Heat Production by Grazing Ewes with Low Forage Mass and Supplemental Grain

Goetsch, A.L. 1998. Heat production by grazing ewes with low forage mass and supplemental grain. J. Appl. Anim. Res., 13: 61–79. Three mature Dorset ewes, with catheters in portal, hepatic and mesenteric veins and a mesenteric artery, were used in a 3 × 3 Latin square (two 28-day periods and one 35-day) to determine effects of level of supplemental corn (0, 0.5 and 1.0% body weight; dry matter) on intake, digestion, grazing behavior and heat production by the whole body and splanchnic and extra-splanchnic tissues with grazing of paddocks low in forage mass. Live and dead forage availability ranged from 1 to 4 kg and 17 to 40 kg dry matter per 0.036-ha paddock, respectively; initial period ewe conditions were 71±2.5 kg shrunk body weight, 47±0.4% fat and 11±0.1% protein; and in periods, 1, 2 and 3 hand-plucked forage samples were 17, 20 and 29% crude protein and 62, 56 and 58% neutral detergent fiber, respectively. Metabolizable energy intake (1.39, 2.32 and 3.16 Meal/day; SE 0.11) and energy accretion (-1.09, 0.02 and 0.39 Meal/day; SE 0.224) increased linearly with increasing corn level (P<0.01 and = 0.04, respectively) and grazing time decreased [(P = 0.06) 76, 63 and 48% of daylight for 0, 0.5 and 1.0% body weight of corn, respectively; SE 4.9]. However, corn level did not affect (P>0.10) whole body heat (2.48, 2.30 and 2.77 Meal/day; SE 0.171), heat increment (0.91, 0.80 and 1.24 Meal/day; SE 0.172), splanchnic bed heat (1.09, 1.12 and 1.05 Meal/day; SE 0.091) or extra-splanchnic tissue heat (1.39, 1.18 and 1.72 Meal/day for 0, 0.5 and 1.0% body weight of com, respectively; SE 0.241). In conclusion, with increasing intakes of corn, total dry matter and metabolizable energy by ewes, increased heat produced in dietary energy metabolism for tissue maintenance or maintenance plus energy accretion may only have compensated for decreased grazing-related or -specific heat production by both splanchnic and extra-splanchnic tissues, resulting in decreased tissue mobilization or increased energy accretion.