Effect of reduced hair coat on performance of feedlot steers during summer heat stress
Heat stress in cattle reduces well-being and performance. The challenge is to develop effective procedures for heat stress mediation over the entire summer period. This necessitates the identification and development of reliable predictors of heat strain in the animal. A 94-day study, using crossbred Angus steers (n=36; average body weight =284 +/- 29kg) was conducted during summer 2013. Animals were stratified by weight, housed in groups of nine among four different pens with ~50% shade coverage, and hair scored (1-4 scale; with higher values indicating a shorter coat). Hair coat was carefully removed using the standard “torched” procedure from half of the steers, with those remaining being unaltered (average hair score – 1.9). Ambient temperature (Ta) and relative humidity were recorded using Hobo H8 Pro data loggers (Onset Computer, Bourne MA) in sun and shade. Range of Ta was 12.2 to 36.6°C, and calculated temperature humidity index was 54.4 to 85.3. Steers were provided a corn-based feedlot diet and water ad libitum, and core temperature (Tcore) measured hourly using intraruminal telemetric boluses (Smartstock, Pawnee, OK). Electronic ID tags (Allflex US Inc., Dallas-Fort Worth, TX) connected to a GrowSafe FI system (GrowSafe Systems Ltd., Airdrie, AB, Canada) provided feed intake (FI) data. Respiration rates (RR) were measured at 0800 and 1700h on select days throughout the study, with measurement frequency increasing with heat events. Data analysis was conducted using ANOVA, (JMP Statistical Software; SAS Institute; Cary, NC) to determine the effect of a reduced hair coat on FI, feed efficiency (FI/ADG), RR, and Tcore. Analysis revealed no effect of torching on daily FI (P=0.85), but an increase in feed efficiency in non torched versus torched (P<0.01). Analysis of mean daily Tcore over the entire period by animal and hour of day showed a 0.21°C lower Tcore value for torched versus non-torched animals (P<0.01). Likewise, maximum daily Tcore was 0.25°C lower in torched versus non-torched animals, with no difference (P>0.10) in daily minimum Tcore. Torching appeared to have no significant effect on average daily respiration rates (P=0.89). These results indicate that reducing the hair coat of steers during summer months may offer a cosmetic benefit along a reduction in core temperature due to an increase in cutaneous heat loss. However, overall feed efficiency was slightly reduced as a result of this procedure. Additional studies are needed to determine the reason for this reduction.
Keywords: heat, stress, steers