implications through machine learning and explainable artificial intelligence. The study also examines the influence of media and public opinion on childbirth in Korea by incorporating news and online community sentiment, as well as sentiment fear indices, as independent variables. To establish the relationship between regional fertility rates and factors, the study employs four machine learning models: multiple linear regression, XGBoost, Random Forest, and Support Vector Regression. Support Vector Regression, XGBoost, and Random Forest significantly outperform linear regression, highlighting the importance of machine learning models in explaining non-linear relationships with numerous variables. A factor analysis using SHAP is then conducted. The unemployment rate, Regional Gross Domestic Product per Capita, Women's Participation in Economic Activities, Number of Crimes Committed, Average Age of First Marriage, and Private Education Expenses significantly impact regional fertility rates. However, the degree of impact of the factors affecting fertility may vary by region, suggesting the need for policies tailored to the characteristics of each region, not just an overall ranking of factors.

Toll-like receptor 4 (TLR4) is known to contribute to the modulation of insulin resistance and systemic inflammation seen in obesity and the metabolic syndrome. The present study was performed to investigate the fertility competence of TLR4 knock out male mice (TLR4 mice) on a high-fat diet (HFD), compared to a normal-chow diet (NCD). The controls included wildtype (WT) mice fed on a HFD or NCD. Six-week-old male mice were fed with either a NCD or HFD for 20 weeks. Body and organ weights, serum levels of glucose, triglycerides and hepatoxicity, sperm quality and spermatogenesis were observed after the sacrifice. Also, randomly selected male mice were mated with virgin female mice after feeding of 19 weeks. The weight of the body and organs increased in WT and TLR4 mice on a HFD compared to those of mice on a NCD. The weights of the reproductive organs did not vary among the treatment groups. The motility and concentration of the epididymal spermatozoa decreased in both WT and TLR4 mice fed a HFD. The pregnancy rate and litter size declined in the HFD-fed WT mice compared to the HFD-fed TLR4 mice. In conclusion, the HFD alters energy and steroid metabolism in mice, which may lead to male reproductive disorders. However, fertility competence was somewhat restored in HFD-fed TLR4 male mice, suggesting that the TLR4 is involved in testis dysfunction due to metabolic imbalance.

본 연구는 한국의 고질적인 사회문제로 되는 저출산 현상의 대안을 제 시하는데, 그 목적이 있다. 미래 적 소유잠재성의 시각에서 출산으로 인 해 국가, 개인, 기업이 얻을 수 있는 것과 상실하게 되는 것들을 파악하 고, 이를 보완할 수 있는 대안을 제시한다. 국가에게 저출산의 지속은 생 존을 위협하며, 자기보존을 어렵게 한다. 출산은 국가의 생존과 관련한 문제로 볼 수 있다. 반면에 오늘날 개인에게 출산과 양육은 자산의 감소 는 물론 현재의 일자리를 위협한다. 저출산의 해결방안은 미래 세대 츨 생을 개인의 상속재산 지분과 연계하며, 국가지원금과 합의된 평균자녀 수와 평균자녀수 분포와 연계하는 것이다. 본 연구에서는 차세대 국가를 이끌어갈 미래 세대 존재를 개인 상속재산과 국가의 예산 및 지원금과 연계하여 저출산의 대안을 제시하였다.

The impact of heat stress (HS) on reproductive performance and its problems in cows remains to be investigated in Bangladesh. The study was, therefore, aimed to evaluate the effect of HS on fertility and reproductive health problems of dairy cows in a selected area of Bangladesh. A total of 1,095 cows from 500 farms were included in this study. The climate-related data were recorded daily basis for every month in a year and temperature-humidity index (THI) values were calculated to determine the level of HS. Concurrently, data on fertility parameters [number of services per conception (NSC), conception rate (CR) and calving to the first service interval (CFSI)], and reproductive problems were collected through a pre-defined questionnaire. The results show that crossbred [Native x Holstein-Friesian, (HF)] cows were more vulnerable (p < 0.05) to a magnitude of HS effects considering physiological parameters of cows [age, body condition score (BCS), parity and milk yield]. Regarding fertility, HS had no effect on NSC, CR and CFSI in both native and crossbred cows (p > 0.05). The findings on the reproductive problems indicate that HS had significant influence on the prevalence of anestrus (χ2 = 21.814, p < 0.05) and retained placenta (χ2 = 24.632, p < 0.05) in cows. Of note, the prevalence of repeat breeding syndrome was 2.5 folds higher in stress condition than in no stress condition. Abortion and dystocia were not influenced by HS. In conclusion, HS does not influence the fertility parameters of cows studied; however, anestrus and retained placenta are likely to occur under HS conditions in cows.

