Impact of growth implants and tannin supplementation on enteric methane emissions and estimated nitrogen excretion in grazing stocker steers
Date
2023
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Abstract
The objective of this experiment is to evaluate the effects of a growth-hormone implant (Revlor-G, Merck Animal Health., Rahway, NJ; 40 mg of trenbolone acetate and 8 mg of estradiol) and tannin supplementation (Silvafeed BX, Silva Team, San Michele Mondovi CN, Italy) on enteric methane (CH4) emissions and estimated nitrogen (N) excretion in stocker cattle. Grazing stocker steers (n = 20; initial BW = 343 ± 14 kg) were trained for three weeks to use a portable automated head-chamber system (AHCS; C-Lock Inc., Rapid City, SD) and SmartFeed Pro automated feeder (C-Lock Inc., Rapid City, SD) for dietary supplementation. After the training period, steers were randomly assigned to one of four treatments: 1) no tannin and no implant (Control [CON]); 2) tannin supplement and no implant (Tannin [TAN]); 3) implant and no tannin (Implant [IMP]); and 4) tannin supplement and implant (Implant + Tannin [IMP + TAN]). The tannin was offered at 0.30% DM tannin intake through 0.5 kg/hd/d sweetfeed mix (Sweetfeed Mix, AgFinity., Eaton, CO). Treatment groups without tannin (Control and Implant) received the same sweetfeed mix ration at 0.5 kg/hd/d without the tannin supplementation. Daily forage intake was estimated using the NRC (1996) forage intake prediction equation. Total intake included the estimated forage, bait (alfalfa pellets from AHCS), and sweetfeed mix. Across the experiment, no animal consistently consumed all 0.5 kg/hd/d of the offered sweetfeed mix. On average, the CON cattle consumed 0.32 kg/hd/d, the TAN group consumed 0.41 kg/hd/d, the IMP cattle consumed 0.44 kg/hd/d, and the IMP + TAN group consumed 0.36 kg/hd/d. Moreover, the lack of a tannin x implant interaction (two-way ANOVA; P=0.24) also suggested sweetfeed mix intake did not depend on either treatment level. In response, we evaluated the effect of tannin supplementation and a growth-promoting implant in a separate analysis and data were analyzed with treatment levels as follows: I1) NO-IMP: All animals that did not receive growth implant; I2) IMP: All animals that did receive growth implant; T1) NO-TAN: All animals that did not receive tannin supplement; T2) TAN: All animals that did receive tannin supplement. The sample size for the evaluation of the tannin effect included: NO-TAN (n = 9; 5 animals were implanted with growth promotant) and TAN (n = 9; 5 animals were implanted with growth promotant), while the growth implant effect included: NO-IMP (n = 8; 4 animals were supplemented tannin) and IMP (n = 10; 5 animals were supplemented tannin). Supplementation with tannin did not impact, animal performance metrics (initial body weight, final body weight, and ADG) across the entire study or within early or late study periods (P ≥ 0.33). Steers supplemented with the NO-TAN supplement tended (P ≥ 0.10) to have greater dry matter intake (DMI) and less CH4 yield (MY) compared to cattle supplemented with TAN. There was no effect of tannin supplementation on enteric CH4 production (g/d; P = 0.24) and EI (P = 0.23). N utilization as measured through blood urea nitrogen (BUN), urine N, fecal N, or fecal P was not different among TAN and NO-TAN animals (P ≥ 0.12). Growth-promoting implants did not affect initial body weight (P = 0.86) or final body weight (P = 0.51). There was no effect of growth hormone implant on average daily gain (ADG) during the 90-d of the study (P = 0.80). However, IMP steers tended (P = 0.10) to have greater ADG during the first half of the study (d 0 to 45). Implanted steers also had greater forage (P = 0.05) and bait intake (P = 0.02), and numerically greater total DMI (P = 0.13) over the 90-d study. For IMP steers, there was no effect (P > 0.19) of growth implant on methane (CH4) production or emission intensity (EI; g CH4/kg gain) during the 90-d study. However, IMP steers had decreased (P = 0.03) EI during the first period. Additionally, the IMP steers tended to have less CH4 yield (MY; g CH4/g DMI, P = 0.09) and BUN (P = 0.08) than NO-IMP steers. There was no growth-promoting implant effect (P > 0.30) on cattle urine and fecal N, creatinine, or fecal P. In summary, supplementing tannin in the diet of grazing stocker steers tended to reduce total estimated DMI but did not affect enteric CH4 emissions compared to steers that received no tannin supplement. Implanting steers with Revalor-G tended to 1) increase total DMI in the 90 d study, 2) increase ADG in the early period (d 0 to 45) and 3) decrease CH4 EI in the first 45 d post-implantation.
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Subject
implant
tannin
methane
cattle