Age Of First Estrus Research Articles

Reproductive Performance of Ongole Grade, Simmental, and Limousin Cattle Given Superovulation Treatment

Reproductive technologies have the potential to enhance livestock productivity, with superovulation being one such method aimed at increasing the number of ovulated oocytes per estrous cycle through hormonal stimulation. This study aimed to evaluate the reproductive performance of three cattle breeds—Ongole Grade (OG) (n=20), Simmental (n=18), and Limousin (n=20)—subjected to superovulation treatment. The cattle, aged 2.5 to 4 years with a body condition score of 3.5 to 4, were intensively managed. Superovulation was induced using CIDR (Controlled Internal Drug Release) for synchronization, followed by follicle-stimulating hormone (FSH) administration. Reproductive performance data, including age at first estrus, number of corpora lutea (CL), and embryo production, were collected over three estrous cycles. A quasi-experimental design was employed with breed as the primary treatment factor, and data were analyzed using analysis of variance (ANOVA). The results indicated that breed had a significant effect (P0.05) on the age of first estrus, with OG cattle reaching first estrus at 621.3±93.3 days, Simmental at 522.4±75.5 days, and Limousin at 570.4±88.1 days. However, no significant differences (P0.05) were observed among the breeds in terms of the number of CL, collected embryos, or transferable embryos across the superovulation cycles.

Asprosin-induced alterations in female rat puberty and reproductive hormonal profiles

Objective To investigate the comprehensive effects of daily chronic asprosin administration on various pubertal and reproductive parameters in female rats. This study aims to elucidate the role of asprosin in regulating the onset of puberty and its influence on hormonal profiles and ovarian histology. Methods Asprosin was administered intraperitoneally (i.p.) at a dose of 500 ng/kg daily for eight weeks. Hormonal assays and histological analyses were performed to evaluate the effects of asprosin on the onset of puberty and reproductive function. Results Daily chronic administration of asprosin accelerated the onset of the first oestrus. Hormonal assays revealed significant elevations in serum levels of Follicle-Stimulating Hormone (FSH) and Oestradiol (E2), while Inhibin B levels decreased. Histological evaluations demonstrated an increased number of primary and secondary follicles in ovarian tissue, without affecting primordial follicle counts or reproductive organ weights. Conclusions Role of adipokines in regulating puberty and reproductive function has increasingly gained recognition. This study aimed to provide the first comprehensive examination of the effects of daily chronic asprosin administration on pubertal and reproductive parameters in female rats. Utilising hormonal assays and histological analyses, asprosin was administered intraperitoneally (i.p.) at a dose of 500 ng/kg, daily, for eight weeks. Our findings revealed that daily chronic administration of asprosin accelerated the onset of the first oestrus. Hormonal assays showed significant elevations in serum levels of Follicle-Stimulating Hormone (FSH) and Oestradiol (E2), while Inhibin B levels decreased. Histological evaluations demonstrated an increased number of primary and secondary follicles in ovarian tissue, without affecting primordial follicle counts or reproductive organ weights. These results provide new insights into asprosin’s role in advancing the age of first oestrus and modulating hormonal profiles, thereby offering potential benefits to the female reproductive system.

Reproduction and Production Performance of Swamp Buffalo (Bubalus bubalis) at the Small-Scale Holder Farmer in Sragen Regency, Central Java, Indonesia

This research aimed to determine the performance of swamp buffalo reproduction and production at the small-scale holder farmer in Sragen Regency, Central Java, Indonesia, from June to September 2021. The method used in this research was a survey with a census (complete) sample determination. Data collection applies to interviews, observations and literature studies. Research parameters used in reproductive performance were calving interval (CI), service per conception (S/C), age of the first estrus, age of first birth and postpartum estrus. In contrast, production performance parameters were chest circumference, body length and estimated body weight. The result of research on reproductive performance showed that the average CI were 13.2±0.9 months, S/C 1.25±0.4 time, age of first estrus 2.7±0.6 years, age of first birth 3.7±0.5 years and postpartum estrus were 30–60 days. The result of research on the production of male buffalo body length was 205.3±1.7, and the body length of female buffalo was 127.2±4.3 cm, whereas the chest circumference of female was 205.3±1.7 cm and the chest circumference of the male was 189±2.8 cm. The estimated body weight of females and males were 516.7±7.7 kg and 445.2±11.9 kg. Based on the result of the research, the characteristics of swamp buffalo reproduction and production in Sragen Regency were classified as good.

