饲粮能量对后备母猪初情期启动的调控作用

母猪营养状况对生殖机能有着重要影响,初情期启动与饲粮能量状况、后备母猪的最低体脂储备是其进入初情期的前提条件.通过科学的营养调控措施,有效满足母猪对饲粮能量的需求,是确保母猪发情正常启动及其后的繁殖周期正常的基本条件.本文主要对母猪发情机制进行阐述,立足调控饲粮中的能量水平和来源2个方面,综述了饲粮能量状况对母猪发情的...     

Leptin: a metabolic signal affecting central regulation of reproduction in the pig

The discovery of the obesity gene and its product, leptin, it is now possible to examine the relationship between body fat and the neuroendocrine axis. A minimum percentage of body fat may be linked to onset of puberty and weaning-to-estrus interval in the pig. Adipose tissue is no longer considered as only a depot to store excess energy in the form of fat. Recent findings demonstrate that numerous genes, i.e., relaxin, interleukins and other cytokines and biologically active substances such as leptin, insulin-like growth factor-I (IGF-I), IGF-II and Agouti protein are produced by porcine adipose tissue, which could have a profound effect on appetite and the reproductive axis. Hypothalamic neurons are transsynaptically connected to porcine adipose tissue and may regulate adipose tissue function. In the pig nutritional signals such as leptin are detected by the central nervous system (CNS) and translated by the neuroendocrine system into signals, which regulate appetite, hypothalamic gonadotropin-releasing hormone (GnRH) release and subsequent luteinizing hormone (LH) secretion. Furthermore, leptin directly affects LH secretion from the pituitary gland independent of CNS input. Changes in body weight or nutritional status are characterized by altered adipocyte function a reduction in adipose tissue leptin expression, serum leptin concentrations and a concurrent decrease in LH secretion. During pubertal development serum leptin levels, hypothalamic leptin receptor mRNA and estrogen-induced leptin gene expression in fat increased with age and adiposity in the pig and this occurred at the time of expected puberty. In the lactating sow serum and milk leptin concentrations were positively correlated with backfat thickness and level of dietary energy fed during gestation as well as feed consumption. Although, these results identify leptin as a putative signal that links metabolic status and neuroendocrine control of reproduction, other adipocyte protein products may play an important role in regulating the reproductive axis in the pig.     

Attainment of Puberty in the European Mouflon (Ovis gmelini musimon) and the Domestic Manchega Ewe (Ovis aries)

The onset of puberty was assessed from plasma progesterone profiles for Mouflon (n = 8) and Manchega (n = 7) female lambs born in April. Four Mouflons exhibited their first ovulation at a mean date of 27 November ± 1.4 days, the mean age being 248.5 ± 3.9 days and the mean body weight 23.8 ± 0.6 kg. The remaining four Mouflons, which had a slower growth rate, attained puberty during the autumn of the following year. Five of seven Manchega lambs attained puberty in their first year at a mean date of 5 Oct ± 3.3, the mean age being 185.6 ± 2.6 days and the mean body weight 41.8 ± 2.0 kg. The mean live‐weight at the onset of puberty was 65.1 and 82% (p < 0.05) of adult body weights for Manchega and Mouflons, respectively. Overall, the results indicate that there is a threshold of body‐weight necessary for the attainment of puberty in the first breeding season for spring‐born lambs, which is very different between both Mouflon and Manchega. When body weight was below 23.8 ±0.6 and 41.8 ± 2.0 kg for Mouflon and Manchega lambs, respectively, first ovulation did not occur until the beginning of the next breeding season. The onset of puberty during the second year of life occurred within the specific reproductive seasons for Mouflon (October–April) and Manchega (July–March) ewes, despite minimal further growth.     

