Puberty In Ewe Lambs Research Articles

Reproductive characterization of hair ewe in the American tropics: a review part 1

Objective: To carry out a reproductive characterization of the breeds of hair ewe in the tropical region of the Americas. Design/Methodology/Approach: A search of scientific information about the reproductive variables of breeds of hair ewe was carried out and the results were analyzed in the Web of Science, Redalyc, Dialnet, PubMed, SciELO, and Latindex databases. Results: We described and discussed the highly-variable onset of puberty in ewe lambs. Similar results were found in adult ewes regarding the duration and occurrence of the estrous, estrous cycle length, seasonal anestrous, ovulation rate, fertility, gestation, and prolificacy. Study Limitations/Implications: Information about the reproductive variables of breeds of hair ewe is poorly known or non-existent. Findings/Conclusions: The onset of puberty in 15-43 kg ewe lambs ranges from 175 to 335 d of age. The estrous cycle of hair ewe in Mexico lasts 17 d in autumn-winter and 21 d in spring-summer. In Brazil, this cycle lasts 17 d in spring-summer and 18 d in autumn-winter. In the United States of America and Venezuela, the estrous cycle length was similar in both periods of the year. The occurrence of the estrous reached 97.1 % in autumn-winter and 76.5 % in spring-summer. The duration of the estrous ranges from 16 to 52 hours. Seasonal anestrous occurs from May to July. The ovulation rate ranges from 1 to 3 oocytes. The percentage of fertility fluctuates between 80 and 100 % in temperate months and reaches 37 % in warm ones. Gestation lasts from 144 to 152 d. Prolificacy ranges from 1.0 to 2.2 offspring per ewe. The lambing interval ranges from 244 to 294 d.

Anti-mullerian hormone as a predictive endocrine marker for selection of White Dorper ewe lambs at prepubertal age

Identifying early puberty in ewe lambs is an important strategy to improve reproductive performance and economic results of sheep herd. The anti-Müllerian hormone (AMH) has become the main endocrine marker for the ovarian reserve of growing follicles in several mammal species. This study aimed to evaluate plasma anti-Müllerian hormone (AMH) levels in 32 prepubertal ewe lambs and their relationship with fertility in the breeding season at 12 months of age. AMH levels and presence of ovulation (corpus luteum - CL) were evaluated at 120, 150, and 180 days of age in 32 prepubertal White Dorper ewe lambs 6 days after the exogenous administration of a single dose of eCG (600 IU). The results showed that plasma AMH levels were similar in prepubertal ewe lambs regardless of age. Ovulation rates was influenced by age (P = 0.04), but not by the plasma concentration of AMH and live weight (P > 0.10). Thirteen ewe lambs from the 32 were intended to breeding, based on recommended minimum weight and body condition score (BCS) for first breeding, and exposed to the ram at 12 months of age to study the relationship between prepubertal AMH concentration and occurrence of pregnancy. Pregnant ewes were the ones with higher concentrations of AMH measured at 150 and 180 days of age (P = 0.064, 150 days; P = 0.014, 180 days) compared to the non-pregnant ones. On the other hand, pregnant and non-pregnant ewes showed no difference (P = 0.84) for AMH concentration determined at 120 days of age. Therefore, we conclude that plasma concentration of AMH at prepubertal age is reliable endocrine marker for the early identification of ewe lambs' reproductive activity and can be used as a tool for selecting fertile females.

Relationship between the leptin, progesterone, body weight, and onset of puberty in ewe lambs

The current study aimed to determine the relationship between serum level of leptin, progesterone hormones, bodyweight with the onset of puberty in the ewe lambs. Eight healthy weaned local breeds of ewe lambs at the age of 90 days were introduced in the study. Body weights were recorded, blood samples serum was collected and stored at -20°C until hormonal assays. Ovaries and ovarian follicles were checked by ultrasound to measure follicular diameter until estrus was detected every two weeks. The result showed that the earliest estrus behavior was noticed at age 202. Significantly increased body weight was recorded during the trial times at P

