Estimating faecal output in reindeer during winter

Integrating spot short-term measurements of carbon emissions and backward dietary energy partition calculations to estimate intake in lactating dairy cows fed ad libitum or restricted

The objective of this study was to use spot short-term measurements of CH4 (QCH4) and CO2 (QCO2) integrated with backward dietary energy partition calculations to estimate dry matter intake (DMI) in lactating dairy cows. Twelve multiparous cows averaging 173±37d in milk and 4 primiparous cows averaging 179±27d in milk were blocked by days in milk, parity, and DMI (as a percentage of body weight) and, within each block, randomly assigned to 1 of 2 treatments: ad libitum intake (AL) or restricted intake (RI=90% DMI) according to a crossover design. Each experimental period lasted 22d with 14d for treatments adaptation and 8d for data and sample collection. Diets contained (dry matter basis): 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot short-term gas measurements were taken in 5-min sampling periods from 15 cows (1 cow refused sampling) using a portable, automated, open-circuit gas quantification system (GreenFeed, C-Lock Inc., Rapid City, SD) with intervals of 12h between the 2daily samples. Sampling points were advanced 2h from a day to the next to yield 16 gas samples per cow over 8d to account for diurnal variation in QCH4 and QCO2. The following equations were used sequentially to estimate DMI: (1) heat production (MJ/d)=(4.96 + 16.07 ÷ respiratory quotient) × QCO2; respiratory quotient=0.95; (2) metabolizable energy intake (MJ/d)=(heat production + milk energy) ± tissue energy balance; (3) digestible energy (DE) intake (MJ/d)=metabolizable energy + CH4 energy + urinary energy; (4) gross energy (GE) intake (MJ/d)=DE + [(DE ÷ in vitro true dry matter digestibility) - DE]; and (5) DMI (kg/d)=GE intake estimated ÷ diet GE concentration. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) and Fit Model procedure in JMP (α=0.05; SAS Institute Inc.). Cows significantly differed in DMI measured (23.8 vs. 22.4kg/d for AL and RI, respectively). Dry matter intake estimated using QCH4 and QCO2 coupled with dietary backward energy partition calculations (Equations 1 to 5 above) was highest in cows fed for AL (22.5 vs. 20.2kg/d). The resulting R(2) were 0.28 between DMI measured and DMI estimated by gaseous measurements, and 0.36 between DMI measured and DMI predicted by the National Research Council model (2001). Results showed that spot short-term measurements of QCH4 and QCO2 coupled with dietary backward estimations of energy partition underestimated DMI by 7.8%. However, the approach proposed herein was able to significantly discriminate differences in DMI between cows fed for AL or RI.

Responses of caribou and reindeer (Rangifer tarandus) to acute food shortages in spring

Migratory caribou and sedentary reindeer (Rangifer tarandus (L., 1758)) can encounter acute food shortages during spring. We examined the response to short-term food restrictions by measuring individual food intake, body mass, and activity of 2-year-old unbred female caribou and reindeer from 25 April to 29 May 2011. Caribou lost 2%–3% of body mass on days when mean dry matter (DM) intakes (60 ± 6 g DM·kg−0.75·d−1) were restricted up to 75%. Caribou regained body mass as intake increased to 98 ± 8 g DM·kg−0.75·d−1 following restriction without a change in digestibility (82%–83%). In reindeer, digestibility increased (78%–83%) as intakes decreased (67–45 g DM·kg−0.75·d−1). Food restriction did not affect activity for either subspecies. We suggest that, at high digestive efficiency, Rangifer have “spare capacity”, to increase DM intake to compensate for lost foraging opportunity or to use patches of emerging high-quality forage. Furthermore, caribou with large fat reserves lost proportionally more body mass, consumed less food, and were less active than leaner caribou. Our data indicate that Rangifer use flexible responses of food intake, digestion, and body condition to maximize survival and reproduction in both migratory and sedentary ecotypes at the end of winter.