Start Of Estrus Research Articles

EMBRYO FLUSHING IN COWS UNDER VARIOUS SUPEROVULATION SCHEMES

The use of biotechnological reproduction methods is a relevant issue since the embryo transfer, obtained after stimulating superovulation, can accelerate reproduction and improve the number of cattle. The purpose of the study was to evaluate the effectiveness of various schemes for stimulating superovulation in cows of the Ukrainian black-pock dairy breed. Therewith, the study analysed the ovarian response to the drug “FSH-Super” under different introduction schemes: Step-up (gradual increase in the dose) and Step-down (gradual dose reduction) and recorded the number of embryos suitable for transplantation. Donor cows were administered the drug “Estrofan” to synchronise the sexual cycle. After 7 days, the drug “Ovarelin” was injected, and after another 7 days, the injection of the drug “Estrofan” was repeated in the same dose. Stimulation of superovulation began on the 10th day of the sexual cycle with the drug “FSH-super” in the form of eight gradually increasing (Step-up) and gradually decreasing (Step-down) doses within 4 days. Artificial insemination was performed 12 and 24 hours after the start of oestrus. During the study, it was discovered that in the group of cows with gradual dose reduction of the drug “FSH-Super”, 83.3% reacted with superovulation, and in the group with the gradual increase – only 71.4%. Therewith, the number of yellow bodies on two ovaries in a donor cow averages 15.6 and 9.2, respectively. An average of 12.4 and 7.8 embryos (Step-down and Step-up) were obtained from the donor, of which 7.8 and 4.2 are suitable for transplantation, respectively. However, in the group of cows with gradually decreasing doses, a higher number of embryos unsuitable for transplantation was obtained – 4.6 and unfertilised oocytes – 2.6, compared with the group of donors with gradually increasing doses, where these indicators are 3.6 and 1.0, respectively. Thus, the use of the drug “FSH-super” to donor cows according to the step-down introduction scheme allows getting more embryos suitable for transplantation. This will allow managing the biotechnological aspects of cattle reproduction and effectively and in a controlled manner accelerate the breeding process in farms of various forms of ownership, fixing the desired genotype in the herd

Dietary effects of drone larves homogenate on the homeostatic constants and the reproductive capacity of Large White gilts

Background: With modern requirements for housing agricultural animals particularly pigs, the manifestation of normal physiological functions significantly changes, especially reproductive one, which is manifested in an insufficiently expressed sexual cycle, reduced resistance due to technological stress. There is a need to develop effective reproductive biotechnologies in pig using organic stimulants of entomological origin, among which a significant place is given to the homogenate of drone larvae (HDL).The aim of the study was to determine the dietary effects of HDL on the formation of prooxidant-antioxidant homeostasis in Large White (LW) gilts,as well as to optimize reproductive function during experimental feedingof HDL.Methods: In the study, gilts representing Large White breed were investigated. A total of 20 gilts representing two groups. The first feeding group (n=10) of LW gilts was fed with the control normal diet, and the second feeding group (n=10) of LW gilts wasfed with the supplement diet i.e., the biological additive of homogenate drone larvae in quantity of 0.5g daily. To assess prooxidant-antioxidant homeostasis in pigs, blood samples were taken from the anterior vena cava into the diestrus phase i.e., 11 days from the beginning of the second cycle after the determination of the immobility reflex and the estrus phase i.e., 24 days after the start of estrus after the determination of the immobility reflex. Intracervical artificial insemination of gilts was performed during 24 and 36 hours after the determination of the immobility reflex, and depending on the manifestation of signs of estrus.Results:Study found an intensification of peroxidation processes during the period of puberty in LW gilts , which wasmanifested in an increase in the content of diene conjugates on the 180th and 210th days of development by 63.6% and 44.1%, respectively.This is confirmed by a significant increase in the number of secondary products of peroxidation - TBA-active complexes in these periods of their development. Studyrevealed that during puberty of gilts the antioxidant defense system wasthe most labile from 6 to 8 months of age, where the variability of PAG components wassignificant in terms of increased activity of superoxide dismutase (p <0.01) and catalase (p <0.05), as well as the amount of reduced glutathione. Moreover, additional feeding of HDLcontributedto the probable slowing down of peroxidation processes in blood, which was confirmed by the lower content of diene conjugates (p <0.05-0.01) and TBA-active complexes (p <0.01-0.001).Conclusions: Study concluded that experimental supplementary feeding ofHDLdiet to LWgiltsstimulatedthe reproductive function during their puberty by reducing the time to the first estrous cycle for artificial insemination, thus improved the fertility in LW gilts.