Cryopreservation of porcine ovarian tissue by vitrification method is a promising approach to preserve genetic materials for future use. However, information is not enough and technology still remains in a challenge stage in pig. Therefore, the objective of present study was to determine possibility of vitrification method to cryopreserve porcine ovarian tissue and to confirm an occurrence of cryoinjuries. Briefly, cryoinjuries and apoptosis patterns in vitrified-warmed ovarian tissue were examined by histological evaluation and TUNEL assay respectively. In results, a damaged morphology of oocytes was detected among groups and the rate was significantly (p < 0.05) lower in vitrification group (25.8%) than freezing control group (67.7%), while fresh control group (6.6%) showed significantly (p < 0.05) lower than both groups. In addition, cryoinjury that form a wave pattern of tissues around follicles was found in the frozen control group, but not in the fresh control group as well as in the vitrification group. Apoptotic cells in follicle was observed only in freezing control group while no apoptotic cell was found in both fresh control and vitrification. Similarly, apoptotic patterns of tissues not in follicle were comparable between fresh control and vitrification groups while freezing control group showed increased tendency. Conclusively, it was confirmed that vitrification method has a prevention effect against cryoinjury and this method could be an alternative approach for cryopreservation of genetic material in pigs. Further study is needed to examine the viability of oocytes derived from vitrified-warmed ovarian tissue.

본 연구는 우리나라 Holstein의 번식형질에 대한 유전모수를 추정하기 위하여, 2009년부터 2013년까지 분만한 농협 젖소개량사업소의 검정자료 경산우 144,793두의 211,899개의 번식기록을 이용하였다. 7가지 형질의 유전 및 오차 (공)분산을 WOMBAT 패키지를 이용하여 분석하였다. CTFS, GL, NRR, NS, FSTC, DO 및 CI의 유전력은 각각 0.064, 0.060, 0.005, 0.014, 0.012, 0.021 및 0.021로 추정되었다. 형질들 간의 유전상관은 –0.910에서 0.995로 나타났다. NRR과 NS, NRR과 FSTC 간에는 부의 유전상관이 나타났으나, DC와 CI는 강한 양의 유전상관을 나타냈다. CTFS와 FSTC는 DO 및 CI와 유의하게 양의 유전상관관계를 나타냈다(0.479~0.862). CTFS와 FSTC 사이의 낮은 유전상관은 두 형질이 서로 다른 유전적 측면에 있다는 것을 의미한다. 본 연구는 번식능력 개량을 위한 기초 자료를 제공할 수 있을 것이라 판단한다.

Rye (Secale cereal L.) is the most tolerant to abiotic stress including low temperature, drought, and unfavorable soil conditions among the winter cereals. Rye is the rapid growth of early spring results from increasing areas for the use of the forage and green manure in the middle part of Korea. “Jungmo2509”, a rye cultivar was developed by the National Institute of Crop Science (NICS), RDA in 2014. It was developed from a cross between “Olhomil”, a self-compatible cultivar, and “Synthetic Ⅱ”, a self-incompatible line. “Jungmo2509” is an erect plant type and of a middle size, with a green leaf color, a yellowish-white colored culm, and a yellowish brown-colored, small-size grain. The heading date of “Jungmo2509” was April 23, which was 5 days later than that of “Gogu”, respectively. But “Jungmo2509“ showed greater resistance to lodging compared to that of the check cultivar, with similar to winter hardiness, wet injury, and disease resistance. “Jungmo2509” was a higher to than “Gogu” in terms of protein content (9.4% and 8.0%, respectively), total digestible nutrients (TDN) (55.7% and 55%, respectively). The seed productivity of “Jungmo2509” was approximately 2.08 ton 10a-1, which was 11% lower than that of the check. Almost all rye cultivars are out-crossing due to genes controlling incompatibility, but “Jungmo2509” is higher seed fertility (56%) than that of Gogu (0%). it has self-compatible genes. “Jungmo2509” is erect in plant type and resistance for lodging. Therefore, “Jungmo2509” can produce uniform seeds for processed grains of human consumption and utilize them as parents for breeding the rye hybrids with high forage yields.

