- Changes in production traits of a genetic strong wool Merino flock mated to genetic fine wool Merino rams
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CHANGES IN PRODUCTION TRAITS OF A GENETIC STRONG-WOOLLED MERINO FLOCK MATED TO GENETIC FINE-WOOLLED RAMS
A.G. Bezuidenhout, A.C. Greyling and J.M. Jansen van Rensburg
Cradock Experimental Station, Cradock 5880
and J.J. Olivier
Grootfontein Agricultural Development Institute, Middelburg CP 5900
When considerable price differences occur between fine and strong wool, the practice to mate strong-woolled ewes to fine-woolled rams usually increases considerably. According to the average clean-wool prices of the past 10 years (1983/84 to 1992/93 season), the price advantage of 20 micron wool over 27 micron wool was for example 107 %. During individual years when exceptionally high wool prices occur, the price difference between fine and strong wool is even higher. In this respect, the price difference between 20 and 27 micron wool was 133 % during the 1988/89 season.
The purpose of this study was to investigate the effect of the practice of mating strong-woolIed ewes to fine-woolled rams, on several other production traits of such a flock.
The experimental flock of genetic strong-woolled ewes (fine x strong) consisted of 50 ewes with an average initial fibre diameter of 29,7 micron which were mated to genetic fine-woolled rams with an average fibre diameter of 20 micron. The production traits of the ewes were compared to that of a strong-wool led control flock (control) of 50 ewes with an average fibre diameter of 25,3 micron. The control flock was mated to strong-woolled rams with an average fibre diameter of 25 micron. Replacement ewes were selected annually from the progeny within each flock. Both flocks were kept on cultivated pastures under irrigation at Cradock Experimental Station. The progeny of each flock was weaned at 100 days of age and also kept on cultivated pastures up to the age of approximately 16 months.
The data of the ewes recorded over 5 years were pooled and analysed by least square mean methods (Harvey 1990).
RESULTS AND DISCUSSION
The changes in average fibre diameter of the ewes in two flocks during 5 consecutive years are displayed in Fig. 1. The average fibre diameter of the experimental flock (fine x strong) decreased by 6,1 micron (21 %). In 1989 the average fibre diameter of this flock was 3,2 micron higher (P < 0,01) than that of the control and during 1993 it was 1,7 micron lower than that of the control as shown in Table 1. During the experimental period, the average fibre diameter of the control flock decreased by only 4,6%.
The average body mass of the experimental flock was initially 6,6 % higher (P < 0,01) than that of the control. During 1993, the body mass of the experimental flock was, however, only 3 % lower than that of the control flock. Over the period of 5 years, the decline in body mass of the experimental flock vs. that of the control flock was 1,21 ± 1,14 kg (P > 0,05)/year. This decline in body mass can be ascribed to the smaller Australian fine-woolled rams which were used. The average clean fleece mass of the experimental flock did not differ significantly from that of the control flock in any year. The same result was found for staple length. However, seen against the significant decrease in fibre diameter of more than 6 microns over the same period, these results are of more significance. As expected, the average crimp frequency of the experimental flock increased significantly (1,04 ± 0,13 crimps/year) against that of the control flock.
It can be concluded that the mating of overstrong-woolled Merino ewes with superfine-wool led rams resulted in a dramatic decline in fibre diameter without significant changes in the other economically important production traits.
The mating of Merino types with extreme fibre diameters is often discouraged by many people in the Merino industry. They raised concern about the mating of extreme types and alleged that it may increase the variance in fibre diameter in the progeny. This allegation was investigated by Olivier et al. (1993). From the progeny of the control and experimental flocks respectively, 23 and 37 wool samples were taken at five different body locations. These locations were at the shoulder, midrib, britch, back and belly.
The average fibre diameter at the different locations is displayed in Fig. 2. As expected, the mean fibre diameter increased from the shoulder to the britch and from the belly to the back. The mean fibre diameter of the experimental group was lower than that of the control group at all the different body locations.
From the results in Fig. 2 it is clear that the fibre diameter of the progeny of overstrong-woolled ewes mated to superfine-woolled rams did not display a bigger variation over the fleece as in the progeny of strong-woolled ewes mated to strong-woolled rams.
The variation in fibre diameter within each sample at each body location was also tested by Olivier et al. (1993), with the results displayed in Fig. 3. For the variation in fibre diameter in each sample, the same pattern as with fibre diameter was found.
It can therefore be concluded that concern for excessive variation in fibre diameter as a result of crossing fine and strong genotypes appears to be unwarranted.
The relatively small negative changes in production traits accompanied by a major reduction in average fibre diameter of the ewe flock, is informative and therefore this practice aimed at decreasing fibre diameter appears to be economically justified.
HARVEY, W.R. 1990. Mixed Model Least-Squares and Maximum Likelihood Computer Program.
OLIVIER, J.J., CLOETE, S.W.P. & BEZUIDENHOUT, A.G. 1993. Differences in mean fibre diameter variance in fine-wool, strong-wool and fine x strong-wool Merino sheep sampled at five body locations. South African Journal of Animal Science 23 (5/6): 201-203.
Karoo Agric, Vol6, No 1, 1994 (17-19)