Onset Of Behavioral Estrus Research Articles

153 The effects of parity and oxytocin or prostaglandin F2α added to insemination doses on reproductive performance of pigs bred in summer

Summer is the least favourable season for swine reproduction, mainly due to long photoperiods and heat stress. Such conditions negatively impinge on the reproductive system of sows and boars, manifesting in debilitated uterine and gonadal function. This situation is exacerbated by the dilution of ejaculates in semen extender before AI. Consequently, there is a noticeable decline in piglet productivity of summer-breeding gilts and sows. The main goal of this study was to determine the effect of oxytocin (OX) or prostaglandin F2α analogue (PG) added to boar semen extender on the duration of insemination and reproductive performance of pigs bred in July and August. A total of 144 females (80 gilts and second-parity sows (G+SP) and 64 multiparous sows (M)) were divided into three groups (n=48 per group). The OX (11 G+SP and 37M) and PG (20 G+SP and 28M) groups were inseminated twice (at the onset of behavioural oestrus and 22-24h later) using semen supplemented with 20IU of OX or 5mg of PG, respectively; the controls (33 G+SP and 15M) were artificially inseminated with non-supplemented inseminate doses. Pregnancy was detected ultrasonographically on gestational day 42, and the number and viability of piglets were recorded at farrowing. Proportions were analysed using chi-square test (Brandt and Snedecor formula), and other numerical data were analysed using two-way analysis of variance and least significant difference test to determine the differences between individual mean values (SigmaPlot, Systat Software Inc.). The mean duration of first insemination was shorter (P<0.05) in M females (80±22s) compared with G+SP females (191±26s) inseminated with PG-supplemented semen, whereas the second insemination was shorter (P<0.05) in M females than in G+SP females artificially inseminated with OX-supplemented semen (93±15s compared with 192±28s). The mean pregnancy rate was lower (P<0.05) in control G+SP females (26/33; 85%) than in OX G+SP females (11/11; 100%). The farrowing rate was less (P<0.05) in control females (36/48; 75%) than in OX females (44/48; 92%), and it was less (P<0.05) in PG G+SP females (14/20; 70%) compared with PG M females (26/28; 93%). The M females in the OX group had more (P<0.05) stillborn piglets per litter compared with their G+SP counterparts (0.6±0.1 vs. 0.1±0.1). Overall, PG females had more (P<0.05) weak piglets per litter (1.2±0.2) compared with the control (0.5±0.2) and OX (0.6±0.2) groups. The present results reveal the occurrence of both beneficial and undesirable effects of PG and OX added to boar semen extender on reproductive performance of breeding pigs in summer. Addition of PG was associated with shorter first-insemination times in older sows compared with G+SP animals but also with lower farrowing rates in younger animals and an overall increase in the number of weak piglets at farrowing. Supplementation of OX was in turn associated with a shorter second insemination and higher pregnancy rates in young females but more stillborn piglets per litter in multiparous sows. The specific causative mechanisms of these associations remain to be elucidated.

194 Usefulness of the Ultrasound Imaging Modalities B-Mode and Colour Doppler Sonography and Serum Progesterone Concentrations for Determining Superovulatory Ovarian Responses in Ewes

The main goal of this study was to assess the usefulness of the 2 imaging modalities—B-mode and colour Doppler sonography—for determining the superovulatory response in ewes. In addition, serum concentrations of progesterone (P4) were examined for correlations with the numbers of laparoscopically detected luteal structures. Oestrus was synchronized in 24 sexually mature Santa Inês ewes with intravaginal P4-releasing devices (CIDR®) inserted for 8 days on a random day of the oestrous cycle. An injection of 37.5 μg of prostaglandin F2α analogue (d-cloprostenol) was given at the time of CIDR® insertion and withdrawal. The superovulatory treatment consisting of 8 consecutive doses of porcine FSH (total dose of 200 or 133 or 100 mg of pFSH; n = 8/total dose) given at 12-h intervals began 48 h before CIDR® removal. All animals received a single injection of 300 IU of eCG concurrently with a first dose of pFSH. On the day of surgical embryo recovery (6 days after the onset of behavioural oestrus), the ovaries of all donor ewes were visualised and examined with transrectal ultrasonography and then with videoendoscopy to identify and enumerate corpora lutea (CL) and luteinized unovulated follicles (LUF). Jugular blood samples were collected just before ovarian imaging for the measurement of circulating P4 concentrations. Ovaries could be easily and repeatedly detected with both the transrectal ultrasonography and videoendoscopic technique. Prematurely regressing CL could not be distinguished from healthy CL using either B-mode or colour Doppler ultrasonography but they were identified by their pale color by using videoendoscopy. All animals responded to the superovulatory treatment and produced ≥4 CL; however, a wide variation in ovarian responses was observed among ewes (range: 4–24 CL/ewe). Three ewes failed to produce healthy CL and had prematurely regressing CL only. In general, LUF were observed in 20/24 ewes (1–5/ewe) and 14/24 ewes had regressing CL (1–22/ewe). The total number of CL (r = 0.78 and 0.83; P < 0.0001) and LUF (r = 0.74 and 0.90; P < 0.0001) enumerated using the B-mode and colour Doppler ultrasonographic technique, respectively, were correlated with that ascertained by videoendoscopy. The determination of the superovulatory response was better by colour Doppler ultrasonography in relation to the B-mode, because it allows a better delimitation of the luteal structures. Serum P4 concentrations were related inversely to the numbers of prematurely regressing CL (r = –0.70; P = 0.0004) and directly to the number of healthy CL (r = 0.69; P = 0.0005). The present results indicate that ultrasonographic imaging and serum P4 measurements on the day of embryo recovery are both very accurate indicators of ovarian responses in superovulated ewes.

