Biomedical subjects

J N Shrestha

Publications and source records attributed to J N Shrestha.

7 recordsLinked to original sources

PubMed1993

The effect of warming velocity on motility and acrosomal integrity of boar sperm as influenced by the rate of freezing and glycerol level.

The effect of thawing velocities ranging from 10 degrees C/min to 1,800 degrees C/min on the motility and acrosomal integrity of boar spermatozoa frozen at 1 degree C/min (suboptimal), 5 degrees C/min, and 30 degrees C/min (optimal) rate was studied with the sperm suspended for freezing in diluent containing 2, 4, or 6% of glycerol (v/v). The influence of thawing on sperm survival depends on the rate at which the sperm had been frozen. In semen frozen at a suboptimal rate of 1 degree C/min, the percentage of motile sperm (FMP) initially fell to 3.5-4.0% when the thawing rose to 200 degrees C/min, but, with further increases in thawing rate, increased and reached peak values (10.3-11.0% FMP) after thawing at 1,800 degrees C/min. The percentage of sperm with normal apical ridge (NAR) also increased moderately with thawing rate, but the degree of improvement decreased as the glycerol level was increased. In semen frozen at 1 degree C/min, acrosomal integrity (NAR) was best maintained in 2% glycerol, reaching 22.9% NAR after thawing at 1,800 degrees C/min. In semen frozen at the optimal rate of 30 degrees C/min, the increases in thawing rates above 200 degrees C/min substantially improved motility. Motility was generally higher in semen protected by 4 or 6% glycerol, with the peak values of 44 or 46% FMP, respectively, after thawing at 1,200 degrees C/min. The proportion of sperm with NAR also increased with thawing rate, but as in the case of suboptimally frozen sperm it was influenced negatively by the glycerol concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrosome↗

PubMed1991

Age at puberty, fertility and litter size of ewe lambs reared under different photoregimens.

Age at puberty, fertility and litter size of ewe lambs of synthetic sire and dam strains raised under different photoregimens were determined. The lambs were bred during January, May or September at 30 to 32 weeks of age. Irrespective of birth date, the lambs were reared under continuous light from birth to 5 weeks of age. From 5 to 20 weeks of age, they were kept under 16 hours of light dairy (16L:8D; Treatment A), 8 hours of light daily (8L:16D; Treatment B), or a split photoperiod of 8 hours total light daily (7L:9D:1L:7D; Treatment C). Subsequently, all lambs were exposed to 9 hours of light daily until after breeding. Lambs were exposed to rams for two estrous periods after treatment with fluorogestone acetate-impregnated intravaginal sponges and pregnant mares' serum gonadotropin (PMSG) to induce synchronized estrus. Although the age at puberty (174 days) was similar among treatments, the incidence of puberty prior to progestagen sponge treatment was higher (approximately 50%) for lambs reared under Treatments A and C than under Treatment B. Fertility and litter size of lambs were not influenced by the previous photoperiod history or by sexual maturity, i.e., puberal or prepuberal, at the start of the sponge treatment. However, strain, age and weight of lambs at breeding influenced significantly the reproductive outcome.

Journal Article↗

PubMed1987

Photoperiod entrainment of testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin cycles in rams in relation to testis size and semen quality.

Adult rams were exposed to photoperiod treatments over 2 years to study the influence of light regimes on pituitary-testicular activity and semen quality. Initially, all rams (12 per group) were exposed to 3 months of long days (16L:8D). Group 1 was then exposed to a regime of continuous short days (8L:16D) and Groups 2, 3, and 4 were exposed to 4 months of short days alternated with 1, 2, or 4 months, respectively, of long days. Every 2 weeks, serum hormone levels and scrotal circumference were determined and semen quality was evaluated. Regular cycles in pituitary and testicular activities corresponding to the period of the lighting regime resulted in Groups 2, 3, and 4, but not in Group 1. In general, the change from long days to short days induced increases in follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone levels, scrotal size and sperm numbers and a decrease in prolactin. The reverse occurred after subsequent exposure to long days. After 4 months of long days, testicular regression was complete, but when long-day exposure was reduced, less regression occurred. With continuous exposure to short days, FSH and testosterone remained above basal levels, prolactin levels were depressed, scrotal size remained near the maximum, and elevated numbers of motile sperm were sustained.

Animals↗

PubMed1987

Inheritance of active and acquired immunity traits in sheep.

