I G Hazelton

University of California, Davis, Davis, California, United States

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Publications (9)11.07 Total impact

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    ABSTRACT: Pregnant Merino ewes were treated with 90 pg murine epidermal growth factor (EGF) per kg body weight at either 25 (n = 80), 50 (n = 40) or 75 (n = 40) days of gestation. Untreated control ewes were included at each gestational age (n = 20, 12 and 12 respectively). Fifteen and twenty per cent of the ewes treated with EGF at days 25 and 50 respectively failed to lamb, significantly more (P < 0.01) than in ewes treated at day 75, where only one ewe failed to lamb, and in control ewes which all lambed. These differences were not reflected in significant differences between the overall percentage of lambs born in each group, as the incidence of abortion in single-bearing ewes was higher than in ewes carrying multiple fetuses. All lambs born alive to EGF-treated ewes appeared normal. Plasma progesterone concentrations measured before treatment and at 8, 24 and 48 h after EGF injection fell significantly in treated ewes relative to controls (P < 0.01 at day 25; P < 0.05 at days 50 and 75) and concentrations were lowest at 8 and 24 h after injection in those ewes which aborted. Following EGF treatment at days 25 and 50 of gestation, abortion occurred in all ewes with very low plasma progesterone concentrations 8 to 48 h after EGF injection, probably as a result of EGF-induced luteolysis. In other ewes plasma progesterone concentrations returned to pretreatment values by 48 h, indicating incomplete luteolysis. The delayed abortion observed in some of these ewes further suggests that other mechanisms of action are involved in EGF-induced abortion.
    Australian Journal of Agricultural Research 01/1991; 42(8). DOI:10.1071/AR9911301 · 1.33 Impact Factor
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    ABSTRACT: Seven transgenic Merino sheep have been produced by the technique of pronuclear microinjection. Two different Sheep Metallothionein-1a-Sheep Growth Hormone fusion genes were used. Four of the transgenic sheep, all of which contained the gene MTsGH5, did not express the transgene. The remaining three sheep carrying the second fusion gene, MTsGH9, expressed the gene at high levels in a variety of tissues and had elevated blood levels of sheep growth hormone.
    Reproduction Fertility and Development 02/1989; 1(2):147-55. DOI:10.1071/RD9890147 · 2.58 Impact Factor
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    ABSTRACT: Forty-six adult merino ewes were immunised against oestradiol-17 beta-6 carbomethyloxime:human serum albumin and 48 comparable ewes were used as controls in an experiment to study the effects of gonadotrophin releasing hormone (GnRH) on ovulatory responses after treatment with pregnant mare's serum gonadotrophin (PMSG). All the ewes were treated with progestogen sponges for 14 days and received 1500 iu PMSG on the 12th day. Twenty-four control and 24 immunised ewes received 25 micrograms GnRH 21.5 hours and 23 hours after the sponges were withdrawn. Plasma samples were collected between 17 and 50 hours after the sponges were withdrawn and assayed for luteinising hormone (LH). Immunisation reduced the proportion of ewes which ovulated and their rate of ovulation. Injection of GnRH increased the proportion of immunised ewes ovulating (P less than 0.0005) and their rate of ovulation (P less than 0.0001). More unovulated follicles were observed in immunised ewes regardless of GnRH treatment (P less than 0.0001). The rate of recovery of eggs was reduced after immunisation. Treatment with GnRH produced a surge of LH of equal magnitude in the control and immunised ewes although not as many immunised ewes ovulated.
    The Veterinary record 07/1987; 120(25):590-2. DOI:10.1136/vr.120.25.590 · 1.63 Impact Factor
