Genetic parameters of production and fertility traits in Hungarian Merino sheep.

IntroductionHungary has a long-standing tradition in Merino breeding and improvement. During the past decades several attempts have been made to introduce a number of other sheep breeds. Although this effort was not in vain the majority of the sheep population is still the Hungarian Merino breed. The adaptability, endurance and excellent wool-producing ability of this breed is first rate and is worth preserving (Veress et al. 1997). The profitability of a sheep production system is determined by both fertility and production traits. Reproduction performance is usually defined as litter weight per dam per year. Progress can be achieved through various ways. One of them is frequent lambing which also has the advantage that lamb production becomes more consistent throughout the year. Another possibility is producing larger litter sizes (LS), and yet a another opportunity for increased production is having lambs with larger weights (WT). Simultaneous enhancement can also be achieved if there is no antagonism between these traits. From these several fertility traits LS from the first to the fifth parity was chosen for analysis as LS is one of the most important traits concerning reproduction performance. Of the production traits, WT measured at various ages, greasy fleece weight (GFW) from the first five shearings, staple length (SL) and fibre diameter (FD) at the age of 1 year were taken into the analysis. According to other studies there are several factors influencing the above mentioned traits, namely age, season of previous lambing (PLS), type of birth (TOB), and sex. In general, LS increased with advancing age (Long et al. 1989; Bunge et al. 1990; Ap Dewi et al. 1996). For GFW the peak of production was achieved in a relatively early age of 3 years, reported by Veress (1969) and by Turner and Young (1969). The effect of PLS on LS was that smaller litters were observed with previous lambing seasons of summer and autumn (Long et al. 1989). TOB and sex effect on WT have been investigated by several authors (Turner and Young 1969, p. 46, 51.; Shrestha and Heaney 1985; Mavrogenis 1988; Bunge et al. 1990; Jurado et al. 1994; Veress et al. 1995; Shrestha et al. 1996). Single-born lambs are heavier than multiples although this difference decreases with age. All authors also agree that male lambs are heavier than females. TOB and sex effect on GFW were reported by Turner and Young (1969). Turner and Young labelled the TOB effect as a ‘maternal handicap’ as the effect is noticeable even in maturity but decreasing by age. Turner and Young (1969) also observed that the WT and GFW of male animals exceeds that of the females, but, unlike with the previous effect, the difference increases with age. There was a negligible difference between sexes in SL and FD. Studying the results of numerous authors, estimates of the genetic parameters of LS, WT, GFW, SL, and FD were found to be generally consistent. Heritabilities of LS ranged from 0.05 to 0.08 (Al-Shorepy and Notter 1996; Ap Dewi et al. 1996; for litter size at first parity only). Ap Dewi et al. (1996) found very high (>0.9) genetic correlations between the first and adult litter size. Heritabilities estimated for WT were higher than those of the fertility traits and ranged in the interval of 0.05–0.47 (Shrestha and Heaney 1985; Long et al. 1989; Bunge et al. 1990; Kumar and Reheja 1993; Jurado et al. 1994; Al-Shorepy and Notter 1996). Genetic correlations between yearling and adult WT were high (Jurado et al. 1994; 0.85; Al-Shorepy and Notter 1996; 0.85–1.0). GFW heritabilities reported by Blair et al. (1985); Turner and Young (1969) were about 0.2 thus also exceeding those of the fertility traits. Regarding the genetic parameters of SL & FD, Notter and Hough (1997); Morris et al. (1996) reported that the heritability of SL and FD was higher than that of GFW (026–0.34; 0.47–0.58). Genetic correlations among production traits were mainly low (Morris et al. 1996; and Turner and Young 1969). The objectives of this paper were to determine whether the characteristics of the Hungarian Merino sheep population correspond with the features given in the literature review. Thus the objectives were to obtain the factors influencing the traits examined and to estimate genetic parameters of LS, WT, GFW, SL, and FD, respectively. [ABSTRACT FROM AUTHOR]