Reproduction, nutrition, developpement最新文献

The aim of this study, conducted in spring born animals, was to analyse if within a group of males of the same age, there is any relationship between the testis diameters (TD) or between the percentages of morphologically abnormal spermatozoa (AS) recorded in the same animal at two periods of its life (be it at two different spring periods or at two stages of its age: ram lamb and adult). Eighteen Ile-de-France ram lambs born in February 1980 and issued from five adult rams whose seasonal variations in TD and AS had been followed for two consecutive years were used in this study. Semen was collected (artificial vagina, 1 ej/male/wk) from October 1980 until December 1983 (slaughter of the animals) every semester during "Periods" (n = 7). Within a same year, the first semester (February to June) was called "Spring", the second (August to December) "Autumn". AS (150 cells/smear) were controlled on each ejaculate and the same week maximum TD of both testes was measured using a calliper. Correlations were calculated for TD and AS between individual values (simple correlations) or between groups of individual values (multiple or canonic correlations) at different periods. These values were chosen as follows: TD: 4th and 5th control for the first period (P1, ram lamb); the three lowest values recorded in April (P2, P4, P6); the three mean highest values recorded in Autumn (P3, P5, P7). AS: the first five measurements in P1; the four highest percentages obtained in March-April in P2, P4, P6 (correlations were not calculated in autumn since AS were very few). 1 a: On the whole, TD increased with the age of the animal until 24-27 months and passed alternatively by minimal (February to April) and maximal (September) values each year. Testis growth due to the effect of photoperiodism started every year in the first days of June. 1 b: Except alterations of semen quality in August 1983 (due to high local temperatures), AS were always higher in Spring than in Autumn, maximal values being reached in February (P4) or in March-April (P2 and P6). Their seasonal variations were thus opposed to those of TD (r = -0,671 between weekly means of AS and TD of the whole group of animals from P2 to P6). II-TD: Individual TD of ram lambs were significantly correlated with those recorded in the same adult animal (P1-P2, P1-P6, but P1-P4 NS) especially in autumn (P1-P3, P1-P5, P1-P7.

Two experiments were designed to study the mechanism for measurement of daylength by ewes. 1) Two groups of 8 adult ewes were exposed for more than one year to either 16L:8D (long days) or 7L:9D:1L:7D alternated every 3 months with 8L:16D (short days). Ovulatory activity was followed during the total duration of the experiment and compared to that of a third group of 8 females under simulated natural conditions of lighting. Plasma prolactin and melatonin were measured in blood samples collected hourly over a 24-h period, more than 1.5 months after a light shift. Ovulatory activity and patterns of prolactin showed that one hour of light given 16 to 17 hours after the onset of the main light phase led to the measurement of a long day by the animals. Plasma melatonin was high during darkness in ewes under 8L:16D or 16L:8D. So, the duration of melatonin secretion was about twice as long in short days (8L:16D) as in long days (16L:8D). Interruption of the dark phase by the light pulse induced a dramatic decrease in the melatonin levels which increased again in only 6 of the 8 ewes studied. 2) Four groups of 7-8 ewes were subjected for at least 6 months to one of the following treatments: 4L:8D, 4L:20D, 4L:32D or 4L:44D. Blood samples were collected twice each week in order to monitor the ovulatory activity and plasma prolactin levels. In addition, to follow the plasma prolactin and melatonin patterns, blood samples were collected hourly over a 48-h period, 4 months after the onset of the experiment. The ovulatory activity was not indicative of the daylength measured by the animals. However, plasma prolactin levels suggested that 4L:8D and 4L:32D were considered as long days and 4L:20D as short days. Four months after the onset of the experiment, a 24-h rhythm of melatonin secretion was found regardless of the photoperiodic treatment: in all groups, low melatonin levels were coincident in time once every 24 h, and high melatonin levels displayed similar coincidence. Low levels of melatonin were observed during each period of light. Melatonin secretion was interrupted by light in groups 4L:8D and 4L:32D, both treatments to which the ewes responded as long days. Results of both experiments are compatible with the hypothesis that periods of melatonin secretion throughout the day are more important than the duration of secretion itself.

To investigate the role of endogenous opioid peptides (EOP) in the inhibitory control of LH secretion in the ram, the acute effects of naloxone (opioid antagonist) on episodic LH secretion were measured in rams at different stages of a reproductive cycle induced by treatment with melatonin. Groups of SCGx rams (functionally pinealectomized) and pineal intact rams were housed under long days (16 h light: 8 h darkness) and treated with alternating 16 week periods with exogenous melatonin (continuous melatonin from silastic implant) and 16 week periods with no exogenous melatonin for 3 or 4 consecutive cycles. The LH response to naloxone (1.6 mg/kg i.v.) was measured at 2-4 week intervals on 9 occasions during one of the treatment cycles. The periodic treatment with melatonin resulted in a clearly defined cycle in the plasma concentrations of LH, FSH, testosterone and prolactin, and associated changes in size of the testes, intensity of the sexual skin flush and moulting of the pelage; maximum size of the testes occurred 8-16 weeks after the start of each melatonin treatment. Naloxone induced an increase in plasma LH concentrations at all times but the response varied in relation to the stage of the melatonin-induced reproductive cycle. During testicular recrudescence, naloxone induced large increases in mean LH concentration (low frequency, high amplitude LH pulses), at the peak of the reproductive cycle naloxone induced smaller increases in plasma LH (high frequency, low amplitude pulses) and during testicular regression naloxone induced only minor increments in plasma LH. The results are consistent with the role of EOP in the inhibitory control of LH secretion with this system most active during the sexually active phase of the reproductive cycle.

Our results show that when myoblasts, isolated at different stages during muscle development, were cultured they formed myotubes expressing distinct phenotypes. An early phenotype was expressed by myoblasts isolated from 4-5 day old embryos and this phenotype could be modulated according to the culture conditions, i.e. seeding of the myoblasts as isolated cells or as reaggregated clumps of cells. An intermediate phenotype was expressed by myoblasts isolated from 7-8 day old embryos and it was independent of culture condition. A late phenotype was expressed by myoblasts isolated from embryos older than 9 days. In this case again, it could be modulated by culture conditions but, this time, modulation was brought about by subculturing the cells before they differentiate. These various phenotypes do not result from environmental differences in the culture but reflect the existence of distinct classes of myoblasts present at these different stages. This was demonstrated by isolating homogeneous clones of myoblasts at these stages and by showing that they express the corresponding phenotype.

The mean retention time (MRT) of particles of ground and pelleted dehydrated lucerne was compared to that of the liquid phase in different parts of the sheep digestive tract. It was not different in the reticulo-rumen but it was greater in the stomachs and the whole tract, mainly because of a faster rate of passage of fluid in the abomasum and small intestine.

Three models of marker passage analysis were compared. None of them was found to be superior in fitting the data. The 3 models provided similar estimates of the mean retention time of hay in the whole digestive tract and in the rumen of calves. Discrepancies between models for other compartments are discussed in relation to sampling sites.

A survey of the incidence of post-parturient fatty liver in high yielding dairy cows was carried out on 74 cows from 34 dairy herds fed grass silage. Triglyceride determination in liver biopsies indicated that 20% of the cows had a moderate or severe fatty liver between 5 and 21 days postpartum.

Urea dilution technique (130 mg/kg live weight) was used to estimate total body water (BW) in 12 goats. Empty body water (EBW) determined by lyophilization was more closely related to urea space (US) than total BW. EBW was estimated with a better precision (CV = 4.7%) from the prediction equation including US measured 20 min after urea infusion and body weight. This urea technique was considered convenient.