Advanced Onset of Puberty in Gilts of Thrifty Genotype (Iberian Pig)

The Iberian pig is an autochthonous breed of the Mediterranean area, reared extensively in the central and southern areas of Spain and Portugal and that is known worldwide for the production of Iberian ham. The characteristics of the Iberian ham are related to its abundance of intramuscular fat, owing to the high capacity of the pig to accumulate fat under its skin and between the muscular fibres. This ability to store excess fat enables survival during periods of scarcity and it has been found in other antique animal breeds and even in humans, being named as the thrifty genotype. The reproductive management of the Iberian pig, in spite of a lack of accurate information unlike in other swine breeds, is based on the assumption of lower reproductive precocity and efficiency than the modern commercial breeds. The current study characterized and compared the onset of puberty in gilts of Iberian breed and meat commercial crosses (Large White × Landrace) reared in the same conditions by assessing weekly plasma progesterone profiles. At the end of the experimental period, when the gilts became 180 days old, the percentage of Iberian females that had reached puberty was 72.2%, with a mean age and weight of 160.5 ± 2.6 days and 92.9 ± 4.7 kg, respectively. The percentage of Large White × Landrace cross‐breed females reaching puberty at 180 days was only 15% (p < 0.05). The mean age and weight were 165.0 ± 4.1 days and 107.8 ± 2.2 kg (p < 0.05), respectively. Thus, converse to the traditional assumption, onset of puberty was advanced in Iberian gilts. These results are important for the reproductive management of the Iberian pig but, at the same time, may set the basis for future studies on the metabolism–reproduction link and, specifically, on the possible relationship between earlier accumulation of fat and attainment of puberty.     

Effects of nutrition and season on the onset of puberty in the beef heifer.

Age at puberty is a major determinant of lifetime reproductive efficiency of beef cows. Research conducted during the past 20 yr has documented the major endocrine events leading to first ovulation in heifers. The critical event seems to be a prepubertal increase in pulsatile LH secretion. Environment influences timing of puberty onset in beef heifers. Nutrition and season are two of the better-defined variables that have been studied. Age at puberty is related inversely to plane of nutrition. The effect of nutrition on sexual maturation involves effects on timing of the prepubertal increase in LH secretion and seems to involve the LH pulse generating system located in the hypothalamus. The precise mechanism by which nutrition influences pulsatile LH secretion has not been elucidated, but signals reflecting metabolic status seem to be involved. Seasonal conditions of the early (birth to 6 mo of age) and late (6 to 12 mo of age) postnatal periods also influence timing of puberty onset in the heifer. Autumn-born heifers attain puberty at younger ages than do spring-born heifers, and exposure to spring-summer temperatures and photoperiods during the second 6 mo of life reduces age at puberty regardless of season of birth. Photoperiod may be the major seasonal cue that influences puberty onset in cattle. Limited evidence suggests that melatonin, a pineal hormone, is involved with transducing photic stimuli into neuroendocrine signals that influence LH secretion. If the physiological mechanisms mediating the effects of nutrition and season on timing of puberty onset are determined, then management strategies for reducing age at puberty can be enhanced.     

The timing of the onset of puberty, extension of the breeding season, and length of postpartum anestrus in the female mouflon (Ovis gmelini musimon).

The timing of the onset of puberty, duration of seasonal ovulatory activity, and length of postpartum anestrus were studied by means of blood plasma progesterone concentrations in a flock of European female mouflons (Ovis gmelini musimon) maintained in captivity under natural photoperiod (40 degrees 25'N). Concentrations of progesterone in the peripheral blood were determined by radioimmunoassay in samples collected from the jugular vein twice a week. First ovulations in the breeding season were highly synchronized and occurred in mid-October. In contrast, the cessation of ovulatory cycles showed significant variation among females and extended from February to May, depending on age, with 2-yr-old animals exhibiting the longest anovulatory period (P < 0.01). When lambing occurred within the breeding season (February-April), 12 out of 26 animals had their first ovulation 25 +/- 1.8 days after parturition. The 14 late-lambing females had the first postpartum ovulation delayed until the next breeding season. March/April-born mouflon lambs that reached a minimum threshold body weight (23.8 +/- 0.6 kg) in their first breeding season reached puberty at 8 mo of age. In those with slower growth rates, however, the prepubertal period was extended throughout the first breeding and nonbreeding seasons, reaching puberty during the breeding season of the following year at 19 mo of age and 27 +/- 0.3 kg body weight. Further, attainment of puberty in ewe lambs born in June/July was also delayed until the breeding season of the following year, when animals had reached a threshold body weight at 17 mo of age.     

