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PubMed1993

The effects of subnutrition on the components of the gravid uterus in the doe.

The effects of subnutrition on the caprine fetus and the other products of pregnancy were investigated in does. Two groups of does were fed on rations calculated to provide 100 and 25% of their energy and protein requirements for maintenance from 19 days before mating until 60 days after mating. Estrus was synchronized in does using PGF(2x). Approximately 60 days after natural mating, pregnant does were slaughtered, and the products of pregnancy were measured. Fetuses from the feed-restricted group were significantly lighter (P<0.05), had shorter crown-rump length (P<0.05), and the uterus contained a smaller volume of fetal fluids (P<0.02). Curved crown-rump length tended to be shorter and fetal placental membranes and cotyledons tended to be lighter (P<0.1) in the feed-restricted group. No significant difference was found between the 2 groups in the head length, number of placentomes, and weight of empty uterus. The number of fetuses affected the number of placentomes (P<0.001), weight of empty uterus (P<0.001), mass of total fetal fluids (P<0.001) and weight of ovaries (P<0.05), but not fetal measurements. Gestation length was found to significantly (P<0.001) affect all the fetal measurements but none of the placental measurements except for the total weight of cotyledons (p<0.001). The results of the study demonstrated detrimental effects of underfeeding on the caprine fetus and placenta.

Journal Article↗

PubMed1993

Use of pregnancy-specific protein-B and estrone sulfate for determination of pregnancy on Day 49 in fallow deer (Dama dama ).

The objective of this study was to determine if pregnancy specific protein-B (PSPB) and estrone sulfate (E(1)SO(4)) could be used to determine pregnancy status in fallow deer (Dama dama ). Forty mature does were synchronized for estrus with an intravaginal progesterone-releasing device (CIDR) and then artificially inseminated via laparoscopy with frozen semen on one day. Ultrasound examination and jugular blood sampling were done 49 days later. Transrectal ultrasonography was done to presumptively determine the pregnancy status at the time of blood sampling. Serum estrone sulfate concentrations were significantly (P < 0.05) greater in pregnant (n=31) than nonpregnant (n=9) females at 49 days of gestation (166.7 +/- 25.9 pg/ml vs 36.3 +/- 11.1 pg/ml, respectively). The percentage of [(125)I]PSPB bound was significantly (P < 0.01) lower when sera of pregnant (n=29) versus nonpregnant (n=9) females was added to RIA tubes (63.7 +/- 1.6% vs 98.1 +/- 1.6%, respectively). There were 30 fawns born from the group of females that were diagnosed pregnant based on ultrasound. We conclude that estrone sulfate and PSPB can be used to determine pregnancy status in fallow deer at 49 days of gestation.

Journal Article↗

PubMed1993

Cryopreservation of embryos as a means of germ plasm conservation in sheep.

Embryos were collected from 4 lines of Targhee sheep between 1986 and 1990. The lines were selected for preweaning growth rate (Lines DH and HW) or for multiple births (Line HT); Line C served as an unselected control group. Estrus was synchronized using fluorogestone acetate-impregnated vaginal pessaries, and ewes were superovulated with FSH. Embryos at the morula or blastocyst stage were surgically recovered from mature ewes at Days 5 to 6 and were frozen following morphological evaluation. The overall average number of freezable embryos per collection was 2.9, and did not differ significantly among years or among lines. Of the embryos collected between 1986 and 1988, 92 were transferred to 53 recipients in 1989, producing 53 lambs. Survival rates were 60.9 and 47.8%, respectively, for embryos evaluated as good and fair after thawing. Good-quality blastocysts yielded the highest survival rate (64.4%). Analyses indicated no significant effects of line, developmental stage or embryo evaluation on the incidence of lambing. It was concluded that embryos of morula or blastocyst stage can be successfully frozen for extended periods. The data on embryo yield and survival following cryopreservation were used to calculate numbers of donors needed to preserve and reconstitute a population of specified size.

Journal Article↗

PubMed1994

Ovulation rate, zygote recovery and follicular populations in FSH-superovulated goats treated with PGF(2alpha) and/or GnRH.

