LD2668 .T4 1954 J62 / Master of Science

Call number: LD2668 .T4 1966 H798 / Master of Science

Call number: LD2668 .T4 1953 D6 / Master of Science

No description available.

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.

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

No description available.

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

No description available.

Call number: LD2668 .T4 1961 S42