Optimal timing of artificial insemination in gilts

In the article it is highlighted the results of research on the features of cervix permeability and optimal periods of fertilization in pubertal gilts. Five high-productive boars of the Large White breed, aged 18-36 months, were used in experiments and evaluated for the quality of sperm. The start of the estrus was carried out using a test boar. In the first experiment to determine the permeability of the cervical canal, 3 groups of the Large White breed were formed for 15 heads in each, which were inseminated at the onset: of the first (1st group), the second (2nd group) and the third period of the estrus at the age of 6 - 8 months. Gilt were fertilized with a sperm dosage of 70 ml of a diluent containing 2 billion of spermatozoa. In the second experiment to determine the optimal timing of insemination, 66 gilt of the Large White breed aged 8 to 9 months, live weight 110-130 kg, with clear signs of the start of proestrus, estrus and diestrus were used. The beginning of the estrus was set twice a day at 7 o'clock and 19 o'clock. The doses of sperm (2 billion of spermatozoa in 70 ml of diluent) were injected into the gilts according to the following scheme: Group I - after the prescribed period of the estrus - 0 hours; Group II - after 6 hours; III - group - 12 hours; Group IV - 18 hours; V - 24 hours; VI - 36 hours. It has been determined that cervical permeability increases with age of gilts and the number of reproductive cycles. In gilts, in the first reproductive cycle, the permeability of the cervical canal is 4.61 cm and intensively increases twice: 1.9 (p <0.001) (2nd estrus) and 2.5 times (p <0.001) (3rd estrus). The introduction of sperm by the intracerviсal method on the third period of the estrus allows them to be fertilized at a level of 86 % and receive 10.2 newborn piglets.Cervix permeability in gilts increases from the beginning of the estrus for the next 24 hours. The high indexes of their reproductive capacity are determined at the introduction of sperm dosage in 24-36 hours after the onset of the estrus. The number of live newborns piglets was maximal when sperm is introduced into cervix of gilts in 12; 24 and 30 hours after the start of the estrus. The live weight of newborn piglets depends on the period of the introduction of sperm into the pigs, being maximal at the start of the estrus, and in 24 and 30 hours after the introduction of sperm. The postponement of the procedure up to 36 hours leads to a decrease of this index (p <0.001). Key words: reproductive cycle, estrus, cervix, fertilization, sperm, gilt.