ODP405 Effects of Gonadotrope-Specific Knockout of Creb on HPG Axis Function in Mice

Abstract Background and Objective Reproduction is regulated by FSH and LH, which are synthesized and secreted by pituitary gonadotropes in response to pulsatile hypothalamic GnRH in a frequency dependent manner. Low and high GnRH pulse frequencies preferentially increase Fshb and Lhb expression, respectively, mediated by preferential coupling to Gαs-PKA-Creb and Gαq-PKC-MAPK-AP1 signaling cascades in vitro. The mouse Fshb proximal promoter contains a half-AP1/half-CRE recognition motif that binds Creb in vitro, and mutation of this half-CRE results in loss of preferential GnRH stimulation of Fshb at low pulse frequencies in immortalized gonadotrope LβT2 cells. Therefore, the purpose of this study was to identify the direct role of Creb on gonadotropin regulation in vivo. We hypothesized that gonadotrope-specific deletion of Creb would influence pubertal timing and/or fertility due to reduced Fshb expression. Methods and Results Gonadotrope-specific Creb knockout (Creb1 fx/fx / Gnrhr GRIC/+; Creb KO) and control (Creb1 fx/fx) mice were generated by Cre-Lox recombination and markers for pubertal onset were evaluated. We observed no differences in body weights of Creb KO and littermate control mice in either females or males from postnatal day (PND) 21 to 3 months of age (n=9/genotype/sex). The age of vaginal opening, a marker of puberty onset in female mice, was not significantly different between female Creb KO (PND 28.4±0.5; n=21) and littermate control (PND 29.5±0.6; n=17) mice. Similarly, the age of first estrus, determined by vaginal lavage and cytology, was not significantly different between Creb KO mice (PND 37.6±1.9; n=9) and littermate controls (PND 36.6±2.2; n=8). Estrous cyclicity was normal over a three-week period in Creb KO and control mice, which spent similar amounts of time in diestrus/metestrus, proestrus, or estrus. Male Creb KO mice tended to show preputial separation at a younger age (PND 28.8±0.3; n=19) compared to littermate control (PND 29.6±0.3; n=22) mice, but the difference did not reach statistical significance (p=0. 06). Conclusions Deletion of Creb from pituitary gonadotropes did not affect the timing of pubertal onset in female mice, but we did observe a trend for male Creb KO mice to have advanced puberty, as measured by preputial separation. Normal pubertal timing does not preclude potential effects of Creb-mediated gonadotropin regulation on folliculogenesis, spermatogenesis, or fertility (including litter size), for which studies are ongoing. Presentation: No date and time listed

The Indonesia’s Racehorse Reproductive Performance

The need for equestrian sport is increasing for local horse grading with Thoroughbred horses used for racehorses. Pamulang Equestrian Centre is one of the horse farms in Indonesia that acts as a pioneer in creating local Indonesian racehorses. The purpose of this paper is to explain the reproductive performance of the Indonesian Kuda Pacu Indonesia (KPI) through a case study at Pamulang Equestrian Centre. Primary data was obtained directly from the documentation and interviews of the farmers. Meanwhile, secondary data was collected from literature studies. Horse farming at Pamulang Equestrian Centre was the result of breeding horses G3 with G3, G3 with G4, G4 with G4, G3 or G4 with KPI that produced KPI. Horse breeding was carried out annually during the breeding season, from August to January. The reproductive performance of male and female KPI at Pamulang Equestrian Centre was mating time from August to January, at the age of first estrus was 12-15 months, the first mating age was 4 years, estrus duration was 7 days, and duration of gestation was approximately 11 Months.