Follicular development and ovulation were examined in superovulated Nubian and Nubian-cross dairy goats following prostaglandin F(2alpha) (PGF(2alpha)) and/or gonadotropin releasing hormone (GnRH) treatment. Estrus was synchronized with Synchromate-B((R)) implants. Superovulation was induced with follicle stimulating hormone (FSH) and augmented with GnRH and/or PGF(2alpha). The PGF(2alpha) treatment was administered on Day 2 of superovulation. Implants were removed from all goats on Day 3 of superovulation. The GnRH treatment was administered 24 h after implant removal. All does were exposed to fertile males for 48 h at the time of GnRH injection. Surgical embryo recovery and ovarian response evaluation were conducted 64 to 78.5 h after implant removal. The number of ovulations was higher with GnRH treatment (18.5 +/- 7; x +/- SEM) than that in the controls (5.3 +/- 4.1; P < 0.05). There were fewer follicles in the GnRH-treated does than in the untreated does (10.9 +/- 2.9 vs 22.1 +/- 3.2; P < 0.05). The number of follicles smaller than 4 mm in diameter (5.8 +/- 0.8) did not differ between treatments. The GnRH-treated does had fewer 4- to 8-mm follicles (4.2 +/- 2.0 vs 9.1 +/- 1.6; P < 0.05) and fewer follicles larger than 8 mm (0.7 +/- 1.4 vs 7.3 +/- 1.6; P < 0.01) than the controls. Predicted times for 1- and 2-cell embryo recoveries were 68.5 and 73.7 h following implant removal, respectively. This study demonstrates that GnRH is an effective supplement used with FSH superovulation regimens in dairy goats. Moreover, GnRH provides for enhanced early embryo collection for DNA microinjection studies.

Journal Article↗

PubMed1994

Further development of a transcervical technique for artificial insemination in sheep using previously frozen semen.

A transcervical technique (the Guelph System for transcervical AI) was used to inseminate 2060 ewes on 65 farms (average 31 ewes, range 5 to 107) in Ontario, Canada, from October 1990 to September 1992, using previously frozen semen. Estrus was synchronized using progestagen pessaries and PMSG with median inseminations done at 54 h from pessary removal. Maiden ewes were not included. Only ewes in which the cervix could be penetrated were inseminated with 150 million spermatozoa per insemination. A total of 1809 were penetrated and inseminated (penetration rate 87.8%). Success of penetration increased from 76.3% in the first 500 ewes to 97.9% in the last 500 (P=0.01). Cervical penetration was more successful in ewes in the accelerated lambing program (92.3%, average 3.1 mo since the previous lambing) than those in the annual lambing program (82.4%, average 7.0 mo since the previous lambing; P=0.06). The lambing rate for ewes bred during the combined traditional breeding seasons (Fall of 1990, 1991, 1992) was 50.7% compared to 24.4% for ewes bred at other periods (P=0.00001). The average time required for handling and insemination decreased from 8.62 min in the first 500 ewes to 3.62 min in the last 500 ewes. The Guelph System for Transcervical AI was found to be successful for cervical penetration in most ewes. Penetration success was affected by period since the last lambing and by inseminator experience. The lambing rate was higher for ewes bred during the traditional Fall breeding seasons than during other times of the year.

Journal Article↗

PubMed1996

Trucking stress at breeding does not lower conception rate of beef heifers.

The goal of this study was to determine whether 1 h of trucking stress before or after artificial insemination (AI) altered the conception rate of beef heifers. Estrus was synchronized in heifers with prostaglandin F(2alpha). The 3 treatment groups consisted of 1) AI (control heifers, n = 93); 2) Truck + AI (trucked for 1 h immediately before AI, n = 81); and 3) AI + Truck (trucked for 1 h immediately after AI, n = 82). All heifers were artificially inseminated by a single technician with semen from a single ejaculate. Blood samples were collected for cortisol measurement 1 h before AI, immediately before and after AI, and 1 h after AI in the AI (n = 6), Truck + AI (n = 9), and AI + Truck (n = 8) groups Pregnancy in heifers was confirmed either at slaughter or by palpation per rectum. Trucking before AI elevated (P < 0.01) serum cortisol concentrations. Artificial insemination alone increased (P < 0.01) serum cortisol concentrations in AI heifers. The increase in serum cortisol concentrations caused by trucking after AI was not significant (P > 0.05). Areas under the cortisol curves in Truck + AI heifers are greater (P < 0.05) than in AI heifers. The conception rates of AI heifers (50.5%), Truck + AI heifers (51.9%) and AI + Truck heifers (58.5%) are not different (P > 0.05). This study demonstrates that 1 h of trucking stress either before or after AI did not lower the conception rate of heifers.

