Influence of ruminal degradable intake protein restriction on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase

Abstract

Two trials were conducted to evaluate the influence of supplemental urea withdrawal on characteristics of digestion (Trial 1) and growth performance (Trial 2) of feedlot cattle during the last 40 days on feed. Treatments consisted of a steam-flaked corn-based finishing diet supplemented with urea to provide urea fermentation potential (UFP) of 0, 0.6, and 1.2%. In Trial 1, six Holstein steers (160 ± 10 kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3 × 3 Latin square experiment. Decreasing supplemental urea decreased (linear effect, P ≤ 0.05) ruminal OM digestion. This effect was mediated by decreases (linear effect, P ≤ 0.05) in ruminal digestibility of NDF and N. Passage of non-ammonia and microbial N (MN) to the small intestine decreased (linear effect, P = 0.04) with decreasing dietary urea level. Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07), N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatment effects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decrease with decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. Ruminal pH was not affected by treatments averaging 5.82. Decreasing urea level decreased (linear effect, P ≤ 0.05) ruminal N-NH and blood urea nitrogen. In Trial 2, 90 crossbred steers (468 kg ± 8), were used in a 40 d feeding trial (5 steers/pen, 6 pens/ treatment) to evaluate treatment effects on final-phase growth performance. Decreasing urea level did not affect DMI, but decreased (linear effect, P ≤ 0.03) ADG, gain efficiency, and dietary NE. It is concluded that in addition to effects on metabolizable amino acid flow to the small intestine, depriving cattle of otherwise ruminally degradable N (RDP) during the late finishing phase may negatively impact site and extent of digestion of OM, depressing ADG, gain efficiency, and dietary NE.

Factors affecting the ruminal microbial composition and methods to determine microbial protein yield. Review

“…More recently, equations have predicted microbial protein production as a linear function of ruminally degradable protein intake in dairy cattle (17) . In addition, in feedlot cattle, a minimum of 100 g of soluble nitrogen/kg of organic matter digested in total tract is required to maximize microbial nitrogen flow (44,45) .…”

“…Decreased feed intake may affect bacterial activity and decrease microbial efficiency due to insuficiency in soluble nitrogen and fermentable organic matter (45) . However, if feed intake restriction is not severe, then microbial efficiency is increased (grams microbial nitrogen/kilograms organic matter fermented), but microbial yield (grams of microbial nitrogen reaching duodenum) is decreased as a consequence of less organic matter fermented in rumen.…”

76 Does supplemental protein and rumen-protected methionine improve performance and digestibility during late-gestation in beef cows?

“…Even when energy requirements are met or exceed, if dietary protein requirements are not met, DMI and digestibility will be reduced (DelCurto et al, 1990). Protein supplementation for cattle increases DM digestibility by enhancing N availability to rumen microbes, meeting microbial N requirements for growth and metabolism (May et al, 2014;Bohnert et al, 2002). For ruminant species, fibre digestion happens almost exclusively in the reticulorumen, whereas only about 10% of NDF is degraded in the hindgut (NRC, 2016).…”

“…Ruminal digestion of fibre is mainly controlled by the microbial population as well as the chemical and physical characteristics of the fibre; however, protein supplementation can also influence fibre digestibility (NRC, 2016). Research clearly demonstrates that as protein supplementation increases, NDF digestibility of the diet will also increase (Hare at al., 2019;May et al, 2014;Bohnert et al, 2002).…”

Influence of mixing supplements (dry or liquid) with monensin or soluble protein on the feeding value of finishing diets for feedlot cattle

“…Nevertheless, in as much as ultraferm N replaced urea N in the LSUF supplement, that replacement could be a factor. In some cases, decreasing the level of supplemental urea in steam-flaked corn-based diets decreased ruminal digestion of NDF (May et al 2014) and starch (Zinn et al 2003;May et al 2014). Whereas, in other studies (Zinn et al 1994(Zinn et al , 2003 urea level did not influence either ruminal fiber or starch digestion.…”