Maternal immune activation accelerates puberty initiation and alters mechanical allodynia in male and female C57BL6/J mice.

The mechanisms that link maternal immune activation (MIA) with the onset of neurodevelopmental disorders remain largely unclear. Accelerated puberty is also associated with a heightened risk for psychopathology in later life, but there is a dearth of evidence on the impacts of maternal infection on pubertal timing. We examined the effects of MIA on reproductive development, mechanical allodynia, and sensorimotor gating in juvenile, adolescent, and adult male and female mice. Moreover, we investigated hypothalamic neural markers associated with the reproductive and stress axes. Finally, we tested the mitigating effects of environmental enrichment (EE), which has clinical relevancy in human rehabilitation settings. Our results show that administration of polyinosinic-polycytidylic acid (poly(I:C)) on gestational day 12.5 led to early preputial separation, vaginal openings, and age of first estrus in offspring. MIA exposure altered pain sensitivity across development and modestly altered prepulse inhibition. The downregulation of Nr3c1 and Oprk mRNA in the hypothalamus of juvenile mice suggests that MIA's effects may be mediated through disruption of hypothalamic-pituitary-adrenal axis activity. In contrast, life-long housing with EE rescued many of these MIA-induced consequences. Overall, our findings suggest that accelerated puberty may be associated with the deleterious effects of infection during pregnancy and the onset of psychopathology.

Effects of age at first breeding and dietary energy levels during the rearing period of replacement gilts on reproductive performance

Context The occurrence of second parity syndrome is a major reason for culling sows depending on the bodyweight and energy level balance during the first lactation. Equally, the nutrition of gilts during the rearing period influences the age of first oestrus, longevity and reproductive performance. Aims The experiment investigated: (1) the influence of gilt mating age (early [EL], middle [MD] and late [LT]) at the first parity on reproductive performance, and (2) the interaction between dietary energy levels (high, 3320 kcal/kg; low, 3120 kcal/kg) and mating age. Methods A total of 120 crossbred (Duroc × Landrace × Yorkshire) gilts were allotted to six treatments according to a 3 × 2 factorial arrangement based on mating age (EL [222 days], MD [244 days] and LT [264 days]) at the first parity and dietary energy levels (high, 3320 kcal/kg; low, 3120 kcal/kg). The average weight of gilts were 141 ± 3, 153 ± 3 and 164 ± 3 for the EL, MD and LT groups, respectively. Results High-energy diets tended to increase the growth rate of gilts (P = 0.083). At insemination, bodyweight and back-fat thickness were higher (P < 0.05) in the LT group. Back-fat thickness at farrowing was lower (P < 0.05) in the EL group. The back-fat thickness loss during lactation was highest in the LT group (P < 0.05) during parity one and two. Feed intake during lactation was significantly reduced (P < 0.05) in the LT gilts in parity one. Insemination age and dietary energy levels had no significant effects on, litter size, litter weight and weaning to oestrus interval. A higher blood insulin-like growth factor (P < 0.05) was observed in the EL gilts during the first service and weaning. Conclusion Based on these findings, early inseminated gilts had a lower bodyweight loss during lactation without affecting litter size or growth, which in the long term may positively impact culling age. Implication This information may guide swine farmers on the most appropriate age to breed gilts at first service for increased reproductive life. The provision of high-energy feeds did not translate into any meaningful interaction towards improving reproductive performance in gilts.