The effects of the number of frozen-thawed ram sperm per single and double intra-cervical artificial insemination (AI) on fertility in ewes were studied. A total of 89 non-pregnant ewes were synchronized for oestrus with two doses of 100 μg PGF2α (Cloprostenol) 9 days apart. The ewes were randomly assigned to one of four groups; D200 (n = 23; double AI with 200 × 106 sperm), S200 (n = 24; single AI with 200 × 106 sperm), D100 (n = 24; double AI with 100 × 106 sperm) and S100 (n = 18; single AI with 100 × 106 sperm). Ewes were inseminated within 12 to 18 h for single AI and, within 10 to 12 h and 16 to 18 h for double AI after the onset of oestrus. The onset of oestrus ranged from 28 to 76 h (54.33 ± 1.28 h). The high percentage (29.2%) of ewes showed oestrus between 51 to 60 h. The non-return rates were highest in group D200 (56.5%) and differed significantly (p < 0.05) from group S100 (11.1%). No ewes were pregnant in group S100, and the pregnancy rates among the remaining groups did not differ. The mean gestation period was 152.8 ± 0.5 days and no difference was observed among the groups. The lambing and multiple birth rates were 100% in group D200. The single and twin lambing was highest in group D100 (33.3%) and group D200 (83.3%), respectively. Only one triplet lambing and the highest lambing size (2.2 ± 0.2) was recorded in group D200. In conclusion, double AI with 200 × 106 sperm showed comparatively most practical for achieving high pregnancy rates and lambing performances in Bangladeshi ewes under field conditions.

감자수염진딧물 (Macrosiphum euphorbiae)의 온도별 발육은 12.5~27.5°C까지 2.5°C 간격 (상대습도 65±5%, 광주기 16L : 8D), 7개 온도조건에서 1~2령, 3~4령의 2단계로 구분하여 조사하였다. 약충의 사망률은 7개 온도 중 6개 온도에서 10% 미만이었으나, 27.5°C에서 사망률은 53.0% 였다. 온도별 발육기간은 15.0°C에서 15.5일, 25.0°C에서는 6.7일로 고온으로 갈수록 발육기간은 짧아졌으나, 27.5°C 에서는 발육기간이 다시 길어져 9.7일이었다. 약충의 발육 영점온도는 2.6°C였고, 유효적산온도는 144.5일도였다. 약충의 발육을 5가지 비선형발육모형에 적용한 결과 Logan6 (r2=0.99) 모형이 발육에 적합하였고, 발육완료분포모형은 2-Weibull과 3-Weibull의 모형 적합성 (r2)이 각각 0.92 와 0.93으로 유사하였다. 성충 수명과 산자 수에서 성충 수명은 온도가 증가함에 따라 짧아지는 경향을 보였고, 산자 수는 20.0°C에서 64.4개로 가장 많은 산자를 생산하였다. 생명표분석에서 순증가율 (R0)은 20.0°C에서 63.2로 가장 컸고, 내적자연증가율 (rm)은 25.0°C에서 1.393로 가장 컸다. 배수증가기간 (Dt)은 25.0°C에서 2.091로 가장 짧았다. 기간자연증가율 (λ)은 25°C에서 가장 컸고 (1.393), 평균세 대기간 (T)은 25°C에서 9.929로 가장 짧았다.

Females of adzuki bean beetle (ABB), Callosobruchus chinensis (L.), a cosmopolitan field-to-storage pest of legumes, release sex pheromone consisting of two isomeric components, 2Z-homofarnesal and 2E-homofarnesal. Two day old virgin ABB adults were exposed to sub-lethal fumigation doses (LC25=0.0056 and LC50=0.0076 mgL-1) of phosphine (PH3) to evaluate the effects on adult longevity, fertility and sex pheromone production. Longevity (female; P < 0.001, male; P < 0.001), fecundity (P < 0.001) and sterility (P < 0.001) were significantly affected. The GC-MS for solid phase micro extraction exhibited the significant reduction of release of both of the pheromone components; 2Z-homofarnesal (P < 0.0038) and 2E-homofarnesal (P = 0.0009) when the females were exposed to LC25 dose of PH3. This study unveils the detrimental effects of PH3 fumigation on some of the biological parameters of ABB.