The intravaginal electrical impedance measurements in monitoring estrous cyclicity, the length of the breeding season and ovarian cysts in goats

The aim of this work was to assess the usefulness of the intravaginal impedance measurements in monitoring estrous cycles, indicating ovarian disorders and determining the duration of the reproductive season in goats. Intravaginal electrical impedance at the vagino-cervical junction was measured using the 2-electrode impedometer (shaft diameter 0.6cm; electrode outer diameter 0.8cm, shaft length 21cm). The outer electrode has a diameter of 0.8cm. The first experiment was carried out on 8 goats during the mid-breeding season and included 2 consecutive estrous cycles. Intravaginal electrical impedance was measured daily and blood samples were taken at time for plasma concentrations of progesterone (P4) and at 4-h intervals during estrus for detection of the luteinizing hormone (LH) peak. The second experiment was conducted in goats (n=4) in which irregular estrous cycles and presence of follicular cysts had been previously observed. Experiment 3 was performed during the transitional period between the breeding season and anestrus (n=8). During the breeding season, the changes in concentration of P4 were highly correlated with the values of intravaginal electrical impedance (r=0.84; P<0.01), and the profile changes of the intravaginal impedance followed a pattern similar to the changes in P4 concentrations. Reduction in vaginal impedance was closely associated with the onset of behavioral estrus and the LH peak. In peri-estrous period, the intravaginal impedance values were 35.65±0.49Ω and were significantly different (P<0.01) than in the luteal phase (57.39±0.37Ω). Positive correlations and similar profile of changes in the intravaginal impedance and concentrations of P4 were also recorded in goats, in which disorders in the course of the estrus cycle were found, caused by the presence of the ovarian follicular cysts. In these goats both the intravaginal impedance and concentration of progesterone remained constant and low level (32.17±0.53Ω, and 0.43±0.03ng/ml, respectively). During the onset of the seasonal anestrus, in spite of the remaining low concentration of P4, intravaginal impedance did not show higher fluctuations, and the correlation between these parameters was negative (r=−0.31; P<0.01). In conclusion, the results demonstrated that measurements of the intravaginal impedance can be useful to monitor the estrous cycle and in goats. Our preliminary results also suggested the usefulness of measurements of intravaginal impedance in signaling the presence of ovary cysts in goats. However, these studies require further follow-up. Moreover, measurements of the intravaginal impedance can constitute an information about the onset of the seasonal anestrus in this animal species.

Benefits of synchronizing ovulation with porcine luteinizing hormone in a fixed-time insemination protocol in weaned multiparous sows

Objective: To determine reproductive performance of weaned sows inseminated twice at fixed times after controlling time of ovulation with porcine luteinizing hormone (pLH) administered at onset of behavioral estrus. Materials and methods: Multiparous sows were randomly assigned to treatment at weaning. From weaning, twice-daily boar exposure facilitated estrus detection. Untreated control sows (n = 150; CONT) were artificially inseminated at least twice. Treated sows (n = 168; LUT) received 5 mg pLH intramuscularly concomitant with the first detection of standing heat. To coincide with the normal working day, sows in estrus in the morning were inseminated at 24 and 30 hours (am and pm), while sows in estrus in the afternoon were inseminated at 24 and 42 hours (pm and am), after pLH administration. Results: For multiparous sows bred on days 4 to 6 after weaning, total-born litter size was greater in LUT than in CONT (12.88 and 11.80, respectively; P &lt; .01), whereas adjusted farrowing rate was not affected by treatment, (LUT, 87.28%; CONT, 83.20%; P &gt; .05). Neither variable was affected by day of breeding or a treatment × day interaction (P &gt; .05). Fewer inseminations (P &lt; .001) were performed in LUT (2.00) than in CONT (2.13). Implication: Double insemination of multiparous sows, timed to coincide with optimal sow fertility, may improve litter size.

