Effect of antibiotic treatments on dairy cow methane production, milk yield and dry matter intake

Application: Assessing the milk yield and methane production, from healthy and antibiotic treated dairy cows using a lasermethane detector (LMD).Introduction: Enteric methane (CH4) in dairy cows is a result of the fermentation of rumen contents and can be affected by the amount and quality of the feed (Moss eta al., 2000). The use of antibiotics to treat diseases such as lameness and mastitis are generally given as an injection and will affect the microbiology of the rumen (Russell & Strobel, 1989) and potentially the efficiency of the rumen (Jewell et al., 2015). Nonintrusive estimates of enteric CH4 can be obtained using a LMD and has been used as a proxy for rumen function (Chagunda et al, 2009). The aims of this study were to assess the production of enteric methane from cows treated with antibiotics and to compare CH4, dry matter (DM) intakes and milk production from treated cows with a paired group of healthy cows.Material and methods: One group of 15 high performance housed dairy cows, milked 3 times a day and treated with prescribed antibiotics, as part of regular veterinary treatment for lameness or mastitis, were paired with a group of healthy untreated cows. The cows were paired on days in milk, parity, genetic merit and feed type. Diet was either High Energy or Standard Energy, designed to supply 11.3 MJ/kg DM or 12.2 MJ/kg DM respectively. Milk yield (MY) was recorded at every milking and feed intake recorded for three consecutive days out of 6, from HOKO feed bins. CH4 emissions were estimated using a LMD, taking two CH4 readings per second, for approximately 4 minutes for each animal after midday milking four days per week for 8 weeks after antibiotic injections, using a procedure described by Chagunda et al. (2013). Liveweights were taken daily with body condition scores recorded fortnightly CH4 readings per animal, grouped by week of experiment and reading day, were log transformed to attain normality of the data, with zero readings excluded. Linearmixed effects models were fitted in R using lmer and Anova packages at a 5% significance level.Results: Average daily MY over the 8 week period after antibiotic treatments for the untreated and treated groups were 30.8 kg and 33.8 kg, respectively. Week 1 gave the largest mean difference in MY (9.8 kg) intake between the untreated and treated cows, with this reduced to 1.8 kg by Week 4 and the remaining weeks gave very similar MY (mean of 0.01 kg). The mean DM intakes over the 8 weeks were 23.0 kg/cow/day for the untreated group and 22.0 kg/cow/day for the treated group. The largest difference in DM intake was in Week 2 with the untreated group consuming on average 3.2 kg DM/cow/day more than thetreated group. The enteric CH4 measurements were greater for the untreated group over the 8 weeks at 33.1 ppm compared to the treated group (32.3 ppm) (Figure 1).Conclusion: The use of routine antibiotics reduced the milk yield, however, enteric methane emissions were reduced at the start of the monitoring period for both the treated and untreated groups. The DM intake was similar for both groups throughout the whole of the 8 weeks. The initial reduction could be a result of the animals’ response to the monitoring, although the treated group methane emissions remained depressed for a week longer than the untreated.Acknowledgements: This research was funded by the Scottish Government RESAS programme 2016-2021References:Chagunda MGG, Ross D and Roberts D J 2009. Computers and Electronics in Agriculture 68, 157-160.Chagunda MGG, Ross D, Rooke J, Yan T, Douglas J-L, Poret L, McEwan NR, Teeranavattanakul P and Roberts DJ 2013. Acta Agriculturæ Scandinavica 63, 68–75.Jewell KA, McCormick C, Odt CL, Weimer PJ and Suen G 2015. Applied and Environment Microbiology 81, 697-710.Moss AR, Jouany JP and Newbold J 2000. Annales de Zootechie 49, 231–253.Russell JB and Strobel HJ 1989. Effect of ionophores on ruminal fermentation. Applied and Environmental Microbiology 55, 1-6