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Biomedical subjects

M Shelton

Publications and source records attributed to M Shelton.

At least 37 records · Page 2Linked to original sources
PubMed1986

An assessment of reproductive wastage in sheep.

Reproductive wastage was evaluated by relating ovulation rate to lambs born or raised in range finewool ewes over a ten-year period. The results indicate that reproductive losses are of large magnitude and that these losses are concentrated in the period of ovulation to implantation and in death losses of lambs born. In this study, 33.5% of the potential lamb crop was lost in the early period. Multiple ovulating ewes showed the greatest embryonic loss. The data do not deviate from the binomial distribution, thus suggesting that these losses are largely due to chance. Further work is indicated in the first seventeen days after ovulation to examine losses due to fertilization failure, chromosomal abnormalities, and implantation failure. Abortion or absorption of the fetus was indicated in only 4% of the ewes sampled. An average of 16% of the potential lamb crop was lost from birth to weaning, with 73% of these losses occurring in the first few weeks. Management practices need to be developed to reduce these losses, and these would be expected to vary from one producer to the next depending on conditions. Increasing ovulation rate is one possible method of improving reproductive efficiency, as results of this study indicate that for each unit increase in ovulation rate, there is an increase of 0.52, 0.46, 0.33, and 0.23 in the average number of embryos surviving, lambs born, lambs marked and lambs weaned, respectively.

Journal Article↗
PubMed1984

Reproductive response to suckling manipulation in Spanish goats.

One hundred and fifty-six Spanish does were used to evaluate the effect of suckling manipulation on postpartum breeding. Does were divided into four herds dependent upon their kidding dates (range from October to January) and location. All kids were nursed ad libitum for approximately 30 days following birth. Groups were then subdivided, and does with kids were randomly allotted to one of the following treatment groups: 1) continuous suckling (CS), 2) once-daily suckling (ODS) or 3) early weaning (EW). Nonlactating does (NL) which lost a kid or aborted were also evaluated for rebreeding performance. At least one fertile male equipped with a marking harness was placed with each treatment group for estrus detection. After 30 days, ODS kids were returned to their dams. The proportion of does exhibiting estrus within 60 days postpartum was greater for ODS and EW does compared to CS does (P<0.05 and P<0.001, respectively). Postpartum interval to first estrus was shorter (P<0.05) for ODS does than for CS does (41.7 and 48.0 days, respectively). The percentage of does conceiving within 60 days postpartum was 25.0, 44.7, 74.4 and 70.7% for CS, ODS, EW and NL does, respectively. The interval from parturition to conception was shorter (P<0.05) for ODS does (43.6 days) than for CS does (50.4 days). Overall kid production was 1.87 kids/doe/year. These results indicate that reducing the suckling stimulus in Spanish does during the breeding season may result in an earlier return to estrus with a greater percentage of does rebreeding within 60 days postpartum.

Journal Article↗
PubMed1984

Comparative effects of verapamil, nifedipine, and diltiazem on contractile function in the isolated immature and adult rabbit heart.

The effects of postnatal development on the systolic and diastolic responses to pharmacologic blockade of the slow inward calcium current were investigated in blood-perfused hearts isolated from immature (14-21-day-old) and adult rabbits. Isovolumic left ventricular developed pressure, resting pressure, and maximal rate of pressure development (+dP/dt) at cumulative doses of either verapamil, nifedipine, or diltiazem were determined by means of an intracavitary balloon. Myocardial contractile function in the immature heart was more sensitive to pharmacologic blockade of the slow inward calcium current than is the adult heart. Doses of verapamil, or nifedipine, that comparably reduced pretreatment developed pressure and +dP/dt were approximately 10-fold less in immature as compared to the adult heart. The dose of diltiazem which reduced developed pressure and dP/dt by 50% was 3-fold less in immature as compared to the adult heart. Verapamil and nifedipine decreased resting pressure in the adult but not in the immature heart. Conversely, diltiazem decreased resting pressure in the immature while not affecting resting pressure in adult hearts. Thus, postnatal cardiac development affects both the systolic and diastolic responses to calcium channel blockade. In addition, diltiazem appears to be qualitatively and quantitatively different from verapamil and nifedipine with respect to the age-related cardiac effects of calcium channel blockade.