Coordination of social signals and ovarian function during sexual development

Social cues, often in the form of priming pheromones, can retard or enhance the rate of sexual development in a variety of mammals. The complex interactions between the social environment and reproduction have been explored most thoroughly in the house mouse. A urinary pheromone produced by females in a group inhibits sexual development, and a urinary pheromone from adult males accelerates onset of puberty in juvenile females. These priming pheromones apparently are detected by the vomeronasal organ and induce the changes in ovarian function via changes in the hypothalamic-pituitary system. Accelerated onset of puberty is not accompanied by deficits in reproductive performance. Puberty acceleration can have important management implications for domestic farm animals. It already is proving useful for manipulation in rearing swine and in synchronizing seasonal reproductive recrudescence in sheep. In cattle, the results are less clear that signals from the bull can hasten onset of puberty in heifers. The effect may be operable only under certain nutritional or other interacting conditions. Presumably, the postpartum anestrus period in the cow can be shortened by stimulation from the bull, although pheromones have not been implicated in this effect.     

Effects of dietary energy on control of luteinizing hormone secretion in cattle and sheep.

Prolonged restriction of dietary energy delays onset of puberty, disrupts cyclicity in sexually mature animals, and lengthens the postpartum anestrous period in domestic ruminants. One important mechanism by which energy restriction impairs reproductive activity seems to be suppression of the increase in LH pulse frequency that is necessary for growth of ovarian follicles to the preovulatory stage. Under-nutrition apparently inhibits pulsatile secretion of LH by reducing LHRH secretion by the hypothalamus. The ability of an animal to sustain a high-frequency mode of pulsatile LH release is related to its metabolic status. Mechanisms linking metabolic status to LHRH secretion have not been fully characterized. Changes in body fat have been associated with changes in reproductive activity, but it is unlikely that body fat per se regulates LHRH secretion. It is possible that pulsatile LHRH release is regulated by specific metabolites and(or) metabolic hormones that reflect nutritional status. Alternatively, availability of oxidizable metabolic fuels, such as glucose and nonesterified fatty acids, may influence activity of neurons that control LHRH release. Our understanding of how the central nervous system transduces information about nutritional status into neuroendocrine signals that control reproduction in cattle and sheep is limited by a lack of information concerning the nature of neurons controlling LHRH release in these species.     

Neuroendocrine,Metabolic and Genomic Cues Signalling the Onset of Puberty in Females

Puberty is the result of a dynamic interaction between genetic factors and environmental cues, all of which lead to the attainment of reproductive capacity. Thus, significant changes in hormone secretion occur from the pre‐pubertal to the pubertal stage. The objective of this review is to provide an update of some endocrine, physiological, metabolic and genetic concepts involved in the establishment of the hypothalamic‐hypophyseal‐gonadal axis function promoting the onset of the reproductive function during puberty. To achieve this purpose, basic aspects of the function of the hypothalamic‐hypophyseal‐gonadal axis, the control of the axis by neurotransmitters and the interaction between reproductive function and metabolic status will be considered. Finally, the role of the novel kisspeptin system and the GPR54 receptor as modulators of puberty will be considered, in addition to the hierarchical expression of the main genes acting as regulators of the onset of puberty.     

初情期启动过程中小尾寒羊下丘脑GnRH基因甲基化状态及表达量关系研究

初情期启动的早晚关系到雌性动物的繁殖性能,GnRH是动物初情期启动过程中的关键基因,其启动子区甲基化状态与GnRH mRNA表达量之间的关系尚不清楚。本研究选择初情期前、临近初情期和初情期雌性小尾寒羊的下丘脑作为样本,利用亚硫酸氢盐测序(BSP)技术和实时荧光定量PCR(qRT-PCR)技术检测了初情期不同阶段小尾寒羊GnRH启动子区的甲基化状态和GnRH mRNA的表达量,并分析二者之间的关系。结果表明:小尾寒羊到达初情期时,GnRH基因启动子区甲基化水平显著降低(P0.05),尤其是在启动子区-570位点降低最明显,而随着初情期的启动GnRH mRNA表达量呈上升趋势。结果提示,初情期启动过程中,GnRH mRNA表达量升高可能与下丘脑GnRH基因启动子区特定位点甲基化水平降低存在一定的关系。     

