PSII-14 Effect of live yeast on greenhouse gas emissions and energy partitioning of growing steers in heat-stress conditions

Abstract

Abstract The objective of this trial was to identify the influence of live yeast supplementation (LY) and temperature exposure (TEMP) on greenhouse gas emissions and energy metabolism of steers receiving a grower diet. The effects of LY and TEMP were investigated using a 2 × 2 crossover design that spanned five periods. Eight Angus crossbred steers (365 ± 32 kg; 41 mo) were randomly split into pairs and housed in four outdoor pens outfitted with an individualized feeding system. Animals were limit fed a grower diet (DIET) at 1.2% SBW with no live yeast supplementation (NOY) or a grower diet top-dressed with 10 g live yeast/d for 14 days (1.2 × 1012 CFU/d). On days 13 and 14, animals were subjected to one of two TEMP conditions, thermoneutral (TN; 18.4 ± 1.1°C, 57.6 ± 2.8 % RH) or heat stress (HS; 33.8 ± 0.6°C, 55.7 ± 2.7 % RH), in two side-by-side, single-stall open-circuit, indirect respiration calorimetry chambers. Data were analyzed using a random coefficients model. Carryover effects were examined and removed from the model if not significant (P > 0.05). There was no effect of DIET, TEMP, or DIET × TEMP (P ≥ 0.752) on enteric methane or carbon dioxide emissions. Similarly, GE, ME, DE, and RE were not influenced by DIET, TEMP, or DIET × TEMP (P ≥ 0.152). Gaseous energy, as a percentage of GE, tended to increase during HS (P = 0.097). Heat energy, as a percentage of GE, had a significant LY carryover effect (P = 0.045), with HS×NOY resulting in less HE than TN×NOY (P = .0495) and HS×LY (P = .084). Live yeast supplementation did not reduce enteric emissions, nor did it improve energy metabolism during heat stress. Further research is required to better understand the dynamic relationship between live yeast and temperature exposure.