Akademik Veri Yönetim Sistemi
Diğer Ülkelerin Sanayi Kuruluşları Tarafından Desteklenmiş Proje, 2023 - 2024
Heat stress can compromise production and health in dairy cattle; the
magnitude of these deleterious effects will be exacerbated by global
climate change. The resistance of cows to heat stress is under genetic
control. Recently, Zoetis has developed 2 novel breeding values for
heat tolerance in lactating Holsteins based upon the change in milk
yield (MILKTHI) or cow conception rate (CCRTHI) with temperaturehumidity index. The goal here was to test whether variation in predicted
transmitting ability (PTA) for heat tolerance is associated with cow
regulation of body temperature during heat stress. Data on afternoon
(1400–1700 h) rectal temperatures during the hot months of the year
(May–August) were collected from lactating cows on farms in Florida
(n = 3), California (n = 1), and Turkey (n = 1) over a period spanning
2007 to 2023. A total of 4,678 values of rectal temperature from 3,620
cows were analyzed by the GLIMMIX procedure of SAS. Models
included parity, stage of lactation, year-farm and with cow as a random
variable. Breeding values were analyzed 2 ways: by comparing rectal
temperatures of cows above and below a PTA of 100 (94.3 ± 4.3 vs.
104.4 ± 3.5 for CCRTHI and 96.3 ± 2.9 vs. 104.3 ± 3.4 for MILKTHI),
and by comparing cows in each quartile of the data set. There was no
significant relationship between MILKTHI and rectal temperature.
Cows with CCRTHI >100 had lower rectal temperature (P < 0.0001)
than cows with CCRTHI <100 (38.70 ± 0.01 vs. 38.62 ± 0.01°C). Similar results were obtained when evaluating CCRTHI quartiles. Rectal
temperature was 38.67 ± 0.06°C (PTA <96.49), 38.63 ± 0.06°C (PTA
>96.49 and <100.33), 38.63 ± 0.06°C (PTA >100.33 and <103.92) and
38.60 ± 0.06°C (PTA >103.92; P = 0.044). The percentage of cows with
high rectal temperature (>39°C) was also lower (P = 0.0062) in cows
in quartile 4 (17.9%) than in quartile 1 (22.6%). Results demonstrate
that CCRTHI is related to body temperature during heat stress. The
fact that CCRTHI but not MILKTHI was related to rectal temperature
is indicative to the more direct relationship between body temperature
and fertility than body temperature and milk yield.