Bisphenol A (BPA) is a common industrial chemical that has been used extensively to make certain plastics and resins since the 1960s. As a potential endocrine disruptors, BPA has been investigated for its impact on fertility/reproduction in animals and humans. However, the molecular mechanisms of BPA action and standard method for detecting BPA-related health hazards are unclear. Considering in-vitro experimental model, we investigated the effects of BPA (0.0001 to 100 μM) exposure on mouse spermatozoa. We revealed that BPA affects several sperm functions by triggering the mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase-A (PKA) activity. High doses of this chemical was also likely for the activation of protein tyrosine phosphorylation in a PKA-dependent signaling consequently induced a precocious acrosome reaction. Simultaneously, BPA has been found to decrease the rate of fertilization and early embryonic development. In addition, BPA induced differential protein expression in spermatozoa were responsible for the pathogenesis of many diseases. Considering in vivo experimental model, we deliberate the effects of gestational BPA exposure (TDI, NOAEL, and LOAEL doses) on both ejaculated and capacitated spermatozoa in F1 adult mice. We confirmed that BPA affects several sperm function in F1 male. These effects appeared to be caused by reduced numbers of stage VIII seminiferous epithelial cells in testis and decreased PKA activity and tyrosine phosphorylation (non-capacitated) in spermatozoa. We also noticed that BPA decreased average litter size as well as compromise the rates of cleavage and blastocyst formation. Proteins differentially expressed in both capacitated/ejaculated spermatozoa play a critical role in energy metabolism, stress responses, and fertility, finally predispose to the development of several diseases. On the basis of these results, we suggest that BPA alter spermatozoa function and the proteomic profile, ultimately affecting their fertility potential. Therefore, it is of critical public health significance to reevaluate the levels of BPA exposure that are currently deemed to be acceptable.

This study was conducted to investigate the optimal artificial insemination (AI) time with diagnostic kit at ovulation time. We already applied the patent about the protein in the cow heat mucose in external reproductive tract. And we would examine the accuracy for detection of cow heat by the kit produced with the protein. Evaluation of optimal heat detection was tried two time at 12 hrs and 24 hrs after the heat. And then, AI service also performed two times with no relation to the results of heat diagnosis by heat detection kit and pregnancy rates were checked with rectal palpation on 60th day after AI. Heat diagnostic results by kit in natural heat after 12 hrs in Hanwoo cows were showed 31.3~75.0% on positive in first heat detection and 33.3~100.0% on positve in second heat detection. In the 1st positive results were significant different (p<0.05), but 2nd positive were not. The results of heat detection showed different result on regional influence and individual cow effects. The pregnancy rates of first trial of heat detection were showed 34.4~78.7% on positive and 21.3~68.8% on negative after the diagnosis by heat detection kit. And the pregnancy rates of next trial of heat detection were showed 33.3~85.7% on positive and 14.3~66.6% on negative after the heat diagnosis. Both positive results of first trial and next trial also were showed significant different (p<0.05), but negative results were not. In positive result, first trial of total pregnancy rates was higher than the next trial of pregnancy, but there showed opposite results on negative results. In conclusion, the optimal heat detection kit is suitable to ordinary Hanwoo cows and it suggested that we have to improve the kit’s accuracy by detecting the materials like proteins related optimal AI time.

Euiam and Paldang Reservoirs have often been facing water quality problems, such as eutrophication, algal blooms and off-flavors by treated wastewater effluent (TWE) in the North-Han and the Han River basins, but little is examined on the direct biological effect of TWE. This study tested algal growth potential (AGP) of four TWEs discharged into Euiam and Paldang Reservoirs to evaluate water fertility in September 2014 and March and September 2015. Test alga was used Anabaena circinalis isolated from Paldang Reservoir. Mean concentration of T-N and T-P in TWEs was 3,956.7 μg N L-1 and 50.8 μg P L-1, and the proportion of NO3-N and PO4-P to the total fraction was 72.1% and 40.8%, respectively. Both N and P were high in TWEs, but much higher N than P concentration indicates strong P-limitation. As a consequence, the maximum AGP was determined by PO4-P concentration (r=0.998, p<0.01). Mean AGP value was 15.4 mg dw L-1 among four effluents indicating its eutrophic condition. Due to the establishment of tertiary (advanced T-P) treatment method in the studied plants recently, P concentration was significantly decreased in TWEs compared to the years prior to 2012. However, P concentration seems to be still high enough to cause eutrophication and algal blooms. Therefore, wastewater treatment to P-free level needs to be considered if effluents are directly discharged into the drinking water resources.