Six hundred sixteen ewes of six strains were inoculated twice with ovalbumin in Freunds' incomplete adjuvant. To quantify the humoral immune response to the foreign antigen, blood samples were collected from all ewes 1 wk post-second injection. Blood samples were also collected between 4 and 40 h of age from their 709 lambs, to examine genetic differences in ability of lambs to acquire maternal anti-ovalbumin antibodies. Titers of anti-ovalbumin antibodies were determined using kinetic enzyme-linked immunosorbent assay (ELISA) techniques. Strain did not affect ewe immune response, but sire within strain was highly significant. In pregnant ewes, anti-ovalbumin antibody titers in 12- and 30-mo-old ewes were higher than those in 21-mo-old ewes. Number of lambs in utero did not significantly affect ewe immune response. Heritabilities of anti-ovalbumin titer from a paternal half-sib analysis were .27 +/- .17 for all ewes and .57 +/- .25 for only the pregnant ewes. The effect of strain of lamb on lamb anti-ovalbumin titer approached significance, and sire within strain was highly significant. Lamb anti-ovalbumin antibody concentration increased as time from birth to blood sampling increased to 18 h but declined thereafter. The size of the litter in which a lamb was born had a highly significant effect on the lamb's acquired immunity, with titer decreasing as litter size increased. The heritability estimate for lamb anti-ovalbumin antibody concentration from a paternal half-sib analysis was .38 +/- .11; it was .28 +/- .15 from the sire variance component of a full-sib analysis. When lamb titer was considered a maternal trait (lambs nested within their maternal grandsires within strains), the maternal grandsire variance component was negative. The average anti-ovalbumin antibody concentration of lambs that died between blood sample collection and 120 d of age was less than the average antibody concentration of lambs that survived (P less than .01).

Animals↗

PubMed1985

Effect of PMSG dosage on the reproductive performance of adult ewes and ewe lambs bred at a progestagen-PMSG synchronized estrus.

The effect of dose of pregnant mares' serum gonadotropin (PMSG) on the reproductive performance of adult ewes and ewe lambs and lamb survival at birth after treatment with fluorogestone acetate (FGA)-impregnated intravaginal sponges and PMSG (250 IU or 500 IU) to synchronize estrus was evaluated. Ewes were exposed to rams for breeding at the synchronized and subsequent estrous cycles. The flock, comprised of three synthetic strains and two control breeds, was maintained in a controlled environment and exposed to an artificial light regimen which alternated at 4-mo intervals from 16h of light daily to 9h of light daily. Trials were conducted during January, May and September at the end of a 9-h daylength cycle. Adult ewes were bred in May and 8 mo later in January. Ewe lambs were bred in September at 6.5 to 7.5 mo of age. The overall reproductive performance of the adult ewes was similar at the two breedings: fertility approximately 90%, prolificacy approximately 2.7, fecundity approximately 240% and lambs born alive approximately 2.4. Dosage of PMSG had no effect. Reproductive performance of ewe lambs was lower and there was a strain x treatment interaction, suggesting greater variability in response. The results indicate there is no advantage to using a higher dose of PMSG in ewes with a natural relatively high fecundity. Moreover, the use of the artificial photoperiod appears to overcome the natural seasonal variation in reproductive performance.

Journal Article↗

PubMed1984

Improved diagnostic accuracy by repetitive ultrasonic pregnancy testing in sheep.

Operator effects and instrument accuracy in using the Scanopreg ultrasonic pregnancy detector in sheep bred at synchronized estrus were studied in three experiments. In the first study, four operators tested the same 101 ewes at 60 and 80 days after breeding. The only significant difference among the four operators was that one operator consistently underestimated pregnancy. Operators did not differ in their diagnoses between days 60 and 80. In the second study, there were no differences between two operators who tested 239 ewes 90 days after breeding. In the third study, one operator tested 318 ewes 60, 70 and 90 days after breeding. The accuracy of diagnosis of pregnancy was at least 90% on each day tested; the corresponding diagnoses of nonpregnancy were 52, 76 and 79% correct. Some ewes that were initially diagnosed as nonpregnant were correctly recognized as pregnant when tested later than day 60. Most of the missed pregnancies were in ewes carrying a single lamb. A second Scanopreg test on day 90 of ewes not diagnosed pregnant on day 60 or 70 identified additional ewes as pregnant. Paired tests (days 70 and 90) recognized 99% of the ewes that eventually lambed.

Journal Article↗

PubMed1984

Sexual activity patterns in rams.

Behaviour was measured in reproductively experienced rams from three crossbred strains and two pure breeds (Suffolk and Finnish Landrace) in an attempt to develop a method for rapid screening of sexually aggressive rams and to measure breed differences in sexual activity. A set sequential pattern of activity need not occur in sexually experienced rams, and components of their sexual behaviour may be influenced by the estrual status of the ewe. The data indicate that the number of attempted mounts is an acceptable selection tool, with a mount following a short period of investigation most likely to be followed by coitus. Two sequential ten minute periods are sufficient for rapid screening of rams for short-term sexual activity levels.

Animals↗