Effects of thermal environment on dairy cattle under a grazing system in the Western Amazon, Brazil

Oliveira, A.V.D.; Reis, E.M.B.; Ferraz, P.F.P.; Barbari, M.; Santos, G.S.; Cruz, M.V.R.; Silva, G.F.; Silva, A.O.L.

doi:10.1590/1678-4162-12743

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Animal Science • Arq. Bras. Med. Vet. Zootec. 74 (06) • Nov-Dec 2022 • https://doi.org/10.1590/1678-4162-12743 copy

Effects of thermal environment on dairy cattle under a grazing system in the Western Amazon, Brazil

[Efeitos do ambiente térmico em bovinos leiteiros em sistema de pastejo na Amazônia Ocidental, Brasil]

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

This study aimed to evaluate the thermal conditions to which animals are exposed and their effect on the comfort/discomfort of dairy herds in a grazing system in the municipality of Sena Madureira, Acre State, Brazil. Eight farms and a total of 113 lactating crossbred cows were evaluated. Dry-bulb temperature (DBT, °C), relative humidity (RH, %), black globe temperature (BGT, °C), and wind speed (v, km h⁻¹) were measured in January, February, and March (rainy season) to calculate temperature-humidity index (THI), black globe-humidity index (GTWBI), and radiant heat load (RHL). Moreover, the animals were measured for the physiological variables: rectal temperature (RT), heart rate (HR), and respiratory rate (RR). Significant differences (P<0.05) were observed for THI, GTWBI, and RHL. THI reached a mean value of 80 on farm G in January. Farm F had a GTWBI value of 79 in February. RHL reached the highest value (510 W m⁻²). RT and HR showed no differences among the analyzed months. Thus, the environmental conditions in which dairy cows are housed at milking time rarely promoted thermal discomfort, with farm G being the most affected by THI.

Keywords:
climate change; ambiance; animal welfare; heat stress; dairy cow

Period	Farm								Mean
Period	A	B	C	D	E	F	G	H
January	74^b	73^c	77^a	77^a	73^a	76^c	80^a	77^a	76^a
February	73^c	77^a	77^a	73^b	76^b	77^a	77^c	72^b	75^b
March	72^a	74^b	77^a	72^c	72^c	75^b	79^b	70^c	73^c
Mean	74^DE	75^CD	77^AB	74^D	75^D	76^BC	79^A	73^E
Adapted from Hahn (1985HAHN, G.L. Management and housing of farm animals in hot environments. In: YOSEF, M.K. (Ed.). Stress physiology in livestock. Boca Raton: CRC Press, 1985. v.2, p.151-174.).
Means followed by different lowercase letters in the column differ statistically by Tukey’s test at a 5% probability (P<0.05). Means followed by different uppercase letters in the row differ statistically by Tukey’s test at a 5% probability (P<0.05).
THI		≤ 74 Normal		75 to 78 Warning		79 to 83 Danger			> 83 Emergency

Period	Farm								Mean
Period	A	B	C	D	E	F	G	H
January	73^c	73^c	75^a	76^a	76^a	75^b	77^b	76^a	75^a
February	75^a	76^a	71^c	72^b	74^c	79^a	76^c	75^b	74^b
March	74^b	75^b	73^b	72^b	75^b	74^c	78^a	72^c	73^c
Mean	74^CDE	74^CD	72^F	73^EF	75^BC	76^AB	77^A	74^DE
Adapted from *Buffington et al. (1981*BUFFINGTON, D.E.; COLLAZO-AROCHO A.; CANTON, G.H. et al. Black globe-humidity index (ITGU) as comfort equation for dairy cows. Trans. ASAE, v.24, p.711-714, 1981.).
Means followed by different lowercase letters in the column differ statistically by Tukey’s test at a 5% probability (P<0.05). Means followed by different uppercase letters in the row differ statistically by Tukey’s test at a 5% probability (P<0.05).
GTWBI		≤ 74 Normal		74 to 78 Warning		79 to 84 Danger			> 84 Emergency

Period	Farm								Mean
Period	A	B	C	D	E	F	G	H
January	434^c	454^c	470^b	477^a	451^b	459^c	516^b	490^b	506^a
February	477^a	482^b	459^c	459^b	477^a	522^a	474^c	565^a	473^b
March	445^b	510^a	496^a	459^b	477^a	479^b	523^a	441^c	470^b
Mean	453^C	482^AB	475^BC	465^BC	468^BC	487^AB	504^A	499^A

Physiological variable	Farm
Physiological variable	A	B	C	D	E	F	G	H
RT (°C)	37.3^ab	37.3^ab	37.3^ab	37.3^ab	37.6^a	36.4^b	37.5^a	37.8^a
HR (beats per minute)	72.1^a	71.9^a	73.0^a	74.0^a	77.3^a	74.7^a	72.7^a	74.7^a
RR (movements per minute)	22.9^ab	22.1^b	22.3^b	25.3^ab	25.7^a	23.5^ab	22.0^b	23.6^ab

Physiological variable	Jan.	Feb.	Mar.
Physiological variable	Mean
Rectal temperature (°C)	37.3^a	37.4^a	37.5^a
Heart rate (beats per minute)	73.4^a	73.2^a	75.5^a
Respiratory rate (movements per minute)	23.9^a	21.6^b	25.0^a

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[1] Corresponding author: valcemira@hotmail.com