PRENATAL AND POSTNATAL WOOL FOLLICLE DEVELOPMENT AND DENSITY IN SHEEPOF 5 GENOTYPES

The pre-natal and post-natal development of wool follicles in sheep of five genotypes with contrasting wool types was examined to provide da ta on which to base studies of physiological factors affecting wool ty pe via follicle development. This study was conducted following Autumn mating in 1992 at Palmerston North, New Zealand (40 degrees S, 176 de grees E). The rate and timing of follicle development in midside skin samples from Romney, Merino, Merino x Romney (M x R), Drysdale and Wil tshire foetuses and lambs collected at weekly intervals from days 76 t o 143 of gestation and 1, 3, 7, 12 and 32 weeks after birth were exami ned. Primary (P) follicle density had a similar pattern of development in each of the genotypes, although the Merino had a significantly gre ater density of P follicles than the other genotypes. There was a diff erence in the rate of P follicle maturation between genotypes with the Drysdale, Wiltshire and M x R completing P follicle maturation before the other two genotypes. However, the majority of P follicles in all genotypes were producing fibres by 111 days of gestation. It was concl uded that the small differences in the density and time of development of the P follicles could not cause the differences in wool type betwe en genotypes. The pattern of development of the secondary (S) follicle population was examined by comparing S:P ratios. The initiation of S follicles began at similar ages in the five genotypes, but initiation was completed earlier in the Romney, Drysdale and Wiltshire than in th e Merino and M x R, as indicated by a significant genotype by age inte raction (P < 0.001). There was no difference between genotypes in S:P ratio from 90 to 104 days of gestation. The S:P ratio of the Romney, D rysdale and Wiltshire did not change significantly from 104 days of ge station until the end of the study, indicating that few S follicles we re initiated in these genotypes after 104 days of gestation. The M x R data showed a significant increase in S:P ratio until 119 days of ges tation and the Merino S:P ratio increased until 126 days of gestation. The period between days 90 and 125 of gestation was identified as bei ng the critical period for the development of different follicle popul ations in Merino and non-Merino genotypes and it is this period which should be the focus for studies to determine physiological factors con trolling secondary follicle development.