Evaluation of melatonin and bromocryptine administration in Spanish goats: III. Effects on hair follicle activity, density and relationships between follicle characteristics

Melatonin treatment for out of season breeding in goats may also affect skin hair follicle activity, thereby influencing the spring growth phase and yield of cashmere. Female Spanish goats (15 does and 65 kids) were allotted to five treatments: control (C), melatonin implants (MI; 18 mg, 42-day release); melatonin and bromocryptine implants (MIB; 225 mg, 60-day release period); oral administration of melatonin (MO; 3 mg/day); oral administration of melatonin and bromocryptine implants (MOB). Treatments began in March (spring), and hair follicle characteristics were monitored monthly from February to May. Mean initial and final body weights were 27.9 ± 1.2 and 35.3 ± 1.2 kg, respectively. The total follicle number was greater (P < 0.05) for the MOB group, compared to the C group in April, while in May the total follicle number was greater (P < 0.05) for the MIB group, compared to the C and MO groups. Secondary follicle numbers were greater (P < 0.05) for the MIB than for C and MO and for MOB versus C, MI and MO groups (P < 0.05). The primary active follicle percentage was correlated (P < 0.001) to the secondary active follicle percentage (r = 0.32), and the correlation (P < 0.01) between secondary active follicle percentage and mean cashmere fiber diameter was r = 0.31. The primary active follicle ratio did not differ between treatments, but the secondary active follicle ratio was greater (P < 0.01) for treatments with melatonin administration, compared to the control in March, April and May. Primary follicle numbers, secondary follicle numbers, total follicle numbers, secondary to primary follicle ratio, primary follicle diameter, secondary follicle and primary to secondary follicle diameter ratio averaged 3.9 ± 0.15 mm2, 26.8 ± 1.22 mm2, 30.8 ± 1.31 mm2, 7.0:1 ± 0.23, 74.0 ± 2.87 μm, 15.6 ± 0.19 μm and 4.7:1 ± 0.18, respectively. Positive correlations were recorded (P < 0.001) for follicular characteristics, such as the secondary follicle number with total follicle number (r = 0.99), secondary to primary ratio (r = 0.68), group follicle number (r = 0.63) and group secondary to primary follicle ratio (r = 0.63), and primary follicle diameter with primary secondary diameter ratio (r = 0.96). Negative correlations were recorded (P < 0.01), for primary follicle number with primary follicle diameter (r = -0.42), secondary follicle diameter (r = -0.33) with secondary and primary follicle ratio (r = -0.48), and primary follicle number with primary and secondary diameter ratio (r = -0.33). Of the follicular groupings, 90% were of the trio primary follicle type, whereas the remaining 10% were of the solo, duo and quartet primary follicular group formations. All primary follicles possessed medullae and some secondary marginal follicles (intermediate type) were medullated, but few follicles of the pure cashmere follicle type had medullae. Hair follicles varied from low, moderate to high density in Spanish goats. Fiber growth rate, fiber diameter and extended follicular activity rate during the spring months suggest that an accelerated breeding program for Spanish goats by melatonin treatment for breeding in the spring could be also profitable by extending the spring cashmere growth phase into a commercially harvestable cashmere length.