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PubMed1981

The role of season in the epidemiology of influenza.

Four types of observations have been used to illustrate the seasonal characteristics of epidemic influenza: (1) The experience of a small population during 28 consecutive years, 1946-74, (2) world influenza outbreaks 1964-75 reported to the World Health Organization, (3) the experience of two widely separated localities at about the same latitude, 1969-74, and (4) the experience of two places at latitudes 30 degrees + on opposite sides of the Equator, 1968-74. The following tendencies are shown. (1) Outbreaks of influenza even in the small community came at approximately the same season almost every year. (2) Outbreaks are globally ubiquitous and epidemic loci move smoothly to and fro across the surface of the earth almost every year in a sinuous curve that runs parallel with the 'midsummer' curve of vertical solar radiation, but lags about six months behind it. Such findings exclude the mediation of seasonal control by any agencies of local distribution, and suggest a direct effect of variations in some component of solar radiation on virus or human host. (3) Antigenic variations in influenza A virus tended to have the same seasonal characteristics as epidemicity. This suggests that epidemicity and virus variation are two facets of one seasonally controlled process. None of these seasonal characteristics can be explained by the current concept of influenzal epidemiology. A new hypothesis recently proposed and recapitulated in the Appendix offers a possible explanation. The primary agency mediating seasonal control remains unidentified.

Australia↗
PubMed2002

The seasonal distribution of campylobacter infection in nine European countries and New Zealand.

In all temperate countries campylobacter infection in humans follows a striking seasonal pattern, but little attention has been given to exploring the epidemiological explanations. In order to better characterize the seasonal patterns, data from nine European countries and New Zealand have been examined. Several European countries with weekly data available showed remarkably consistent seasonal patterns from year to year, with peaks in week 22 in Wales, week 26 in Scotland, week 32 in Denmark, week 30 in Finland and week 33 in Sweden. In Europe, the seasonal peak was most prominent in Finland and least prominent in Scotland and Austria. In New Zealand the seasonality was less consistent since the peak was more prolonged. Possible explanations for the seasonal peaks are discussed. Research into the causes of campylobacter seasonality should help considerably in elucidating the sources of human infection.

Campylobacter Infections↗
PubMed2005

Seasonal variations of phenolic compounds in Australia-grown tea (Camellia sinensis).

Seasonal variations of phenolic compounds in fresh tea shoots grown in Australia were studied using an HPLC method. Three principal tea flavanols [epigallocatechin gallate (EGCG), epicatechin gallate (ECG), and epigallocatechin (EGC)] and four grouped phenolics [total catechins (Cs), total catechin gallates (CGs), total flavanols (Fla), and total polyphenols (PPs)] in fresh tea shoots were analyzed and compared during the commercial harvest seasons from April 2000 to May 2001. The levels of EGCG, ECG, and CGs in the fresh tea shoots were higher in the warm months of April 2000 (120.52, 34.50, and 163.75 mg/g, respectively) and May 2000 (128.63, 44.26, and 183.83 mg/g, respectively) and lower during the cool months of July 2000 (91.39, 35.16, and 132.30 mg/g, respectively), August 2000 (91.31, 31.56, and 128.64 mg/g, respectively), and September 2000 (96.12, 33.51, and 136.90 mg/g, respectively). Thereafter, the levels increased throughout the warmer months from October to December 2000 and remained high until May 2001. In the warmer months, the levels of EGCG, ECG, and CGs were in most cases significantly higher (P < 0.05) than those in the samples harvested in the cooler months. In contrast, the levels of EGC and Cs were high and consistent in the cooler months and low in the warmer months. The seasonal variations of the individual and grouped catechins were significant (P < 0.05) between the cooler and warmer months. This study revealed that EGCG and ECG could be used as quality descriptors for monitoring the seasonal variations of phenolics in Australia-grown tea leaves, and the ratio (EGCG + ECG)/EGC has been suggested as a quality index for measuring the differences in flavanol levels in fresh tea shoots across the growing seasons. Mechanisms that induce seasonal variations in tea shoots may include one or all three of the following environmental conditions: day length, sunlight, and/or temperature, which vary markedly across seasons. Therefore, further studies under controlled conditions such as in a greenhouse may be required to direct correlate flavonoid profiles of green tea leaves with their yields and also to with conditions such as rainfall and humidity.

Australia↗
PubMed2005

Minimization of seasonal sucrose losses across Robert's-type evaporators in raw sugar manufacture by pH optimization.

