Dry-period heat stress increases methane emission intensity by reducing milk yield in the subsequent lactation

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.