Ovarian and endocrine responses to prostaglandin F2α (PGF2α) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F2α (PGF2α) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF2α (15mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF2α treatment (2.3±0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7±0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF2α injection (3.0±0.6ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF2α treatment (2.0±0.3ovulations/ewe; P>0.05). The mean interval from PGF2α to emergence of the next follicular wave (1.0±0.4 and 4.0±0.0d, respectively; P<0.001) and the interval from PGF2α treatment to the next FSH peak (0 and 3.5±0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7±0.2, and six ewes ovulated both before and after the onset of estrus (3.0±0.5ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1±0.3 or 5.5±0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF2α at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF2α-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.

Follicular, endocrine and behavioural dynamics of the Indian rhinoceros (Rhinoceros unicornis) oestrous cycle

Longitudinal ultrasound, behaviour and endocrine evaluations were conducted, over 14 to 18 months, in two young female Indian rhinoceroses (Rhinoceros unicornis) to characterize the oestrous cycle. Both females showed the same pattern of follicular development producing a large follicle (10-12 cm diameter) on one of the ovaries that persisted for 8.5 +/- 4.68 days before spontaneously ovulating. Ovulation occurred in all eight cycles monitored in a 6- to 7-year-old female versus 10 out of 14 cycles monitored in a 5- to 6-year-old female. Ultrasound examinations confirmed follicular collapse 48 h following the onset of behavioural oestrus in ovulatory cycles, while anovulatory cycles were associated with the formation of a haemorrhagic follicle. The day of behavioural oestrus corresponded to peak urinary oestrogen conjugate concentrations for each cycle, but anovulatory cycles had lower concentrations on the day of behavioural oestrus compared with ovulatory cycles. A transient increase in urinary progesterone metabolite concentrations was detected 1 day prior to ovulation. Irregular urinary progesterone metabolite profiles followed anovulatory cycles, reflecting varying degrees of follicular luteinization. In an attempt to ensure that a cycle would result in ovulation in the 5- to 6-year-old female, a GnRH treatment was tested during two separate cycles. Administration of GnRH on the day of behavioural oestrus resulted in an increase in urinary luteinizing hormone concentrations 2 h following injection. Regardless, ovulation did not occur in response to treatment. This study provides the first ultrasound data on ovarian activity in the Indian rhinoceros and establishes normal physiologic and behavioural relationships during the oestrous cycle that may facilitate the breeding of this species in captivity.

The influence of adverse or gentle handling procedures on sexual behaviour in fearful and confident sows

In the present study, the influence of handling during lactation on fear of humans and on sexual behaviour in the presence and absence of a human was investigated. Prior to handling, the sows were selected as being either fearful ( n=24) or confident ( n=24) towards humans based on their reactions to a human that entered their home pen. Within each group, half of the sows were handled either adversely or gently twice daily during the last 6 days prior to weaning until the end of the following oestrus. On the day of weaning, the sows were tested for their fear of humans in human approach tests in their home pen and in a novel arena. In order to determine when oestrus set in and whether ovulation took place, the back pressure test was performed by the stock persons from the fourth day after weaning and until the end of oestrus, and the sows were subjected to trans-rectal ultrasonographical scans from 12 h after onset of behavioural oestrus. Finally, a T-maze test was applied to investigate the sexual behaviour of the sows with and without the handler present on the third day after weaning until the end of oestrus. One of the stimulus compartments of the T-maze contained a boar and the other was empty. When the handler was present the handler stood in the goal area in front of the boar pen. The back pressure test and the trans-rectal scans revealed that all the sows came into oestrus during the experimental period. In the human approach test in the home pen the confident sows showed a significantly shorter latency to stay within 0.5 m of the handler ( P=0.02), to sniff the handler ( P=0.007) and to root ( P=0.04). The gently handled sows had a longer latency to freeze ( P=0.0001), shorter latency to root ( P=0.01), a tendency for shorter latency to stay within 0.5 m of the handler ( P=0.10) and to sniff the handler ( P=0.07) than the adversely handled sows. Handling and fear class affected the behaviour in the novel arena in a similar way. Thus, irrespective of fear classes, handling affected the sows and adverse handling generally made the sows more fearful of humans. The results of the T-maze test before oestrus revealed that the adversely handled sows and the fearful sows spent shorter time standing at the boar pen when the handler was present than when the handler was not present, whereas the opposite was the case for the gently handled sows and for the confident sows, respectively ( P<0.001). During oestrus, however, only the fearful sows that were handled adversely spent significantly less time close to the boar when the handler was present compared to when the handler was not present ( P<0.05), whereas all other sows spent an equal amount of time standing close to the boar whether the handler was present or not. Thus, in contrast to the pre-oestrus observations, during oestrus, adverse handling only affected the fearful and not the confident sows. This indicates that it is possible to improve oestrus behaviour and thus the possibility to detect oestrus by gentle handling of fearful sows.

