Files
Abstract
A multi-step approach was used to evaluate the effects of including exogenous feed enzymes in creep feeds formulated for beef calves. The first experiment consisted of testing 4 different enzymes (endo-1,4--xylanase, endo-1,3(4)--glucanase, endo-1,4--glucanase, and -amylase) and their combinations in an in vitro batch culture fermentation using rumen fluid collected from 6-month-old beef calves. Traits such as production of volatile fatty acids, production of methane, and in vitro dry matter digestibility were quantified, and the best enzyme supplement was chosen to be used in the second experiment: an in vivo feeding trial. This second trial was conducted over a period of 2 years and used 4 different cow-calf herds at 2 research stations. The cow-calf herds were split into similar groups and their performances were monitored for approximately 100 days in each year. Upon conclusion of this feeding trial, the third step took place. In this final step, the contents of the forestomach of 27 calves were collected by esophageal tubing, and immediately after this procedure, and all calves were weaned, grouped together, and offered a common diet. Four weeks later, a second collection procedure was performed on the same 27 calves, and samples obtained on both days were subjected to microbiome analysis using 16S rRNA gene paired-end sequencing. Results from the first step identified endo-1,4--xylanase at 3,000,000 units per tonne of dry matter as the best candidate for the subsequent in vivo trial, and after testing this treatment for 2 years, this conjecture was confirmed: calves fed this treatment had greater average daily gains than calves receiving other treatments. Results from the microbiome analysis revealed some shifts in calves ruminal microbial population; however, most of the fluctuations were not of great magnitude. Therefore, we concluded that factors such as an increased amount of energy intake due to supplementation, and increased metabolizable energy due to addition of endo-1,4--xylanase were probably more important than any shifts observed in the microbial community. Consequently, we presumed that these factors had a greater contribution on the observed differences in calf growth when the feeding trial was conducted.