Variation in growth characteristics of Dorset ewes in a production competition.

Abstract

VARIATION IN GROWTH CHARACTERISTICS OF DORSET EWES IN A PRODUCTION COMPETITION B. W. CLEMENTS* and N.M. FOGARTY* Eleven Poll Dorset and nine Dorset Horn studs each entered six ewe weaners in a production competition in September 1973. These were run together at Cowra, New South Wales for 12 months. Significant (P < 0.01) variation was found between the Poll Dorset studs for fat depth over the 12/13th rib, but not for growth rates. No significant variation was found for weight gains or fat depth between the Dorset Horn studs. Poll Dorset ewes gained significantly (PC 0.01) more weight than Dorset Horn ewes for first weight gain (approximately four to ten months of age) and total weight gain. These results and the value and application of information obtained from this competition are discussed. I. INTROIXJCTION Production competitions compare animals from a number of flocks in a common environment. They are used to create & awareness of and interest in objective measurement of economically important characters. Merino production competitions have been held for a number of years. Generally wethers have been used to compare characters associated with wool production over a 12 month period (Turner and Young 1969; Beasley 1974). Production competitions for meat sheep breeds such as the Dorset have been initiated only recently. The Dorset is the major sire breed used for prime lamb production in Australia and thus the characters of importance for this role are related to lean meat production. The Central Western Dorset Production Competition held at Cowra is an annual competition, jointly run by the Cowra Pastoral, -icultural and Horticultural Association and the New South Wales Department of Agriculture (Fogarty and Harris 1975). There is a dearth of published information on variation in Dorsets in Australia. This competition provides a unique opportunity to assess variation, between strains (Poll Dorset and Dorset Horn) and between studs, for growth and fat characteristics. II. MATERUM ANDMETHODS Sheep and location Eleven Poll Dorset and nine Dorset Horn (DH) studs each entered six ewe lambs approximately four months of age in September 1973. Each breeder chose his lambs, which were required to be born within a specified six week period; Entries came from a wide area of the state and included a number of important studs. The ewes were run together for 12 months on Cowra Agricultural Research Station, which is located in a prominent Dorset stud area.The ewes grazed perennial ryegrass/ subclover and lucerne pastures, which provided a high level of nutrition through out the .year. * Department of Agriculture, Agricultural Research Station Cowra. 49 Seven ewes died and a further six were not considered in the analysis due to illness or injury affecting their growth.. The 107 ewes included in the analysis were the progeny of 48 different sires. (b) Measurements . Fasted liveweights were taken on three occassions, on arrival in September 197.3, in February 1974 and at the end of the-12 month period in September 1974. Fat depth between the 12/15th rib was measured on the live animals using a Scanogram in September 1974. As there was a positive correlation ( r= 0.24) between liveweight and fat depth, the latter was adjusted to a constant liveweight basis (60 kg) for the competition. ( C ) Analysis Least squares analyses of variance were used to examine the effects of strains, studs within strains and sires within studs for weight gains. Initial liveweight was fitted as a covariate in the analyses to remove the effect of pre-test environment (age and nutrition) on subsequent performance. If it was a non significant source of variation the data was re-analysed without the covariate. The same variables, excluding initial liveweight, were included in the analysis of adjusted fat depth, III. RfEULTS (a) First weight gain Significant (P< 0.01) variation was found between the PD studs for first weight gain. When initial liveweight was included as a covariate the variation between the PD studs was reduced to non significance. The ranges in least squares means for the PD and DH studs were 4.3 and-5.5 kg respectively (Table l)0 The variation between the DH studs was not significant. PD ewes gained significantly -(P4 0.01) more weight than DH ewes Table 2). Between sires within studs variation was also significant I PC 0.05). The inclusion of initial liveweight as a covariate in both these analyses had little effect. (b) s econd weight gain Variation between PD studs and between DH studs was not significant for second weight gain. PD ewes were not significantly different from DH ewes (Table 2). The variation between sires within studswas not significant. Initial liveweight as a covariate had no effect on ayly of the analyses. (c) Total weight gain There was significant variation between the PD studs (PC 0.05), but not between the DH studs. The inclusion of initial liveweight as a covariate ,reduced to non significance the variation between PD studs, but had little effect on the DH studs. PD ewes gained significantly (PC 0.01) more weight than DH ewes Table 2). Variation between sires within studs was significant l PC 0.05). Neither analysis was affected by the inclusion of initial weight as a covariate. (d) Fat depth Between studs variation for adjusted fat depth was significant (Pe 0.01) in PD ewes and accounted for 52% of the variation, but was 50 not significant for DH ewes. The range in least squares means for PD studs was considerably higher than the range in DH studs i.e. 5.3 mm xe 1.3 mm (Table I). Adjusted fat depths of PD ewes were not significantly different from DH ewes (Table 2). Variation between sires within studs was not significant. TABLE:1 Ranges of least squares means for PD and DH studs IV. DISCUSSIGfl The lack of variation for growth between studs within strains was not surprising, considering the close relationship that exists between studs. This is due to the very small numb&of studs supplying rams for stud breeding in New South Wales and the widespread practice of linebreeding to popular animals from these studs (Fogarty, unpublished data). + This widespread use of linebreeding has led to a high level of inbreeding, in the DH breed (Fogarty, unpublished data) and a similar situation probably exists in the PD breed. Thus some expression of heterosis could be expected in.progeny of crosses between the strains (Weiner and Hayter, 1974). This could partly explain the superiority of the PD ewes in this competition since some at least were heterozygote progeny of DH ewes. This superiority of the PD ewes for growth could also be due to genetic superiority, however this cant-t be confirmed due to the limited number of studs and animals represented. . The significant between sires within studs variation for first weight gain may be biased, since it is based on progeny which have been 51 selected. However it does suggest that selection and use of superior sires in these studs could lead to an improvement in growth rates. Fat depth is of considerable concern to many Dorset breeders, and some are attempting to select lean animals within their studs. The heritability of fat depth is moderate to high (Carpenter 1968) and selection would be expected to change this trait. The varying ability of breeders to assess fat in live sheep and the importance they place on it both in their breeding programme and selection of entrants could be responsible for the large variation in fat depth of PD ewes. The design of this 'production 'competition, 'with its limited sampling of ewes and sires within studs cannot be expected to define real differences between s.tuds. The competition was initiated, primarily to promote objective evaluation of growth and fat traits in Dorset sheep. It provides a better alternative to the present system of show ring judging where type and preparation are paramount. IV. ACKNOWlJ3DGE3!U3NTS We wish to thank Messrs. D. C. Harris, G, R. Woods, M. W. Lollback, Cowra P,A. & H. Association and the stud breeders for their assistance* and Mr. J. Evans for his help with the statistical analysis. v. REFERENCES CARPENTER, 2. L. (1968) - 'Indicators of Meatiness and their Inheritance' Proc. Symposium on Genetic Improvement of Wool and Production. Texas A & M University, McGregor Texas. BEASLEY, P. S, (1974) - Queensland Agricultural Journal 100: 190. FOGARTY, N. M. and HARRIS, D. D, (1975) - Agric. Gazette- N.S.W. 86(3): 32. T-y H, N, and YOUNG, S. S. Y. (I 969) - '&uantitative Genetics in Sheep Breeding' (Macmillan Press: Melbourne.) WEINER, G. and HAYTER, S. (1974) - Vrossbreeding and Inbreeding in Sheep' Agricultural Research Council. Animal Breeding Research Organisation Report - January 1974. 52