Journal Article↗

PubMed1975

Pre-ovulatory elevation of rat ovarian prostaglandins F, and its blockade by indomethacin.

Prostaglandins of the F series have been measured, by radioimmunoassay, in ovaries of prepubertal rats in which first estrus was synchronized by injection of pregnant mare serum gonadotropin. Marked elevations, up to 20-fold, were observed approximately in parallel with the endogenous luteinizing hormone surge which occurs on the evening of proestrus, and within 4 h after injection of exogenous luteinizing hormone on the morning of proestrus. Injection of indomethacin, 0.8 mg per rat, at 14:45 on proestrus, prevented the increase in ovarian prostaglandins F without significantly reducing the proestrous elevation of serum luteinizing hormone. These observations support elevation of serum luteinizing hormone. These observations support a physiologic role of prostaglandins F in rat ovarian responses to luteinizing hormone.

Animals↗

PubMed1991

Dynamics of ovarian follicular development in cattle during the estrous cycle, early pregnancy and in response to PMSG.

Ovarian follicular dynamics of cattle were examined during the estrous cycle, early pregnancy and in response to PMSG. Number and size of follicles were monitored by ultrasonographic examinations. During the estrous cycle, distinct periods of follicular dominance (measured by the increase in difference in size between the largest and second largest follicle) occurred in both the luteal (Days 6-8) and proestrus (18-22) phases of the estrous cycle (two follicular waves). Associated with the well timed development of the first dominant follicle was a change in distribution of follicle numbers in small (less than 5 mm; increased on Days 2-4), medium (6-8 mm; increased on Days 3-5) and large (greater than or equal to 9 mm; increased on Days 6-9) follicular size classes. Follicular development was greater on the ovary bearing the CL for the period that the CL was present. The dominant follicle formed during the first follicular wave was capable of ovulating (6 of 8 heifers) following an injection of a synthetic analogue of prostaglandin F-2 alpha on Day 9 of the estrous cycle. During early pregnancy (Days 6-34), follicular development (size of largest follicle, number of follicles and total accumulated size of all follicles) on the ovary bearing the CL was suppressed between Days 24 and 34 of pregnancy. This was a local effect in that follicular development was sustained on the contralateral ovary. Therefore, the CL or conceptus may be regulating follicular development in a manner to help prevent luteolysis. Associated with the injection of PMSG was an initial increase in the number of small follicles followed by their recruitment into medium and large size classes leading to ovulation. Number of follicles greater than 5 mm on the Day of estrus was related (r = .97) to the number of subsequent embryos and oocytes collected. Ultrasonography is a valuable technique to monitor ovarian follicular dynamics in cattle, and can thereby be used to infer changes in physiological and endocrine states.

Animals↗

PubMed1992

GnRH in the infundibular stalk-median eminence is related to percentage body fat in carcasses of beef cows.