EVALUATION OF PRODUCTIVE AND REPRODUCTIVE PERFORMANCES OF BLACK BENGAL GOATS IN RAJSHAHI GOVERNMENT GOAT DEVELOPMENT FARM IN BANGLADESH

Background: The Black Bengal goat (BBG) is well adapted food animals with profitable productive and reproductive traits being naturally reared to enhance economic status and food security in rural people. Bangladesh government has taken program through establishment of ‘Government Goat Development Farms’ (GGDF) to enhance the goat rearing activities of the smallholders at rural level but the research reports on the productive and reproductive performances of goats in these GGDF are very limited. Objective: The main objective of this study was to evaluate the productive and reproductive performances of the BBG reared in semi-intensive system at the Rajshahi GGDF Materials and Methods: The Rajshahi GGDF had 398 goat populations of which 121 does were selected to study the productive and reproductive performances during the period from July 2010 to June 2011. The age of first estrus, conception rate by natural service, gestation length, post-partum heat, kidding interval, litter size, survivability of kids, morbidity and mortality of kids and their seasonal influence were studied. Results: The age of young female BBG showed 1st estrus varied from 180 to 270 with an average of 204  27 days. The conception rate varied from 88 to 100 with an average of 97% with natural services. The gestation length varied from 145 to 182 with an average of 150  5 days. The post-partum heat period varied from 60 to 90 days with an average of 69  7 days. The kidding interval varied from 199 to 268 with an average of 219  13 days. The litter size varied from 1 to 3 with an average of 2. Out of 234 kids borne, 47.44% were male and 52.56% female with higher mortality in male (10.81%) than female (5.69%) with an overall average mortality of 8.12%. There was no significant influence of season and parity on the birth weight of kids. However, the heavier birth weight of kids was recorded in male (1.38 kg) than female (1.17kg) kids. The birth of twin kids (56.41%) was found significantly (p < 0.0001) highest in comparison to triplets (26.92%), single (11.54%) and quadruplet (5.13%). Conclusions: The results support promising breeding and reproductive efficiency of BBG under local environmental conditions and therefore, there is a need to be improved milk yield of dam and control of morbidity and mortality in BBG kids. It may be concluded that the productive and reproductive performances of the BBG reared by using semi-intensive system of management appears to be encouraging at the Rajshahi GGDF which could be extended and compared to research findings with other four GGDF in Bangladesh.

Identification of Reproductive Activity of Donggala Cattle at Post Puberty and Post Partum Periods

The aim of the study is to investigate condition and reproductive activity of Donggala cattles during post-puberty and post-partom periods. The study was carried out for 12 months at Donggala, Palu and Sigi Districts where major populations of Donggala cattles were kept by farmers. A total of 200 heads of Donggala cattles belonged to the local farmers were sampled. The animals were categorized as heifers when they were 10 – 18 months old and cows at 18 – 24 months old. Data colected inthis study were from structured interview and direct observation. Variables measured were body condition score, live body weight, age of puberty, age of first estrus and first mating, days open, service per conception rate, non return rate and conception rate either during post puberty or post partum. Data found in this study were describe descriptively. The results of the study indicated that the age of puberty was late as live body weight body condition score of Donggala were low. First mating of Donngala heifers was much dependant upon live body weight. Heavier cattles tended to mat earlier than the lighter cattles. Heavier catlles had better service per conception rate, non return rate and conception rate either at post puberty or post partum periods. In conclusion, the cows with high body weight had earlier first estrus, first mating and better service per conception rate, non return rate and conception rate than those cows with low live body weight. Keywords: Donggala cattle, reproductive efficiency, post puberty, post partum DOI : 10.7176/JBAH/9-6-05 Publication date :March 31 st 2019

Investigation into the effect of season on oestrus in gilts over two years of climate adaptation

