Seasonal changes in one seed juniper intake by sheep and goats in relation to dietary protein and plant secondary metabolites

Abstract

Plant secondary metabolites (PSM) and nutrients can influence patterns of feed intake of small ruminants. Their effects depend on the type and amounts of PSM and nutrients fed. We hypothesized that one-seed juniper intake of goats and sheep would change in response to seasonal variations of PSM concentrations and type and amount of CP fed. To test this hypothesis, we fed 12 does (46.7 ± 1.25 kg) and 12 ewes (74.9 ± 1.23 kg) freshly harvested one-seed juniper branches in summer, fall, winter, and spring. Animals also received isoenergetic diets (1.6% BW) with either addition of a high rumen degradable (RDP, 12.5% CP) or undegradable (RUP, 12.5% CP) protein source or with no addition of supplemental protein (Control, 5% CP). Juniper branches were offered in unrestricted amounts for 30 min prior to feeding treatment diets and short-term intake was determined for 10 d per season. One-seed juniper leaves contained a diverse mix of terpenes, phenolics, and condensed tannins which were positively correlated to each other ( P < 0.05) and varied seasonally in concentration and composition ( P < 0.05). Juniper intake was greater for goats than sheep ( P < 0.05), and twice as high for animals fed high CP diets 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 ( P < 0.05) than in summer, winter, and spring, respectively. Addition of high RDP and RUP sources into diets induced different patterns of juniper intake across seasons, herbivores, and individual animals. In each diet treatment, a distinct subset of a few PSM explained 30–78% of overall variation in juniper intake of goats and sheep. This study suggests that increases in dietary protein levels can increase voluntary intake of one-seed juniper of small ruminants during seasons when PSM levels are low. Diets with protein sources of different degradability can potentially influence juniper intake of small ruminants differently, probably due to different nutrient–PSM associations that may result in different detoxification capabilities and post-ingestive experiences that influence individual juniper preference.