Mature Hereford cows (n = 28) were used to determine the effect of percentage body fat on secretion of LH and content of GnRH in the infundibular stalk-median eminence (ISME). Cows were fed to maintain, lose, or gain weight to achieve body condition scores (BCS; 1 = emaciated; 9 = obese) of 3 to 7. Then cows were fed to maintain weight and body condition. Before slaughter, estrus was synchronized using two injections of prostaglandin F2 alpha(PGF) 11 d apart. Five d after the second PGF injection, cows were given 100 micrograms of GnRH (im) and serum samples were obtained. LH was quantified using RIA. The anterior pituitary and ISME were obtained within 45 min of death. Anterior pituitary weight and LH concentration, total GnRH in the ISME, total carcass fat, and percentage carcass fat were determined. BCS of cows at the time of slaughter influenced percentage carcass fat (P less than .001), total GnRH in the ISME (P less than .02), and maximum LH after GnRH treatment (P less than .09), but did not influence pituitary weight or concentration of LH in the pituitary. Content of GnRH in the ISME averaged 76 +/- 12, 32 +/- 14, 27 +/- 13, and 24 +/- 13 ng for cows with BCS of 3, 5, 6, and 7, respectively. BCS was correlated (P less than .001) with percentage carcass fat (r = .94) and total fat in the carcass (r = .92). Total GnRH in the ISME was negatively correlated (P less than .005) with BCS (r = -.54), percentage carcass fat (r = -.55), and total carcass fat (r = -.49).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗

PubMed1994

Cumulus and oocyte maturation and in vitro and in vivo fertilization of oocytes in relation to follicular steroids, prolactin, and glycosaminoglycans throughout the estrous period in superovulated heifers with a normal LH surge, no detectable LH surge, and progestin inhibition of LH surge.

Crossbred heifers (n = 103) were synchronized to estrus with prostaglandin (PGF2 alpha) and superovulated with follicle stimulating hormone (FSH-P). Animals were ovariectomized every 12 hr after the PGF2 alpha injection (n = 7 to 9/time) up to 108 hr to monitor the follicular, hormonal, and oocyte changes associated with follicular development and ovulation. Twenty-eight animals were implanted with Norgestomet implants 12 hr before PGF2 alpha and ovariectomized at 72, 84, 96, and 108 hr post PGF2 alpha injection to monitor effects of progesterone and suppression of the luteinizing hormone (LH) surge on oocyte maturation and quality. Follicular fluid was collected and analyzed for progesterone, estradiol, prolactin, and glycosaminoglycan content in conjunction with cumulus maturation and nuclear stage of oocyte maturation. Analysis of in vivo matured oocytes by in vitro fertilization was carried out at 60, 72, 84, and 96 hr post PGF2 alpha and in vitro matured oocytes at 12 to 108 hr post PGF2 alpha. No developmental changes in cumulus cells surrounding the oocyte of small follicles was noted (< or = 4 mm dia) indicating a static population. Medium (> 4 < or = 8 mm) and large size (> 8 mm) follicles developed to the corona radiata and loose cumulus stages in animals in which an LH surge was detected but cumulus status remained primarily in the tight cumulus stage for animals without an LH surge. The estradiol-to-progesterone ratio for tight cumulus (TC), corona radiata (CR), and loose cumulus (LC) stages was 1.8 +/- .1, 1.0 +/- .1, and .4 +/- .2, respectively (P < .01). Nuclear maturation of oocytes in small follicles from animals without a detectable LH surge seem to indicate early maturation (48 to 72 hr post PGF2 alpha) in conjunction with a high percent of degenerate oocytes not seen in animals exhibiting an LH surge. Oocytes from medium size follicles matured to germinal vesicle breakdown (GVBD) and early meiosis (metaphase I; MI) stages of development in all treatments. Most oocytes were degenerate in Norgestomet-implanted animals. Oocytes from large follicles (> 8 mm dia) from animals exhibiting an LH surge were in MI and metaphase II (MII) stages (48 to 84 hr post PGF2 alpha) in preparation of ovulation whereas oocytes from animals not exhibiting an LH surge had oocytes that early matured to MII (48 to 72 hr post PGF2 alpha), later regressing to degenerate oocytes (84 to 108 hr). Follicular progesterone, estradiol, and prolactin increased with oocyte maturation, particularly in medium and large follicles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Fertility in the ewe following cervical insemination with fresh or frozen-thawed semen at a natural or synchronised oestrus.