Changes in preoptic and hypothalamic levels of progesterone receptor mRNA across the oestrous cycle of the ewe.

We measured the levels of progesterone receptor (PR) mRNA in the hypothalamus and preoptic area (POA) of the ewe across the oestrous cycle. Perfusion-fixed hypothalamic tissue was collected from sheep killed during the luteal and follicular phases and during behavioural oestrus. Blood samples taken at the time of tissue collection verified that the oestrous ewes were undergoing a preovulatory luteinizing hormone (LH) surge. Matched sections were taken from the POA, periventricular nucleus (PeVN), ventromedial nucleus (VMN) and arcuate nucleus of each animal. In situ hybridization was performed using a sheep specific, (35)S-labelled riboprobe for PR and semiquantitative image analysis was conducted on emulsion-dipped slides. The number of silver grains per cell was greater in the VMN and arcuate nucleus of oestrous ewes than in luteal and follicular phase ewes; there was no cyclic variation in the level of PR mRNA expression in the cells of the POA and PeVN. The number of labelled cells per mm2 in the VMN was higher in the oestrous ewes than in luteal phase and follicular phase ewes. The number of labelled cells in the PeVN was also higher in the oestrous ewes than in follicular phase ewes, but there was no cyclic variation in the POA and arcuate nucleus. In the ewe, the onset of behavioural oestrus corresponds to the onset of the preovulatory LH surge and increased PR mRNA expression at this time is likely to be due to the high concentrations of circulating oestrogen that precede this period.

Stag exposure advances the lh surge and behavioral estrus in eld's deer hinds after cidr device synchronization of estrus

The impact of male presence or absence on the timing of the preovulatory LH surge and estrus was studied in 3 experimental groups (n = 6/group) of Eld's deer hinds pretreated with intravaginal progesterone-releasing devices (CIDR-type G) as follows: Group 1 = indirect male contact barn; Group 2 = direct male contact barn; and Group 3 = male isolation barn. For all hinds, the duration of the preovulatory LH surge averaged 2.5 ± 0.5 h, whereas mean peak preovulatory and basal LH concentrations were 2.9 ± 0.2 ng mL 1 and 0.27 ± 0.03 ng mL 1, respectively. Nine of 12 male-exposed hinds exhibited a preovulatory LH surge within 24 to 32 h postCIDR device withdrawal, whereas 0 of 6 male-isolated hinds exhibited a preovulatory LH surge during the same time period. Onset of behavioral estrus (45.2 ± 2.3, 52.7 ± 5.7 and 66.3 ±1.8 h, respectively) was significantly advanced (P < 0.05) after CIDR device withdrawal in male exposed hinds (Groups 1 and 2) compared with male isolated hinds (Group 3). These data suggest that stag exposure is important for modulating the timing of the preovulatory LH surge and behavioral estrus after synchronization of estrus with exogenous progestagens.

The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between electrical resistance of the vaginal mucosa and serum concentrations of estradiol (E 2) and progesterone (P 4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonprolific Western white-faced and 7 prolific Finn ewes, during the mid-breeding season (October to December). Transrectal ultrasonography of ovaries was performed once a day to confirm ovulation and monitor follicle growth (follicles ≥3 mm in diameter) and development of corpora lutea (CL). Jugular blood samples were collected daily for radioimmunoassay (RIA) of estradiol and progesterone. In all ewes, a decline in vaginal impedance (to <40 ohms) was closely associated with the onset of behavioral estrus. In both breeds of sheep, there was no significant correlation between daily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E 2:P 4 ratio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = −0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = −0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = −0.36, P = 0.052, respectively) but not during the remaining portion of the luteal phase in either breed. In conclusion, vaginal mucous impedance appears to be primarily controlled by progesterone, but it also changes in response to shifts in the E 2:P 4 ratio when progesterone concentrations are low. Impedometric characteristics of the vaginal mucosa in cyclic ewes are an indicator of serum concentrations of progesterone and E 2: P 4 ratios during the terminal stage of the estrous cycle.

