- A comparison of kemp and medulated fibres in the fleece of Angora and Angora x Boer goat genotype kids
|Last update: November 22, 2010 02:03:50 PM|
A COMPARISON OF KEMP AND MEDULLATED FIBRES IN THE FLEECE OF
ANGORA AND ANGORA X BOER GOAT GENOTYPE KIDS
Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg Cape, 5900, South Africa
Email: Gretha Snyman
A project aimed at developing an easy care, hardy goat, with a relatively high reproductive ability and good carcass characteristics, and which will also produce good quality mohair, free from kemp and medullated fibres, was initiated at the Jansenville Experimental Station in South Africa in 1988. Two genotypes, viz. a 75 % Angora goat : 25 % Boer goat (G1) and a 87.5 % Angora goat : 12.5 % Boer goat genotype (G2) were subsequently established. The objective of this paper is to evaluate the amount of kemp and medullated fibres in the fleeces of the kids of these two established genotypes against that of pure bred Angora goat kids.
Data from G1- (n=921), G2- (n=827) and Angora (n=361) kids born from 1992 to 2000 were available. Kids were shorn at five months of age for the first time, and subsequently at 10, 14 and 18 months of age. Prior to the second, third and fourth shearings, fleece samples were taken on three positions on the back line (between the withers, in the lumbar region and posterior to the tail) of each kid. These samples were mixed for each kid and used for objective measurement of kemp and medullated fibres with a projection microscope. The amount of kemp and medullated fibres was also assessed subjectively on a linear scale ranging from one to 50 prior to the second, third and fourth shearings. General linear model procedures of SAS were used to analyze the data. Two mathematical models were fitted for all traits. The first included fixed effects due to birth year (1992 to 2000), genotype (G1, G2, Angora), sex (male, female), rearing status (birth status in the case of birth weight; single, twin, triplet), age of dam (2 to 8 years), birth year x genotype interaction, birth year x sex interaction and linear regression on age of kid at recording (except for birth weight), as well as residual error. In order to evaluate the effect of generation number on medullation, a second model was fitted to data from G1- and G2-kids only. This model included the same fixed effects as the first model, with the addition of the following effects: generation number (1st, 2nd, 3rd) and genotype x generation interaction.
Significant differences in amount of kemp and medullated fibres in the fleece were evident among the three genotypes, where G1-kids generally had the highest amount of medullated fibres, followed by the G2-kids and then the Angora kids. The amount of medullated fibres in the fleece at 10 months of age ranged from 1.04±0.05 % for G1-kids, to 0.76±0.05 % for G2-kids and 0.36±0.08 % for Angora kids. The amount of kemp fibres in the fleece at the same age was 0.13±0.01 %, 0.04±0.01 % and 0.00±0.01 % respectively for the three genotypes. A similar trend was observed at 18 months of age, as well as for the subjective kemp scores at all ages.
Generation of the kid had a marked effect on medullation in the fleece, where 3rd generation kids had significantly less medullated fibres in their fleeces than the corresponding 2nd and 1st generation kids. This trend was, however, not significant for the G2-kids at 18 months of age.
Subjective kemp score is only suitable to identify animals with a high proportion of visual kemp. The exceptionally low level of kemp in South African mohair was achieved mainly through subjective selection against kemp for many decades. As most medullated fibres cannot be identified visually, a limited amount of these fibres is still present in the South African mohair clip. A further decrease in medullation can only be achieved through selection based on objective measurement.
In the experimental animals, where objective selection against medullation was carried out from the start, medullation in G1-kids was decreased from 1.47 ±0.15 % and 1.34±0.14 % at 10 and 18 months of age in 1st generation kids, to 0.74±0.11 % and 0.69±0.10 % in 3rd generation kids respectively. Similarly, medullation in the G2-kids decreased from 1.01±0.14 % and 0.75±0.12 % in 1st generation kids to 0.40±0.15 % and 0.38±0.14 % in 3rd generation kids respectively. Thus, by basing selection on objective measurements, medullation was nearly halved from the 1st to the 3rd generation in both genotypes.
Individual goats, free from kemp and medullated fibres, are already present in both genotypes. As soon as a kemp free herd has been established, selection should be aimed at improving fleece quality traits, such as fibre diameter, style and character.