295 Effects of Prenatal Testosterone Excess on Puberty Attainment of First-Generation ewe Lambs

Abstract Prenatal testosterone excess causes reproductive perturbations in sheep that recapitulate those seen in women with polycystic ovary syndrome (PCOS). Obesity has a significant role in the development and severity of the PCOS phenotype. Our objective was to investigate the effects of testosterone excess from gestational days (GD) 60-90 (unlike the GD 30-90 model, these animals are not virilized) and postnatal body weight (BW) gain on puberty in first-generation ewe lambs. Pregnant Suffolk ewes received testosterone propionate (T; 100 mg) or corn oil (C) i.m. twice weekly from GD 60-90 (term=147d). Ewe lambs were weaned ~3 mo of age. Control and T lambs were assigned to gain either 0.3 kg/d (C and T-maintenance) or 0.4 kg/d (T-overfed). Maintenance diet was designed to promote optimal growth without excess fat deposition. Overfed ration was designed to achieve a BW ~30% above that of maintenance. Progesterone concentrations were measured via radioimmunoassay in blood samples collected twice weekly from ewe lambs (n=15/group) during the first breeding season. Puberty was defined as when progesterone concentrations were < 0.5 ng/mL for four consecutive samples followed by three consecutive samples ≥0.5 ng/mL. Six animals (C, n=1; T-maintenance, n=3; T-overfed, n=2) did not attain puberty during the study and puberty was assigned as last day of sampling. Average daily gain was not different among treatments (C, 0.23±0.02kg; T-maintenance, 0.25±0.01kg; T-overfed, 0.27±0.02kg). Age at puberty did not differ between groups (C, 274.6±9.9d; T-maintenance, 270.0±11.3d; T-overfed, 266.0±10.2d). Similarly, BW at puberty did not differ across treatments (C, 50.44±2.2kg; T-maintenance, 52.5±2.4kg; T-overfed, 57.3±2.5kg). In conclusion, unlike GD 30-90 exposure which advanced puberty, GD 60-90 exposure did not affect age and BW at puberty in ewe lambs. Collectively, these studies suggest that GD 30-60 is a critical developmental window in which prenatal testosterone excess advances puberty in female sheep. Research support: NIH-NICHD (R01HD099096).

Feeding Tall Fescue Seed during Mid and Late Gestation Influences Subsequent Postnatal Growth, Puberty, and Carcass Quality of Offspring.

Simple SummaryLittle is known about the exposure to ergot alkaloids, a class of mycotoxins, during fetal development on subsequent post-weaning growth, puberty, and carcass quality of the offspring. This study evaluated post-weaning growth, puberty attainment, and carcass quality in lambs that were exposed to endophyte-infected or endophyte-free tall fescue seed during different stages of gestation. Puberty was delayed in ewe lambs that were exposed to ergot alkaloids during late gestation. Ergot alkaloid exposure had minor effects on growth and carcass traits in wether lambs fed high concentrates but alterations in fat deposition and tenderness were observed. These results indicate that exposure to ergot alkaloids during gestation does alter subsequent post-weaning puberty attainment and body composition of the offspring.Weaned lambs (n = 82), born to ewes fed endophyte-free (E−) or endophyte-infected (E+; 1.77 mg hd−1 d−1 ergovaline + ergovalinine) tall fescue seed from d 35 to 85 of gestation (MID) and/or d 86 of gestation to parturition (LATE), were used to examine how ergot alkaloid exposure during fetal development altered subsequent puberty attainment or carcass quality. Lambs were weaned at 75 d of age and separated by sex to assess puberty in ewe lambs (n = 39) and to evaluate growth, carcass and meat quality in wethers (n = 43). Data were analyzed with maternal fescue treatment, stage of gestation, and two-way interaction in the model. Age at puberty tended (P = 0.06) to be longer for ewe lambs born to dams fed E+ fescue during LATE gestation versus those fed E−. Post-weaning average daily gain tended to be higher (P = 0.07) for wether lambs born to dams fed E+ fescue seed during MID gestation compared to E−. Exposure to ergot alkaloids during fetal growth altered (P < 0.10) longissimus muscle weight and color, lipid deposition, fatty acid composition, and shear force values of semimembranosus muscle in wether lambs. These results indicate that exposure to ergot alkaloids in utero does alter subsequent post-weaning puberty attainment and body composition in offspring.

Implications of carbohydrate sources and rate of body weight gain on puberty in ewe lambs in tropical climate conditions.

