EFFECTS OF COLD ON DIGESTIBILITY, RETENTION TIME OF DIGESTA, RETICULUM MOTILITY AND THYROID HORMONES IN SHEEP

Abstract

In the first of two experiments, 12 closely shorn yearling wethers received grass hay either in the long form or pelleted form and were acclimated to temperatures of 0.8, 10.1 and 17.7 C. Feed was provided for each treatment at an equivalent intake level of approximately maintenance. The sheep receiving long hay consumed less water than those receiving hay pellets. Water consumption decreased with decreasing temperature. The apparent digestibilities of DM, E, N and ADF were lower for the pelleted hay than for the long hay (P < 0.001). The digestibilities of DM, E and ADF were lower (P < 0.05) when the sheep were at 0.8 C than at 17.7 C, but there were no significant ration × temperature interactions. In the second experiment, six closely shorn sheep receiving a pelleted hay ration at the maintenance level were exposed for 4–6 wk to temperatures of 21.2 and 1.3 C. DM digestibility was reduced (P < 0.05) in the cold by 0.18 percentage units per degree (C) drop in temperature. Mean retention times, determined from the fecal excretion patterns of ¹⁴⁴Ce following a single injection into the rumen, decreased (P < 0.05) from 38.5 h in the warm environment (21.2 C) to 32.5 h in the cold (1.3 C). The mean number of reticulum contractions per hour was increased (P < 0.001) from 60 at 21.2 C to 72.5 at 1.3 C. Serum thyroxine (T₄) and triiodothyronine (T₃) concentrations were significantly (P < 0.05) higher in sheep exposed to the cold compared to the sheep in the warm temperature treatment. It is concluded that pelleting hay does not alter the depressing effect of cold environmental temperatures on digestibility and that the effect of temperature on digestibility is likely due to a change in rate of passage of digesta through the altimentary tract.