INSEMINACIÓN ARTIFICIAL POR LAPAROSCOPIA EN OVINOS BAJO CONDICIONES DE CAMPO EN EL VALLE DEL MEZQUITAL, HIDALGO

Objetivo: Evaluar la técnica de inseminación artificial por laparoscopia (IAL) bajo condiciones de campo en variables reproductivas en ovejas y sus impactos sociales con ovinocultores de la región del Valle del Mezquital, Hidalgo.
 Diseño/ metodología/ aproximación: El diseño experimental fue completamente al azar. Se utilizaron 387 ovejas distribuidas en 7 Municipios y 14 unidades de producción ovinas (UPO), de las razas: 162 Katahdin, 145 Hampshire, 45 Dorset y 35 Suffolk. El estro se sincronizó con esponjas intravaginales por 11 días, dos días antes del retiro se aplicó 400 UI de gonadotropina (eCG). La IAL se llevó a cabo a las 50 h post sincronización del estro en cada una de las UPO.
 Resultados: La respuesta e inicio del estro no mostró diferencias (P > 0.05) entre las diversas razas de ovejas. El porcentaje de ovejas gestantes presentó diferencias por la raza (P ? 0.05), la Katahdin mostró mayor tasa de gestación a pesar de las condiciones de campo y diversidad en las UPO; sin embargo, la prolificidad entre las razas fue semejante.
 Limitaciones del estudio/ implicaciones: Se sugiere la inclusión de nuevas razas de pelo que cumplan con las expectativas de los ovinocultores y satisfagan la demanda del producto para el comercio de la barbacoa.
 Hallazgos/ conclusiones: La técnica de IAL y el protocolo hormonal en la sincronización del estro presentan resultados favorables en gestación y prolificidad, por lo que resultan ser efectivos para el Programa de Mejoramiento Genético de Ovinos en la región del Valle de Mezquital, Hidalgo, México.

195 Effect of feeding a licorice extract to Japanese Black cows on embryo production performance after superovulation treatment

The objective was to determine the effect of feeding a licorice extract that contains glycyrrhizic acid, which is known to have a liver function-enhancing effect, on embryo production performance after superovulation treatment in Japanese Black cows. Japanese Black breed cows (n=136) that had calved 1 to 4 times and had normal uteri as seen by ultrasonography after at least 40 days from the last calving were used as test animals. Animals in the treatment group (n=90) were continuously fed 20g head−1 d−1 of a licorice extract (Kanzou, Fabric Onishi Co. Ltd., Osaka, Japan), with at least 13% glycyrrhizic acid content) once a day, mixed with the formula feed, for 60 to 90 days starting from around the day of calving until ova/embryos were collected. The control group (n=46) received no Kanzou from the day of the last calving until ova/embryo collection. A total of 20 Armour units (AU) of FSH (Antorin R, Kyoritsu Seiyaku Corporation, Kanagawa, Japan) from porcine pituitary was given intramuscularly (IM) twice a day, morning and evening, for 3 consecutive days (decreasing dose schedule: 5 AU×2, 3 AU×2, and 2AU×2) as the superovulation treatment to the cows at 8 to 11 days post-oestrus in both groups. Prostaglandin F2α 25mg and 15mg (IM) were administered in the morning and evening, respectively, on the third day of FSH administration. Artificial insemination was done at 12 and 24h after the start of oestrus, and ova/embryos were collected using a uterine reflux method on Day 7 post-oestrus. The mean numbers of ova/embryos and transferable embryos collected and the mean embryo quality scores (according to the IETS guidelines) in the treatment and control groups were compared by t-test. A chi-squared test was used to compare the proportion of transferable embryos in the 2 groups. There was no significant difference in the mean number of ova/embryos retrieved between the treatment group (21.7±11.8) and the control group (15.8±11.3), although the former tended (P=0.07) to yield more ova/embryos. There was significant difference (P<0.05) in the mean number of transferable embryos collected in the treatment group (13.1±8.3) than in the control group (8.1±5.3). The mean embryo quality score was significantly greater (P<0.01) in the treatment group (1.6±0.4) than in the control group (2.2±0.6). The proportion of transferable embryos in the treatment group (60.3±26.4%) was also significantly higher (P<0.05) than in the control group (51.2±26.0%). In conclusion, feeding a licorice extract to Japanese Black cows for 60 days or longer improves the quality of embryos obtained after superovulation treatment and leads to an increase in the mean number of transferable embryos per cow.

