The aim of B. Sc. Thesis was to review the literature on the photoperiod and rearing of heifers, especially their growth, mammary gland development and onset of puberty. Most studies have shown a positive effect of long day photoperiod (16 hours of light and 8 hours of darkness) compared to natural and short day photoperiod (8 hours of light and 16 hours of darkness) on heifer growth. The long photoperiod affects the release of several hormones, most notably decreased melatonin and increased IGF-1 and prolactin. This results in increased growth, especially of skeletal and muscle tissue, and decreased growth of fat tissue. The differences are more evident in younger animals. Prolongation of the photoperiod leads to increased growth of mammary glands, especially parenchymal tissue, which may result in higher milk yield. The influence of a longer photoperiod is also reflected in an earlier onset of the first estrus and puberty.
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