This study examined the changes in age at first oestrus, the weaning-to-oestrus interval (WEI), and duration of oestrus (DE) in a Yorkshire sow population during two years of adaptation from a northern (55°48′N, 9°13′W) European region to a southern (44°03′N, 23°35′W) one. The adaptation process induced a grouping effect of gilts around the mean age of the onset of puberty. Autumn and spring were characterized by the most enhanced gilt grouping effect at 201 to 210 days of age. The same effect was found for oestrus duration, which declined from a 12- to 96-hour range in the first year to an 18- to 90-hour range in the second year. The mean age of first oestrus was 0.8 days significantly lower in the second year compared with the first; the maximal lowering (1.7 days) occurred in the winter season. The WEI decreased significantly from the first to the second year in all four seasons, by a mean annual value of 0.88 days (15.9%). DE increased by 6.5 hours (significantly for all seasons) from the first year to the next. DE showed an ascending evolution from winter to spring and descending from summer to autumn, during each monitored year. Adaptation influences the oestrus in sows. The age to puberty and WEI tended to decrease, while DE tended to increase, with a simultaneous decrease in the variability of these oestrus parameters.

Pengaruh Perbedaan Ketinggian Tempat Terhadap Capaian Hasil Inseminasi Buatan Pada Kambing Peranakan Ettawa

<p>This study was conducted to assess the reproductive performance and achievements of AI in goat reared in lowland and highland areas. The study used a survey method in two rural areas with the highest goat population. For lowland areas selected Karangwuni village while highland areas was Sidomulyo village. The results showed that for the lowland areas vs. the highland for reproductive performance were as follows: age of first estrus (10 vs 9.3 bl), age of first mating (13.2 vs 12.5 bl),<br />mating system 100% natural, post partum mating (4.2 vs 4.6 months), S / C (1.5 vs. 1.6). Understanding of farmers about the pregnant female: anestrus post-AI (85.7 vs. 22.2%), stomach down (14.3 vs. 0.00), the condition of the udder (0.00 vs 77.8%). Achievement results of AI (37.5 vs. 40%). Based on the results of the study concluded that the reproductive performance of goat in lowland areas was generally very similar to the highland areas, thus the development of large-scale goats in the lowland areas is recommended.<br />Key words: natural mating, artificial insemination, PE goats, lowland, highland</p>

Pengaruh Perbedaan Ketinggian Tempat Terhadap Capaian Hasil Inseminasi Buatan Pada Kambing Peranakan Ettawa

<p>This study was conducted to assess the reproductive performance and achievements of AI in goat reared in lowland and highland areas. The study used a survey method in two rural areas with the highest goat population. For lowland areas selected Karangwuni village while highland areas was Sidomulyo village. The results showed that for the lowland areas vs. the highland for reproductive performance were as follows: age of first estrus (10 vs 9.3 bl), age of first mating (13.2 vs 12.5 bl),<br />mating system 100% natural, post partum mating (4.2 vs 4.6 months), S / C (1.5 vs. 1.6). Understanding of farmers about the pregnant female: anestrus post-AI (85.7 vs. 22.2%), stomach down (14.3 vs. 0.00), the condition of the udder (0.00 vs 77.8%). Achievement results of AI (37.5 vs. 40%). Based on the results of the study concluded that the reproductive performance of goat in lowland areas was generally very similar to the highland areas, thus the development of large-scale goats in the lowland areas is recommended.<br />Key words: natural mating, artificial insemination, PE goats, lowland, highland</p>

In utero bisphenol A exposure disrupts germ cell nest breakdown and reduces fertility with age in the mouse

Bisphenol A (BPA) is a known reproductive toxicant in rodents. However, the effects of in utero BPA exposure on early ovarian development and the consequences of such exposure on female reproduction in later reproductive life are unclear. Thus, we determined the effects of in utero BPA exposure during a critical developmental window on germ cell nest breakdown, a process required for establishment of the finite primordial follicle pool, and on female reproduction. Pregnant FVB mice (F0) were orally dosed daily with tocopherol-striped corn oil (vehicle), diethylstilbestrol (DES; 0.05μg/kg, positive control), or BPA (0.5, 20, and 50μg/kg) from gestational day 11 until birth. Ovarian morphology and gene expression profiles then were examined in F1 female offspring on postnatal day (PND) 4 and estrous cyclicity was examined daily after weaning for 30days. F1 females were also subjected to breeding studies with untreated males at three to nine months. The results indicate that BPA inhibits germ cell nest breakdown via altering expression of selected apoptotic factors. BPA also significantly advances the age of first estrus, shortens the time that the females remain in estrus, and increases the time that the females remain in metestrus and diestrus compared to controls. Further, F1 females exposed to low doses of BPA exhibit various fertility problems and have a significantly higher percentage of dead pups compared to controls. These results indicate that in utero exposure to low doses of BPA during a critical ovarian developmental window interferes with early ovarian development and reduces fertility with age.