Factory staff must consider all costs to make sound economic decisions on how to improve the performance of evaporators, which includes knowing optimum pH levels to minimize sucrose losses. A factory study was conducted to determine the effects of target final evaporator syrup (FES) pH values across the season on sucrose losses. The factory operated Robert's type calandria evaporators, with two (2787 and 2322 m2) preevaporators in parallel and three sets of triple-body evaporators (1148 m2 each) in parallel; Rt values were 11.4 and 9.5 min in the two preevaporators, respectively, and increased from 10.0 to 21.8 min across the triple bodies. Gas chromatography was used to determine sucrose losses as Delta%glucose/%sucrose ratios on a degrees Brix basis. Most sucrose losses to acid hydrolysis occurred in the preevaporators. Increasing the target pH of the FES or clarified juice (CJ) systematically reduced losses of sucrose; however, scaling effects overrode pH effects in later bodies. Seasonal effects on evaporator sucrose losses were dramatic. In the early season when cane quality was lowest, higher amounts of impurities catalyzed further hydrolysis of sucrose. In the late season, resilient scale built-up across the season contributed to higher hydrolysis. An optimum target FES pH of approximately 6.3-6.5 measured at room temperature (equivalent to a CJ pH of approximately 7.1-7.3) is recommended, with a higher target FES pH in the early season or when processing immature cane, to reduce excessive losses. Across the evaporation station, the juice/syrup pH decreased up to the 2nd body with a consistent increase in the 3rd body due to evaporation of volatile acids into the condensate. Equations to assess the economic implications of evaporator sucrose losses are described. A target FES pH of 5.9 caused a season average sucrose loss of 0.55% equivalent to 1.52 lbs sucrose lost/ton of cane and a minimum USD 390,400 loss in profits. In contrast, a target FES pH of 6.5 reduced this sucrose loss to 0.36% and 1.01 lbs sucrose lost/ton of cane and saved the factory a minimum of USD 131,100.

Carbohydrates↗
PubMed1997

Seasonal variation in the secretion of mammotrophic hormones in normal women and women with previous breast cancer.

Hormones such as melatonin whose serum concentrations vary seasonally have been previously implicated in the growth of breast cancer. The present study was undertaken to identify possible seasonal variation in a range of mammotrophic hormones which could exert a chronobiologic influence in women with breast tumours. Fifteen premenopausal women with a history of previous breast cancer (BC subjects) and 10 control women underwent 2-hourly serum sampling for 24 h at both summer and winter solstice for measurement of melatonin, growth hormone (GH), insulin-like growth factor-I (IGF-I), cortisol, prolactin and thyrotrophin (TSH). Hormone secretion at the different seasons was compared by measuring the area under the 24 h serum hormone concentration x time curves and by time series analysis of summer-to-winter differences in hormone concentration. Control women had significantly higher GH and IGF-I levels in summer compared to winter and significantly higher cortisol secretion in winter than summer. In contrast, BC women had no significant seasonal difference in IGF-I concentrations and had a reversal of the normal seasonal pattern of melatonin secretion, although seasonal changes in GH production were similar to controls. Prolactin and TSH showed no significant summer/winter variation in either group. Thus, seasonal variations in hormone secretion seen in normal women were, with exception of GH, absent or reversed in women with a previous history of breast cancer. As a result these individuals may be exposed to an asynchronous hormonal stimulus which could influence tumour growth. These changes could reflect a constitutional abnormality in BC women or may have been induced by the previous breast tumour.

Breast Neoplasms↗
PubMed2000

Impact on immunization of seasonal cycle of chickenpox.

The objective of this work was to study the effect of incorporating a seasonal term in a compartmental age-structured theoretical transmission model, on the performance of vaccination strategies for chickenpox. The epidemiologic parameters are taken from data or are based on a review of literature. We used a realistic age-structure model (RAS): It is a model that incorporate both age and seasonal structure. The seasonality was introduced in the model with the addition of sinusoidal forcing term. This seasonal term varies between 0 and 1. From a susceptible/exposed/infectious/removed (SEIR) model with or without age-structure, the pattern of time series is dramatically modified after introducing a seasonal term. This dynamic ends to the transition to chaos. Regarding the evaluation of vaccination strategies, the results of the model without seasonality may be disturbed when the seasonality is introduced, especially during the first 30 years of simulations.

Chickenpox↗
PubMed2001

Seasonal changes in human sperm chromatin condensation.

