Multiple studies have documented the negative effects of heat stress (HS) on milk production and intake in dairy cattle, including during the dry period.However, its impact on enteric methane (CH 4 ) production has only been evaluated in lactating cows whereas carry-over effects from the dry period on the subsequent lactation remain unexplored.We hypothesized that HS in the dry period would decrease milk yield and increase CH 4 intensity in the subsequent lactation.Forty dry cows were enrolled and housed in a free-stall barn equipped with individual feed bunks.Cooled cows (DCL, n = 19) had access to shade, soakers, and fans, while heat-stressed cows (DHT, n = 21) had shade only.After calving, all cows were moved to a neighboring pen with individual feed bunks and provided with shade, soakers, and fans.At ~80 d in milk, a GreenFeed unit was placed in the barn to measure enteric gas output over 4 weeks in a randomized complete block design, conducted in 3 cohorts of 4-week periods.Individual dry matter intake, milk yield, daily CH 4 , CH 4 yield and CH 4 intensity were recorded.Dry matter intake was similar between groups (DCL = 27.4 ± 0.7, DHT = 26.8 ± 0.6 kg/d ± SEM) whereas DHT decreased milk yield (DCL = 53.5 ± 2.1, DHT = 45.8 ± 1.9 kg/d ± SEM).However, energy corrected milk was similar between groups.Daily CH 4 did not differ between treatments (DCL = 318.7 ± 10.6, DHT = 325.1 ± 9.8 g/d ± SEM) whereas DHT increased CH 4 intensity (DCL = 6.0 ± 0.3, DHT = 7.2 ± 0.3, g/kg of milk yield ± SEM).The results of our study confirm the negative effects of heat stress during the dry period on the next lactation milk yield and CH 4 intensity.
Onan-Martinez et al. (Mon,) studied this question.