The objectives were to evaluate the effects of two non-fibrous carbohydrate sources and the rate of body weight gain on puberty status in ewe lambs. Sixty ewe lambs (½ Dorper × ½ Santa Ines) with an initial body weight of 25.1 ± 4.1kg and 102.8 ± 1.5days old were distributed in a randomized complete block design with 10 blocks and 3 treatments. The trial lasted 119days, in which performance was evaluated on days 28, 56, 84, and 119, and puberty status was every week evaluated by progesterone concentration. The treatments were characterized by the inclusion of different carbohydrate sources in the diets in order for ewe lambs to reach different rates of body weight gain: CORN, total diet containing 46% of corn (% DM); PCP, total diet containing 46% of pelleted citrus pulp (% DM); and HAY, total diet containing 80% of coastcross hay (% DM). The CORN- and PCP-based diets were formulated for an average daily gain (ADG) of 0.200kg/day and a HAY-based diet for an ADG of 0.100kg/day. There was an interaction between treatments and experimental periods for dry matter intake (DMI) (P < 0.01), in which lambs in the CORN treatment presented DMI similar to PCP in the first and second periods, but lambs from the PCP treatment presented lower DMI than the CORN treatment in subsequent periods. In all periods, the body weight, average daily gain, and feed efficiency of CORN lambs were similar to PCP lambs, but higher than HAY lambs. The age at puberty was not affected by treatments; however, lambs fed with non-fibrous carbohydrate sources reached puberty heavier (P < 0.0001) than lambs from the HAY treatment. Despite the high increase in body weight for lambs fed with non-fibrous carbohydrate sources, it did not affect the age of puberty.

Endocrine basis for puberty in heifers and ewes

Maturation processes that culminate in puberty and sexual maturity are initiated before birth, continue through prepuberty (> 50 days before puberty) and peripuberty (50 days before puberty) and are completed early after puberty. The hypothalamus is the primary site of change during transition to sexual maturity. Maturation of the hypothalamus results from decreased negative feedback of oestradiol that leads to increased frequency of release of LH pulses. Increased tonic release of LH pulses during sexual maturation is the primary endocrine factor that regulates the onset of puberty in ewe lambs and heifers. Increased frequency of release of LH pulses enhances development of ovarian follicles which produce enough oestradiol to induce behavioural oestrus and a preovulatory surge of gonadotrophins. In later stages of peripuberty, ovulation or luteinization of follicles results in transient increases in progesterone for shorter periods than is typical for luteal phases of the oestrous cycle of mature ewes and cows. Transient increases in progesterone are not generally preceded by behavioural oestrus. After the demise of the transient luteal structures, puberty is attained with occurrence of the first behavioural oestrus that is accompanied by ovulation and development of a corpus luteum with a typical lifespan. At puberty, all components of the hypothalamic-pituitary-ovarian axis are in place for oestrous cycles to be expressed. Factors that can influence the pubertal rise in release of LH pulses are genotype, gender, season of year when pubertal age is attained, growth or nutritional intake, social cues or treatment with exogenous progestins. Sexual maturation continues after puberty with an enhanced probability of pregnancy occurring from actions of ovarian steroids at the uterus.

Detection of chromosomal segments underlying scrotal circumference in ram lambs and age at onset of puberty in ewe lambs

Scrotal circumference (SC) is highly correlated with total sperm production and quality of the produced semen. In ewe lambs, puberty is an important reproductive trait and extreme delay in reaching puberty will have a negative effect on breeding efficiency. To identify genomic regions (QTL) underlying variation in SC and age at onset of puberty in ewe lambs (AP), a whole genome scan was performed with 169 microsatellites covering the ovine autosomes. Progeny (360 animals) from six half-sib families in a population of Kermani sheep, an indigenous fat tailed sheep breed in south-east of Iran, were recorded for SC and AP. Linkage analysis using the interval mapping approach indicated a total of 21 QTL for the studied traits on nine chromosomes (OAR1, 2, 3, 5, 6, 9, 11, 18 and 24), including a 5% genome wide significant QTL for SC on OAR5. There was evidence for the overlap of QTL affecting SC and AP on OAR5 and OAR9. The size of the QTL effect ranged from 0.8 to 1.6 in units of the phenotypic standard deviation. Although QTL for testis size in ram lambs have been mapped, this is the first report of QTL for age at onset of puberty in ewe lambs. Pursuing the underlying causes of these QTL may shed light on the molecular aspects of male and female reproductive development in sheep.

