Animal Molecular Breeding, 2024, Vol.14, No.6, 370-379 http://animalscipublisher.com/index.php/amb 371 2 Understanding Goat Reproductive Cycles 2.1 Seasonality and breeding cycles in goats Goats are inherently seasonal breeders, with their reproductive cycles influenced by various environmental and physiological factors. In temperate regions, goats typically exhibit seasonal breeding patterns, with the breeding season occurring in the fall and winter months. This seasonality is primarily driven by changes in photoperiod, which is the length of day versus night (Fatet et al., 2011). In contrast, goats in tropical regions may breed year-round, although food availability can significantly impact their reproductive cycles, often leading to prolonged anoestrous and anovulatory periods during times of scarcity (O'Sullivan et al., 2019). The degree of seasonality can also vary between breeds, with some displaying more pronounced seasonal breeding behaviors than others. 2.2 Influence of photoperiod and climate on reproduction Photoperiod is a critical environmental cue that regulates the reproductive cycles of goats. Changes in daylight length signal the onset of the breeding season, with shorter days typically triggering reproductive activity (Zarazaga et al., 2021). This photoperiodic response is particularly evident in temperate regions, where the breeding season aligns with shorter day lengths in the fall and winter. In subtropical and tropical regions, while photoperiod still plays a role, other factors such as climate and food availability can also influence reproductive cycles (Khan et al., 2019). For instance, photoperiodic treatments have been used to stimulate sexual activity in bucks during the non-breeding season, thereby inducing and synchronizing estrous behavior in does through the 'male effect' (Chasles et al., 2019). 2.3 Impact of seasonal breeding on production efficiency Seasonal breeding in goats has significant implications for production efficiency. The seasonality of reproduction leads to corresponding fluctuations in the production of milk, cheese, and meat, which can result in variable incomes for producers (Delgadillo, 2011). To mitigate these fluctuations and stabilize production throughout the year, various breeding management strategies have been developed (Hameed et al., 2020). These include hormonal treatments to synchronize estrus and ovulation, as well as photoperiodic treatments combined with the 'male effect' to induce out-of-season breeding (Delgadillo et al., 2014). Additionally, targeted nutritional supplementation, such as using dairy cow feed leftovers, has been shown to enhance reproductive performance in goats during the anestrous season, thereby improving overall production efficiency (Table 1) (Machado-Ramos et al., 2023). By understanding and manipulating the factors that influence goat reproductive cycles, producers can achieve more consistent and efficient production outcomes (Habeeb and Kutzler, 2021). 3 Seasonal Breeding Strategies 3.1 Synchronization of estrus cycles Hormonal treatments are widely used to synchronize estrus cycles in goats, facilitating out-of-season breeding and improving reproductive efficiency. These treatments typically involve the use of progesterone analogs combined with gonadotropins such as pregnant mare serum gonadotropin (PMSG) or human chorionic gonadotropin (hCG) to induce ovulation and synchronize estrus (Fatet et al., 2011). For instance, the use of PMSG and prostaglandin (PGF2α) has shown high estrus response rates and improved conception and kidding rates in goats (Table 2) (Wondim et al., 2022). Additionally, kisspeptin analogs like C6 have emerged as promising alternatives to PMSG, offering longer-lasting effects and enhanced activity (Decourt et al., 2014). Natural methods of synchronization, such as photoperiodic treatments and the male effect, are gaining popularity due to their hormone-free approach. Photoperiodic treatments manipulate the light exposure to mimic seasonal changes, thereby inducing estrus and ovulation. The male effect involves the sudden introduction of a male to a group of anestrous females, which triggers neuroendocrine changes leading to estrus and ovulation. These methods, while effective, often result in lower fertility rates compared to hormonal treatments (Luo et al., 2019).
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