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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Physiological and nutritional factors affecting oestrous activity and pregnancy in the ewe, with emphasis on the role of melatonin

Wigzell, Susan January 1989 (has links)
In seven experiments carried out under natural-daylength conditions at 57oN, Scottish Blackface and Border Leicester x Scottish Blackface ewes of varying physiological states and nutritional regimes received daily at 1500 h an oral dose of either melatonin dissolved in water and alcohol or the vehicle alone. Throughout the experiments blood samples were collected thrice weekly for progesterone, prolactin and follicle stimulating hormone concentrations (FSH) and at 10 to 15 minute intervals for periods of up to 24 h for luteinizing hormone (LH). Ovulation rates were determined by laparoscopy. When given from the beginning of June and mid-March respectively melatonin advanced and reversed the breeding season, the reversal being as effective in ewes with an extended lactation as in those weaned early or those that had not bred in the previous year. Short-term treatment (30 days) with melatonin during mid-anoestrus not only failed to advance the breeding season but delayed it. Longer term treatment (60 to 90 days) produced transient oestrous cyclicity with ewes returning to anoestrus within one month after the end of treatment. For ewes on a low plane of nutrition melatonin increased ovulation rate at first behavioural oestrus and appeared to reduce embryo mortality. In all experiments melatonin suppressed plasma prolactin 10 to 15 days after the start of treatment with levels remaining low throughout the period of treatment except during late pregnancy. There was no evidence that melatonin promoted a progressive increase in the frequency of the pulsatile release of LH or had any stimulatory effect on FSH secretion in the first 6 weeks of treatment. It did however increase plasma progesterone concentrations in the post-oestrus period.

The use of hormones for earlier lambs

Johnson, Morris Lyle. January 1954 (has links)
LD2668 .T4 1954 J62 / Master of Science

Effect of flushing and exogenous gonadotropin treatment on reproductive performance of estrus synchronized mature ewes

Hoppe, Peter C. January 1966 (has links)
Call number: LD2668 .T4 1966 H798 / Master of Science

Semen quality and libido of rams of different mutton breeds in the summer months

Doane, Ted H. January 1953 (has links)
Call number: LD2668 .T4 1953 D6 / Master of Science

Genetic improvement of lean meat production in terminal sire breeds of sheep

Cameron, Neil Donald January 1988 (has links)
No description available.

Genetic influence on predictability of reproductive potential of rams

Moore, Céline. January 1986 (has links)
No description available.

Genetic and environmental variation in production components of purebred and crossbred ewes

Nawaz, Mohammad, 1957- 13 December 1990 (has links)
Coopworth sheep, a newly available genotype, were compared with other genotypes in two trials to assess cumulative lamb and wool production and contributing components related to survival, reproduction and growth, and for the effects of ewe body weight on reproductive traits. In a third trial, various genotypes generated in the process of upgrading native Kaghani sheep, were evaluated for lamb and wool production. In the first two trials six ewe genotypes, generated by mating Coopworth (C), Polypay (P) and Suffolk (S) rams to Polypay and Coopworth-type ewes, were exposed to Hampshire rams for spring lambing from 1986 through 1990. Overall conception rate averaged 96% and ranged from 93% for S X C ewes to 97% for P X C ewes. Sire breeds were not different in ovulation rate but daughters of Polypay dams averaged .18 higher ovulation rate than daughters of Coopworth dams (P<.05). Uterine efficiency for twin ovulators was .86 with little variation among sire breeds; however, daughters of Polypay ewes had a mean uterine efficiency of .93 compared to .78 for daughters of Coopworth ewes (P<.05). Mean litter size at birth averaged 1.63 and ranged from 1.45 for C ewes to 1.75 for S X P ewes. Ewes from Polypay dams had higher mean litter size (P<.01) than those from Coopworth dams (1.73 vs 1.54), but differences between sire breeds were not significant. Ewes from Suffolk sires weaned the heaviest lambs while ewes from Polypay sires weaned the greatest number of lambs, resulting in similar weight of lamb weaned per ewe mated. Adjustment of lamb production for ewe metabolic body size resulted in Coopworth-sired ewes being more efficient than the heavier Suffolk-sired ewes. Coopworth-sired ewes produced 32% more wool than ewes sired by the other two breeds. Combining lamb and wool production in an index resulted in a range of less than 2% among sire breeds for gross productivity per ewe mated. Productivity of Rambouillet ewes studied under Pakistani conditions declined significantly over time. Crossbred lambs were generally heavier at weaning than Rambouillets, while wool production was highest in purebred Rambouillet ewes followed by genotypes related closely to Rambouillets. In all trials crossbreds generally excelled purebreds in overall productivity; the degree of superiority depended on genotypes involved in the crosses. / Graduation date: 1991

Maternal and peri-ovulatory nutritional effects on the expression of the Inverdale (FecX1) fecundity gene in texel X Scottish hillbreed sheep

Alink, Frances. January 2009 (has links)
Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on June 26, 2009). Includes bibliographical references.

Maternal and peri-ovulatory nutritional effects on the expression of the Inverdale (FecX1) fecundity gene in texel X Scottish hillbreed sheep

Alink, Frances January 2009 (has links)
Experiments were carried out to test the effects of maternal nutrition (0.5 versus 1.0 x maintenance) during early foetal life and peri-ovulatory nutrition on the reproductive performance and associated parameters of Scottish hillbreeds (North Country Cheviot and Scottish Blackface) crossed with Texel sires carrying or not carrying the X-linked Inverdale (<i>FecX<sup>I</sup></i>) gene. Undernutrition of the dam resulted in reduced birthweights of single male lambs, reduced plasma progesterone concentrations of ewe lambs and a tendency for reduced ovulation rates in ewe lambs and shearlings (non-carriers) but litter size was not affected. Heterozygous carriers of the Inverdale gene showed a mean increase in ovulation rate of approximately 0.35 as ewe lambs, and approximately 0.65 the following year, the latter resulting in a mean litter size increase of approximately 0.6. Plasma progesterone concentrations were lower for <i>FecX<sup>I</sup></i> gene-carriers as ewe lambs and also as adults in a flock that had been flushed prior to mating, suggesting that the increased feed intake could have had a suppressing effect on the concentrations of this hormone. It is postulated that this could have resulted in the large number of peri-natal losses associated with gene-carrier ewes in the same flock, since neonatal vigour of offspring of gene-carriers was not affected in the SAC experimental flock that had not been flushed pre-mating. Presence of the <i>FecX<sup>I</sup></i> gene is associated with a reduction in birthweight of approximately 0.5 kg which could be due to the reduced placental efficiency of gene-carrier dams. At puberty and as shearlings gene-carriers remained lighter than their non-carrier counterparts. Throughout the shearling breeding season the increase in ovulation rate associated with this prolificacy gene remained constant.

Maternal feed intake and myogenesis in sheep

Quigley, Simon Paul January 2004 (has links)
"March 2004" / Bibliography: leaves R1-24 / xix, 209 p., A54, R24 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / "This thesis describes two models developed to investigate the effect of maternal feed intake on muscle cellularity and myogenic gene expression of fetal sheep." --p. vi.

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