Aging↗
PubMed1980

Thymic abnormalities and growth hormone deficiency in dogs.

A high frequency of occurrence of a wasting disease, unthriftiness, and retarded growth was observed in a group of inbred Weimaraner dogs. Affected pups had a small thymus gland, with a marked absence of thymic cortex. A litter of eight pups from a sire and dam that were known to have produced affected offspring was chosen for further study. The pups had normal concentrations of WBC and gamma-globulins and were able to produce antibody in response to Brucella abortus. Two pups in the litter developed a wasting syndrome and responded well to therapy with thymosin fraction 5. One pup that survived the wasting syndrome had a significant (P < 0.05) depression of its lymphocyte blastogenic response to phytohemagglutinin compared with its surviving littermates. Pups from this litter also lacked a normal increase in plasma growth hormone concentration after the injection of clonidine HCl. These pups had concurrent abnormalities of the thymus-dependent immune function and in growth hormone metabolism. The syndrome in these pups has some features in common with the syndrome in the Ames or Snell-Bagg strains of immunodeficient dwarf mice.

Animals↗
PubMed1978

Reproduction and breeding of goats.

Reproduction and genetics of the goat are reviewed with a view of increasing their contribution to mankind. The goat contributes most in tropical regions (within 30 degrees of the equator). The most important product from the goat is milk with meat a close second. Other products are minor. Reproductive rate is a problem only with the Angora goat, but increased reproduction with any type of goat would contribute to improved efficiency. Also, a knowledge of the reproductive phenomenon is necessary for effective management. Genetic studies of goats are limited, but this should not limit improvement programs. Excellent genotypes for producing milk and fiber are available, but adaptation to tropical conditions is needed. Even within temperature regions, there is little evidence of progress in breeding for milk production. Little has been done on the development of the goat as a meat animal. Also, research on crossbreeding for milk or meat production is limited.

Abortion, Veterinary↗
PubMed1975

Deficiency of immunological and phagocytic function in aboriginal children with protein-calorie malnutrition.

Infection, associated with protein-calorie malnutrition (PCM), is a widespread and important health problem in young Aboriginal children. Clinical obervations have suggested these children to have impaired immune resistance to infection. Children were fivided by anthropometric criteria into three groups: moderately malnourished; showing effects of previous PCM; normally nourished. Numbers and function of T and B lymphocytes and neutrophils were measured in these groups to give an assessment of systemic immune resistance. Primary antigen recognition and blastogenic response of T-lymphocytes were significantly impaired in the malnourished groups. Normal or increased numbers of B and T lymphocytes, and normal secondary antibody response to tetanus toxoid inoculations were found in all groups. Serum opsonin levels, C3 concentrations, immunoglobulin levels, neutrophil numbers and phagocytic activity were normal or increased in all groups. The malnourished children showed relative impairment of neutrophil chemotaxis, metabolic response to phagocytosis and intraphagocytic bactericidal activity. The findings suggested that children with moderate or lasting effects of PCM had multiple dificiencies in the funnction of their immune defence mechanism which may profoundly influence the prevalence, chronicity and mortality of infections diseases in Aboriginal communities.

Australia↗
PubMed1975

Posthitis in Angora wethers.

Posthitis was diagnosed as an economic problem of Angora wether goats. Affected goats had a scabby or ulcerated prepuce, with a distorted or pinhole preputial orifice. Some goats were able to urinate only by excessive straining. Cultural examination revealed a Corynebacterium sp capable of hydrolyzing urea, similar in all respects to the organism associated with a similar problem with Merino wethers in Australia. Necessary predisposing factors are considered to be a castrated animal consuming a high protein diet and infection with the urea-hydrolyzing organism.

Animals↗
PubMed1969

Potentially lethal radiation damage: repair by mammalian cells in culture.

Less than optimum conditions with regard to cell division after x-irradiation provide the necessary environment in which mammalian cells can repair potentially lethal radiation damage. The kinetics of repair suggest that, during the repair process, a transient, unstable cellular state occurs which prevents cell division in complete growth medium. The capacity for repair appears to be dependent on cell age.

Animals↗