PURPOSE: The aim of this study was to investigate possible seasonal changes in human sperm parameters, especially chromatin condensation. METHOD: In a first run, 3155 patients attending the andrological outpatient clinic at the Centre of Dermatology and Andrology at Justus Liebig University, Giessen, Germany, from January 1992 to October 1995 were examined for sperm count, motility, vitality, and chromatin condensation. RESULTS: The respective results were correlated according to season. Significant seasonal changes were observed in chromatin condensation and sperm count, with mean maximum values (for chromatin condensation and sperm count) of 86.24% aniline blue-negative spermatozoa in January and 68.75 x 10(6) mL-1 in April. To confirm the observation of seasonal changes in sperm chromatin condensation in Germany on the Southern Hemisphere, 179 patients attending the Reproductive Biology Unit at Tygerberg Hospital, Tygerberg, South Africa, were examined by means of the aniline blue stain from April 1999 to April 2000. For chromatin condensation, a significant seasonal change shifted by 4-5 months was observed on the Southern Hemisphere. However, no seasonal variations could be found for the sperm count. CONCLUSIONS: Our results clearly demonstrate seasonal changes in sperm count and chromatin condensation. In contrast, no circannual relation was observed for motility and vitality.

Chromatin↗
PubMed2003

Seasonal variation in consumption and plasma concentrations of fatty acids in Japanese female dietitians.

OBJECTIVE: To study seasonal variation in intake and plasma concentrations of fatty acids (FAs) in Japanese female dietitians. SUBJECTS AND METHODS: We assessed consumption of FAs based on four season 7 consecutive day weighed diet records from 71 Japanese female dietitians in 1996-1997. Using overnight fasting venous blood, plasma concentrations of FAs were analyzed by gas chromatography. Seasonal variation in consumption and plasma concentrations was examined by ANOVA for repeated values, followed by Tukey's multiple t-test. We calculated Spearman's partial rank correlation coefficients (CCs) between intake and plasma concentrations of FAs. Furthermore, we computed inter-seasonal Spearman's partial rank CCs for consumption and plasma concentrations of FAs. RESULTS: Statistically significant seasonal differences were observed in consumption for most FAs, except for myristic acid, monounsaturated FAs, oleic acid, n-6 polyunsaturated FAs (PUFAs), linoleic acid, gamma-linolenic acid, alpha-linolenic acid, PUFAs/saturated FAs, and n-6 PUFAs/n-3 PUFAs, and for most plasma concentrations, except for stearic acid, gamma-linolenic acid, n-3 PUFAs, alpha-linolenic acid, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and n-3 highly unsaturated FAs (HUFAs). However, statistically significant Spearman's partial rank CCs between intake and plasma concentrations were observed for EPA, DHA, n-3 HUFAs, n-6 PUFAs/n-3 PUFAs and n-6 PUFAs/n-3 HUFAs for almost all seasons. CONCLUSIONS: Seasonal variation exists in consumption and plasma concentrations of FAs, so that this should be taken into account in epidemiological analyses, including case-control and cohort studies.

Adult↗
PubMed2003

Seasonality in suicide: a study of farming suicides in England and Wales.

Seasonality in suicide rates has long been reported. Spring peaks in suicide deaths have been positively correlated with the proportion of the workforce engaged in agriculture. Some studies have indicated that suicides using violent methods are more likely to show seasonality. Recent research has suggested that seasonal patterns have diminished. This study examined deaths in male farmers, an occupational group which might be expected to be more vulnerable to seasonal influences because of the nature of their work and the relatively high proportion of farmers using violent methods for suicide. Data on suicides between 1982 and 1999 by males in England and Wales aged 15 years and over were provided by the Office for National Statistics. Seasonal patterns of suicide in farmers and nonfarmers were examined by nonparametric tests and harmonic analysis. No significant seasonal variation was found for farmers. For nonfarmers, although a chi-square test showed significant variation in monthly distribution, this was not found when a harmonic analysis was applied. There was no significant difference in the variation of violent suicides throughout the year. This study reinforces recent findings that seasonal variation in suicide appears to be diminishing, even in an occupational group where this might be expected.

Adolescent↗
PubMed2001

Recruitment of CD1a+ Langerhans cells to the nasal mucosa in seasonal allergic rhinitis and effects of topical corticosteroid therapy.