The relationship between milk progesterone and milk traits during estrus in dairy Cows

The aim of this study was to evaluate relationship between milk progesterone concentration (P4) and milk traits at the start of estrus time and 12h after start of the estrus in dairy cows. The 96 milk samples of 48 Lithuanian dairy cows without reproduction disorders and 90–100 days after calving were evaluated. Cows were classified into two groups based on milk yield per day: less than 30 kg (n=20) and e”30 kg (n=28). Data were categorized by milk fat and protein content at the start estrus and 12h after start of estrus to evaluate relationship between P4 and milk traits examined. P4 at estrus time in dairy cows was significantly positively correlated with milk yield (P less than 0.001), whereas it was negatively correlated with milk protein (P less than 0.05-P less than 0.01) and fat at 12h after start of estrus. Dairy cows with F/P from 1.0 to 1.5 had the lowest P4 in milk. Results of the pregnancy in dairy cows were related with lower P4 and milk yield level (P less than 0.001), higher milk fat (P less than 0.05) and milk protein content (P less than 0.001). These cows had 1.90 times lower prevalence of the signs of subclinical ketosis (P less than 0.05) at estrus time when compared with non-pregnant cows. As a result, it was clearly demonstrated that P4 in dairy cows can help to evaluate and improve the reproductive properties of cows.

Altrenogest treatment before weaning improves litter size in sows.

The study aimed to assess whether altrenogest treatment, fed before weaning (from -8 to -2days), could improve fertility of sows showing reproductive seasonality. Ninety sows (50 in winter-spring [WS] and 40 in summer-autumn [SA]) were randomly selected and assigned to control (C; 27 in WS and 20 in SA) or altrenogest treatment (A; 23 in WS and 20 in SA) groups. The diameter and number of ovarian follicles were transrectally scanned at the onset of oestrus. Oestrus was evaluated twice daily from weaning to day 8 post-weaning. Sows in oestrus were post-cervically inseminated at 0 and 24hr after the onset of oestrus with liquid stored semen (1.5×109 sperm/doses), and farrowing rates (FR) and total piglets born (LS) were recorded. More (p<.01) sows showed no signs of oestrus within 8days after weaning in SA (30%) than in WS (2%), without differences between A and C groups. The diameter (cm) of the follicles at the onset of oestrus was larger in A than in C sows (0.76±0.01 vs 0.73±0.01; p<.01), irrespective of the season. No differences in the number of follicles were found. FR did not differ between seasons and groups, being always above 85%. LS was larger (p<.01) in A (14.00±0.46) than C (12.27±0.44) sows, irrespective of the season. In conclusion, a short-term altrenogest treatment at the end of lactation improves the total number of piglets born from weaned sows, probably by promoting a better and more homogeneous follicular development at the start of oestrus.

Sociosexual behaviours in cycling, intact female rats (Rattus norvegicus) housed in a seminatural environment

Groups of 3 males and 4 females were housed in a seminatural environment for a period of 8 days. Female sociosexual behaviours were recorded and analysed from the beginning of behavioural oestrus (defined as the first lordosis response observed in the environment) until the end of oestrus (defined to occur at the moment of a lordosis that was not followed by another one within 60 min). The duration of behavioural oestrus varied between 4.05 and 10.87 h, with a mean of 7.41 ± 0.49 h. In order to analyse changes in behaviour during oestrus, the entire period was divided in 5% segments for each female. The frequency and/or duration of some behaviours changed during the period of oestrus, while others remained stable. Most remarkable among the latter are the frequency of lordosis and the lordosis quotient. From the start of oestrus until the end, the females responded with lordosis to every male mount. Rejections were most frequent at the beginning of the period of oestrus. Then there was a decline, and thereafter rejections remained at a low level, even when the end of oestrus was approached. Paracopulatory behaviours reached a maximum towards the end of the first quarter of the oestrus period. There was no evident decline at the end of oestrus. Females having a high frequency of lordosis showed more paracopulatory behaviours and were pursued more by the males than females with low lordosis frequency. When the behaviour of females with a large number of offspring was compared to that of females with a low number of offspring, no difference in sexual behaviours was found. Comparisons between the females’ behaviour in response to preferred (either defined as the male producing the largest number of lordosis responses or as the male that was most sniffed by the female) and non-preferred males revealed a few minor differences. Location of behaviour was also analysed. Comparisons were made between the environment’s open area and burrow and between different sectors in these parts. Some important differences were found. This is the first detailed description of female rat sociosexual behaviour during the entire period of behavioural oestrus in a seminatural environment.