Artificial insemination (AI) in sheep is currently limited by the poor fertility obtained following non-surgical intracervical insemination of frozen-thawed semen. An exception to this general finding is the non-return rate of around 58% reported for large scale on-farm AI in Norway. The objective of the present study was to determine if similar results could be obtained under Irish conditions. Comparisons were made between semen collected, and frozen, from rams in Norway (NOR) and Ireland (IRL). The effects of synchronisation and inseminator were also examined. Parous ewes (n=297) of various breed types were inseminated to a natural (N) or synchronised (S) oestrus with either fresh (from Irish rams) or frozen-thawed (IRL and NOR) semen. Ewes were randomly assigned, within breed, to the following treatment groups: (i) Fresh-N: n=28, (ii) Fresh-S: n=30, (iii) IRL-N: n=62, (iv) IRL-S: n=50, (v) NOR-N: n=68, (vi) NOR-S: n=59. Within each group, ewes were inseminated by an experienced Norwegian or by an Irish inseminator. Pregnancy rate did not differ significantly between ewes inseminated to a natural or synchronised oestrus nor between Norwegian and Irish frozen semen. The proportion of ewes pregnant after insemination with fresh semen was 0.82 and 0.70 (treatments i and ii) compared with 0.40, 0.52, 0.34 and 0.37 (treatments (iii)-(vi)) for frozen semen (P<0.001). Corresponding litter sizes (+/-S.E.), adjusted for ovulation rate, were 2.9+/-0.22, 3.3+/-0.23, 2.2+/-0.21, 1.7+/-0.21, 2.2+/-0.21 and 2.1+/-0.21 (fresh versus frozen; P<0.001). There was an interaction between semen type (fresh or frozen) and oestrus type (N or S) for litter size due to an increased adverse effect of frozen semen on litter size in synchronised ewes (P<0.05). Pregnancy rate was significantly influenced by breed of ewe (P<0.01) and inseminator (P<0.05). These results suggest that ewe breed may be a critical determinant of the potential for the exploitation of cervical insemination of frozen-thawed semen in sheep breeding programmes.

Animals↗

PubMed2004

Regulation of frequency of luteinizing hormone pulses by magnitude of acute change in circulating concentration of progesterone of female cattle.

The hypothesis was the greater the magnitude of acute increase in circulating concentration of progesterone of female cattle, the greater the acute inhibitory effect on frequency of pulsatile LH release. From Day 0 to 4 of the treatment period, females without functional corpora lutea were treated with varying doses of progesterone to result in varying concentrations of progesterone within the typical physiological range in blood. From Day 4 to 7, cattle were treated with a single dose of progesterone to achieve a similar circulating concentration of progesterone among all females in the study. Therefore, from Day 0 to 4 relative to Day 4 to 7 of the treatment period, females had a: (1) large (3.1 ng/ml), (2) moderate (2.5 ng/ml), or (3) small (0.5 ng/ml) increase in concentration of progesterone in blood. Frequency of LH pulses was greater (P <0.10) in females with the greatest magnitude of change in concentration of progesterone during the first 24 h following the change in concentration as compared with females with the moderate or small of change in concentration of progesterone suggesting our working hypothesis should be rejected. The greater the magnitude of acute change in concentration of progesterone, however, the longer time required for re-initiation of release of LH pulses of the amplitude of pulses that preceded the change in concentration of progesterone.

Animals↗

PubMed2004

Natural methods for increasing reproductive efficiency in small ruminants.

This paper describes three strategies to improve the reproductive performance of small ruminants in ways that lead to "clean, green and ethical" animal production. The first is aimed at control of the timing of reproductive events for which we turn to the socio-sexual inputs of the "male effect" to induce synchronised ovulation in females that would otherwise be anovulatory. The second strategy, "focussed feeding", is based on our knowledge of the responses to nutrition and aims to develop short programs of nutritional supplements that are precisely timed and specifically designed for individual events in the reproductive process, such as gamete production, embryo survival, fetal programming and colostrum production. The third strategy aims to maximise offspring survival by a combination of management, nutrition and genetic selection for behavior (temperament). All of these approaches involve non-pharmacological manipulation of the endogenous control systems of the animals and complement the detailed information from ultrasound that is now becoming available. The use of such clean, green and ethical tools in the management of our animals can be cost-effective, increase productivity and, at the same time, greatly improve the image of meat and milk industries in society and the marketplace.

Animal Feed↗

PubMed2005

Effects of oestradiol and some of its esters on gonadotrophin release and ovarian follicular dynamics in CIDR-treated beef cattle.

