Reproduction, nutrition, developpement最新文献

1) The effects of limiting time of access to forage (twice 1 hr 30 min vs continuous access) on feeding behavior and reticulo-ruminal fill were studied with two hays: a late cut grass hay and an early second cut lucerne hay. 2) With continuous access to forage, voluntary intake of lucerne hay was higher (1,693 g dry matter (DM) per day) than that of grass hay (974 g DM per day). Lucerne hay was eaten more rapidly and needed less mastication per g DM. With limited time of access, eating rates were increased, but voluntary intake was maintained only with the grass hay. 3) With continuous access to forage, rumen pool sizes (RPS) of fresh matter, DM, organic matter (OM), and fibre were higher after the evening main meal than after the morning main meal. RPS were always lower with lucerne hay, except after the evening meal. With limited time of access, RPS after the morning meal were higher than those reached by continuous access, but this was not true after evening meal. 4) The net removal of DM and OM, but not of fibre were increased during the main meal, and turnover rates of DM, OM and fibre were higher for lucerne hay. 5) These results confirm that the maximum degree of rumen fill is involved in the control of voluntary intake. However, rumen fill does not seem to control intake during the whole day and other factors may be involved, specially with rapidly digestible hays.

The control of seasonal reproductive activity in sheep and goats in open sheds, needs extra-light (E) during the photosensitive phase (equivalent to long days, LD), followed by treatment with melatonin (equivalent to short days, SD). In autumn-born Ile-de-France or Lacaune ram lambs, 2 months of E followed by decreasing daylength for 90 days, advanced onset of the first breeding season by allowing males to reach their maximum testis volume and sperm production earlier than for untreated ram lambs. Substitution of decreasing daylength with melatonin implants allowed a transient increase in testis volume. Adult Ile-de-France rams maintained under short light rhythms with 2 month-period, demonstrated, during at least 2 consecutive years, a testis volume equivalent to that observed during the normal breeding season. These light-treated rams produced, during non-breeding season, spermatozoa in the same quantity and quality as during the normal breeding season. In anovulatory out-of-season dairy goats, E treatment was demonstrated to be necessary before melatonin treatment and melatonin to be necessary after E treatment to stimulate oestrous and ovulatory activities. Stimulation of the anovulatory females by the introduction of treated males ("male effect"), appeared to be necessary to obtain maximum stimulation of the treated females. Two months of E, followed by melatonin treatment (daily injection or drenching or subcutaneous implants) allowed cycles with ovulation to be maintained for more than 2 months. Although effective for control of out-of-season reproductive activity, melatonin slightly decreased milk production when applied soon after kidding. So, total control of reproduction in sheep and goats by manipulation of photoperiod in open sheds and melatonin treatments appears feasible in both sexes.

Hibernating snails (Helix aspersa) were activated by placing them in environmental chambers under either long-day (LD 18:6) or short-day (LD 8:16) lighting conditions. One day after activation all the snails were injected with (3H-thymidine (5 microCi/g wet weight) in order to estimate the duration of spermatogenic phases under long and short-day cycles. Our histological and autoradiographic observations show that long-day cycles have a positive influence on the development of the male cell line, which becomes apparent from the third week of exposure. While in long-day snails labeled spermatozoa were identifiable 28 days after (3H)-thymidine injection, in short-day snails neither labeled spermatozoa nor spermatids were present in the gonads of animals killed as late as 39 days post-injection. These data strongly suggest that the photoperiod, besides acting on spermatogonial proliferation (Sokolove et al., 1983; Gomot and Griffond, 1987), has an important effect on the second meiotic division. In the course of spermatogenesis in Helix aspersa, the step from secondary spermatocyte to spermatid is probably the most sensitive to environmental factors.

Photoperiod is the proximate cue which times the reproductive period of the sheep and the role of daylength as a "zeitgeber" is evaluated in this report. Although sheep are regarded as a short-day breeding species, the reproductive period of the Suffolk ewe begins on daylengths which are on average 2.5 hours longer than those on which it ends. The reasons for this apparent anomaly are considered. Experimental evidence is presented which demonstrates that the transitions between the breeding season and anoestrus are not actively generated by changing ambient photoperiod. Rather the ewe expresses an endogenous circannual rhythm of reproduction and the role of daylength is to entrain this reproductive rhythm to a period of 365 days. It appears that only portions of the annual cycle of photoperiod are necessary to synchronize the breeding season, however, additional photic cues may be required to produce a reproductive period of normal duration.

Masticatory muscles mediate the action of functional orthopedic appliances on mandible growth. When young rats were treated for four weeks with a postural hyperpropulsor of the mandible, an appliance designed to increase condylar cartilage growth rate, the proportion of fast non-fatigable fibres in the lateral pterygoid muscle increased significantly. Concomitantly, the amount of slow-myosin light chains increased in fibre extracts. This slow myosin originated from IIA fibres. By functional orthopedic treatment, the lateral pterygoid muscle was enriched in less fatigable fibres; the changes observed in the lateral pterygoid muscle were close to changes observed in other muscles after training.

Although artificial control of the light cycle can be used to regulate the seasonal reproductive cycle of many animals under laboratory conditions, such regulation is often not possible in a standard agricultural environment. An alternative strategy for regulating the seasonal reproductive cycle of photoperiodic animals is to use drugs that either mimic the effects of light on reproductive function or that induce an alteration in the way the circadian clock system is entrained by the light cycle. The ability to use drugs to achieve these objectives has been demonstrated in the laboratory, but it remains to be determined if such an approach can be used to regulate the breeding season of farm animals under normal agricultural conditions.

In Pleurodeles waltlii, peptidase-1 is a dimeric enzyme which has been shown to be controlled by two codominant alleles, Pep-1A and Pep-1B (Ferrier et al., 1980, 1983), linked respectively to the Z and W sex chromosomes. The enzymatic patterns obtained after starch gel electrophoresis were used routinely to identify the sexual genotypes of animals reared in our laboratory. We describe here three new patterns that were encountered in standard females, in sex-reversed animals and in thelygenous females. The inheritance data indicated the occurrence of a third codominant allele, Pep-1 beta, linked to the W sex chromosome. The discovery of this new allele does not impair peptidase-1 polymorphism as a reliable tool for ZZ, ZW and WW genotype identification.