Hormonal control of reproduction in small ruminants

Reproduction of small ruminants can be controlled by several methods developed in recent decades. Some of these involve administration of hormones that modify the physiological chain of events involved in the sexual cycle. Methods which utilise progesterone or its analogues are based on their effects in the luteal phase of the cycle, simulating the action of natural progesterone produced by the corpus luteum after ovulation, which is responsible for controlling LH secretion from the pituitary. Use of prostaglandins is an alternative method for controlling reproduction by eliminating the corpus luteum and inducing a subsequent follicular phase with ovulation. Finally, the discovery of the properties of melatonin in photoperiod-dependent breeding animals opened up a new methodology to control reproduction in these species, inducing changes in the perception of photoperiod and the annual pattern of reproduction. Use of hormones to induce oestrus has allowed increased use of artificial insemination in small ruminants, a very useful management tool, considering the difficulty of detecting oestrus in these species. At commercial level, synchronisation of oestrus allows control of lambing and kidding, with subsequent synchronisation of weaning of young animals for slaughter. Also, it allows more efficient use of labour and animal facilities. Multiple ovulation and embryo transfer programmes are also possible with the use of oestrus synchronisation and artificial insemination. Finally, hormonal treatments have also been used to induce puberty in ewe-lambs and doelings.

Kisspeptin activates the hypothalamic–adenohypophyseal–gonadal axis in prepubertal ewe lambs

The onset of puberty in mammals involves an increase in the pulsatile release of GNRH and LH. The KISS1 gene is essential for pubertal development, and its product, kisspeptin, stimulates the release of LH. The objective of this study was to determine the effects of kisspeptin in the hypothalamic-adenohypophyseal-gonadal axis of prepubertal ewe lambs. Ewe lambs (28 weeks of age) were treated intravenously with saline (control, n=6) or kisspeptin (20 μg kisspeptin; n=6) every hour for 24 h. Kisspeptin stimulated pulse-like release of LH within 15 min following injections, and increased the frequency and amplitude of LH pulses, and mean circulating concentrations of LH and estradiol. A surge-like release of LH was observed in four kisspeptin-treated lambs beginning 17 h after the onset of treatment, and all four lambs had elevated circulating concentrations of progesterone within 5 days post-treatment. However, circulating concentrations of progesterone decreased within 2 days after the initial rise in three of the four ewe lambs, indicating that induced luteal activity was of short duration. The proportion of lambs that were pubertal (defined by circulating concentrations of progesterone above 1 ng/ml for at least 7 days) by 35 weeks of age (8/11) and the mean age at puberty (32 ± 1 weeks) for those reaching puberty within the experimental period did not differ between treatments. Results support a role for kisspeptin in the activation of the hypothalamic-adenohypophyseal axis leading to the onset of puberty in ewe lambs.

Serum luteinizing hormone, growth hormone and insulin-like growth factor-I after releasing hormone challenge in prepubertal ewe lambs selected for twinning

Two studies evaluated hormonal markers as indicators of the onset of puberty in Debouillet sheep selected for twinning. In Trial 1, 29 ewe lambs (50 ± 0.5 kg, 159 to 187 d of age) were given 10 μg GnRH (iv) on September 15 and blood was collected at 30 min intervals after the injection for 2 h. Additional samples were taken twice weekly and progesterone (P 4) was measured. The day that serum P 4 was greater than 1 ng/mL for 2 consecutive sampling days was classified as the day of puberty. Average day of puberty was October 12 (average age at puberty was 199 d) and ewes with values less or greater than the average were classified as early or late, respectively. Average weight at GnRH challenge was 50 kg and ewes weighing less or more were classified as light or heavy, respectively. Early ewes weighed more (P = 0.01) and reached puberty sooner (P = 0.01) than late ewes. Heavy lambs reached puberty earlier, weighed more at GnRH challenge, and had more LH area under the curve (AUC, P < 0.05) than light ewes. In Trial 2, we gave 27 ewe lambs (54 ± 0.9 kg, 173 to 189 d of age) a single iv injection of 10 μg GnRH and 10 μg GHRH on September 17. Average day of puberty was October 13, average weight was 54 kg, and average age at puberty was 208 d. Categories were designated as described for Trial 1. Early lambs reached puberty sooner (P = 0.01) and weighed mored (P = 0.01) than late lambs, but the puberty groups had similar LH AUC (P = 0.64) and GH AUC (P = 0.75), whereas IGF-I was greater (P = 0.01) in early puberty ewes than in late puberty ewes. Heavy lambs reached puberty earlier (P = 0.06), weighed more (P = 0.01), and tended (P = 0.11) to have more GH AUC than light ewes. No difference was observed in LH AUC or IGF-I between weight groups (P > 0.15). Results suggest that serum LH after GnRH is not a reliable indicator of the onset of puberty in ewe lambs selected for twinning, but heavier ewes tended to produce more GH after a GHRH challenge and reach puberty earlier than lighter ewe lambs.

