Evaluation of production and reproduction of three South African Angora goat CYP17 genotypes
Two CYP17 genes, located on different loci and expressing enzymes with significantly different activities, have been identified in the South African Angora goat population. Three unique genotypes (named He, Hu, and Ho), which differed not only in the genes encoding CYP17, but also in copy number were subsequently identified in the Angora goat. The aim of this study was to evaluate the production and reproduction performance of these three genotypes. Bodyweight, fleece and reproduction data, and blood samples from 466 Angora ewes from three flocks were obtained from the GADI-Biobank. Data had been collected on Flock 1 from 2000 to 2015, Flock 2 from 2000 to 2014 and Flock 3 from 2000 to 2010. Bodyweight data included birth weight, weaning weight, 8-, 12-, and 16-month bodyweight, as well as bodyweight recorded annually for the ewe flock before mating. Fleece data included fleece weight and fibre diameter recorded at the second and third shearings at 12 and 18 months old, respectively. Fleece weight, fibre diameter, style and character were also recorded annually for the ewe flocks during the winter shearing. Individual reproduction records included information on whether the ewe had kidded, whether the ewe had aborted, number of kids born, stillborn kids, kids that died soon after birth, kids reared by a foster mother, kids reared as orphans, number of kids weaned and total weight of kids weaned. Total lifetime reproductive performance of genotyped ewes was calculated for number of kids born, number of kids weaned, and total weight of kids weaned. Blood samples were also collected from 100 sexually active Angora rams from four sources. CYP17 genotyping was carried out using an ARMS-qPCR (amplification refractory mutation system qPCR) assay. Serum testosterone was quantified using high performance liquid chromatography mass spectrometry. The distribution of the ewes across the three CYP17 genotypes was 36.7% He, 51.5% Hu, and 11.8% Ho, and was in accordance with the distribution of the Angora veld rams (38.0% He, 46.4% Hu, and 15.6% Ho). In this study, animals of the Hu genotype were heavier from weaning age onwards, although this difference in bodyweight was significant only at 8 months old and in the adult ewes. No differences were observed between the Heand Ho animals. Adult ewes of the He genotype (1.35 kg) produced heavier (P <0.05) fleeces than the Hu(1.27 kg) and Ho (1.24 kg) genotypes. Fibre diameter of the fleeces of the Hoewes (33.0 μm) was higher than that of the fleeces of the He ewes (32.2 μm; P <0.05) and the Huewes (32.7 μm; P >0.05). No significant differences were recorded in reproductive performance among the genotypes, although the Hoewes had the lowest (1.03 and 0.89) and the He ewes the highest (1.07 and 0.93) number of kids born and weaned per year respectively. Results on the rams indicated that the CYP17 genotype had no effect on testosterone production by Angora rams. From the results of this study no evidence could be found that selection for any of the three genotypes would adversely affect any growth, mohair production or reproduction function of Angora ewes. A breeding strategy incorporating selection for productive traits and the CYP17 genotype, aimed at increasing the frequency of the ACS+ gene and thus the He genotype in the population, could be followed without having a negative effect on the genetic progress of productive traits.
Keywords: Bodyweight, fleece weight, number of kids weaned, testosterone, weight of kids weaned