Relationship between nutrition and reproduction in beef cattle

The primary nutrient consideration for optimum reproductive performance in beef cattle is energy. Low energy intake delays the onset of puberty in heifers and bulls. Heifers should reach approximately 66 per cent of mature body weight by 14 to 15 months of age and be bred 30 days prior to breeding the main cow herd. Body conditioning scores (BCS) (1 = emaciated, 9 = obese) should be used to evaluate pregnant cows entering their third trimester. Cows should calve with body conditioning score 5 to 7. Forage quality and environmental factors influence maximum dry matter intake and nutrient requirements and must be considered in the clinical setting. Crude protein dietary content should be 11 to 12 per cent for lactating beef cattle. Mineral (calcium, phosphorus, magnesium, potassium, sulfur, sodium, chloride) nutrition is not a major cause of decreased reproductive performance in beef cattle. Trace mineral deficiencies (particularly selenium, copper, and zinc) can cause decreased reproductive performance. Diagnosis of these trace mineral deficiencies can be confirmed by elemental analysis of blood or tissues.     

Normal Values for the Scrotal Circumference in Rams of Gotlandic Breed

Selection of fertile sires is crucial for profitable lamb production. Males with larger testes tend to sire daughters that reach puberty at an earlier age and ovulate more ova during each oestrus period. Measurement of the scrotal circumference (SC) is thus an essential part of the breeding soundness evaluation. Testicular size varies with breed, age and time of the year. No SC values or recommendations for minimal values have been established in any of the Scandinavian domestic sheep breeds. Data were recorded of the SC, age and weight in 245 ram lambs and 27 mature rams of the Gotlandic breed, which is the breed that constitutes about 50% of the Swedish sheep population. For the ram lambs, the overall mean SC was 28.9 (+/-1.9) cm at an average age of 170 (+/-9) days and mean weight of 53.5 (+/-7.0) kg, and the mean SC varied between 27.1 and 29.6 cm depending on age and weight. For mature rams (17-54 month old), the mean SC was 32.4(+/-2) cm. To provide a practical tool for exclusion of rams with sub-optimal reproductive capacity (abnormal testes or those with small testes because of delayed puberty) a threshold value was established based on the average SC minus 2 SD. The calculated minimal SC is 26 cm for ram lambs >5.5 months of age with a body weight of >50 kg. For mature rams, minimum SC is 28 cm regardless of weight and age.     

日粮能量水平对五指山猪生长性能、初情期启动及血清激素含量的影响

试验旨在研究不同日粮能量水平对五指山猪生长性能、初情期启动及血清激素含量的影响。选择20头日龄(30±2)d、体重(2.5±0.6)kg、健康的断奶五指山母猪,随机分为2个处理,分别为NRC组(标准组:饲喂基础日粮,按正常的后备母猪饲喂标准量投放饲料)和0.7 NRC组(限饲组:按NRC组70%的投饲量投喂),每个处理10个重复,每个重复1头猪,试验期10周。结果表明,断奶后6~10周时NRC组体重显著高于0.7 NRC组(P<0.05);NRC组平均日增重显著高于0.7 NRC组(P<0.05);日粮能量水平对五指山猪初情期日龄有显著影响(P<0.05),限饲(0.7 NRC)可延缓五指山母猪发情期启动;0.7 NRC组母猪初情期时背膘厚度显著低于NRC组(P<0.05),初情期时0.7 NRC组母猪背膘厚度降低39.7%左右;初情期时,NRC组血清中卵泡刺激素(FSH)、黄体生成素(LH)、雌二酮(E₂)和瘦素(Leptin)含量均显著高于0.7 NRC组(P<0.05)。由此可知,提高日粮能量水平有利于母猪初情期的启动和发情表现。     

Effect of sex ratio of the birth litter on subsequent reproductive performance of gilts

