No abstract

To assess the relative bioavailability of bis-glycinate bound Cu, 90 Angus-cross steers (265 ± 21 kg) were blocked by body weight (BW) to pens with GrowSafe bunks and randomly assigned to dietary treatments (14-18 steers/treatment): 0 mg supplemental Cu/kg dry matter (DM; CON), 5 or 10 mg supplemental Cu/kg DM as Cu sulfate (CS5; CS10) or bis-glycinate bound Cu (GLY5; GLY10). Steers received a high antagonist growing diet (analyzed 4.9 mg Cu/kg DM, 0.48% S, and 5.3 mg Mo/kg DM). Steers were weighed at the beginning (d -1 and 0) and end (d 125 and 126) of the trial to determine average daily gain (ADG) and gain:feed (G:F). Blood was collected from all steers on d 0, 28, 56, 84, and 126. Liver samples were collected on d -3 or -2 and d 123 or 124. Data were analyzed using ProcMixed of SAS (experimental unit = steer; fixed effect = treatment and block). Plasma Cu was analyzed as repeated measures (repeated effect = day). Plasma and liver Cu concentrations were regressed against total Cu intake using ProcGLM to calculate relative bioavailability of GLY. Final BW and overall ADG were greatest for CS5 and CS10 and least for CON and GLY5 (P = 0.01). Overall DMI was not affected by treatment (P = 0.14), but overall G:F tended to be greatest for CS5, CS10, and GLY5 and least for CON (P = 0.08). Total and supplemental Cu intake was greatest for steers supplemented either source at 10 mg Cu/kg DM and least for CON (P < 0.01). However, total and supplemental Cu intake was greater for CS5 than GLY5 (P < 0.01). Final liver Cu concentrations were greatest for CS10, least for CON, CS5, and CS10, and intermediate for GLY10 (P < 0.01). Final plasma Cu was greatest for steers supplemented either source at 10 mg Cu/kg DM (P < 0.01). Relative bioavailability of GLY was 82% compared to CS based on liver Cu (P < 0.01) but did not differ based on plasma Cu (P = 0.60). The lesser bioavailability of GLY relative to CS could be due to a high concentration of dietary antagonists and lower solubility of GLY (68.9% relative to CS) in pH conditions (5.2) similar to the ruminal pH of a beef animal consuming a high concentrate diet. Future studies should examine the effects of bis-glycinate bound Cu fed in blended combination with inorganic Cu sulfate to determine the most effective blend of sources for feedlot cattle experiencing varying amounts of dietary Cu antagonists.

To assess efficacy of bis-glycinate bound Zn, 36 crossbred wethers (34 ± 2 kg) were sorted by body weight into three groups and stagger started on a Zn deficient diet (18 mg Zn/kg dry matter; 22.5% neutral detergent fiber) for 45 d prior to a 15-d metabolism period (10 d adaptation, 5 d collection). On d 46, lambs were randomly assigned to dietary treatments (4 lambs treatment-1group -1): no supplemental Zn (CON) or 15 mg supplemental Zn/kg dry matter (ZINC) as Zn sulfate (ZS) or bis-glycinate (GLY; Plexomin Zn, Phytobiotics). Blood was collected from all lambs on d 1, 44, 56, and 61. Liver, jejunum, and longissimus dorsi samples were collected after euthanasia on d 61. Gene expression was determined via quantitative real-time polymerase chain reaction. Data were analyzed using ProcMixed of SAS (experimental unit = lamb; fixed effects = treatment, group, and breed) and contrast statements assessed the effects of supplemental Zn concentration (ZINC vs. CON) and source (GLY vs. ZS). After 15 d of Zn supplementation, plasma Zn concentrations were greater for ZINC vs. CON and GLY vs. ZS (P ≤ 0.01); tissue Zn concentrations were unaffected (P ≥ 0.27). Liver Cu concentrations were lesser for ZINC vs. CON (P = 0.03). Longissimus dorsi Mn concentrations were greater for ZINC vs. CON (P = 0.05) and tended to be lesser for GLY vs. ZS (P = 0.09). Digestibility of DM, OM, and NDF was lesser for ZINC vs. CON (P ≤ 0.05); ADF digestibility tended to be greater for GLY vs. ZS (P = 0.06). Nitrogen retention (g/d) tended to be greater for GLY vs. ZS (P = 0.10) and N apparent absorption was lesser for ZINC vs. CON (P = 0.02). Zinc intake, fecal output, retention, and apparent absorption were greater for ZINC vs. CON (P ≤ 0.01). Apparent absorption of Zn was -5.1, 12.8, and 15.0% for CON, ZS, and GLY, respectively. Nitrogen and Zn retention and apparent absorption were not correlated for CON (P ≥ 0.14) but were positively correlated for ZINC (retention P = 0.02, r = 0.52; apparent absorption P < 0.01, r = 0.73). Intestinal expression of Zn transporter ZIP4 was lesser for ZINC vs. CON (P = 0.02). Liver expression of metallothionein-1 (MT1) tended to be greater for GLY vs. ZS (P = 0.07). Although Zn apparent absorption did not differ between sources (P = 0.71), differences in post-absorptive metabolism may be responsible for greater plasma Zn concentrations and liver MT1 expression for GLY supplemented lambs, suggesting improved bioavailability of GLY relative to ZS.

Producers wishing to background cattle may not have access to grain in certain regions of the country or when grain price is high. Sugar sources may replace grain under these circumstances. The objective of this study was to determine optimum sugar concentration based on daily gain and feed conversion in high-forage diets fed to growing cattle. Ninety-two Angus crossbred (Ranch 1) steers (n = 60; 339 + 11 kg BW) and heifers (n = 32; 309 + 14 kg BW), and 89 Red Angus crossbred (Ranch 2) steers (338 + 16 kg BW) were randomly allocated (5 to 7 hd/pen) within ranch and sex to one of 15 pens in each of two (north or south side) locations within a deep bedded confinement feedlot. Target dietary treatments were designed to contain supplemental sugar inclusion of 0%, 3.5%, 7% or 10.5% (8, 7, 8 or 7 replicate pens in each treatment, respectively) using a molasses-based supplement containing 56.8% sugar and 7.4% urea. Diets were comprised (DM basis) of hay (12%), corn silage, dry distillers grains (14.5%), dry rolled corn and a liquid supplement (5%); corn grain and corn silage inclusion varied from 21% to 32% and from 29% to 36%, respectively, to accommodate supplemental sugar. This resulted in dietary sugar concentrations of 4.3%, 7.3%, 10.3% and 13.3% or 0%, 3%, 6%, and 9%, respectively, as supplemental sugar. As concentration of sugar increased, DMI increased linearly (P < 0.006) with no change in ADG (P = 0.22) resulting in linearly decreasing feed conversion efficiency (P = 0.032). Iterated ME concentration of supplemental sugar was similar to that of corn grain (P > 0.06). Given the appropriate conditions, sugar may replace dry rolled corn and corn silage in high roughage diets for growing cattle.