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.

Reproductive characteristics of Ethiopian highland sheep: I. Genetic parameters of testicular measurements in ram lambs and relationship with age at puberty in ewe lambs

A study was conducted to estimate heritabilities of, and genetic correlations among, body weight (WT) and testicular measurements — scrotal circumference (SC), testicular diameter (TD), testicular length (TL) and epididymal diameter (ED) — in ram lambs between 6, 9 and 12 months old, and relationship of the testicular traits with age at puberty in ewe lambs (AP). Two fat-tailed sheep breeds, the Horro and Menz, indigenous to the Ethiopian highlands were studied. Experimental lambs were produced by mating 250 oestrus-synchronized ewes of each breed to 10 sires in a single-sire mating system over three mating periods which produced, for this study, a total of 361 ram lambs and 148 ewe lambs, with substantial pedigree information, in two dry seasons (October/November 1992 and 1993) and one wet season (June/July 1993). Mean AP was 322.7 days. Breed was not significant ( P > 0.05) for all testicular measurements, except ED at 9 months for which the Horro had a higher ( P < 0.01) value (20.6, s.e. 0.38 versus 19.3 s.e. 0.30). Horro ewe lambs had their first oestrus 28 days earlier ( P < 0.05) than the Menz. Heritability estimates were obtained from a sire model (M1) and from an individual animal model with additive direct and maternal effects (M2). The maternal effect was not fitted in M2 for AP. Repeatability and heritability estimates were also obtained by analysing records at the three ages in a repeated measures model (M3). M1 and M2 heritability estimates were generally low to moderate but were associated with large standard errors. Heritability estimates for testicular measurements were generally similar to those for WT. Among the testicular measurements, SC had the highest heritability estimates at 6 (0.45, s.e. 0.24 for M1) and at 12 months (0.41, s.e. 0.21 and 0.41, s.e. 0.20 for M1 and M2, respectively). Model 3 heritability estimates were 0.29 (s.e. 0.14), 0.24 (s.e. 0.12), 0.09 (s.e. 0.07), 0.11 (s.e. 0.08) and 0.12 (s.e. 0.08) for WT, SC, TD, TL and ED, respectively. Only repeatability estimates for WT (0.34, s.e. 0.02) and SC (0.25, s.e. 0.03) were significant. Heritability of AP was estimated at 0.16 (s.e. 0.21) by M1 and 0.14 (s.e. 0.19) by M2. Genetic correlations of AP with testicular measurements, especially with SC (−0.57, s.e. 0.38 and −0.78, s.e. 0.33, at 9 and 12 months, respectively) and TD (−0.72, s.e. 0.33 and −0.83, s.e. 0.48), were desirable and generally high. Adjustment of testicular measurements for liveweight consistently resulted in a reduction in estimates of heritability and genetic correlations. SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in these breeds.

Advancement of puberty in ewe lambs by active immunisation against inhibin early in life

Abstract Active immunisation of lambs early in life with inhibin can advance puberty and increase ovulation rate but these effects appear not to be mediated through changes in FSH concentrations. The aims of this study were to advance puberty in ewe lambs and determine if increased plasma concentrations of gonadotropins are responsible for the advancement of puberty. Ewe lambs were immunised at 3, 7 and 15 weeks of age against either a synthetic inhibin alpha subunit peptide 1–32 conjugated to human serum albumin (HSA), or an inhibin preparation purified from porcine follicular fluid (porcine monoclonal purified inhibin; pMPI), or HSA alone (control immunogen). Immunisation with inhibin alpha peptide 1–32 produced antibodies which bound iodinated native bovine inhibin and advanced puberty (time of first ovulation) and increased ovulation rate but did not significantly increase plasma FSH concentrations, although LH concentrations were lower (P This study confirms that active immunisation of ewe lambs early in life against inhibin advances puberty via a mechanism which does not significantly increase plasma gonadotrophin concentrations. Immunisation to advance puberty also results in persistent increases in ovulation rates in later breeding seasons.