Use of short-term progestin treatment to resynchronize the second estrus following synchronized breeding in beef heifers

Two trials were conducted to evaluate the efficacy of short-term progestin administration to resynchronize the second estrus after artificial insemination in yearling beef heifers. In Trial 1 crossbred yearling heifers (n = 208) were synchronized with Syncro-Mate-B (SMB) and artificially inseminated (AI) between 48 and 54 h following implant removal. Implant removal is defined as Day 1. Following AI, the heifers were randomly assigned to 1 of 2 experimental groups. Group 1 heifers were fed melengestrol acetate (MGA) daily from Day 17 to 21 at a rate of 0.5 mg/head, while Group 2 control received no exogenous progestin during this period. Synchrony of estrus was defined as the 3-d period in which the highest number of heifers expressed behavioral estrus in each group. There was no difference (P < 0.05) in the pregnancy rate during the second estrus due to MGA supplementation. More MGA-treated heifers (P < 0.01) expressed estrus in a 3-d period than the controls. In Trial 2, yearling heifers (n = 108) were synchronized with 2 injections of PGF 2α (second PGF 2α injection is designated as Day 1) administered 14 d apart with AI 12 h after the onset of behavioral estrus. The heifers were then randomly assigned to 1 of the following 3 treatment groups after initial AI: 1) MGA fed at 0.5 mg/head daily from Days 17 to 21; 2) norgestomet administered in 6.0-mg implants from Days 17 to 21; 3) untreated control heifers. Blood samples were collected on Day 21 and analyzed for progesterone (P 4). Elevated P 4 (> 1 ng/ml) on Day 21 indicated pregnancy to the first insemination. Synchrony among the 3 groups of heifers was similar (P > 0.10); however, the second estrus was less (P < 0.05) variable in the MGA and norgestomet treated heifers. During the resynchronized second estrus, conception rates were not affected by progestin treatment (MGA 40%, norgestomet 64%, and control 62%; P > 0.10). However, a proportion of heifers treated MGA 10% 4 36 and norgestomet 3% 1 36 expressed behavioral estrus during second estrus even though they were diagnosed as pregnant from first service by elevated P 4 levels on Day 21. We conclude that short-term use of progestin from Days 17 to 21 following AI causes closer synchrony of estrus; however, inseminating pregnant heifers that exhibit behavioral estrus may cause abortion.

Importance of 6 p.m. in Hamster Timekeeping Evidenced by Computer Analysis of Wheel-Running Activity

We addressed the question whether the clock signal for hamsters to become active occurs at sundown throughout summer or at some constant time after noon (p.m. time). Ten female golden hamsters housed in wheel cages in a windowless room were exposed to 24-h light/dark (LD) cycles simulating the equinoxes (LD 12: 12), when the sun sets at 6 p.m. and rises at 6 a.m., and summer (LD 14: 10, 16: 8, and 18: 6), when the sun sets after 6 p.m. and rises before 6 a.m. The onset of behavioral estrus, a mask-free phase marker of the same clock that controls wheel-running, was observed every 4 days, and wheel revolutions were recorded every 5 min for 52 days. Computer analysis of the 5-min values averaged for all 10 hamsters revealed a clear onset of running for each LD exposure. Time in the windowless room is referenced to mid-L (room “noon”) of the LD cycles. Although L-off ranged from 6 p.m. in LD 12: 12 (6 h after mid-L) to 9 p.m. in LD 18: 6, estrus began close to 4 p.m. and running close to 6 p.m. in every LD c...

Effects of work and diet on progesterone secretion, short luteal phases and ovulations without estrus in postpartum F 1 crossbred dairy cows