BACKGROUND: Local antigen presentation may be necessary for both primary and recall T-cell responses to grass pollen in hay fever patients. We examined the effect of seasonal allergen exposure on nasal mucosal antigen-presenting cell (APC) populations and the effects of topical corticosteroid therapy. METHODS: Nasal biopsies were collected from 46 grass pollen-sensitive seasonal rhinitis patients before the grass-pollen season. A second biopsy was collected during the pollen season, when patients had received 6 weeks' treatment with either fluticasone propionate (200 microg, twice daily) or placebo. Cell populations in biopsy sections were quantified by immunocytochemistry. RESULTS: Significant increases in submucosal and epithelial CD1a+ Langerhans cells, but not CD68 + macrophages or CD20 + B cells, were observed during the pollen season. Seasonal increases in CD1a+ Langerhans cells were inhibited by corticosteroid therapy. CONCLUSIONS: Recruitment of CD1a+ Langerhans cells to the nasal mucosa during natural seasonal allergen exposure may contribute to local T cell responses. Topical corticosteroids may act, at least in part, by inhibiting effective allergen presentation to T cells through inhibition of recruitment of Langerhans cells to the nasal mucosa.

Administration, Topical↗
PubMed2000

Seasonal variation in hospital admission for bipolar disorder, depression and schizophrenia in Tasmania.

OBJECTIVE: Seasonal variation has been reported for both affective disorders and schizophrenia. The current study examines seasonal variation in admissions in schizophrenia, depression and bipolar disorder in Tasmania, the southernmost state of Australia. METHOD: All admissions with a diagnosis of schizophrenia, bipolar disorder and depression in Tasmania between 1983 and 1989 were examined for evidence of seasonal variation in admission patterns. RESULTS: Using the modified Kolmogorov-Smirnov statistic defined by Freedman no significant seasonal variation was found in admissions with diagnoses of mania, depression or schizophrenia. There was a significant seasonal variation in admissions with schizoaffective disorder (winter peak). CONCLUSION: There is no significant seasonal variation in admissions with schizophrenia, depression or bipolar disorder in Tasmania. This may be due to a combination of geographical location and the stringent test of seasonal variation used in the current study.

Bipolar Disorder↗
PubMed2001

Seasonal changes of humoral and cellular immune responses to Japanese cedar (Cryptomeria japonica) pollen allergens in Japanese monkeys (Macaca fuscata) with pollinosis.

The natural occurrence of Japanese cedar [Cryptomeria japonica (CJ)] pollinosis has been reported in Japanese monkeys (Macaca fuscata). The present study was designed to investigate seasonal changes in immunological reactions to CJ pollen allergens in monkeys with CJ pollinosis. Blood samples were collected from six monkeys with CJ pollinosis before and after CJ pollen season. Seasonal changes in specific IgE and IgG to major allergens (Cry j 1 and Cry j 2) were observed before and after CJ pollen season. The humoral responses decreased significantly before CJ pollen and increased after CJ pollen season. Similar seasonal changes in peripheral blood mononuclear cells proliferative responses to CJ allergens were observed before and after CJ pollen season. These humoral and cellular immune responses might serve as a biomarker for assessing new immunotherapies for monkeys with pollinosis.

Allergens↗
PubMed2004

Seasonal variation in total energy expenditure and physical activity in Dutch young adults.

OBJECTIVE: The impact of season on energy expenditure and physical activity is not well quantified. This study focused on summer-winter differences in total energy expenditure (TEE) and physical activity. RESEARCH METHODS AND PROCEDURES: Twenty-five healthy Dutch young adults, living in an urban environment, were measured in the summer season and the winter season. TEE was measured using doubly labeled water, and sleeping metabolic rate (SMR) was measured during an overnight stay in a respiration chamber. Subsequently, the physical activity level (PAL = TEE/SMR) and activity-related energy expenditure [(0.9 x TEE) - SMR] were calculated. Maximal mechanical power (Wmax) was determined with an incremental test on a cycle ergometer. Body composition was measured with hydrostatic weighing and deuterium dilution using Siri's three-compartment model. RESULTS: There was no difference in TEE between seasons. PAL was higher in summer than in winter (1.87 +/- 0.22 vs. 1.76 +/- 0.18; p < 0.001), and the difference was higher for men than for women (0.20 +/- 0.14 vs. 0.05 +/- 0.16; p = 0.04). The difference in PAL between seasons was dependent on the initial activity level. There was a strong linear relation (R2 = 0.48) between PAL and physical fitness (Wmax/fat-free mass), but Wmax/fat-free mass did not change between seasons in response to the lower PAL in winter. DISCUSSION: The extent of the changes in PAL is of physiological significance, and seasonality in physical activity should be taken into account when studying physical activity patterns or relationships between physical activity and health.

