Sources of variation and genetic profile of spontaneous, out-of-season ovulatory activity in the Chios sheep

Abstract

<p>Abstract</p> <p>Organising the breeding plan of a seasonally breeding species, such as sheep, presents a challenge to farmers and the industry as a whole, since both economical and biological considerations need to be carefully balanced. Understanding the breeding activity of individual animals becomes a prerequisite for a successful breeding program. This study set out to investigate the sources of variation and the genetic profile of the spontaneous, out-of-season ovulatory activity of ewes of the Chios dairy sheep breed in Greece. The definition of the trait was based on blood progesterone levels, measured before exposing the ewes to rams, which marks the onset of the usual breeding season. Data were 707 records, taken over two consecutive years, of 435 ewes kept at the Agricultural Research Station of Chalkidiki in northern Greece. When all available pedigree was included, the total number of animals involved was 1068. On average, 29% of all ewes exhibited spontaneous, out-of-season ovulatory activity, with no substantial variation between the years. Significant sources of systematic variation were the ewe age and live weight, and the month of previous lambing. Older, heavier ewes, that had lambed early the previous autumn, exhibited more frequent activity. Heritability estimates were 0.216 (± 0.084) with a linear and 0.291 with a threshold model. The latter better accounts for the categorical nature of the trait. The linear model repeatability was 0.230 (± 0.095). The results obtained in this study support the notion that spontaneous out-of-season ovulatory activity can be considered in the development of a breeding plan for the Chios sheep breed.</p

Genome-Wide Association Study Demonstrates the Role Played by the CD226 Gene in Rasa Aragonesa Sheep Reproductive Seasonality

“…Hanocq et al [ 8 ] reported relatively high heritability and repeatability estimates (0.20 and 0.30, respectively) for SOA in the Merinos d’Arles breed. Similar heritability of SOAs was found in the Chios breed in Greece [ 9 ] and in the Latxa breed in Spain [ 10 ]. Hence, the estimation of genetic parameters for SOA indicated that this trait could be used in selection [ 11 ].…”

Invited review: Current state of genetic improvement in dairy sheep

“…The ability to breed out of season is a desirable characteristic; the sooner ovarian activity starts in early spring, the earlier the ewe will get pregnant, lamb, and start lactation. Genetic control of seasonality between and within breeds has been clearly demonstrated (Hanocq et al, 1999;de Heredia et al, 2002;Avdi et al, 2003). Heritability of spontaneous ovulatory activity in early spring ranged between 0.10 (de Heredia et al, 2002) and 0.20 (Hanocq et al, 1999).…”

Seasonality of oestrus, ovulation and ovulation rate of Sicilo‐Sarde sheep

“…Nevertheless, the state of reduced seasonality can also be extended to the Sicilo‐Sarde sheep with reference to the index defined by Lindsay and Signoret () that the percentage of spontaneously ovulating females in spring is a good indicator of the depth of anoestrus and of the breed ability to respond to the ‘Ram Effect’. In our study, 50% of adult and maiden females were found ovulating in April while in Greece, for example, 29% of the Chios breed ewes exhibited spontaneous, out‐of‐season ovulatory activity in early May, as determined by blood progesterone levels (Avdi et al., ).…”