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At least 613 records · Page 34Linked to original sources
PubMed1990

Population dynamics of Trichostrongylus colubriformis in sheep: mathematical model of worm fecundity.

A mathematical model was constructed to predict the egg production of Trichostrongylus colubriformis worms as a function of worm age and host experience of infection. The model set egg production at zero until the worm was 14 days old, when a linear increase to maximum egg production levels occurred over 7 days. It was assumed that egg production remained at maximum levels until a threshold total worm burden was exceeded, when an exponential decline in egg production occurred. The rate of decline was assumed independent of worm age or worm burden. The estimated parameters (maximum egg production, threshold, lag and rate of decline) were optimized by fitting values predicted from the model to faecal egg counts observed in continuously infected sheep, giving R2 = 0.80. The model was validated against faecal egg counts obtained in two other continuous infection experiments, one performed at the same laboratory and the other in Britain.

Animals↗
PubMed1993

The influence of formalin, benzocaine and hyposalinity on the fecundity and viability of Polylabroides multispinosus (Monogenea: Microcotylidae) parasitic on the gills of Acanthopagrus australis (Pisces: Sparidae).

Adult Polylabroides multispinosus exposed in vivo to formalin (200 p.p.m. in sea water, 30 min) deposited a similar number of eggs in 24 h in vitro as did control parasites (sea water, 35 parts per thousand, p.p.t., salinity) and worms exposed in vivo to benzocaine (40 p.p.m. in sea water, 10 min). Worms laid more eggs at 30 p.p.t. salinity in vitro than at 20, 35, 10 and 5 p.p.t. salinity (in decreasing order). Formalin (200 p.p.m., 30 min) decreased the viability of recently laid eggs, the survival of oncomiracidia, removed 70% of juvenile and adult worms from the gills, but decreased only slightly the viability of eggs exposed in utero or after eyespots developed in vitro. Salinities below 30 p.p.t. reduced viability as did an increase in temperature from 24 to 28 degrees C. All adult and juvenile worms were removed by baths in formalin (400 p.p.m., 25 min) or fresh water (1 h).

Animals↗
PubMed1987

Gonadotrophins, fecundity genes and ovarian follicular function.

The Booroola Merino is a sheep breed having a major gene(s) (F) influencing its ovulation-rate. Homozygous (FF), heterozygous (F+) and non-carriers (++) of the gene have ovulation-rates of greater than or equal to 5, 3 or 4 and 1 or 2 respectively with the durations of each oestrous cycle and oestrous behaviour being similar in all genotypes. Although the principal site(s) of gene expression are obscure, FF genotypes have mean plasma concentrations of FSH and LH which are higher than in the F+ ewes, which in turn are higher than in the ++ animals. Thus, the FF and F+ animals provide a unique system in which to examine ovarian function under continual exposure to elevated gonadotrophin concentrations. At the ovarian level, F gene-specific differences in follicular development and function were noted. In small follicles (0.1-1.0 mm dia.), the basal levels of cAMP and the in vitro synthesis of cAMP, progesterone, androstenedione and oestradiol-17 beta in response to LH and FSH were significantly influenced by genotype (FF greater than F+ greater than ++; P less than 0.05). In larger follicles (1-4.5 mm dia.) the granulosa cells from FF and F+ ewes were more responsive to FSH and/or LH than in ++ ewes with respect to cAMP synthesis and they also had higher levels of aromatase activity. In vivo, the ovarian secretion-rates of oestradiol from greater than or equal to 5 ("oestrogenic") follicles in FF ewes, 3-4 such follicles in F+ ewes, and 1-2 such follicles in ++ animals during the follicular phase were similar. In FF and F+ ewes, the preovulatory follicles ovulated at a smaller diameter (i.e. 3-5 mm) than in ++ ewes (greater than 5 mm diam.) and also produced smaller corpora lutea. Thus, after continual exposure to elevated levels of gonadotrophins, follicles may synthesize steroid and mature at smaller diameters compared to those exposed to normal levels of FSH and LH.

Animals↗