Abstract
The increased emphasis placed on lamb production in Brazil points to the need for a better knowledge of the annual pattern of reproductive activity in ewe lambs. This study evaluates the annual estrous activity pattern of hair and wool ewe lambs raised in southeast Brazil. Estrous characteristics were recorded for 12 months in ten Santa Inês and 21 Romney Marsh and Suffolk ewe lambs. Santa Inês ewe lambs exhibited a greater length of the normal estrous cycle (14 to 19 days) than Romney Marsh and Suffolk ewe lambs (17.0 ± 0.1 days vs. 16.5 ± 0.2 and 15.9 ± 0.2 days). All the ewe lambs presented a greater number of periods of estrus per animal per month for single estrous cycles (up to 26 days) during autumn and winter. During spring and summer there was a reduction of this number but this decline varied according to the breed. For Santa Inês ewe lambs the reduction was only significant in the summer. For wool ewe lambs the reduction was significant in both seasons but was more accentuated for Romney Marsh. The Romney Marsh ewe lambs had a more restricted breeding season than Suffolk and both presented optimal estrus activity in autumn and winter. Santa Inês ewe lambs had a continuous distribution of estrous cycles along the year, although presenting a reduction in the number of estrous periods in the summer. The ewe lambs of three breeds presented characteristics of sexual immaturity, like irregular estrous cycles and silent ovulations.
Highlights
Reproductive activity in sheep is characterized by a seasonality influenced by several factors such as photoperiod, latitude, temperature, nutrition and breed (Hafez, 1952; Mbayahaga et al, 1998)
The Brazilian territory extends over a great variation of latitudes (5o16’ N to 33o45’ S) and the characteristics of the cyclic reproductive activity of ewe lambs varies considerably depending on the region
The length of single and multiple (27 to 57 days) estrous cycles demonstrated in Table 1 showed breed differences (P < 0.01) only on the length of normal (14 – 19 days) cycles
Summary
Reproductive activity in sheep is characterized by a seasonality influenced by several factors such as photoperiod, latitude, temperature, nutrition and breed (Hafez, 1952; Mbayahaga et al, 1998). In the Northeast, the sheep flock is constituted only of hair meat breeds, being Santa Inês the most widespread breed Their females present cyclic reproductive activity along the year (Figueiredo et al, 1980; Girão et al, 1984). In the southern region there is a predominance of wool breeds, specialized for both wool (Merino and Polwarth) and meat production (Corriedale, Romney Marsh and Suffolk). Ewe lambs of such breeds present seasonality of their cyclic reproductive activity (Silva & Figueiró, 1980; Ribeiro et al, 1996)
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