Adult↗
PubMed2001

Seasonality of growth in Shanghai infants (n=4128) born in 11 consecutive years.

OBJECTIVE: To describe the seasonal growth patterns in Shanghai infants, to explore seasonal time lag between weight gain and length gain, and to investigate the long-term effect of birth season on early postnatal growth. DESIGN: Community-based longitudinal study. SETTING: Shanghai, People's Republic of China. METHOD: Children were followed up monthly from 1 to 6 months, 3 monthly from 6 to 12 months, and 6 monthly from 12 to 24 months. SUBJECTS: A total of 6018 children born between 1 January 1980 and 31 December 1990. MAIN OUTCOME MEASURES: Weight gain, length gain and change in body mass index (BMI) over the seasons of the year. RESULTS: The infants tended to grow faster in height in spring and summer, and faster in weight and BMI in autumn and winter. The seasonal effect on weight gain and length gain is largely independent. The mean length value at 1 month of age was about 2.0 cm higher in infants born in May to July than in those born in November to February. At 24 months of age this difference was reduced to about 0.7 cm. CONCLUSIONS: There is a clear and consistent seasonality in growth in Shanghai infants. The seasonality seems to act independently on weight and length. Birth month has some association with attained size, but this is reduced during the first 2 y of life.

Body Height↗
PubMed1998

Activation of B-lymphocytes during pollen season. Effect of immunotherapy.

BACKGROUND: B-lymphocytes play an important part in the allergic reaction as producers of IgE antibodies. OBJECTIVE: To investigate the cell surface expression of the activation antigens CD23, CD40 and HLA-DR on B-lymphocytes in birch pollen allergic patients before and during birch pollen season and to study the effect of immunotherapy. METHODS: The study included 24 birch pollen allergic patients half of whom were treated with immunotherapy against birch pollen before the start of the season. Eleven of the 24 patients had asthma. Blood samples were taken and lung function was registered before the season began and before the immunotherapy treatment in January to February and during the season in May. The relative number of B-lymphocytes (CD19+) of the lymphocyte population and the cell surface expression of CD23, CD40 and HLA-DR on B-lymphocytes was measured by the use of flow cytometry. RESULTS: In the control group of patients the relative number and concentration of B-lymphocytes, the cell surface expression of CD23, CD40 and HLA-DR on B cells, and the serum concentration of IgE increased during season compared with before season. In contrast, in the immunotherapy treated patients no changes in the number of B cells or cell surface expression of CD23, CD40 and HLA-DR were demonstrated. CONCLUSION: The elevated expression of CD23, CD40 and HLA-DR on B cells, combined with increased levels of IgE in allergic patients during season could be explained by the effect of cytokines produced by activated TH2 cells. A shift from TH2 to TH1 cells might be the mechanism after the absence of signs of B-cell activation in immunotherapy treated patients. The prevention of increased cell surface expression on B cells by immunotherapy may constitute a significant mechanism behind the beneficial effects of immunotherapy in the treatment of pollen atopy.

Adult↗
PubMed2000

Thyroid hormone acts centrally to programme photostimulated male american tree sparrows (Spizella arborea) for vernal and autumnal components of seasonality.

Thyroid hormone and long days interact to programme American tree sparrows (Spizella arborea) for seasonality (i.e. thyroid hormone-dependent photoperiodic gonadal growth, photorefractoriness, and postnuptial moult). This study explored in radiothyroidectomized (THX) males given thyroid hormone replacement therapy whether thyroid hormone acts within the brain and, additionally, the identity of the putative tissue-active thyroid hormone. The minimum dose (30 ng) of L-thyroxine (T4) that restored all components of seasonality when given i.c.v. daily during the first 21 days of photostimulation restored no component of seasonality when given s.c. The same dose of L-triiodothyronine (T3) also was ineffective when administered s.c., but restored photoperiodic testicular growth (though neither photorefractoriness nor postnuptial moult) when admiministered i.c.v. Three of seven birds given a 10-fold lower dose of T4 (3 ng) exhibited thyroid hormone-dependent photoperiodic testicular growth, albeit damped. The other four birds given 3 ng T4 and all birds given 3 ng T3 responded like THX controls, exhibiting only slight thyroid hormone-independent photoperiodic testicular growth. The highest dose (300 ng) of T3 restored all components of seasonality only when administered i.c.v. daily during the first 49 days of photostimulation. This demonstration in American tree sparrows is the first in any species that the thyroid-dependent transition from the breeding season to the non-breeding season can be effected by T3. The same dose of reverse T3 administered daily over the same 49 days restored photoperiodic testicular growth in only half of 10 subjects and photorefractoriness and moult in none. Collectively, the data support the hypothesis that thyroid hormone acts centrally to programme photostimulated male American tree sparrows for all components of seasonality. The most parsimonious interpretation of the data, including the threshold-like effect of 3 ng T4, favours T4 as the tissue-active thyroid hormone for vernal as well as autumnal events, but does not entirely exclude T3.