Records on age at puberty from 1,555 gilts and total number of pigs born in litters of 1,187 gilts from the Nebraska gene pool population were used to evaluate the effects of uterine environment on subsequent reproductive performance. Independent variables were line, year, line x year, proportion of males in the birth litter (sex ratio), number born in the birth litter (fraternity size) and sex ratio x fraternity size. Sex ratio, fraternity size and their interaction influenced age at puberty (P less than .01) but not number born (P greater than .2). Partial regression coefficients indicated that age at puberty tended to decrease as sex ratio increased, particularly in small litters. Although the regression coefficients were relatively large, sex ratio, fraternity size and their interaction accounted for only 1.3% of the variation in age at puberty within line x year subclass. These results offer little encouragement for the use of sex ratio as a phenotypic selection criterion for improvement of reproductive performance in gilts. Results suggest that female swine are similar to rodents in response to uterine environmental effects.     

Effect of increasing pre-pubertal concentrate levels on reproductive and lactation performance of Nili-Ravi Buffalo heifers

The objective of this study was to determine the effect of increasing total nutrient supply by increasing level of concentrate supplementation in forage-based diet of growing Nili-Ravi buffalo replacement heifers on pre-pubertal growth rate and its impact on age at puberty and post-pubertal productive and reproductive performance. Twenty-eight Nili-Ravi buffalo heifers of 7 ± 1 month age were divided into 3 groups. The treatments were 3 levels of concentrate (crude protein (CP) = 17.9%, metabolisable energy (ME) = 2.66 Mcal/kg), i.e. 0.5, 1, and 1.5% of the body weight referred as low, medium, and high treatments, respectively. Irrespective of pre-pubertal treatment, all the heifers received similar feed after puberty up to completion of their first lactation. The results of the study showed a similar response across the treatments in age, weight, and condition at puberty, weight at calving, lactation length, and yield. The medium and high treatments resulted in poor reproductive performance because of higher services per conception and less number of heifers confirmed conceived compared with low treatment. The low treatment resulted in less mortality compared with medium and high treatments. The feeding cost per animal at puberty, conception, and calving was lowest for treatment low as compared with medium and high. In conclusion, the results of the study showed that Nili-Ravi buffalo heifers achieved puberty at 23 months with feeding of concentrate (CP = 17.9%, ME = 2.66 Mcal/kg) during pre-pubertal stage at the rate of 0.5% of the body weight with better reproductive performance.

     

Body growth and plasma concentrations of metabolites and metabolic hormones during the pubertal period in female Shiba goats

It has been shown in various species that the onset of puberty is closely associated with body growth and nutritional state rather than age. The present study was conducted to determine the timing of puberty and to clarify body growth and metabolic changes around the pubertal period in female Shiba goats. Blood samples were collected between 10 to 38 weeks of age from 12 female goats, and plasma concentrations of progesterone, metabolites (glucose, nonesterified fatty acid, ketone body and acetic acid) and metabolic hormones (insulin and insulin-like growth factor-I (IGF-I)) were analyzed. Physical parameters (body weight, withers height and body length) were also measured at the blood sampling. The week when plasma progesterone concentrations first exceeded 1.0 ng/ml was designated as the onset of puberty. The results showed that the average age of the onset of puberty was 27.0 +/- 0.9 (mean +/- SEM) weeks in female Shiba goats. When the goats reached puberty, the average values of body weight and goat body mass index ((body weight (kg)/withers height (cm)/body length (cm)) x 10(3)) were 12.2 +/- 0.5 kg and 5.7 +/- 0.2, respectively. No particular change associated with puberty was apparent for plasma concentrations of the metabolites examined. Plasma insulin concentrations were maintained at lower levels until the onset of puberty, and then they began to gradually increase. Plasma IGF-I concentrations began to gradually increase 1 to 4 weeks before the onset of puberty and this increase continued throughout the peripubertal period. These results imply that IGF-I acts as a peripheral nutritional signal to trigger the onset of puberty in Shiba goats.     

