Abstract
The reduction in enteric methane (CH(4)) emissions from cattle continues to be one of the top priorities in order to contribute to the sustainability of beef production in the U.S. The cow-calf segment of the beef industry is responsible for 61% of the total greenhouse gas emissions directly related to beef production. While many strategies have been studied to mitigate enteric CH(4) emissions, very few of them focus on the cow-calf segment. Therefore, this study evaluated the effect of internal and external parasite control strategies on animal performance and CH(4) emissions in lactating Angus crossbred beef cows. The study was conducted from May to October of 2023 and 2024. Forty-eight multiparous cow-calf pairs were utilized in each year. The experiment followed a randomized complete block design with four treatments in a 2 × 2 factorial arrangement. Factors included using or not internal (INT) or external (EXT) parasite control methods. Each year on d 0, animals were sorted by age and weight, randomly grouped into four cow-calf pairs assigned to 12 different pastures (n = 4 cow-calf pairs/pen, 3 pens/treatment each year), received the first dose of parasite control and a permeation tube containing ±3.4 g of sulfur hexafluoride (SF(6)) gas with an average release rate of 5.78 mg/d was dosed via oral. Internal parasite control involved administering a drench containing 11.36% albendazole (45 mL/cow). For EXT parasite control, animals were equipped with ear tags coated with 50% organophosphate insecticides (2 ear tags per cow and 1 per calf) and treated with a pour-on application of 1% permethrin synergized with 1% piperonyl butoxide. On d 1, the pour-on was re-applied on every sampling day thereafter. On d 1, 35, 70 (weaning day), and 105, body weight (BW) and body condition score (BCS) were recorded, and photographs of the cows’ right-lateral side were taken to determine horn fly load. Enteric CH(4) emissions were collected using the SF(6) tracer technique. With Year 1 only analyzed thus far, there was no significant effect of INT, EXT, or INT×EXT interaction (P > 0.05) on CH(4) emissions. Similarly, BW, BCS, and fly counts had no effect on daily CH(4) emission rates (P > 0.05). However, when CH(4) was expressed as per calf’s weight gain, fly counts had a significant effect (P < 0.05), with CH(4) emissions increasing by 0.034 g/d per each additional fly per cow. This study demonstrated that horn fly load may affect CH(4) emissions intensity in cow-calf production systems when expressed per kg of calf produced.