Animals↗
PubMed1998

Allergen-induced synthesis of interleukin-5, but not of IgE, is a key mechanism linked to symptomatic episodes of seasonal allergic rhinitis in sensitized individuals.

Some individuals with detectable levels of Japanese cedar (Criptomeria japonica) pollen-specific immunoglobulin (Ig)E in serum have no apparent nasal symptoms during the pollen season. The response of CD4+ T-helper (Th) cells to the pollen allergen might differ fundamentally between asymptomatic and symptomatic individuals who are already sensitized to the pollen. The aim of this study was to discern the possible differences in responses of peripheral blood mononuclear cells (PBMCs) to the pollen allergen between asymptomatic and symptomatic subjects who have been sensitized to the pollen. This study included 20 non-atopic healthy volunteers (non-atopic group) and 48 patients who had detectable levels of the pollen-specific IgE before the pollen season in 1997. In the review of nasal symptoms during the pollen season 1997, 24 patients had typical symptoms of seasonal allergic rhinitis (symptomatic group), and the remainder had no seasonal aggravation of nasal symptoms (asymptomatic group). Peripheral blood mononuclear cells (1.0 x 10(7) cells/well) were obtained from each individual during the pollen season and cultured in the absence or presence of 12.5 microg of Cry j 1 for 4 days. The concentrations of IgE, interleukin-5 (IL-5), and interferon-gamma (IFN-gamma) in the culture supernatants were measured. The levels of IgE produced by Cry j 1-stimulated PBMCs of the asymptomatic and symptomatic groups were significantly higher than those of the non-atopic group, but did not differ between the asymptomatic and symptomatic groups. The levels of IL-5 produced by Cry j 1-stimulated PBMCs did not differ significantly between the non-atopic group and the asymptomatic group, but the levels of IL-5 were significantly higher in the symptomatic group than in the asymptomatic group as well as the non-atopic group. The levels of IFN-gamma produced by Cry j 1-stimulated PBMCs did not differ significantly among the three groups. In conclusion, our study has suggested that Japanese cedar pollen-induced synthesis of IL-5, but not of IgE or IFN-gamma, is likely to be a key mechanism linked to the symptomatic episode of seasonal allergic rhinitis in individuals sensitized to the pollen.

Adolescent↗
PubMedDate not supplied

Relationship between MT1 melatonin receptor gene polymorphism and seasonal physiological responses in Ile-de-France ewes.

The gene encoding the MT1 melatonin receptor in sheep has a restriction fragment length polymorphism (RFLP) site to the MnlI enzyme whose incidence is associated to the expression of seasonality in several breeds. The aim of this study was to examine the relationship between this genetic marker and the physiological effects of MT1 receptor gene polymorphism on several seasonal functions in Ile-de-France ewes. The study was performed using 12 pairs of half-sib adult Ile-de-France ewes. Within each pair, ewes were selected on the basis of their genotype at the MnlI RFLP site: group +/+ and -/- (presence and absence of MnlI restriction site, respectively). No difference in the dates of the beginning, the end or the length of the breeding season was observed between groups during the two-year study. The seasonal changes in prolactin secretion were not different between groups. Similarly, wool growth rate and primary follicle activity, measured for one year, varied with the time of the year in the same way in the two groups. Our study therefore failed to show any relationship between MT1 polymorphism and reproductive seasonality in Ile-de-France ewes. This suggests that the influence of this polymorphism on the regulation of seasonal function is dependent upon the breed and/or environmental conditions. The MT1 polymorphism can explain only a small part of the genetic variability of seasonal functions and the implication of other genes must be investigated.

Animals↗