Szent István University Postgraduate School of Veterinary Science ...

1. Introduction
In traditional technologies, sheep' dairy products are typically seasonal goods. Due to the
race’s inherent seasonal reproduction activity, their manufacturing is restricted to early
summer. However, great commercial interest is attached to the continuous milk production. In
small ruminants, gestagen+eCG (equine chorionic gonadotropin) treatment is widely used for
cycle induction to get out-of-season fertility. Although these protocols are permitted in dairy
flocks, in view of the increasing consumer requirements, it is better to refrain from the use of
sexual steroids in reproduction management of milked livestock. An alternative solution for
the future is to try to form flocks, where most of the ewes are cyclic during the whole year –
also out of the traditional autumn breeding season – allowing fertilization also in spring
besides autumn. Based on researches concerning primarily different merino lines, we know
that the ability of perennial cyclicity is genetically determined in sheep, and is in connection
with melatonin receptor 1a (MT1) polymorphism, although the underlying mechanism is not
known in details at the moment (Pelletier et al. 2000, Notter et al. 2003). At the same time
numerous preconditions can influence the manifestation of this capacity: such as age, body
condition (BC), and pheromone-exposure. In genotypes which are genetically capable of year-
long ovarian cylicity, the use of long-known natural or near-natural breeding technologies
(e.g. few days increased energy supplementation; flushing, pheromone exposure by
introduction of vasectomized rams to ewes, photoperiodic and/or melatonin treatment) might
gain new dimension, and contribute to clean, green and ethical animal breeding.
The growing demand for clean technologies in animal breeding led to the development of
novel management tools also in dairy cow. Better understanding of the physiology of
seasonality and the importance of the photoperiodic signal in its regulation led to the
emergence of technologies which use long-day photoperiodic treatment to increase milk yield
in dairy cow (Dahl et al. 2000). Later the positive link between long-day photoperiodic
treatment and increased milk yield was also proven in goat (Mabjeesh et al. 2007). This drew
our attention to a possible limitation of using melatonin implants for cycle induction in sheep.
Treatments acting through the melatonin pathway to induce cycle in the short-day breeder
sheep may negatively influence milk production in lactating dams.
Although seasonality of reproductive activity is less expressed in males compared to females
rams also show year-round variation in sexual behaviour, testicular size, and quality of semen.
To maximize the out-of-season reproductive performance not only ewes but also rams should
be treated accordingly. Administration of melatonin in the non-breeding season was shown to
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