Abstract:
The suitability of lithium chloride as a marker for supplement intake was examined in grazing sheep. Eight merino weaners (10 months), grazing improved pasture, were individually fed cottonseed meal pellets coated with lithium chloride, and plasma lithium concentrations were then measured over the next 29 h. The results of this study showed that after ingestion of lithium, plasma lithium concentrations rose to reach a maximum 4 h later. This maximum remained substantially constant between 4 and 14 h after lithium ingestion and then declined slowly. The use of plasma lithium concentration (scaled for liveweight) 4-9 h after lithium ingestion facilitated accurate prediction of supplement intake. In a following experiment, 732 Merino weaners (10 months) were split into two groups by randomized stratification. These groups were fed a cottonseed meal supplement at either 55 or 110 g head-1 day-1 In order to estimate individual supplement intake over a 62 day period the supplement was coated with lithium chloride on three occasions at monthly intervals. The results of the three estimates of intake showed that within mobs (n = 366/mob) large variation in supplement intake existed. Both the heritability (0.17) and repeatability (0.48) of supplement intake as estimated from paternal half-sib analysis were significantly different from zero.