Effect of ambient temperature on nutrient digestibility and nitrogen balance in sheep fed brown-midrib maize silage

Effect of feeding whole-crop corn silage as dietary roughage on physiological and digestive response of sheep under heat exposure

The present study was conducted to investigate the effect of feeding whole-crop corn silage (WCS) compared with mixed hay (MH) or grass silage (GS) on physiological and digestive responses of sheep at thermoneutral temperature (20°C) or exposed to heat (30°C). Six sheep were fed ad libitum with one of three diets in a replicated 3 × 3 Latin square design for 24 days. After 14 days’ adaptation, they were exposed to thermoneutral (20°C) and then heat exposure (30°C) for 5 days each. Rumen sample was collected on Day 4, whereas physiological response and nitrogen (N) balance were carried-out for three successive days in each exposure period. Respiration rate and rectal temperature of WCS-fed sheep were lower (P < 0.05) than of MH and GS fed sheep and both were higher (P < 0.01) during heat exposure. The intakes of dry matter (DM) and N and the digestibilities of N and neutral detergent fibre were lower (P < 0.05) for the WCS diet than for MH and GS diets and they did not differ between two temperature exposures. However, WCS-fed sheep had higher (P < 0.05) digestibilities of DM and organic matter, as well as metabolisable energy intake (M/D) than the sheep fed MH or GS diet, and there was no temperature effect on them. As DM and N intakes were lower for the WCS diet, the variables of rumen fermentation were also lower (P < 0.05) than the other two diets except propionate and butyrate concentrations, and they did not differ between temperature exposures except NH3 concentration. In conclusion, physiological responses were improved in the WCS diet and this approach thus shows promise for feeding heat-exposed animals. However, as results were inconsistent in terms of nutrient intake and digestibility, further work is needed and we suggest investigating the effect of feeding WCS with supplemented N.

Effect of Simulated Heat Stress on Digestibility, Methane Emission and Metabolic Adaptability in Crossbred Cattle

The present experiment was conducted to evaluate the effect of simulated heat stress on digestibility and methane (CH₄) emission. Four non-lactating crossbred cattle were exposed to 25°C, 30°C, 35°C, and 40°C temperature with a relative humidity of 40% to 50% in a climatic chamber from 10:00 hours to 15:00 hours every day for 27 days. The physiological responses were recorded at 15:00 hours every day. The blood samples were collected at 15:00 hours on 1st, 6th, 11th, 16th, and 21st days and serum was collected for biochemical analysis. After 21 days, fecal and feed samples were collected continuously for six days for the estimation of digestibility. In the last 48 hours gas samples were collected continuously to estimate CH₄ emission. Heat stress in experimental animals at 35°C and 40°C was evident from an alteration (p<0.05) in rectal temperature, respiratory rate, pulse rate, water intake and serum thyroxin levels. The serum lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase activity and protein, urea, creatinine and triglyceride concentration changed (p<0.05), and body weight of the animals decreased (p<0.05) after temperature exposure at 40°C. The dry matter intake (DMI) was lower (p<0.05) at 40°C exposure. The dry matter and neutral detergent fibre digestibilities were higher (p<0.05) at 35°C compared to 25°C and 30°C exposure whereas, organic matter (OM) and acid detergent fibre digestibilities were higher (p<0.05) at 35°C than 40°C thermal exposure. The CH₄ emission/kg DMI and organic matter intake (OMI) declined (p<0.05) with increase in exposure temperature and reached its lowest levels at 40°C. It can be concluded from the present study that the digestibility and CH₄ emission were affected by intensity of heat stress. Further studies are necessary with respect to ruminal microbial changes to justify the variation in the digestibility and CH₄ emission during differential heat stress.