The effects of work and diet supplementation on progesterone secretion and on incidence of short luteal phases and ovulations without estrus was investigated in 40 postpartum F 1 crossbred dairy cows. These cows were allocated to 1 of 4 treatment groups: Group SPNW, supplement-nonworking; Group SPW, supplement-working; Group NSNW, nonsupplement-nonworking; and Group NSW, nonsupplement-working. After calving, working cows pulled sledges with a load of 300 to 450 Newtons(N); 4 hours per day 4 days per week, for a total of 100 days over a 1-year period. All cows were fed natural grass hay ad libitum while the supplemented cows were fed 3 kg of concentrate per head per day. The proportion of cows which showed behavioral estrus by 1 year post partum was 100, 100, 60 and 20% for Group SPNW, SPW, NSNW and NSW cows, respectively. Based on plasma progesterone concentrations, ovulation started 62 days earlier than onset of behavioral estrus. A total of 73 ovulations occurred by 1 year post partum. Forty-nine (67.1%) and 26 (32.9%) ovulations occurred in the supplemented and nonsupplemented cows while 33 (45.2%) and 40 (54.8%) ovulations occurred in the working and nonworking cows, respectively. Of the total ovulations, 26 (35.6%) were not associated with behavioral signs of estrus and occurred in 13 (32.5%) cows. The incidence of ovulation without estrus was higher (P<0.05) in working (42.4%) than in nonworking (30%) cows and in nonsupplemented (41.7%) than in supplemented (32.7%) cows. Short luteal phases occurred in 32.5% of the cows before the establishment of normal estrous cycles. In working cows, diet supplementation off-set the negative effect of work on the onset of estrus and conception. However, a relatively higher number of cows in Group SPW had ovulations without estrus before a normal estrous cycle was established. The incidence of short luteal phases or ovulations without estrus did not influence the pregnancy rate in subsequent normal estrus periods. In conclusion, in the supplemented cows, work did not influence the proportion of cows showing estrus and conceiving, but it significantly delayed the postpartum anestrus interval. In the nonsupplemented cows, reproductive activity was impaired in both working and nonworking cows, but was pronounced in working cows. However, once pregnancy was established there was no effect of work on the maintenance of pregnancy. Our study shows that with appropriate feeding regimens lactating crossbred cows could be used for draught purposes without any detrimental effects on fertility, but calving intervals would be extended. Finally, the physiological mechanisms involved in anestrus and ovulations without estrus and the significance of such phenomena in affecting postpartum reproductive performance and fertility in working cows require further investigation.

Synchronization of estrus in dairy goats given norgestomet and estradiol valerate at various stages of the estrous cycle

Summary Dairy goats were given subcutaneous implants with 3 mg of norgestomet (nor) and im injections of 0.625 mg of estradiol valerate and 0.375 mg of norgestomet on day 0 of the estrous cycle (estrus; nor 0, n = 18), on postestrus day 4 (nor 4, n = 18), or on postestrus day 11 (nor 11, n = 15). Ear implants were removed after 9 days. Mean (± se) hours from removal of ear implants to onset of estrus and proportion of goats responding were 36 ± 3.8 and 83%, 33 ± 4.0 and 61%, and 36 ± 2.7 and 93% for groups nor 0, nor 4, and nor 11, respectively. There were no significant differences between treatment groups in time to onset of estrus. The percentage of goats in group nor 11 that had signs of estrus was significantly greater than the percentage of goats in group nor 4. Of the goats in groups nor 0, nor 4, and nor 11 that had signs of estrus, 53, 55, and 86%, respectively, had onset of behavioral estrus between 24 and 48 hours after implant removal. All goats that had signs of estrus had onset of behavioral estrus between 12 and 72 hours after implant removal. Mean (± se) hours from removal of ear implants to time of peak concentrations of luteinizing hormone (lh) were 49 ± 4.1, 49 ± 3.8, and 49 ± 4.0 for groups nor 0, nor 4, nor 11, respectively (not different). The percentage of goats in group nor 11 that had lh peaks was significantly greater than the percentage of goats in group nor 4. Of the goats that had estrus, there was no difference between groups in the percentage, which also had an lh peak. On the basis of progesterone profiles from does in group nor 0, functional corpora lutea had formed in 3 of 18 does while the ear implants were in place. In group nor 4, concentrations of progesterone were &lt; 1.0 ng/ml in 6 of 18 does at the time of implant placement, suggesting that these does had not formed functional corpora lutea by postestrus day 4. Eight of 18 does in group nor 4 had concentrations of progesterone &gt; 1.0 ng/ml at 48 hours after implant removal, suggesting that the estradiol valerate in the injection had not prevented the formation of functional corpora lutea after the previous estrus in these animals. All does in group nor 11 had concentrations of progesterone &gt; 1 ng/ml on the day of implant placement. Progesterone concentrations had decreased to &lt; 1 ng/ml in all but 1 doe in group nor 11 by the day of implant removal, suggesting that the corpora lutea from the previous estrous cycle had undergone luteolysis prior to the time of implant removal in most of these animals. This method of synchronization of estrus was effective in dairy goats, although goats that were in the early luteal phase at the time of treatment did not respond consistently.

How hamsters keep time: the 6 pm to 6 am light-sensitive period.