Three experiments were conducted to: (1) compare the effect of three oestradiol formulations on gonadotrophin release in ovariectomised cows; (2) compare the effects of either oestradiol-17beta (E-17beta) or oestradiol benzoate (EB), given at two doses, on the synchrony of ovarian follicular wave emergence in CIDR-treated beef cattle; and (3) determine the timing of ovulation of the dominant follicle of a synchronised follicular wave following administration of E-17beta or EB 24h after progesterone withdrawal. In Experiment 1, ovariectomised cows (n = 16) received a once-used CIDR on Day 0 (beginning of the experiment) and were allocated randomly to receive 5mg of E-17beta, EB or oestradiol valerate (EV) plus 100mg progesterone i.m. The CIDR inserts were removed on Day 7. There were effects of time, and a treatment-by-time interaction (P < 0.0001) for plasma concentrations of both oestradiol and FSH. Plasma oestradiol concentrations peaked 12h after treatment, with highest (P < 0.01) peak concentrations in cows given E-17beta; estradiol concentrations subsequently returned to baseline by 36 h in E-17beta-treated cows and by 96 h in EB- and EV-treated cows. Plasma FSH concentrations decreased by 12h after oestradiol treatment in all groups (P < 0.0001), reached a nadir at 24h, and increased by 60 h in all groups; plasma FSH reached higher (P < 0.02) concentrations in E-17beta-treated than in EB- or EV-treated cows. In Experiment 2, non-lactating Hereford cows (n = 29) received a new CIDR on Day 0 (beginning of the experiment), and were assigned randomly to receive 1 or 5mg of E-17beta or EB i.m. on Day 1. On Day 8, CIDR were removed and PGF was given. Transrectal ultrasonography was done once daily from 2 days before CIDR insertion to 2 days after CIDR removal, and then twice-daily to ovulation. Although there was no difference among groups in the interval from oestradiol treatment to follicular wave emergence (4.2 +/- 0.3 days; P = 0.5), 5mg of E-17beta resulted in the least variable interval to wave emergence (P < 0.005), compared with the other treatment groups which were not different (P = 0.1). For the interval from CIDR removal to ovulation, there were no differences among groups for either means (P = 0.5) or variances (P = 0.1). In Experiment 3, beef heifers (n = 32) received a once-used CIDR on Day 0 (beginning of the experiment) plus 100mg progesterone i.m. and were assigned randomly to receive 5mg E-17beta or 1mg EB i.m. On Day 7, CIDR were removed and all heifers received PGF. On Day 8 (24h after CIDR removal), each group was subdivided randomly to receive 1mg of either E-17beta or EB i.m. There was no effect of oestradiol formulation on interval from treatment to follicular wave emergence (4.1 +/- 0.2 days; P = 0.7) or on the median interval (76.6h; P = 0.7) or range (72-120 h; P = 0.08) from CIDR removal to ovulation. In summary, oestradiol treatments suppressed FSH in ovariectomised cows, with the duration of suppression dependent on the oestradiol formulation. Both E-17beta and EB effectively synchronised ovarian follicular wave emergence and ovulation in CIDR-treated cattle, and the interval from CIDR removal to ovulation did not differ in heifers given either E-17beta or EB 24h after CIDR removal.

Animals↗

PubMed2005

Influence of level of nutrition during late pregnancy on reproductive productivity of red deer I. Adult and primiparous hinds gestating red deer calves.

