Setting the derivative of the function with respect to Te
equal to zero predicted that the MEm reached a minimum
at 24.3°C. Linear effects of temperature on MEm
were reported by Sakomura et al. (2003) and Romero et
al. (2009b). Linear effects are appropriate when temperatures
are within a narrow range and close to the thermoneutral
zone (Sakomura, 2004). Romero et al. (2009b)
used a much more restricted range of temperatures
(21 ± 1.12°C) compared to the current study (22.4°C ±
3.97°C). Rabello et al. (2006), Salas et al. (2011), and
Reyes et al. (2012) all reported quadratic effects of temperature
on MEm. The current study predicted that MEm
should decrease with increasing temperatures to 24.3°C,
after which MEm should increase. Similarly, Reyes et al.
(2012) predicted decreasing MEm as ambient temperatures
increased from 14°C to 27°C and increasing MEm
thereafter. Anecdotally, hens housed at 27°C in the current
study exhibited periodic signs of heat stress, such
as panting and wing dropping to dissipate heat. Both
activities require expenditure of energy (Dale and Fuller,
1980). Rabello et al. (2006) observed increasing MEm
requirements at temperatures above 26°C in broiler
breeder hens. Small differences in heat stress thresholds
in the current study compared with those of Rabello et
al. (2006) and Reyes et al. (2012) may be due in part to
factors such as feeding level, strain, age, body composition,
activity, and feathering.
Setting the derivative of the function with respect to Teequal to zero predicted that the MEm reached a minimumat 24.3°C. Linear effects of temperature on MEmwere reported by Sakomura et al. (2003) and Romero etal. (2009b). Linear effects are appropriate when temperaturesare within a narrow range and close to the thermoneutralzone (Sakomura, 2004). Romero et al. (2009b)used a much more restricted range of temperatures(21 ± 1.12°C) compared to the current study (22.4°C ±3.97°C). Rabello et al. (2006), Salas et al. (2011), andReyes et al. (2012) all reported quadratic effects of temperatureon MEm. The current study predicted that MEmshould decrease with increasing temperatures to 24.3°C,after which MEm should increase. Similarly, Reyes et al.(2012) predicted decreasing MEm as ambient temperaturesincreased from 14°C to 27°C and increasing MEmthereafter. Anecdotally, hens housed at 27°C in the currentstudy exhibited periodic signs of heat stress, suchas panting and wing dropping to dissipate heat. Bothactivities require expenditure of energy (Dale and Fuller,1980). Rabello et al. (2006) observed increasing MEmrequirements at temperatures above 26°C in broilerbreeder hens. Small differences in heat stress thresholdsin the current study compared with those of Rabello etal. (2006) and Reyes et al. (2012) may be due in part tofactors such as feeding level, strain, age, body composition,กิจกรรม และ feathering
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