Effects of 3-nitrooxypropanol on methane emission, growth and feed intake in growing calves from 5 months of age.

This study aimed to test the effect of 3-nitrooxypropanol (3-NOP) on methane (CH4) emission, feed intake, and body weight (BW) of calves from 5 mo of age. Seventy calves were enrolled in the acclimatization period (3 wk), after which 60 calves were selected based on their ability to use the automated feed bins and the GreenFeed system. Calves (N = 60), a mixture of males and females and either Holstein Friesian or Belgian Blue, were blocked in pairs by sex, breed, and BW, and within block randomly assigned to 1 of 2 dietary treatments: a partially mixed ration (PMR) supplemented with (1) a placebo concentrate (CTL), or with (2) a 3-NOP concentrate (on average 121 mg 3-NOP/kg dry matter of total ration). The acclimatization period was followed by a baseline measurement period (2 wk), and afterwards the treatment period (12 wk) started where the calves received 1 of the 2 dietary treatments. The calves also received up to 1,280 g/day bait in the GreenFeed system, which was used for emission measurements. For analyses, all data were averaged for the baseline measurement period and for different periods in the treatment wk: 1-3, 4-6, 7-9 and 10-12. Upon 3-NOP supplementation, CH4 production (g/d) was reduced by 31.3% in wk 1-3, by 27.1% in wk 4-6, by 30.0% in wk 7-9, and by 30.7% in wk 10-12 compared to CTL (P < 0.01), and CH4 intensity (g/kg BW) was reduced by 30.0% in week 1-3, by 25.8% in wk 4-6, by 27.9% in wk 7-9, and by 28.6% in wk 10-12 compared to CTL (P < 0.01). Over the entire treatment period, 3-NOP calves had a reduction of 29.8% for CH4 production (P < 0.01), 19.4% for CH4 yield (g/kg dry matter intake; DMI) (P < 0.01), and 27.9% for CH4 intensity (g/kg BW) (P < 0.01). Calves receiving 3-NOP had a lower total DMI (6.1 kg/d) compared to CTL (6.9 kg/d) (P < 0.01), driven by a lower DMI of PMR. In every period, 3-NOP calves had a lower BW compared to CTL (over the entire treatment period: 251 vs. 258 kg, P < 0.01). The 3-NOP group and the CTL group did not differ in initial BW, but calves in the 3-NOP group had a lower final BW (290 kg) compared to CTL (301 kg) (P < 0.01). Despite the decreased DMI and growth performance, gain-to-feed ratio (kg BW gain/kg DMI) did not differ between the treatment groups. It can be concluded that 3-NOP persistently decreases CH4 emission in growing beef calves from 5 to 8 mo of age, but that it takes a longer period of time to grow the cattle to a similar body weight due to the decreased growth performance.