Genetic and phenotypic parameters between yearling, hoggetand adult reproductive performance and age of first oestrus in sheep

The aims of this study were to quantify the relationship between age of first oestrus and yearling reproductive performance in maternal-cross ewes in the Information Nucleus Flock data and to estimate genetic and phenotypic correlations between early and later reproductive performance defined as three ages, yearling, hogget and adult in both Merino and maternal-cross ewes. Information on 2218 yearling records, 2047 hogget records and 910 age of first oestrus records were used in the analysis of maternal-cross ewes, whereas 3286 hogget and 2518 adult reproductive records were used in analysis of Merino ewes. Heritability estimates for yearling reproductive performance in maternal-cross ewes ranged from 0.08 ± 0.09 for ewe fecundity to 0.16 ± 0.05 for number of lambs born and were generally higher than hogget heritability estimates for both maternal-cross and Merino ewes. Age at first oestrus was found to have a low heritability, 0.02 with standard errors of 0.07 and 0.06 with and without weight fitted as a covariate. Genetic correlations between age at first oestrus with and without weight fitted as a covariate and yearling reproductive performance were positive, ranging from 0.07 ± 0.49 with lamb survival to 0.94 ± 0.39 with number of lambs born, which was unexpected. Correlations between traits from the same age class were high in both breed groups. Genetic correlations between yearling and hogget performance in maternal-cross ewes were generally lower than one, ranging from 0.46 ± 0.68 for lamb survival and 0.79 ± 0.50 for fertility suggesting that yearling and later reproductive performance are related but genetically different traits. In Merino ewes, the genetic correlations between hogget and adult performance followed a similar pattern. The small number of records in this study generated high standard errors for estimates, which restricts the conclusions that can be drawn. Overall, this study supports current practice used by ‘Sheep Genetics’, the Australian genetic evaluation system for sheep, in considering yearling reproductive performance as a trait separate from later parities for genetic evaluation purposes.

LA CABRA Y LOS SISTEMAS DE PRODUCCIÓN CAPRINA DE LOS PEQUEÑOS PRODUCTORES DE LA COMARCA LAGUNERA, EN EL NORTE DE MÉXICO

A baseline study was conducted in the Comarca Lagunera in the North of Mexico to evaluate the potential for implementation of a breeding program. A questionnaire was applied to 64 producers to document the production system. A phenotypic characterization of the goat population was performed; body measurements of 509 animals were recorded. The systems differentiated in production intensification, distance to urban areas and type of employees. Animal feeding is based on grazing with minimum supplementation. Body measurements including: height at withers (77.0 ± 0.3 cm), chest circumference (87.0 ± 0.3 cm) and body length (78.0 ± 0.3 cm), increased until 4 years of age. Age of first estrus, age of first service, kidding intervals, lactation length and kiddings per doe averaged, respectively, 6.9 months, 8.3 months, 1 year, 7.4 months and 6.3 kiddings. Most (40 %) producers evaluate their females on production and phenotype basis, recording is not done. The main source of males is form outside of the herd, without consideration of adaptation and productivity traits. All producers expressed that goats with high percentage of genetically improved European breeds showed adaptation problems. A community-based system, that allows access to improved animals and which considers the producers’ objectives, was considered important.

