Intermediate Periodicities in Juniper Consumption and Sampling Strategies to Estimate the Diet of Free-Grazing Goats

Abstract

We conducted this study to describe the intermediate-term periodicities in percentage juniper (Juniperus spp.) in goat diets and to develop optimal sampling schemes to estimate individual animal variation in juniper consumption. Fecal samples were collected from 12 multiparous female Angora goats on Monday and Thursday for a 24-mo period. Percentage juniper in the diet was determined using fecal near-infrared reflectance spectroscopy. Spectral analysis was used to determine the presence and length of cyclic variation in juniper consumption during growing and dormant season periods. Significant periodicities were found for 37% and 68% of the goats in the dormant and growing seasons, respectively. Cycle lengths varied from 9 d in the dormant season to 7 or 8 d in the growing season. The simple coefficient of determination between a two-sample moving average and the mean of all observations on individual goats was highest during a 3-mo period in the spring, which indicates that samples collected in the spring provided the best estimate of the yearlong percentage juniper in the diet. Monte Carlo simulations for 7-d cycles showed the root mean squared difference between estimated and population mean for two samples with 2 or 3 d between samples was only 1% greater than the root mean square difference for three or four samples collected every other day. The optimal sampling strategy for determining the dietary percentage of a species is to collect two samples separated by one-half of the cycle length.

Key Words: biological rhythms, diet selection, goat, juniper, periodogram, spectral analysis