A recent review of the pineal literature revealed that when hamsters are exposed to 24-hour light:dark (LD) cycles with less than 12 hours of darkness (summerlike, SLD), the nightly period of pineal melatonin synthesis (PPMS) begins close to the midpoint of the dark period ("midnight") and ends at lights-on irrespective of the length of the dark period or time of day presented. New evidence based on the onset of behavioral estrus every 4 days indicated that the 24-hour hamster clock controlling timing of estrus (4:30 PM) and the PPMS has a 12-hour light-sensitive period (LSP) set to 6 PM-6 AM in LD 16:8 (dark 8 PM-4 AM, SLD) by a balance in opposing actions of evening and morning light [Alleva: Pineal Research Reviews, Volume 5, Alan R. Liss, Inc., New York, 1987]. Present experiments focus on how this balance is maintained. When lights-off was advanced to 6 PM in SLDs ranging from LD 12.5:11.5 (dark 6:15 PM-5:45 AM) to 18:6 (dark 9 PM-3 AM), the onset of estrus later that day was advanced in every SLD. However, when lights-on was delayed to or beyond 6 AM, the onset of estrus was unaffected. Thus, the balance is maintained by a resistive force (blocking without a delaying action) of evening light and an advancing action of morning light. In this balancing process all evening light from 6 PM to lights-off but only the first 5 minutes or less of morning light were involved. The advancing action of morning light was characterized in LD 13:11 and 18:6 by imposing on the night before estrus a 5:30 PM-6:30 AM dark period scanned with a 15-minute light pulse. Shifts in onset of estrus later that day were plotted vs. time of the light pulse. The resulting phase response curves (PRCs) were similar and comprised only an advancing curve, which rose about 10 PM, peaked at 2 AM, and returned gradually to normal at 6 AM. In contrast, a PRC obtained from LD 12:12 (dark 6 PM-6 AM) was sinelike, comprising a 6 PM-9 PM delaying curve followed by an advancing curve similar to those from SLD. An hypothesis based on these findings is presented to explain how hamsters would keep constant AM-PM time throughout summer.

Time of onset of estrus in gilts

An experiment was conducted to determine when, during a 24-h period, gilts show the onset of behavioral estrus. Beginning on Day 16 of their first estrous cycle, 42 crossbred gilts were observed at 0600, 1200, 1800, and 2400 h for the onset of their second estrus. Fifty-five percent of the gilts had shown onset of estrus by 0600 h. None of the gilts showed the onset of estrus from 0600 to 1200 h, whereas 24% and 21% of the gilts had shown onset of estrus by 1800 and 2400 h, respectively. Chi-square analysis demonstrated that more (P < 0.025) gilts had shown onset of estrus by 0600 than by 1200, 1800, and 2400 h. When the data were combined for estrous checks by 0600 and 1800 h, 76% of the gilts had their onset of estrus by 0600 h as compared to 24% of the gilts by 1800 h (P < 0.005). In conclusion, more gilts had shown onset of estrus by 0600 h than at any other 6-h period.

Oestrus synchronization and fixed-time artificial insemination in the weaned sow

Reproductive performance was assessed in multiparous weaned sows in which double fixed-time AI was used in association with the injection of oestradiol benzoate (OB) to synchronize post-weaning oestrus. After weaning (day 0), groups of 25 sows were either injected with ethyl oleate (group 1, controls), or 10μg OB/kg body weight (b. wt.) (group 2) on the morning of day 2, or 10μg OB/kg b.wt. on the morning of day 3 (group 3). Group 1 sows were inseminated 8–16 h after the onset of behavioural oestrus and again 24 h later. Group 2 and 3 sows were inseminated on the afternoons of days 4/5 and 5/6, respectively. Sows were allocated to treatment with respect to parity and litter-size born, and no differences existed in pre-treatment reproductive performance between groups. The mean weaning-to-oestrus interval in group 1 sows was 5.66 ± 0.14 days; 49/50 OB-treated sows were in oestrus when inseminated, indicating the efficacy of OB in promoting an early and synchronous return to oestrus. Conception rates were 19/25, 8/25 and 14/25 for groups 1, 2 and 3, respectively, and the difference between groups 1 and 2 was significant (ifP< 0.01). Ovulation rates, assessed in pregnant sows at 28 to 40 days of gestation, were not significantly different (18.32 ± 0.76, 17.00 ± 0.93 and 16.64 ± 0.83 for groups 1, 2 and 3, respectively) but embryonic survival was affected by OB treatment and was significantly lower (ifP< 0.01) in group 2 (36.8%) than in control (64.4%) sows. In non-pregnant sows the ovulation rate at slaughter was similar in all groups, indicating that there was no residual effect of OB treatment on ovarian function. Five of the group 2 sows had cystic follicles at slaughter. It is concluded that the time of oestrogen treatment after weaning has a critical effect on reproductive performance in the sow. Work on further refinements of the dose and mode of administration of oestrogen, as well as the timing of injection in individual herds is, therefore, needed in order to determine whether treatment with oestradiol can be effectively used for oestrus synchronization in association with fixed-time mating or AI.