Caractérisation morphométrique et reproductive des taureaux et vaches N'Dama du Congo

This work describes a morphometric and reproductive study conducted on male and female N'Dama cattle in Congo. The study was concentrated on a herd having an average live weight of 255.1 ± 19.8 kg and 249.7 ± 26.4 kg respectively for male and female animals at 3 years of age. The regular coat is fawn with black legs. Some animals are piebald with occasional white patches and brown sprays.Some average body measurements were evaluated: the wither height (115.3 ± 1.1 cm and 111.8 ± 0.9 cm), the length of the body from point of shoulder to point of buttock (143.7 ± 3.1 cm and 140.8 ± 3.2 cm) and the heart girth (158.2 ± 4.2 cm and 144.4 ± 1.3 cm) respectively for male and female animals.When considering puberty as the age of first oestrus, by the overall behavioural criteria, the age of puberty fluctuated around 458 ± 26 days with a weight of 168 ± 18 kg. When considering puberty as the moment where a cycle similar to that of an adult ready to be fertilized is established, the results were different: the age of puberty became 779 ± 119 days with a weight of 182 ± 16 kg.The N'Dama heifers born in the rainy season are more precocious (461.2 ± 33 days) with a weight of 184.6 ± 21 kg, against 767 ± 22 days and 191.8 ± 21 kg during the dry season. The number of calves born from a breeding dam was 0.8.In our study, sire puberty was reached between 16 and 20 months, for a weight of 151.8 ± 16 kg. A positive correlation (r = 0.49 ± 0.1) was obtained between scrotal circumference and puberty weight.

Effects of Zeranol and Monensin on Reproductive Performance of Replacement Heifers

Effects of zeranol and monensin, alone or in combination, on replacement heifer growth and reproductive performance were investigated. Over a period of 6 yr, 311 Hereford x Angus heifers were stratified by age and weight at weaning randomly assigned to one of four treatments: control (C); two 36-mg implants of zeranol administered on d 1 and 96 (Z); 200mg of monensin, daily (M); or zeranol+monensin (ZM). Diets included meadow hay+1.4kg barley+.05kg of biuret during the 196-d wintering phase. Initial weights averaged 166kg. Heifers in the M and ZM treatments had 18% greater (P<.05) ADGs than those in C or Z. Age at first estrus was younger (P<.05) for implanted heifers compared to heifers not implanted. First breeding conception rates were reduced (P<.05) for Z and ZM compared to C and M while second breeding conception rates also differed with M and Z heifers higher (P<.05) than C and ZM. Age at conception in the first breeding was older (P<.01) for Z- and ZM- treated heifers than C or M. Calving interval for Z was shorter (P<.01) than C but not different (P>.1) from M or ZM. Zeranol increased (P<.05) the attrition rate of heifers by over 50% compared to C and M in the first calving year. Second breeding attrition rate was higher (P<.01) for C and ZM treatments than for M or Z.Pelvic size tended to be larger (P<.1) at time of breeding in ZM heifers and incidence of dystocia was lower (P<.05) in implanted heifers. Results indicate that two implants of zeranol reduced first calf conception rate, delayed conception, and decreased age of first estrus. An increased attrition rate within the first year was also observed in implanted heifers. Monensin appeared to counteract some of the negative effects of zeranol on reproductive performance and reduced culling rates over the first two calving seasons.

Seasonal Changes Associated with Puberty in Female Rats: Effect of Photoperiod and ACTH Administration1