Dietary protein or energy restriction influences age and weight at puberty in ewe lambs

The working hypothesis was that restricted protein content in diets of prepubertal ewe lambs would delay time of onset of puberty to a greater extent than restricted energy content. Restriction of dietary protein (metabolizable protein, MP) or energy (ME) intake on age and weight at puberty was studied in ewe lambs in two experiments. In Experiment 1, 85 crossbred ewe lambs were assigned by weight to one of five dietary treatment groups: control (CTL; 18 mg ME day −1 and 173 g MP day −1); energy restricted (ER; 10.2 mg ME day −1 and 96 g MP day −1); protein restricted (PR; 11 mg ME day −1 and 66 g MP day −1); ER for 9 weeks then switched to CTL (ER/CTL); PR for 9 weeks then switched to CTL (PR/CTL). Ewe lambs were weighed biweekly, bled weekly, and serum was assayed for progesterone to determine time of puberty. Average age at puberty differed among lambs fed the various diets ( P < 0.01). Ewe lambs in the CTL group were younger and weighed more at puberty. Lambs fed diets restricted in protein or energy content were similar in age at puberty. Dietary switching, ER/CTL and PR/CTL, affected body weight and gain ( P < 0.05), but did not result in changed age at puberty compared with lambs fed ER or PR diets. In Experiment 2, two breed types (maternal type and meat type) were used to compare responses of dietary protein restriction to dietary energy restriction. In Experiment 2, lambs ( n = 60) were assigned to either the CTL, PR or ER diets. Lambs in the CTL group gained more weight than lambs fed the PR diet and lambs fed the PR diet gained more weight than lambs fed the ER diet ( P < 0.05). Diet affected age ( P < 0.001), but not weight at puberty ( P = 0.13). Dietary energy and protein restriction influenced age at puberty in ewe lambs with energy restriction having a greater influence on delaying onset of puberty than protein restriction. Realimentation did not overcome effects of previous feed restriction by inducing an earlier age at puberty than ewe lambs fed the ER or PR diet throughout the experimental period. Body weight gain prepuberty is more important than type of dietary restriction (protein or energy) with regard to impacting age at puberty. We, therefore, reject the working hypothesis that dietary protein restriction prepuberty would have a greater impact in delaying onset of puberty than dietary energy restriction.

Effect of photoperiod before and after birth on puberty in ewe lambs.

Previous studies have shown that exposure to long days followed by short days after 12 wk of age advances the onset of puberty in ewe lambs. The aim of this experiment was to determine whether or not puberty would be advanced by exposure of lambs to such a photoperiodic regime when the long days were given before birth and the short days immediately after birth. Ewes kept in natural photoperiod (NP) were housed on January 15 and allocated at random to one of four treatments: 1) NP/NP, natural photoperiod before and after parturition (n = 26); 2) SD/SD, short days (SD; 9L:15D) before and after parturition (n = 27); 3) LD/NP, long days (LD; 18L:6D) before parturition and NP after parturition (n = 27); and 4) LD/SD, LD before parturition and SD after parturition (n = 26). Mean (+/- SEM) birth date for all lambs was March 20 +/- 1 day, and the number of days of exposure to long and short days prior to parturition was 64 +/- 2 and 67 +/- 2 days, respectively. From ewes on the four treatments, 24, 20, 14, and 16 female lambs, respectively, were reared. Lambs were weighed at birth and at weekly intervals after weaning. Reproductive activity in ewe lambs was assessed from serum progesterone concentrations in blood samples collected twice weekly from August 1 until puberty was reached or the experiment terminated on November 17 (34 wk after birth).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of tetrathiomolybdate on growth rate and onset of puberty in ewe-lambs