Bisphenol‒A (BPA) is a known endocrine‒disrupting chemical used extensively to manufacture plastic bottles, canned food linings, thermal receipts, and other commonly used items. BPA is capable of inducing chromosomal alterations in germ cell line, thereby produced transgenerational effects on brain function, social recognition, reproductive diseases, sperm quality, gene expression, and obesity. Here, we aimed to investigate the transgenerational effects of BPA on murine male fertility. Six-week-old male mice (F0) were gavaged with corn oil (control), two different doses of BPA (5 mg, and 50 mg·kg bw-1·day-1),andethinylestradiol(EE,0.4mg·kg bw-1·day-1), dailyfor6weeks. Treated male mice were mated with wild‒type female and sibling pairs were bred up to the third generation (F3) in a similar manner with no further BPA exposure. Testes and spermatozoa were collected from 14-week-old males of all generation (F0 to F3) to evaluate testis weight, sperm function, and fertility. We found that high concentration of BPA significantly increased testicular weight in F2. Although the sperm viability, capacitation status, and intracellular ROS levels were not affected by BPA, however, sperm count, motility, hyperactivated motility, and intracellular ATP levels were significantly altered by BPA, dose dependently. In majority of the cases the effects were prominent in F2 followed by F1 and F0, whereas the effects were diminished in F3 generation. Simultaneously, high concentration of BPA significantly decreased cleavage and blastocyst formation rate in both F1 and F2. Similar inhibitory effects on cleavage and blastocyst were also noted in F1 by low dose of BPA. Depending on these findings we conclude that BPA decreases the fertility potential of exposed males and has an adverse impact on sperm function and fertility in subsequent generations.

Sperm adhesion molecule 1 (SPAM1) and Hyaluronidase 5 (HYAL5) has been well-known as assistants for sperm penetrate through the cumulus mass surrounding the ovulated eggs. However, so far their role in mammalian fertilization remain elusive, because mouse sperm lacking SPAM1 or HYAL5 were still capable of penetrating the cumulus mass despite a delayed dispersal of cumulus mass. Those data collectively demonstrated that SPAM1 or HYAL5 deficiency alone was not sufficient to cause male infertility in mice. In the present study, SPAM1 and HYAL5-simultaneous deficient male mice model was generated. Because of inhibition in sperm hyaluronidases, SPAM1 and HYAL5-deficient male mice produced significantly smaller numbers of offspring than hetero type and wild type mice. Hyaluronic acid degradation assay and cumulus oocyte complex dispersal assay as well as sperm motility assay using double knock out sperm and extracts had severe adverse effects on the dispersal of cumulus oocyte complex, which was the main reason for the impaired fertility of double knock out male sperm. Moreover, hyaluronic acid degradation assay using human sperm extracts revealed that sperm hyaluronidase has a principal role in sperm penetration through the cumulus oocyte complex. In conclusion, our results suggest that sperm hyaluronidase deficiency may be sufficient to cause male sterility in mammal because SPAM1 and HYAL5 deficiency sperm not impaired the sperm motility in hyaluronic acid but also cumulus oocyte complex penetration.

Jeju Black Cattle (JBC) is an indigenous species of Korea and their mass production and industrialization are required for this high quality indigenous species. For production of elite JBC zygotes, selection of high quality sperm is necessary for in vitro fertilizatioin. In this study, we compared the sperm fertility and developmental capacity of IVF embryos using various JBC sperm (Bull A, B and C). The frozen semen was thawed and confirmed sperm viability and motility. In addition, frozen-thawed sperm was used for a chlorotetracycline(CTC) staining assay and in vitro fertilization. Sperm were classified into three staining patterns. The F pattern is indicative of uncapacitated sperm, the B pattern is indicative of capacitating and capacitated sperm and the AR pattern is indicative of acrosome-reacting sperm or acrosome-reacted sperm, respectively. Several kinds of JBC sperm was inseminated in 44 ㎕ IVF drop contained 10 oocytes with sperm concentration of 1 × 106 cells/ml, and then 2 ㎕ heparin and 2 ㎕ PHE (20 μM penicillamine, 10 μM hypotaurine, 2 μM epinephrine) were added. The sperm viability and motility were higher in sperm 3 species (n=8). When we confirmed sperm capacitation, F pattern and B pattern rate were higher than AR pattern in sperm A group. After IVF, the rates of cleavage and blastocyst development were higher in sperm C group compared to other sperm group. However, the cell number of blastocyst was higher in sperm E group. These results demonstrate that the use of sperm C was effective in production of elite JBC IVF embryos. Additional experimental data are required for more accurate analysis.

