The increasing drought seasons due to the climate change effect contributes to a scarcity in the nutrients contained in feedstuffs. Consequently, researchers have proposed alternatives for solving this problem by including additives to rations to enhance growth and feed efficiency. Moreover, the use of some additives like yeast, enzymes, monensin and recently glucogenic precursors as supplements improves animal performance by a shift in the ruminal functions
(Bell et al., 2017). Thus, yeast cultures promote bacterial activity and energy acquisition derived from fiber degradation
(Broadway et al., 2015), whereas monensin improves gain efficiency
(Felix and Loerch, 2011). Additionally, the inclusion of 1,2-propanediol and calcium propionate as glucogenic precursors in the supplementation of diets increases the production of propionic acid in rumen
(Ferraro et al., 2016). Furthermore, glucogenic precursors were primarily used as energetic additives in dairy cows to prevent ketosis by decreasing â-hydroxybutyrate in blood
(Chiofalo et al., 2005). However, no further and comparable studies have been developed to evaluate the effects of supplementing glucogenic precursors with other feed additives. Thus, it is assumed that supplementation of glucogenic precursors, yeast cultures and monensin affect the growth performance, fermentation and digestive characteristics. Therefore, this research aimed to evaluate the supplementation of monensin, yeast culture and a mix of glucogenic precursors on growth performance and digestive characteristics of feedlot beef cattle.
Surgical and animal handling procedures used in this study were conducted according to the Animal Protection Committee of Durango State (México).
Trial 1. Growth performance
This study was conducted at the Juarez University of Durango State, Mexico. Eighty crossbreed steers (261±8 kg as Bulk Weight, BW) were used in a 120-d trial to evaluate the supplementation of 40 mg/kg of monensin (DM), 10 g/a/d of yeast culture (
Saccharomyces cerevisiae) and 20 g/a/d of a mix of glucogenic precursors (1,2-propanediol and calcium propionate) into four experimental diets (Table 1). Upon arrival, steers were vaccinated and treated for parasites before the experimentation begins. Eventually, steers were grouped by weight and randomly assigned to 16 pens. Diets and water were offered
ad libitum. Feed efficiency (FE) was calculated as follows:
Trial 2: Ruminal fermentation and total tract digestion
Four Brangus steers (260±5 kg as BW) with cannulas in rumen and proximal duodenum were used. Animals were housed into individual pens. Experimental diets were offered at 08:00 and 16:00 h using chromic oxide (2.5 g/kg) as a digesta marker and restricting DMI to 3% of BW (Table 1). Each feeding period lasted 14 d, where 12 d were used for dietary adaptation and the latter 2 d for collection. Duodenal and fecal samples were collected twice daily for each steer (07:50 and 13:50 h) and processed for further analysis. Ruminal samples were obtained in the last day of collecting period via ruminal cannula 4 h after feeding and strained, measuring pH immediately. Consequently, subsamples of 10 ml were placed into tubes further analyses of volatile fatty acids (VFA) and ammonia N (NH3-N) according to
Galyean (2010). Feed, duodenal and fecal samples were analyzed for dry matter (DM), ashes and nitrogen
(AOAC, 2000) and neutral detergent fiber (NDF) (Van
Soest et al., 1991). Additionally, duodenal flow and fecal excretion of DM was calculated using chromic oxide as marker
(Hill and Anderson, 1958).
Statistical analysis
The experimental data were analyzed as follows: for Trial 1, a randomized complete block design experiment was considered and PROC MEANS and GLM of
SAS (2002) were used; for Trial 2, a 4´4 Latin Square design was used. Means comparison for both trials was evaluated with the Tukey’s multiple range test and considered significant at P<0.05.
Growth performance
Table 2 presents changes in final live weight and ADG which increased with supplementation (P<0.05). Otherwise, no changes were observed in DMI (P>0.05). However, D3 and D4 increased the FE compared to D1 (P<0.05). These results agreed with reports by
Barreras et al. (2013) and
Lei et al. (2013) who observed increases in ADG and FE with monensin and yeast. Apparently, by using yeast and glucogenic precursors, more feed is converted into live weight increasing its FE.
Patterson et al. (2003) reported that
S. cerevisiae and the mix of the glucogenic precursors increased the microbial efficiency and promotes a higher supply of metabolizable protein to body development of cattle.
Ruminal fermentation and total tract digestion
Results for fermentative parameters are presented in Table 3. No changes were observed in pH (P>0.05). NH3-N showed reductions due to supplementation (P<0.05).
Yang and Russell (1993) reported that monensin might decrease ruminal proteolytic activity, resulting in low NH3-N concentrations. Apparently, these additives are capable to increase by-pass protein by decreasing ruminal NH3-N production and proteolysis by enhancing the energy use in rumen. Likewise,
S. cerevisiae decreased the NH3-N concentration. These results agreed with
Liu et al., (2009) and
Alshaikh et al. (2002).
D4 presented the lowest total volatile fatty acids (TVFA) (P<0.05). However, the supplementation increased propionate concentration in all diets (P<0.05). No differences were observed in acetate and butyrate concentrations among diets (P>0.05). Likewise, similar results were registered previously by different authors
(Zinn et al., 1999; Meyer et al., 2009; Vyas et al., 2014). Additionally, yeast supplementation enhances bacterial activity which may use lactate to produce propionate
(Long et al., 2013).
Results in Table 4 present an increase in the ruminal digestion of organic matter (OM) due to supplementation (P<0.05). Likewise, yeast and the mix of glucogenic precursors increased the ruminal digestion of NDF (P<0.05), which presumes an enhancement of cellulolytic bacteria activity. However, digestion of N was reduced with supplementation. This result agrees with NH3-N results showed previously in this research and previous studies
(Zinn and Borquez, 1993). In addition, N flow to duodenum increased with supplementation (P<0.05). These results confirm that these additives increase by-pass protein. Otherwise, no changes were observed in OM and NDF flow to duodenum (P>0.05). Moreover, OM, NDF and N digested in total tract were not affected by supplementation (P>0.05). These results suggest that total N digested in total tract as well as DMI are similar with and without supplementation. However, supplementation enhances the feed conversion and increases by-pass protein to duodenum, guaranteeing higher growth performance and better efficiency in ruminal fermentation.
