Abstract | Seasonal variation in plant secondary metabolites (PSM) can influence voluntary intake levels of one-seed juniper (Juniperus monosperma Englem. Sarg.) of sheep and goats. Supplemental nutrients could mitigate the deterrent effects of juniper PSM. We determined the concentration of mono-and sesqui- terpenes, total phenolics and condensed tannins in one-seed juniper leaves in summer, fall, winter, and spring, and tested their effects on juniper intake of 12 Western White Face ewes (74.9 ± 1.23 kg) and 12 Boer-Spanish does (46.7 ± 1.25 kg) fed isoenergetic diets (1.6% BW) with no supplemental protein (Control, 5% CP) or with addition of a rumen degradable (RDP, 12.5% CP) or undegradable (RUP, 12.5% CP) protein supplement. Animals were fed unrestricted amounts of freshly harvested juniper branches for 30 min and short-term juniper intake was determined for 10 d per season. Total terpenes, total phenolics, and condensed tannins varied across seasons (P<0.05), and were positively correlated to each other (P<0.05). Juniper intake was greater for goats than sheep (P<0.05), and twice as high for supplemented vs. control animals (P<0.05). Juniper intake in the fall, when levels of plant secondary metabolites were highest, was 41, 58, and 52% less than in summer, winter, and spring (P<0.05), respectively. Supplements with RDP and RUP promoted different patterns of juniper intake among seasons (P<0.05), herbivores (P<0.05), and individual animals (P<0.05). This study suggests that supplemental protein can increase voluntary intake of one-seed juniper of small ruminants during seasons when plant secondary metabolite levels are low. Proteins of different degradability appear to affect seasonal patterns of juniper intake differently. |