Growth rates of females from a Romane sheep breed flock reared in rangelands and effects of an early or late first mating regime on their offspring.

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English. Benefits in lifetime production of the ewe is often determined by the particular characteristics of the growth during the first stages of their life, including the related decision of the age at first mating. The objective of this work was to characterize the growth rates of the young female (from birth to first mating) from the Romane sheep breed, in a flock reared under the Mediterranean rangelands conditions of France. The effects of 2 contrasted first mating regimens (Early; 7 mo vs. Late; 19 mo old) on the individual growth rate of the ewe lamb and their first offspring were also evaluated. A database was built based on historical data that were extracted from the INRA database (GEEDOC). Data from 1359 females born during the period 2002–2012 were collected, processed and interpreted using SAS (9.3). From the total, 762 and 597 females were submitted to the Early or Late regimen, respectively. The effects of the litter size at their birth (singletons; SING vs. multiple; TWIN) and the age of their dams at birth (primiparous, PRIM vs. multiparous, MULT) were considered. The growth curves were built for both population (Early; 39.7 ± 0.07 kg and Late; 50.6 ± 0.04 kg BW at first mating) of ewes lambs. Significant interactions of the litter size at birth and the dam’s parity were found for BW at birth and BW at weaning. Overall, the ewes lambs born from MULT × SING and PRIM × TWIN dams showed the highest (4.7 ± 0.03 and 26.2 ± 0.15 kg) and lowest (3.3 ± 0.01 and 22.5 ± 0.09 kg) BW at birth and weaning, respectively. Even if submitting the ewes lambs from the actual flock to the Late regimen constituted a change on the reproductive management policy of the farm (from 2010), data showed that females submitted to Late corresponded to those having a weaker growth from birth to weaning. When analyzing the growth traits of their first offspring, the first litter size (1.8 ± 0.01 vs. 2.1 ± 0.01 lambs/lambing) and its total weight (6.2 ± 0.03 vs. 7.4 ± 0.02 kg) were different (P < 0.0001) for ewes submitted to the early or late regimen, respectively. Other related carry over effects during the whole productive life of this females’ population and their offspring are currently being analyzed.