Artificial insemination with cryopreserved sperm from feline epididymides stored at 4 °C

Recovering and storing sperm from the epididymides of males of rare felidae is useful for preserving the species. The objective of the present study was to determine pregnancy rates following artificial insemination (AI) of frozen-thawed epididymal sperm, which were cryopreserved following low-temperature storage of the epididymides. In this study, these sperm were used for unilateral intrauterine AI (UIUAI) or unilateral intratubal AI (UITAI) using 40 × 10 6 and 10 × 10 6 sperm, respectively. The caudal epididymides of 17 cats were stored at 4 °C for 24 h after castration. Artificial insemination of seven female cats was performed on Days 3 or 4 (start of estrus = Day 1) by UIUAI, 20 h after injection of 100 IU hCG to induce ovulation. Furthermore, UITAI at 24 h (UITAI-24) or 30 h (UITAI-30) after hCG were also done (five cats per group). It was noteworthy that AI by UIUAI and UITAI-24 was performed before ovulation, whereas AI by UITAI-30 was performed after ovulation. Pregnancy rates were 28.6% (2/7) by UIUAI, 80% (4/5) by UITAI-24, and 20% (1/5) by UITAI-30. Litter size was one or two by UIUAI, and one to four by UITAI. Spontaneous abortion occurred on Days 25–30 of pregnancy in one of the two female cats pregnant following UIUAI, and in two of five female cats pregnant following UITAI. Based on the high pregnancy rate obtained with 10 × 10 6 sperm in the UITAI-24 group (AI performed before ovulation), we concluded that this was the most appropriate method for AI with frozen-thawed epididymal sperm after initial low-temperature storage of epididymides.

Gene expression patterns in four brain areas associate with quantitative measure of estrous behavior in dairy cows

BackgroundThe decline noticed in several fertility traits of dairy cattle over the past few decades is of major concern. Understanding of the genomic factors underlying fertility, which could have potential applications to improve fertility, is very limited. Here, we aimed to identify and study those genes that associated with a key fertility trait namely estrous behavior, among genes expressed in four bovine brain areas (hippocampus, amygdala, dorsal hypothalamus and ventral hypothalamus), either at the start of estrous cycle, or at mid cycle, or regardless of the phase of cycle.ResultsAn average heat score was calculated for each of 28 primiparous cows in which estrous behavior was recorded for at least two consecutive estrous cycles starting from 30 days post-partum. Gene expression was then measured in brain tissue samples collected from these cows, 14 of which were sacrificed at the start of estrus and 14 around mid cycle. For each brain area, gene expression was modeled as a function of the orthogonally transformed average heat score values using a Bayesian hierarchical mixed model. Genes whose expression patterns showed significant linear or quadratic relationships with heat scores were identified. These included genes expected to be related to estrous behavior as they influence states like socio-sexual behavior, anxiety, stress and feeding motivation (OXT, AVP, POMC, MCHR1), but also genes whose association with estrous behavior is novel and warrants further investigation.ConclusionsSeveral genes were identified whose expression levels in the bovine brain associated with the level of expression of estrous behavior. The genes OXT and AVP play major roles in regulating estrous behavior in dairy cows. Genes related to neurotransmission and neuronal plasticity are also involved in estrous regulation, with several genes and processes expressed in mid-cycle probably contributing to proper expression of estrous behavior in the next estrus. Studying these genes and the processes they control improves our understanding of the genomic regulation of estrous behavior expression.