The effects of intravenous tetrathiomolybdate (TM) treatment on growth rate and onset of puberty in ewe-lambs were investigated in March-born Sulfolk × Mule Lambs. One group ( n = 6, mean weight 13.5 ± 0.9 kg) was treated with 25 mg tetrathiomolybdate intravenously twice weekly for 34 weeks; the second group ( n = 6, mean weight 13.5 ± 0.9 kg) served as controls. TM treatment significantly depressed liveweight gains in the treated group compared with the controls (97.8 ± 2.5 g/day versus 114 ± 4.8g/day respectively, P < 0.001). Puberty was attained at a significantly earlier age in the controls compared with the TM-treated lambs (245 ± 4 days versus 268 ± 7 days respectively, P < 0.02). The weights at onset of puberty were similar for both groups. The LH responses of the lambs to exogenous oestradiol injections were not significantly affected by TM treatment although the LH peak heights were lower in the TM-treated groups than in the controls. Mean LH pulse frequency and amplitude were similar in both groups. Tetrathiomolybdate treatment affected copper metabolism by significantly depressing ( P < 0.005) the amount of plasma copper soluble in 10% trichloracetic acid. The results of this study show that intravenous tetrathiomolybdate reduces growth rate in ewe-lambs and delays the onset of puberty, although with little effect on the pattern of LH secretion.

Reproductive characteristics of lambs actively immunized early in life with inhibin-enriched preparations from follicular fluid of cows.

Active immunization of Merino and crossbred ewe lambs early in life with a partly purified inhibin derived from bovine follicular fluid (bFF) advanced their puberty. This occurred whether the lambs were immunized from 3 weeks of age or from 9 weeks of age or just 3 times between 3 and 9 weeks. However, the effect was more obvious with multiple injections starting at 3 weeks of age. The ovulation rate of the immunized lambs was significantly higher than that of the control ewes. When lambs were subjected to multiple immunizations the increased ovulation rate persisted in Merinos for at least 1 year after immunization ceased. The lambs injected 3 times only (at 3, 6 and 9 weeks of age) did not show any increase in ovulation rate. Plasma concentrations of FSH and LH measured in blood samples taken 1 week after immunization were not significantly different between the treatment groups. Daily sperm output in the urine and testis diameter were measured in ram lambs from the same breeds and flocks as the ewe lambs. Immunization with the inhibin preparation from 3 weeks of age resulted in a significant increase in daily sperm output (4255 +/- 701 vs 2344 +/- 344 x 10(6), P less than 0.01) and testis diameter (5.21 +/- 0.3 vs 4.33 +/- 0.2 cm, P less than 0.05) in Merino rams examined in the non-breeding season when the rams were aged 23 months. Although the same trend was seen in the following year the differences were not significant. Immunization from 9 weeks of age had no effect. A similar increase in daily sperm output was seen (at 20 and 25 months of age) in crossbred rams immunized from 3 weeks of age but the difference was not significant. Plasma concentrations of FSH (but not LH) in samples from rams immunized from 3 weeks of age were significantly higher than those of control rams at 7 and 60 weeks of age in Merino rams and at 23 and 31 weeks of age in crossbred rams. Plasma FSH concentrations at 21 and 26 weeks of age in the Merino rams immunized from 3 weeks of age were higher than those of control lambs, and these increases preceded a significant (P less than 0.05) increase in testicular diameter at 30 weeks of age (4.99 +/- 0.2 vs 4.37 +/- 0.2 cm). These results suggest that active immunization early in life with an inhibin-enriched fraction from bFF advances puberty in ewe lambs.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH.

Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.

Pinealectomy delays puberty in ewe lambs.

Fifteen pinealectomized and 15 unoperated ewes were exposed to constant light for 3 weeks before and 10 weeks after lambing. Fourteen pinealectomized and 15 unoperated ewes were allowed to lamb outdoors. Five ewe lambs born in constant light to the 2 groups of dams were pinealectomized at 10 weeks of age. Ewes and lambs were then returned to the field. Puberty (determined by weekly progesterone analysis) was significantly delayed (P less than 0.05) in the pinealectomized ewe lambs. Median pubertal age in pineal-intact ewe lambs was 37 weeks compared to 49 weeks in pinealectomized lambs. Constant light during the first 10 weeks of life had no effect upon puberty onset nor did the pineal status of the dam. Control lambs entered seasonal anoestrus at the time pinealectomized ewe lambs were entering puberty. Pinealectomized lambs entered anoestrus at the same time as control lambs were beginning their second breeding season. These results confirm a key role of pineal-mediated hormonal signals in the control of puberty in the sheep.