Effects of supplemental zinc on growth, carcass characteristics, and liver abscess formation in steers with experimentally induced ruminal acidosis challenge.

The study's aim was to evaluate the effect of dietary Zn supplementation on steer performance, biomarkers of inflammation and metabolism, and liver abscess formation in response to a mild acidosis challenge. Forty-two steers (417 ± 3.99 kg; n = 6/pen) were housed in pens with bunks designed to measure individual dry matter intake (DMI) and fed one of two diets containing either 0 (CON; n = 18) or 90 mg Zn/kg from a Zn-amino acid complex (Zn-AA; n = 18; AvailaZn; Zinpro) for 109 d. Six additional steers were fed the CON diet and did not undergo the acidosis challenge (NON; n = 6). The acidosis challenge included restricting steers to 50% of the previous 7 d daily DMI on days 46 and 47, steers were individually provided 10% of DMI as cracked corn (as-fed) at 0800 h followed by ad libitum feed access 2 h post-grain consumption. Steer was the experimental unit, and two contrasts were constructed: NON vs. CON and CON vs. Zn-AA. Blood samples were collected on days 40, 48, 53, 69, 80, and 108 and analyzed as repeated measures. Final body weight and overall average daily gain (2.29, 2.30, and 2.31 ± 0.920 kg/d for CON, Zn-AA, and NON, respectively) were not different (P ≥ 0.74) between treatments. By design, DMI was greater (P < 0.01) for NON compared to CON on day 46 but was not different (P ≥ 0.41) for the rest of the experiment. While hot carcass weight (423, 428, and 424 ± 7.9 kg for CON, Zn-AA, and NON, respectively) and ribeye area were not different (P ≥ 0.53) due to treatment, marbling score tended (P = 0.06) to be greater in CON compared to Zn-AA. The 12th rib backfat thickness was greater (P = 0.05) in NON vs. CON steers. Liver abscess incidence tended to be greater (P = 0.12) in CON (24% abscesses) vs. Zn-AA (6% abscesses). NON had a greater incidence (P = 0.05; 50% abscesses) compared to CON. Overall, blood fibrinogen and leukocyte counts were not different between treatments (P ≥ 0.67); however, neutrophil-to-lymphocyte ratio tended to be greater in NON vs. CON (P = 0.08). Serum aspartate aminotransferase and gamma-glutamyl transferase concentrations were greater in NON vs. CON (P ≤ 0.02), and serum alkaline phosphatase concentration was lesser in CON vs. Zn-AA (P < 0.01). Overall, dietary Zn supplementation tended to lessen incidence of liver abscesses with limited impacts on overall cattle performance. Shifts in liver enzymes may represent opportunities to identify cattle with liver abscesses earlier in the feeding period.

Effects of supplemental Zn concentration and trace mineral source on immune function and associated biomarkers of immune status in weaned beef calves received into a feedlot.

Low-risk, weaned Angus-crossbred steers (n = 72; 284 ± 25 kg) were used in a 42-d receiving study. Steers were housed in pens (n = 6 steers per pen) equipped with GrowSafe bunks for determination of individual animal feed disappearance. Dietary treatments (n = 24 steers per treatment) included: 1) trace minerals (TM) from an organic source (Availa4; Zinpro Corp., Eden Prairie, MN) at 7 g·steer-1·d-1; for 42 d (ORG); 2) ORG for entire 42-d plus AvailaZn (Zn amino acid complex, Zinpro Corp., Eden Prairie, MN) to provide 1,000 mg Zn·steer-1·d-1 for first 14 d (ORG+Z); 3) inorganic TM sources to supplemented at equivalent concentration as in ORG for 42-d (ING). Cattle were weighed on day -1, 0, 14, 41, and 42. Whole blood was collected (n = 72 steers) on day 0, 14, and 42. Liver biopsies were conducted (n = 36 steers; 3 steers per pen) on day 0, 14, and 42. Flow cytometry measures were conducted using whole blood on day 1, 14, and 42 for determination of circulating frequencies of immune cell populations. There was a tendency for improved overall average daily gain (P = 0.07) where both ORG and ORG+Z were greater than ING. Final body weight did not differ (P = 0.21) and overall dry matter intake was unaffected by dietary treatment (P ≥ 0.18). However, overall gain-to-feed ratio was improved (P = 0.01) in steers supplemented organic TM (ORG and ORG+Z) compared to ING. Plasma Zn concentration did not differ at any time point during the study (P ≥ 0.20). Liver Zn concentration did not differ between treatments on day 0 or 42; however, on day 14 ING tended (P = 0.09) to be greater than ORG+Z with ORG being intermediate. Plasma Cu was unaffected by dietary treatment (P ≥ 0.34) on day 0, 14, and 42. Plasma Fe did not differ on day 0 or 42 but tended to be greater in ORG and ORG+Z compared to ING (P = 0.08) on day 14. Dietary treatment did not alter (P ≥ 0.22) liver Fe or Mn concentration at any time point. Frequency of total circulating natural killer (NK) and CD8 T cells measured on day 0, 14, and 42 did not differ (P ≥ 0.07). However, cell surface markers of activation (CD16, CD44, and CD8) on NK cells measured on day 14 did differ because of treatment (P ≤ 0.05). Results presented herein indicate TM from an organic source supplemented to steers during receiving can positively influence growth rate and feed efficiency. Regardless of source, TM supplementation affected markers of immune function but did not influence the prevalence of circulating NK and CD8 T-cell populations.