The present study aimed to relate feed intake of red deer hinds during late pregnancy to dam body condition, foetal development and calf growth. Across 3 years, multiparous (n=33) or primiparous (n=18) hinds with known conception dates were housed in individual pens from days 150-220 of pregnancy, during which time they were each offered one of three daily allowances of pelletised rations (11 MJME/kg DM; 16% CP): high (H; ad libitum), medium (M; approximately 30% less; multiparous hinds only) and low (L; approximately 50% less). Restricted intake levels were retrospectively calculated from the mean intake of H hinds in the previous week. Hinds were returned to pasture at day 220 and calving was closely monitored. Liveweights, body condition score (BCS), and lactation score (LS) of hinds were recorded weekly from day 130 of pregnancy until calves were weaned at 12 weeks of age. Calves were tagged and weighed at birth, and subsequently weighed at 7 and 12 weeks of age. Additionally, hinds in the first year of study underwent CT scans on days 150 and 215 of pregnancy to assess compositional changes of the dam and conceptus. Mean daily ad libitum intakes of H hinds increased from 1.8 to 2.0 kg DM (0.6-0.7 MJME/kg0.75) at around day 150 to 2.8-3.2 kg DM (0.8-0.9 MJME/kg0.75) by day 220. Those of M and L hinds peaked at 1.8 and 1.6 kg DM, respectively, by day 220. This was reflected in significant treatment effects on liveweight gain and change in BCS and LS by the time of calving. CT scans indicated a significant treatment effect by day 215 on the mass of hind tissues (fat and lean) and a non-significant trend on conceptus/foetal weights. Despite apparent differences in foetal growth trajectories, there were no discernable treatment effects on sex-adjusted birth weights. However, there was an unexpectedly wide spread in calving dates that reflected considerable variation in gestation length. Furthermore, gestation length was negatively correlated with change in hind liveweight (but not BCS) between days 150 and 220 of pregnancy for all groups of hinds (P<0.05). Of three neonatal calf mortalities, none were related to overweight (dystocia) or underweight (non-viability) calves. Subsequent growth rates (g/day) of surviving calves did not reflect prior treatment of their dams, although variation in birth date influenced weights on specific dates. It is concluded from this study that while variation in nutrition to hinds during the last trimester may strongly influence foetal development, under conditions of modest feed imbalance, variation in gestation length compensates to ensure optimisation of birth weight.

Animal Nutritional Physiological Phenomena↗

PubMed2004

Myogenesis in sheep is altered by maternal feed intake during the peri-conception period.

The effect of varying short-term maternal feed intake during the peri-conception period on the development of ovine fetal muscle at mid-gestation was investigated. Superovulated donor Merino ewes (n = 24) were fed a roughage/grain pelleted diet (10.1 MJME/kg dry matter) at either 1.5x maintenance (H; high) or 0.5x maintenance (L; low) from 18 days before until 6 days after ovulation. Embryos were transferred to recipient ewes (n = 60) on day 6. Singleton fetuses were collected on day 75 of gestation and placental weights, fetal body dimensions and fetal organ and muscle weights recorded. The number, type and size of muscle fibres and the dry matter, RNA, DNA and protein content in the semitendinosus muscle were determined. Maternal feed intake did not influence body dimensions, organ development or muscle weights in the fetus. However, L feed intake decreased total muscle fibre number in the fetus by approximately 20% (P = 0.06) compared to H feed intake. This resulted from a reduced secondary to primary fibre ratio (P < 0.05) and indicated that secondary fibre formation occurred at a reduced rate in L fetuses. In addition, protein:DNA ratio tended to be lower in muscles of L fetuses (P < 0.1). It is concluded that restricting feed intake over the peri-conception period reduces or delays myogenesis in fetal sheep. The potential mechanisms by which nutritional availability during this period may influence subsequent myogenic development are discussed.

Animals↗

PubMed2005

Pregnancy rate following GnRH + PGF 2alpha treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment.