Pituitary a-Subunit Messenger Ribonucleic Acid Remains Elevated during the Latter Stages of the Preovulatory Luteinizing Hormone Surge*

In this study, pituitary alpha-subunit mRNA amounts were assessed during the latter stages of the preovulatory LH surge in the normal cycling ewe. The times chosen were 15 and 25 h after the onset of behavioral estrus, designated E+15 and E+25. These mRNA values were correlated with pituitary and serum LH concentrations to assess the possible role of subunit synthesis during these times of the cycle, and then compared to values obtained from hybridizations of RNAs from animals in other groups representing defined stages of the cycle. One of these groups included animals during the midluteal phase (day 12), whose amounts were assigned a value of 1. It was observed that the amounts of alpha-subunit mRNA in E+15 and E+25 groups, as measured by translations and cDNA hybridizations, were approximately 10-fold higher than the day 12 values and were roughly similar to those observed in a group examined 5 h after estrus. Thus, it is evident that the alpha mRNA levels are not only elevated during the LH surge, but also remain high at a time when both serum and pituitary LH concentrations have fallen dramatically, suggesting the involvement of changing mRNA amounts in the feedback systems associated with the maintenance of pituitary and serum gonadotropin amounts.

Luteinizing hormone beta-subunit mRNA amounts increase during the preovulatory surge of luteinizing hormone in the ewe: the highest levels are observed at the completion of the peak.

Amounts of mRNA for luteinizing hormone (LH) beta-subunit were assessed during selected times in the normal estrous cycle of sheep. These times spanned the luteal phase through the preovulatory LH surge, and included groups designated as: (i) day 12 of the cycle (day 12); (ii) 24 hr before the onset of the expected behavioral estrus (E - 24); and (iii) 5, 15, and 25 hr after the onset of behavioral estrus (E + 5, E + 15 and E + 25). These groups were characterized by criteria such as serum and pituitary LH concentrations, serum progesterone, and ovarian morphology. Specific LH beta-subunit mRNA was evaluated by Northern transfers, using a specific bovine LH beta cDNA probe. Slopes were determined using a linear regression analysis and then expressed as fold stimulation relative to the values for the day 12 group. The results indicate that LH beta mRNA amounts increase after day 12, reaching a value of approximately 12-fold by E + 25. When correlated with serum and pituitary LH amounts, it is observed that the amounts of beta mRNA increase in a fashion parallel to serum and pituitary LH concentrations through the time E + 5. After this time, LH beta mRNA amounts continue to increase despite a dramatic fall in both serum and pituitary LH. These results suggest that LH beta mRNA amounts are regulated during the LH preovulatory surge.

Efficacy of using vaginal conductivity as an indicator of the optimum time to breed in swine.

Two experiments were conducted to test the efficacy of using vaginal conductivity measurements to predict ovulation time in swine. In Exp. 1, 10 normally cycling 6-mo-old purebred Hampshire gilts were tested daily through two estrous cycles in order to characterize conductivity patterns. In all females, onset of behavioral estrus was verified by daily observation in the presence of a sexually active boar. Significant changes in vaginal conductivity by day of the cycle were detected in all females tested, with a high degree of variation among individuals. A 10% increase in conductivity occurred 12 to 24 h after the onset of estrus, which is coincident with the time normally associated with high fertility. In Exp. 2, 46 prepubertal crossbred and purebred Yorkshire gilts and 17 multiparous purebred Yorkshire and Duroc sows were assigned randomly to eight treatment groups. All females were checked twice daily for the onset of estrus and vaginal conductivity readings were taken from approximately 3 d before estrus until breeding. Females were bred by artificial insemination or handmated at times determined either by detection of estrus alone or when a 10% increase in conductivity readings occurred relative to the onset of estrus. Similar conception rates were achieved in animals bred after a 10% change in vaginal conductivity as compared with detection of estrus. These results indicate that vaginal conductivity measurements during estrus provided a reliable basis for determining the time to breed swine. However, there was no advantage associated with the use of vaginal conductivity.