Genetic and environmental effects on hogget wool production of various crosses between the Dorset Horn, Merino and Corriedale breeds of sheep.

Abstract

Proc. Aust, Soc, Anim. Prod. Vol. 18 GENETIC AND ENVIRONMENT AL EFFECTS ON HOGGET WOOL PRODUCTION OF VARIOUS CROSSES BETWEEN THE DORSET HORN, MERINO AND CORRIEDALE BREEDS OF SHEEP W.S. PITCHFORD* and T.S. CH'ANG* SUMMARY This study investigates the importance of various genetic and environmental effects on clean fleece weight (CFW) and fibre diameter (FD) of hogget sheep Merino and resulting from all possible crosses between the Dorset Horn, Corriedale breeds. All environmental effects were influential in determining The most important CFW and FD, with year of birth being the most important. genetic effects in determining CFW and FD were additive (direct) effects. Overall, crossbreds exceeded purebreds Maternal effects were less important. by 13% for CFW and 2% in FD. IN!X!RODUCXION together desirable characteristics of Crossbreeding is a means of bringing In addition to the qualities of the breeds themselves, two or more breeds. Often crossbred there may be specific advantage in a particular cross. than the mean of the two parent breeds; this performance is greater increased performance is known as hybrid vigour or heterosis. Crossbreeding plays an important role in the Australian sheep industry, Returns from wool and meat are important especially for lamb production. sources of income for lamb producers. This study investigates the relative importance of various genetic and environmental effects on hogget clean fleece weight (CFW) and fibre diameter (FD), the two major traits determining fleece value, METHOD The sheep in this study were raised at Arding, near Armidale, N-S-W. Lambs were born each year from 1973 to 1982. Data for rams born in 1977 and 1978 are not available. Lambs were generally born during October, marked in measurements were taken a t December, weaned in January and hogget approximately 15 months of age in the following January, although this did vary from year to year. Ram lambs were not castrated. Numbers of sheep in each cross are shown in Table 1. A model including factors of breed of sire (BOS), breed of dam (BOD), the interaction between breed of sire and breed of dam (BOS*BOD), year of birth traits WV f and age of dam (AOD) (2-9 years) was fitted to the two using least squares techniques (Harvey 1964). Initial analysis showed significant SEX*BOS and SEX*BOD interactions so the present analyses were done separately for rams and ewes. Linear contrasts between least squares means used to calculate direct were genetic (gI), total maternal (mT), and individual heterotic (h1) effects as shown in Alenda et al. (1980). RESULTS AND DISCUSSION Environmental effects Age of dam effects on ewes CFW were significant (P<O,OS) and all other factors in the model had a significant (PcO.01) effect on the two traits and both sexes * CSIRO, Division of Animal Production P-0. Box 239, Blacktown, N.S.W. 2148. 332 Proc. Aust. Soc. Anim, Prod. Vol. 18 in this study. BOS*BOD) than accounted for for accounted 72% CFW; Ewes: CFW and 9% for 38%. Variation in FD was due more to genetic effects (BOS, BOD, environmental effects (YR & AOD). Environmental effects The more variation in CFW than genetic effects, model most of the variation in each of the traits (Rams: 74% FD; 76% FD; 67% CFW). The coefficient of variation was 19% for FD. The residual correlation between the two traits was around Hogget rams from mature dams had 10% higher CFW (P<O.Ol) and 5% higher FD (P<O,Ol) and hogget ewes had 4% higher FD than those from maiden (2 year old) dams. Differences in CFW between ewes from maiden and mature dams were not significant. _ Turner et al, (1968) reported that Merino lambs from mature ewes had 7% higher CFW and 1% higher FD than lambs from maiden ewes. This effect is probably similar to that of being a twin lamb compared to a single. birth was the most important determinant of CFW and had a similar Year of effect to BOS and BOD on FD. Effects were similar for rams and ewes. The highest CFW was of those born in 1973 and was 112% higher than 1979, the lowest. The FD of those born in 1973 was 21% higher than 1979. Those born in 1973 were shorn at weaning and at 15 months whereas those born in 1979 were shorn in the September at 11 months of age, which probably explains the huge yearly variation. By fitting year as part of the model yearly differences have been corrected for sufficiently to allow accurate estimation of genetic effects, It was found that ewes had 2% higher CFW and 3% higher FD than rams. This is opposite to what was expected but previous studies in the Armidale area (Turner and Jackson 1978) found, in all the years studied, hogget Merino ewes had higher CFW and, in most years, a higher FD than their male Analysis of hogget body weight data counterparts. from this experiment (Pitchford unpublished) has shown that rams weighed more than ewes at the