Studies were conducted between December 1976 and February 1978 examining the influence of season and photoperiod on the sensitivity of female rats to the inhibitory effects of adrenocorticotropin (ACTH) on sexual maturation. Female rats were reared from birth in either a 14 h light:10 h dark schedule (14 hL:10 hD) or an 8 h light:16 h dark schedule (8 hL:16 hD). ACTH was administered daily, starting at 21 days of age and continuing until vaginal opening (VO) or day 40. Rats were examined for age of VO, estrous stage at VO, body weight at VO, age at first estrus and the number of ova ovulated at first estrus. ACTH significantly delayed VO and the age of first estrus in rats raised in 8 hL:16 hD schedules. Body weight at VO was also reduced in these animals but ova counts were not altered by ACTH treatment. In rats raised in 8 hL:16 hD, ACTH had a significant seasonal effect on the age of VO, age of first estrus and the estrous stage at VO. Rats were most responsive to the retarding effects of ACTH on VO and first estrus during the winter months and ACTH had little effect on these parameters during the summer. During the winter months, a larger number of ACTH-treated rats were in diestrus at VO compared with summer when the predominant smear was either proestrus or estrus. In 14 hL:l0 hD schedules, ACTH significantly delayed the age of first estrus, but had only marginal effects on the other parameters of sexual maturation. No seasonal differences in response to ACTH were observed in this photoperiod. These data show that there is a seasonal responsiveness to the effects of ACTH on sexual maturation which is operational only in a reduced photoperiod.

Effect of melengestrol acetate on the bovine ovary.

To investigate the relation of ovarian morphology to increased body weight gain during administration of melengestrol acetate (17-acetoxy-6-methyl-16-methylenepregna-4,6-diene-3,20-dione, or MGA, a progestagen), ovaries of 100 Holstein dairy heifers were examined for characteristics of follicular maturation, signs of lipid secretion, and the presence of steroid-producing-type cell organelles. The heifers were fed either a normal or a high-protein level ration with or without 0.30–0.45 mg daily of MGA from 2.5 months of age to the age of first estrus or to breeding age (120 cm withers height). The high-level ration effect was not consistently mediated by the special development of ovarian structures. MGA effect, like the weight-gain effect, was consistently evident after the time of first estrus. MGA suppressed estrus and ovulation, and resulted in the presence in the ovary, after regression of corpora lutea, of an increased number of large follicles. The largest follicles corresponding in structure to developing proestrous, mature estrous, or early atretic follicles contained hypertrophied theca interna cells showing lipid secretion signs and ultrastructural characteristics of steroid synthesis. The majority of the largest follicles, however, were atretic or late atretic and did not contain steroid-type cells. The development of replacement follicles was evident in ovaries with late atretic largest follicles. The weight-gain effect of MGA may therefore be associated with a steroidogenic, probably estrogenic, effect in the cow.

Puberty in the buffalo-cow

Thirty-five buffalo heifers were tested daily with fertile males to ascertain the age and live weight at first possible oestrus and conception. Patterns of sexual behaviour were recorded while rectal palpation was carried out to define the conditions of the ovaries and to diagnose pregnancies. The mammary gland development, as well as the intensity of lactation, were noted post partum.1. Pubertal matings were allowed with less certainty than adult matings. The signs of oestrus were intensified by the recurrence of heat and association with the male. Homosexuality was only observed in the first and second oestrus.2. The average age of first oestrus, first conception and first calving were 406, 647 and 963 days respectively. The body weight at first oestrus and first conception were 198 and 319 kg. respectively.3. The number of services/conception ranged from 1 to 7 with an average of 4·25. The number of silent heats/female ranged from 1 to 4 with an average of 1·65. The period elapsing from first oestrus to first conception ranged from 52 to 438 days. Before conception, there was a period of anoestrus which ranged from 115 to 314 days, this was probably due to weak oestrus symptoms.4. The live weights at 28, 84, 140, 196, 252 and 308 days were correlated with the age and live weight at first oestrus as well as the live weight at first conception.5. All the buffalo-cows except two which showed oestrus conceived. Fourteen animals calved normally while fourteen aborted after 131–318 days. The gestation period ranged from 312 to 321 days with an average of 316 days. The birth weight of young ranged from 33 to 40 kg. Seven animals were not lactating while seven gave 1–2 kg. of milk.6. Puberty phenomenon is a gradual phenomenon and is attained in steps: sexual desire, ovulation, oestrus, conception, pregnancy then lactation.