Anestrous and lactating Bos taurus by Bos indicus crossbred cows with minimum body condition were studied to determine the efficacy of GnRH+PGF 2alpha combinations for induction of estrus and/or ovulation on pregnancy rate during the months of the year when temperatures are greater. On day 0 (start of treatment), cows were assigned randomly to either treatment or control groups. Treated cows (n = 74) received i.m. 200 microg of GnRH on day 0 and 150 microg of PGF 2alpha 7 days later (day 7). On day 7, treated cows were equally distributed to each of three protocols: (1) Select Synch (n = 25), artificial insemination (AI) 12 h after exhibiting estrus from day 7 (PGF 2alpha injection) until day 12; (2) Ovsynch (n = 24), 200 microg of GnRH at 48 h after PGF 2alpha (day 9) + timed-AI (TAI) 16-20 h later; (3) CO-Synch (n = 25), 200 microg of GnRH + TAI at 48 h after PGF 2alpha (day 9). Control cows (n = 25) received no treatment + AI 12 h after exhibiting estrus from days 0 to 12. Detection of estrus was performed daily during the early morning and evening hours from days 0 to 7 in all the cows, and from days 7 to 12 in the cows treated with Select Synch and in the control group, with the aid of a sterilized bull. Palpation per rectum and transrectal ultrasonography were used on days -30, -20, -10 and 0 to confirm anestrus (absence of CL and no signs of estrus at each evaluation) but with ovarian follicles > or = 10 mm on day 0. Pregnancy rate was 0% for Select Synch, 21% for Ovsynch and 28% for CO-Synch (P < 0.05). In conclusion, the Ovsynch and CO-Synch protocols resulted in greater pregnancy rates compared with the Select Synch protocol in Bos taurus/Bos indicus cows with minimum body condition that were anestrous and lactating during the summer months in a tropical environment.

Anestrus↗

PubMed2005

Effect of artificial insemination on submission rates of lactating dairy cows synchronised and resynchronised with intravaginal progesterone releasing devices and oestradiol benzoate.

This study investigated the hypothesis that a reduction in submission rates at a resynchronised oestrus is not due to the resynchrony treatment involving intravaginal progesterone releasing devices (IVDs) and oestradiol benzoate (ODB) but is associated with artificial insemination (AI) at the first synchronised oestrus. In Experiment 1, cows were synchronised for first oestrus with IVDs, with ODB administered at the time of device insertion (Day 0, 2 mg IM) and 24 h after removal (Day 9, 1 mg IM) and PGF(2alpha) injected at the time of device removal. Cows were then either inseminated (I) for 4 days or not inseminated (NI) following detection of oestrus (first round of AI). Every animal was resynchronised for a second round of AI by reinsertion of IVDs on Day 23 with administration of ODB (1 mg IM) at the time of insertion as well as 24 h after removal (Day 32). Cows detected in oestrus and inseminated for 4 days at the second round of AI were resynchronised for a third round by repeating the resynchrony treatment starting on Day 46 and inseminating cows on detection of oestrus for 4 days. In Experiment 2 the same oestrous synchronisation and resynchronisation treatments were used, but the timing of treatments differed. The cows had their cycles either presynchronised (treatment start Day -23) without AI and then resynchronised, starting on Day 0, for the first round of AI for AI at detected oestrus for 4 days, or they were synchronised (treatment start Day 0) for the first round of AI. In Experiment 1, 91.4% (64/70) and 92.6% (63/68) (P = 0.79) of cows in the I and NI treatments, respectively, were detected in oestrus after the initial synchronisation. At the second round of AI, submission rates for insemination were lower in the I group compared to the NI cows (74.5%, 35/47 versus 92.6%, 63/68, respectively; P = 0.007). Pregnancy rates (proportion treated that were classified as becoming pregnant) in I and NI cows 4 weeks (61.4%, 43/70 versus 63.2%, 43/68) and 7 weeks (77.1%, 54/70 versus 69.1%, 47/68) after the AI start date (AISD) did not differ significantly between treatments. In Experiment 2, presynchronisation and then resynchronisation of oestrous cycles before the first round of AI did not affect oestrous detection rates at the first round of AI (100%, 44/44 versus 98.0%, 50/51; P = 0.54), or pregnancy rates 1 week (63.6%, 28/44 versus 60.8%, 31/51; P = 0.70), 4 weeks (72.7%, 32/44 versus 76.5%, 39/51; P = 0.76) and 7 weeks (81.8%, 36/44 versus 88.2%, 45/51; P = 0.40) after AISD compared to cows that had their cycles synchronised for the first round of AI. These findings support our hypothesis that a reduction in submission rates at a resynchronised oestrus is associated with AI at the first synchronised oestrus and not due to a resynchrony treatment involving IVDs and ODB. This study supports the concept that early embryonic loss following AI at a synchronised oestrus could cause a reduction in submission rates following resynchronisation of oestrus, although investigation of the effect of passing an AI catheter or semen components were not studied per se.

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