time of sampling. The rams in this experiment were left entire and so rams and after weaning, ewe lambs were run separately however management differences were minimised by regular rotation of paddocks. Genetic effects As stated above, BOS, BOD, and BOS*BOD effects were important (P<O.Ol) for both traits. The main effects (BOS, BOD) were much more important than the interaction (BOS*BOD), but the significant interaction indicates that non-additive effects are present, Individual, or direct, genetic effects measure the additive portion of the genotype; that which is transmitted from parent to offspring. Maternal effects as calculated in this study measure the differences between reciprocal crosses. measures Individual heterosis the mean the deviation from of the parent breeds and is, therefore, a measure of the non-additive genetic effects. As shown in Table 1, the cross with the highest CFW was the COxMO and the lowest, the DH. Dorset Horn had the highest FD and the Merino the lowest. Sex differences were not significant SEX*BOS and reflected in the purebred than DH ewes; Merino rams higher CFW than ewes, consistent over all breed combinations, as shown SEX*BOD interactions in previous analyses. This means (Table 1): Dorset Horn rams had 17% lower and ewes had the same CFW; and Corriedale rams had by is CFW 6% 333 Proc. Aust, Soc. Anim. Prod, Vol. 18 Table 1 Least squares (2 s-e.) means for hogget wool production of various breed crosses Abbreviations: CFW, clean fleece weight (kg); FD, mean. fibre diameter (urn); DH, Dorset Horn; MO, Merino, CC, Corriedale a The sire breed is given first in the crosses Table 2 Genetic effects of various breeds on hogget wool production (mean + 8-e. ) * contrast is significantly different from zero (P<O.OS) ** contrast is significantly different from zero (P~0.01) Abbreviations: CFW, clean fleece weight (kg); FD, mean fibre diameter (urn); DH, Dorset Horn; MO, Merino; CO, Corriedale a estimates pooled for the two reciprocal crosses involved Direct genetic effects (Table a-l-1 breeds. Direct effects were some important differences. followed by the Merino and the the greatest FD, the Merino the than the mean of the population. 2) were significant for both traits and similar for the two sexes although there were The Corriedale transmitted the greatest CFW, Dorset Horn. The Dorset Horn transmitted least and the Corriedale was slightly greater These simply reflect the different selection 334 Proc. Aust. Soc, Anim. Prod. Vol.98 been placed on these breeds over the years, pressures that have Direct The effects on CFW varied more in the ram than the ewe. effects may be summarised as follows: g' DH ram < ewe; g1 MO ram = ewe; g1 CO ram > ewe. Maternal effects were generally not important although there was a positive This may be a similar effect to that of effect of the Merino damon CFW. However, other the twin versus single effect or the mature ewe effect. studies on this experiment (Pitchford unpublished) have shown a significant negative effect of the MO dam on birth and weaning weights, so the increased CFW effect is not just caused by increased nutrient availability because that favours growth as well. There must be something about the Merino dam that favours increases in CFW. Perhaps the effect is a pre-natal effect conducive to follicle development. The slight negative effect of the Dorset Horn dam on rams' CFW and the Corriedale dam on rams' FD should also be noted. were similar Heterosis estimates for the two sexes, they were positive for CFW for all crosses. There was also a positive heterotic effect (P<O.Ol) on FD for DH/CO crosses for both sexes and MO/CO cross ewes. The greatest heterosis for both traits was .with DH/CO crosses. Merino crosses tended to show less heterosis, On average, crossbreds exceeded purebreds by 13% for CFW and only 2% for FD. McGuirk (1967) found that in the Border Leicester by Merino cross heterosis was 10% for CFW. Sidwell et al. (1971) found that for ewes, heterosis was 6% for CFW and 2% for FD. Gallivan et al. (1987) found heterosis was -9% for wool grade and 13% for greasy fleece weight, In conclusion, although the effect of heterosis on wool traits is not as clear cut as it is for traits such as fertility, prolificacy, fitness and growth rates there is still ample evidence that crossbreeding can increase fleece weights without substantially increasing fibre diameter. ALENDA, R., MARTIN, T-G., LASLEY, J.F. and ELLERSIECK, M.R. (1980). J. Anim. Sci. 50:226, GALLIVAN, C., HOHENBOKEN, W.D. and VAVRA, M. (1987). J. Anim. Sci. 64:43. HARVEY, W.R. (1964). 'Computing Procedures for a Generalized Least-Squares Analysis Program.' (Fort Collins: Colorado). McGUIRK, B-J, (1967). Wool Technol. and Sheep Breed. 14:73. SIDWELL, G-M., WILSON, R-L. and HOURIHAN, M-E. (1971). J. Anim. Sci. 32:1099. TURNER, Helen Newton, BROWN, G.H. and FORD, G.H. (1968). Aust. J. Agric. Res. 19:443. TURNER, Helen Newton and JACKSON, N. (1978). Aust. J. Agric. Res. 29:615. 335