Mathematical optimization to improve cows’ artificial insemination services

Engineering tools and mathematical optimization are applied in this study to plan the work of the agents of the cow artificial insemination service (inseminator) in Israel. Time is crucial in insemination as the chances of conception decline with increasing delay between the start of estrus and insemination. About 1,090 artificial inseminations of cows are performed daily in Israel. They involve 412 farms in 283 villages, and are performed by 29 inseminators; the work plan should balance the work load among the inseminators. To this end, the working time of an inseminator in each village is required. Thus, a model to predict the working time in a village was developed. Subsequently, a mathematical optimization model was designed and solved, which aims to allocate customers to trips and to determine the itinerary of each trip to minimize total distance/time. The main benefits included a 21.4% reduction in total traveling time and a 55% reduction in the difference between the lengths of the longest and shortest working days. Moreover, the longest delay in reaching an estrous cow is reduced from 7.6 to 5.9h (i.e., by 1.7h), which may increase the conception ratio by some 7%. In addition, the trade-off between work balance and total traveling time was studied.

Indução da ovulação em cabras, fora da estação reprodutiva, com LH e GnRH e com estro induzido por progestágenos

Quarenta e cinco cabras foram sincronizadas com o uso de esponjas intravaginais impregnadas com 60mg de acetato de medroxiprogesterona (MAP) por nove dias, associadas com 200UI de gonadotrofina coriônica equina (eCG) e 37,5µg de cloprostenol no sétimo dia. Os animais foram separados em três grupos e receberam, 24 horas após a retirada das esponjas, solução salina ou hormônios, no seguinte esquema: T1 (controle) - 1ml de solução salina; T2 - 5mg de hormônio luteinizante (LH) e T3 - 12,5µg do hormônio liberador de gonadotrofina (GnRH). Houve diferença (P&lt;0,05) na porcentagem de animais em estro, 100,0%, 73,3% e 66,6%, para T1, T2 e T3, respectivamente. Na mesma ordem, não houve diferença (P&gt;0,05) quanto ao intervalo da retirada da esponja ao aparecimento do estro, que foi, em média, 34,8, 29,3 e 31,5 horas, respectivamente. O intervalo médio da retirada da esponja à ovulação foi de 46,6, 52,1 e 41,6 horas, respectivamente, com diferença significativa entre T2 e T3 (P&lt;0,01). As ovulações ocorreram, em média, 21,3, 26,8 e 22,3 horas após as aplicações (P&gt;0,05). A aplicação de LH e do GnRH para induzir e sincronizar a ovulação em cabras fora da estação reprodutiva não apresentou resultados satisfatórios.

The effect of administering a dopamine agonist (Cabergoline) on follicular and luteal development during pro-estrus and estrus in the female greyhound

To study the effect of the dopamine agonist Cabergoline, on ovarian activity in the female dog during pro-estrus and estrus, 6 greyhounds were treated with 5μg/kg per os of Cabergoline for 20 days beginning on the first day of pro-estrus; 6 animals were left untreated (controls). Ovarian morphology was determined by ultrasound examination once a day during pro-estrus and twice a day during estrus. Follicles were divided into three classes on the basis of their diameter: F1 (<3mm), F2 (3–6mm) and F3 (>6mm). The presence and diameters of post-ovulatory follicles (F-POST) and corpora lutea (CL) were also recorded. Blood samples were taken once a day during pro-estrus and twice a day during estrus. The plasma was assayed for LH, prolactin and progesterone by radioimmunoassay.There were no differences between Cabergoline-treated and control dogs in the duration of pro-estrus or estrus. There was a progressive increase in follicle diameter from the start of pro-estrus when follicles were mainly class F1 to the day of estrus when follicles were mainly class F3. Three days after the start of estrus, the first F-POST follicles were detected. This pattern of development continued and on day 5 the first CLs were detected. By day 9, only CLs were detected. The peak of pre-ovulatory LH was within 3 days of estrus and ovulation was detected in all animals within 3 days of the LH peak. There were no differences in LH concentrations between groups. Plasma prolactin levels varied between animals and were reduced in treated dogs, however, this was not statistically significant (P=0.12). Plasma progesterone levels were below 1.0ng/ml before the LH surge and thereafter gradually increased. There were no differences in plasma progesterone concentrations between treated and control dogs. In conclusion these results show that the administration of the dopamine agonist Cabergoline during pro-estrus and estrus did not affect the duration of pro-estrus or estrus or the pattern of follicular and luteal development in female dogs.