Iron is required for cell viability but is toxic in excess. While the iron-mediated malfunction of testicular cells is well appreciated, the underlying mechanism(s) of this effect and its relationship with fertility are poorly understood. Ferritin is a ubiquitous intracellular protein that controls iron storage, ferroxidase activity, immune response, and stress response in cells. Ferritin light chain protein (FTL) is the light subunit of the Ferritin. Previously, we had identified the FTL in bovine spermatozoa following capacitation. In present study, to investigate the role of Ferritin in sperm function, mice spermatozoa were incubated with multiple doses (1, 10 and 100 μM) of sodium nitroprusside (SNP), an iron donor. SNP was increased Ferritin levels in a dose-dependent manner. The Ferritin was detected on the acrosome in spermatozoa by immunocytochemistry. Short-term exposure of spermatozoa to SNP increased tyrosine phosphorylation and the acrosome reaction (AR). Finally, SNP affected a significant decrease in the rate of fertilization as well as blastocyst formation during early embryonic development. On the basis of these results, we propose that the effects of Ferritin on the AR may reduce overall sperm function leads to poor fertility in males and compromised embryonic development.

본 연구는 현재 국립축산과학원 가축유전자원세터에서 보유 하고 있는 재래닭을 순수화된 품종인 것으로 판단하고, 일반 적으로 이용되고 있는 산란사료 및 사양관리 방법을 적용하여 특히, 동절기에 있어 재래닭의 정자의 보존 기간과 수정률 및 초기배자의 생존율을 각각 비교함으로써 재래닭의 생산성 향 상을 위한 기초자료를 제공하고, 나아가 표준능력을 고찰하고 자 수행하였다. 본 시험에 사용된 공시계는 39주령의 재래닭 6계통 적갈색(R, Red Brown Strain), 황갈색(Y, Yellow Brown Strain), 회갈색(G, Gray Brown Strain), 흑색(L, Black Strain), 백색(W, White Strain) 그리고 오계(O, Ogol Strain)를 대상 으로 하고 대조군으로는 3계통 즉, 외래도입종 중에서 대표적 인 다산종인 White Leghorn (F Strain), Rhode Island (C Strain) 그리고 육용종인 Cornish (H Strain)의 수정률 및 초기배자 생존율을 조사하였다. 단 한번의 인공수정 후, 3 주간 생산된 알의 수정률 확인을 한 결과, 재래닭의 경우, 6 계통간의 유의 적인 차이는 없지만 93.3 ~ 100.0비율로 인공 수정 후, 2일째 부터 수정률이 6일째 동안 최고 높음을 확인했다. 6일째까지 상대적으로 일정하게 높은 수정률을 유지하다가 7일부터 17일 째 까지 점진적으로 감소함을 확인했다. 17일 이후 생산된 알 의 경우 무정란임을 확인 할 수 있었다. 재래닭(R, Y, 그리고 O) 21일간 생산된 알의 배발생정지율의 결과, 인공수정 후, 약 4일째 생산된 알(3 ~ 6일)에서 외래도입종 3품종간의 유의적인 차이는 보이지 않았지만, 배발생정지율이 0%임을 확인하였다. 세 품종 모두 약 7일째 생산된 알부터 배발생정지율이 13.8 ~ 26.7%로 급격히 증가하고 12일부터 감소하는 것을 확 인했다. 재래닭 3 계통의 결과도 인공수정 후, 약 4 일째 생 산된 알에서 외래도입종 3 품종과 유사한 패턴을 나타내면서 배아 사망율이 6 일째까지 0%를 보였다. 금후, 체내 정자보존 기간이 수정률 및 초기배자 생존율에 미치는 영향을 좀더 엄 밀하게 조사하기 위해서는 정액 성상 및 활력 검사와 더불어 암탉의 주령에 따른 변화도 함께 보다 세부적이고 입체적인 방법의 체계적인 조사가 반드시 필요하다고 할 수 있겠다.

European countries are experiencing long–term downtrends in fertility and consequently ageing of their populations. Fertility rates are now below replacement levels (2.1 children per couple) in nearly all countries. Obviously, a decrease in natural population growth rate should be expected. These demographic trends are likely to impose very heavy penalties on the economies of European countries. In response to this plight, various governments have designed specific policy measures to raise the level of fertility so as to address the challenges that ageing populations present. From the debate, it appears that, the effectiveness of these policies somewhat have mixed outcomes. This signifies that, no single policy is likely to solve the problem. This calls for the effective combination of the various interventions. However, it is unlikely that, fertility rates will increase overnight. Somehow, governments could consider immigration of the right mix of personnel to keep the economy going until such a time that the natural population growth rate reaches the required level. However, immigration when not effectively managed could even create more problems than ageing and low fertility will do.