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    ABSTRACT: Ewes were immunized against androstenedione (Fecundin) and assigned to be mated 14 days (179 ewes Group C) or 25 days (174 ewes Group B) after a booster immunization with Fecundin. The anti-androstenedione titres at these times were 6790 and 3240 respectively (P less than 0.01). The remaining 169 ewes were untreated controls (Group A). Ewes were mated to entire rams (12 rams to 180 ewes) at their second oestrus after synchronization of oestrus. Immunization against androstenedione caused a shortening of the time from sponge removal to mating (Day 0) and a decrease in the percentage of ewes mated by the rams. Also, ovulation rate was increased after immunization (P less than 0.01), being 1.42, 2.16 and 1.93 for Groups A, C and B respectively. Egg recovery rates on Day 2 were lower in immunized ewes and there was some indication that fertilization rates were lowered. On Day 13 after mating a higher proportion of blastocysts was recovered from ewes in Group A than from those in Groups B and C. Immunization resulted in lower fertilization rates and smaller blastocysts with lower mitotic indexes (P less than 0.01). At Days 24-32 of pregnancy fetal weight was lower in the immunized ewes. At all sampling stages, the proportion of ewes pregnant (fertility) was lowered in immunized ewes. The results of the present study show that significant reproductive wastage occurs in androstenedione-immunized Merino ewes, with lower rates of embryo recovery and delayed embryonic development being found in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)
    J Reprod Fertil 12/1986; 78(2):423-31. DOI:10.1530/jrf.0.0780423
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    ABSTRACT: The effects of active immunization against oestradiol-17 beta on the ovarian response to pregnant mare serum gonadotrophin (PMSG) was investigated in Merino ewes. Immunized (79) and control (41) ewes were synchronized with intravaginal sponges, given either 750 or 1500 i.u. PMSG and then mated to rams or inseminated laparoscopically with fresh diluted semen. All control ewes mated naturally exhibited oestrus and 40 out of 41 control ewes ovulated. The ovulation rate was higher in the controls receiving 1500 i.u. PMSG than in those ewes which received 750 i.u. PMSG (10.2 v. 3.3). Immunization against oestradiol-17 beta resulted in antibody titres varying from 100 to more than 100 000 in plasma taken 1-4 days after mating. The ovarian response increased significantly in the lowest titre group (100-1000) in conjunction with stimulation with 1500 i.u. PMSG. In these ewes the ovulation rate increased over controls (16.7 v. 10.2) as did the total ovarian response, which includes follicles greater than 10 mm diameter (22.3 v. 11.1). The total ovarian response was also increased in those ewes given 750 i.u. PMSG which had titres in the 1000-10 000 and 10 000-100 000 range, but this was not accompanied by significant increases in the ovulation rate. In general, the higher titre levels (greater than 1000) were correlated with decreases in the proportion of ewes showing oestrus and ovulating and in the embryo recovery rate. The 1500 i.u. PMSG treatment group with the highest titres (greater than 10 000) also showed a significant drop in the ovulation rate as compared to the 1500 i.u. PMSG controls.
    Australian journal of biological sciences 02/1985; 38(3):339-45. DOI:10.1071/BI9850339
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    Theriogenology 01/1985; 23(1):211-211. DOI:10.1016/0093-691X(85)90117-7 · 1.85 Impact Factor
  • Theriogenology 01/1984; 21(1):248-248. DOI:10.1016/0093-691X(84)90348-0 · 1.85 Impact Factor
  • Theriogenology 01/1984; 21(1):222-222. DOI:10.1016/0093-691X(84)90322-4 · 1.85 Impact Factor
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    ABSTRACT: This work is the first of 3 replicate experiments designed to define the extent and nature of embryonic loss in both control and androstenedione-immunized Merino ewes. Fertilization and embryonic recovery rates at day 2 tended to be lower in the immunized group, even though the mean ovulation rate of this group was significantly higher (1.88 v 1.47). The incidence of chromosomally abnormal embryos at day 2 (= 12%) corresponds with the observed drop in pregnancy rate (=10%) between day 2 and 13 in both groups. There was a further drop in the pregnancy rate of the control ewes by day 30. The mean fecundity of both groups at day 30 was 1.06.
    Reproduction in Sheep, Edited by DR Lindsay, DT Pearce, 01/1984: chapter Reproductive wastage and chromosomal abnormalities in early embryos from androstenedione-immune and control ewes: pages 137-139; Cambridge University Press., ISBN: 0-521-30659-0