Leptin expression in ruminants: nutritional and physiological regulations in relation with energy metabolism

Leptin, mainly produced in adipose tissue (AT), is a protein involved in the central and/or peripheral regulation of body homeostasis, energy intake, storage and expenditure, fertility and immune functions. Its role is well documented in rodent and human species, but less in ruminants. This review is focused on some intrinsic and extrinsic factors which regulate adipose tissue leptin gene expression and leptinemia in cattle, sheep, goat and camel: age, physiological status (particularly pregnancy and lactation) in interaction with long-term (adiposity) and short-term effects of feeding level, energy intake and balance, diet composition, specific nutrients and hormones (insulin, glucose and fatty acids), and seasonal non-dietary factors such as photoperiod. Body fatness strongly regulates leptin and its responses to other factors. For example, leptinemia is higher after underfeeding or during lactation in fat than in lean animals. Physiological status per se also modulates leptin expression, with lactation down-regulating leptinemia, even when energy balance (EB) is positive. These results suggest that leptin could be a link between nutritional history and physiological regulations, which integrates the animal's requirements (e.g., for a pregnancy-lactation cycle), predictable food availability (e.g., due to seasonal variations) and potential for survival (e.g., body fatness level). Reaching permissive leptin thresholds should be necessary for pubertal or postpartum reproductive activity. In addition to the understanding of leptin yield regulation, these data are helpful to understand the physiological significance of changes in leptin secretion and leptin effects, and how husbandry strategies could integrate the adaptative capacities of ruminant species to their environment.     

Effects of exogenous somatotropin (ST) on gonadal function in ruminants and swine.

During the past 15 years, many investigators have examined the effects of somatotropin (ST) on growth and lactation in farm animals. Throughout this period, concerns about potential effects of ST on reproduction have been expressed. The objective of the present review will be to focus on the effects of exogenous ST on the hypothalamic-pituitary-gonadal axis. Plasma progesterone is increased when recombinant bovine (rb)ST is given to cattle, early in lactation, and also to sheep. Also, the release of progesterone from cultured swine and human luteal cells is increased by ST. Treatment with rbSt increases the numbers of small follicles, but does not increase the ovulatory rate of ruminants. Doses of ST similar to those used to increase milk production do not affect the secretion of testosterone or spermatogenesis in rams or bulls. Stimulatory and inhibitory effects of exogenous ST on reproductive function of gilts have been reported. Daily injections of porcine ST (pST) delayed puberty and expression of estrus after puberty. Daily administration of pST increased the number of small follicles, but not of medium follicles, whereas administration of pST by using a sustained release implant increased the number of medium follicles. Size and weight of reproductive organs and concentration of testosterone are not affected when pST is administered for at least 42 d. However, pST enhanced testicular development and spermatogenesis when given to neonatal boars. In summary, administration of exogenous ST at doses known to alter milk production and carcass composition may have subtle positive and/or negative effects on the reproductive systems of cattle and swine; however, these effects appear to be transient.     

Effects of Feeding Maize Stover and Cottonseed Cake on Onset of Puberty in Bunaji (Bos indicus) Heifers

A study was conducted to determine the influence of maize stover and cottonseed cake supplementation on age and live weight at onset of puberty in Bunaji heifers. A total of 49 pre-pubertal Bunaji heifers approximately 12 months of age were allotted randomly to one of two treatments of feed supplementation: (i) supplementation with maize stover and (ii) supplementation with cottonseed cake. The heifers were monitored for a period of 18 months for first observable oestrus or onset of puberty. The maize stover group were given maize stover (crop residue) supplementation ad libitum during the dry season; in the cottonseed cake group each heifer received 500 g of cottonseed cake per day during the dry season. The heifers supplemented with cottonseed cake attained puberty at an earlier age (23.9+/-1.2 months) than the heifers supplemented with maize stover (28.2+/-1.3 months; p<0.05). Similarly, heifers on the cottonseed cake supplementation attained puberty at a live weight of 270.5+/-3.5 kg; while the heifers on maize stover attained puberty at 237.6+/-5.8 kg (p <0.05). The cottonseed cake-supplemented heifers had higher daily gains than the maize stover-supplemented heifers. It is concluded that provision of cottonseed cake as a supplement for heifers hastened the onset of puberty when compared to the maize stover supplemented heifers. Puberty can be achieved at an early age with improved nutrition and this can in turn reduce the generation interval and thus increase the rate of genetic gain of indigenous animals. Provision of protein supplements in cattle is recommended, especially in the tropics where marked seasonality of rainfall results in extremely poor pastures and herbage and low available protein.