Effects of Dietary Protein and Energy Intake on Body Reserve Deposition and Milk Production in Caribou and Reindeer

Abstract

An experiment was conducted in 1989 to determine the effects of energy and protein intake and the energy/protein ratio on (1) the deposition of body fat and body protein and (2) milk production in female caribou (Rangifer tarandus granti) and reindeer (Rangifer tarandus tarandus). Four diet treatments (high energy/high protein; high energy/low protein; low energy/high protein; low energy/low protein) were randomly assigned within each group of four lactating caribou, four non-lactating caribou, four lactating reindeer, and four nonlactating reindeer. Daily feed intakes were recorded for each individual, and body weights were measured every 2 to 4 days for both cows and calves. Body composition, determined using the tritiated water technique, and milk production, determined using the doubly labeled water method, were obtained every 3 weeks for 12 weeks. Body weight changes in both lactating and nonlactating females were primarily governed by energy intake. The efficiency of utilization above maintenance was the same for both lactation classes. The propensity to deposit fat was greater in lean than in fat animals and increased with time. Energy intake was significantly correlated with fat deposition in nonlactating females only. Energy intake was not significantly correlated with fat deposition in lactating females because surplus energy was directed towards increased milk production. However, females with low fat reserves allocated a lower portion of their resources to milk production than females with large fat reserves. The energy/protein ratio, protein intake, and subspecies were generally insignificant factors in determining patterns of tissue deposition or milk production.