Dietary effects of protected fat, soybean meal, and heat-treated soybean meal on performance, physiological parameters, and behavioral measurements of early-fattening Hanwoo steers under heat stress conditions.

OBJECTIVE

This study evaluated the effects of increased levels of dietary total digestible nutrient (TDN) and crude protein (CP) using protected fat (PF), soybean meal (SB), and heat-treated soybean meal (HSB) on performance, physiological parameters, and behavioral measurements of early-fattening Hanwoo steers under heat stress conditions.

METHODS

Thirty-six steers (480.9±58.6 kg, 15.9±1.4 months) were assigned to 4 treatments: control (TDN 75%, CP 15%, rumen degradable protein [RDP]:rumen undegradable protein [RUP] = 62:48); PF (TDN 82.5%, CP 15%, RDP:RUP = 62:48); PF+SB (TDN 82.5%, CP 16.5%, RDP:RUP = 62:48); and PF+SB+HSB (TDN 82.5%, CP 16.5%, RDP:RUP = 48:52) for a total of 16 weeks with division of 4 weeks. The average temperature-humidity index (THI) was 82.9 (1st; moderate), 76.9 (2nd; mild), 70.9 (3rd; comfort), and 65.8 (4th period; comfort).

RESULTS

Dry matter intake during whole period did not differ among treatments but decreased by 34% and 19%, respectively during 1st and 2nd compared to 4th. Average daily gain (ADG) of PF+SB+HSB was higher (p<0.05) than that of control during the 1st period, and those of both PF+SB and PF+SB+HSB were higher (p<0.05) than Control during the 2nd. The ADG during whole period was in the order of PF+SB+HSB (1.23), PF+SB (1.18), PF (1.11), control (0.98 kg/d) (p<0.05). As THI increased, rectal temperature and all blood parameters increased, while blood glucose levels decreased (p<0.05). Behavioral changes during 1st period compared to 3rd included decreases in lying (24%), walking (48%), and eating (40%), and increases in total standing (50%) and drinking (43%) (p<0.05). Rumination during standing was 38% higher, and rumination during lying was 32% lower (p<0.05).

CONCLUSION

This study demonstrates 10% of increased levels of dietary TDN using PF and CP considering RUP can prevent performance reduction in early-fattening of heatstressed Hanwoo steers and have positive effects on performance recovery from post-heat stress.