Effects of grazing willow fodder blocks upon methane production and blood composition in young sheep

Abstract A 79-day rotational grazing experiment was conducted over the summer and autumn of 2007 to compare effects of grazing willow ( Salix spp.) fodder blocks, a combination of small trees ( i.e ., 1.0 m) and herbage, or perennial ryegrass ( Lolium perenne )/white clover ( Trifolium repens ) control pasture on breath methane (CH 4 ) emissions, concentrations and solubility of CH 4 and sulphur hexafluoride (SF 6 ) tracer gas in blood, and haematology variables in young growing female sheep ( i.e ., hoggets). Measurements of gases in blood followed a double equilibration technique with two ( n  = 20) replicate per treatment. Ten ewe hoggets in each replicate were dosed on day 22 with intraruminal slow release SF 6 capsules, an inorganic tracer gas used to calculate CH 4 emissions. Breath samples were collected over 5-day periods in weeks 5 (period 1) and 11 (period 2). Total condensed tannin (CT) concentrations calculated in the diet selected by the willow fodder block sheep was 12 g CT kg/dry matter intake, with negligible amounts in control pasture hoggets. Compared to control pasture, grazing willow fodder blocks reduced CH 4 emission/kg metabolic body weight (BW 0.75 ) by 20% in period 1 ( P 4 concentrations (ng/mL blood) were similar for both groups on day 36, but higher ( P 6 blood concentration being higher ( P 4 concentration was 75% in period versus 84% in period 2. Methane and SF 6 Ostwald solubility coefficients in blood were similar in both periods for sheep grazing willow fodder blocks and the control pasture. Hoggets grazing willow fodder blocks had lower BW gain (65 g/day), carcass weight (16.1 kg) and carcass fatness (9.2 mm) than hoggets grazing control pasture (102 g; 18.3 kg; 11 mm). Hoggets dosed with SF 6 capsules had lower ( P P =0.063), platelet ( P =0.073) and monocyte ( P =0.072), white blood cell and total lymphocyte counts ( P 4 emission between periods from grazing willow fodder blocks may be due to more willow leaf being eaten during the CH 4 measurement period in period 1 than in period 2.