Evidence for maternal regulation of early conceptus growth and development in beef cattle.

Fifty-one cyclic beef cows were mated with fertile bulls. At 36 h after the start of oestrus, cows were assigned to receive sesame oil (controls) or progesterone (100 mg) on Days 1, 2, 3 and 4 of pregnancy. Peripheral plasma concentration of progesterone was measured until slaughter on Days 5 or 14. Cows were randomly assigned to be slaughtered on Days 5 or 14 or remain intact and palpated per rectum on Day 40 to verify pregnancy. Uteri on Days 5 and 14 were flushed for recovery of luminal protein and conceptus tissue. Conceptus and endometrial tissues were cultured with [3H]leucine and submitted to two-dimensional-PAGE and fluorography. Administration of progesterone increased peripheral plasma progesterone concentration on Day 2-5. Conceptuses recovered from progesterone-treated cows on Day 14 were advanced in development compared to conceptuses from control cows. Conceptuses recovered from progesterone-treated cows were viable as polypeptides associated with maintenance of pregnancy in cattle were synthesized and released at an earlier time and pregnancy was maintained beyond Day 40. Early progesterone stimulation altered the synthesis and release of polypeptides from endometrial explant cultures on Day 5. Results indicate a role of progesterone in the maternal regulation of conceptus growth and development in early pregnancy of cattle.

Multiple mating and siring success during natural oestrus in the ewe

Ewes were each mated on four separate occasions, at 3, 9, 15 and 21 h after the start of oestrus and at each time by a different ram. The progeny were assigned to sires by blood typing, supplemented by resemblance between lambs and rams. The paternity of 64 lambs, born to 41 ewes, was established: 2 were conceived at a 3-h mating, 27 at 9h, 23 at 15 h and 12 at 21 h. The optimum time for a ram to inseminate, when in competition with others, is therefore 9-15 h after onset of oestrus, and this finding accords with behavioural observations. Ewes tended to lamb during the same half of the day as that when they had come into oestrus.

Serum profiles of luteinizing hormone, progesterone and total estrogens during the canine estrous cycle.

Serum levels of LH, total estrogen and progesterone were measured daily by radioimmunoassay during proestrus, estrus and early diestrus in five beagle bitches. Occurrence of the LH peak relative to the onset of estrus was quite variable ranging from 3 days before to 7 days after the onset of estrus. Serum LH levels were elevated for 3 days with a peak value of 25 ± 2 ng/ml reached 2.4 days after the start of estrus. LH levels were ≤ 2 ng/ml when measured at other times during the estrous cycle. Estrogen titers ranged from 84 ± 39 pg/ml at 9 days before the LH peak to 175 ± 15 pg/ml coincident with the LH peak. A broad estrogen peak was evident beginning 5 days before and continuing for 5 days after the LH peak. An estrogen surge was seen in 4 of 5 dogs immediately preceding or coincident with the LH peak suggesting that LH release in the bitch is triggered by a sharp elevation in estrogen levels. Serum progesterone levels rose from ≤ 5 ng/ml before the LH peak to 46 ± 6 ng/ml 6 days afterwards.

The fertility of ewes injected with synthetic oxytocin following artificial insemination

In an experiment involving the artificial insemination of 246 Corriedale ewes with 0.1 m1 of undiluted ram semen, the intramuscular injection of 200 mU or 800 mU of synthetic oxytocin following insemination, either 0-14 or 14-24 hours after the start of oestrus, had no effect on fertility.