The receiving phase of the beef cattle production cycle occurs when calves are initially placed into the feedlot. During this time cattle are often exposed to stressors such as new environments, unfamiliar feedstuffs, and new pathogens. Together these stressors can result in lesser feed consumption. Along with lower total feed consumption, it is during this time that cattle likely require greater amounts of specific trace minerals (TM) to mount an effective immune response and maintain adequate growth. Therefore, this study aimed to evaluate the effects of supplemental Zn concentration and TM source on the immune function and associated biomarkers of immune status in weaned beef calves received into a feedlot. In this study, the more bioavailable, organic TM source supplemented to steers during receiving positively influenced growth rate and feed efficiency. Plasma TM concentration of steers in this study was adequate and was minimally influenced by TM source or concentration. These results also show TM supplementation, regardless of source, can alter markers of activation within immune cell populations.

Evaluation of feeding ruminal-protected folate and cobalt pectinate on growth performance, carcass characteristics and plasma vitamin B12 and folate status in finishing beef steers.

A large pen feedlot study was conducted to evaluate the response of yearling steers fed novel sources of rumen-protected folate (RPFA) and cobalt (cobalt pectinate; Co-PECT) on plasma levels of vitamin B12 and folate, growth performance, and carcass characteristics. A total of 2,100 steers (initial BW = 381 ±â€…45.2 kg.) were enrolled in the study at the time of randomization with 2,091 steers started on treatment diets following the transition to the finishing diet. A generalized randomized block design with sampling error (GRBD) with two treatments and 15 pen replications per treatment (5 blocks × 6 pens/block; 30 pens total with 70 steers/pen) were evaluated with pen serving as the experimental unit. A control (CON) treatment consisted of the standard finishing diet while the test diet consisted of the standard finishing diet providing 3.0 mg ∙ kg-1 DM of RPFA and 1.0 mg ∙ kg-1 DM total supplemental cobalt with approximately half coming from Co-PECT (TEST). Blood samples were collected from 60 randomly selected steers at study initiation and prior to shipping for plasma B12 and folate measurement. Data were analyzed with the model including fixed effects of treatment, block, and treatment within block interaction. Live growth performance was not affected by treatment; however, carcass-adjusted performance and hot carcass weight were numerically improved by TEST in 3 of the 5 blocks (treatment × within block interaction, P ≤ 0.03) of cattle. Plasma levels for both folic acid and vitamin B12 were extremely low at study initiation and increased over the course of the feeding period. Feeding TEST increased (P < 0.01) plasma B12 levels compared to CON by the completion of the trial; however, mean levels would still be considered marginal. Plasma folate was lower (P < 0.05) in TEST steers at the beginning of the study, with no difference between treatments by the time cattle were shipped. Results suggested that cattle coming into the feedlot may be of low or marginal status in both plasma folate and vitamin B12. While the status of folate and B12 improved in both CON and TEST with days on feed, providing RPFA and Co-PECT further helped improve vitamin B12 status; although, overall levels remained low, which may have affected the overall response to RPFA. Additional research is required to better understand the role of B vitamin supplementation for growing-finishing feedlots and develop methods for assessing the status and improving potential responses.

Initial Liver Copper Status in Finishing Beef Steers Fed Three Dietary Concentrations of Copper Affects Beta Agonist Performance, Carcass Characteristics, Lipolysis Response, and Muscle Inflammation Markers.

Ninety-three Angus-crossbred steers (470 ± 35 kg) were assigned to a 3 × 2 factorial to determine the effects of Cu status and beta agonist (BA) on performance, carcass characteristics, lipolytic rate, and muscle inflammation. Factors included Cu supplementation (mg Cu/kg dry matter (DM)) at: 0 (LO), 10 (MED), or 20 (HI) from Cu amino acid complex (Availa Cu; Zinpro) with no BA (NoRAC) or 300 mg·steer-1·day-1 of ractopamine hydrochloride (RAC; Optaflexx; Elanco) for final 28 days of 88-day trial. Linear and quadratic effects of Cu status within BA treatment were tested. Pre-BA gain was not affected by Cu supplementation (p ≥ 0.57), although day 53 liver Cu quadratically increased (p = 0.01). Average daily gain and muscle IL-8 gene expression quadratically increased (p ≤ 0.01), with MED having greatest gain and gene expression. Ribeye area tended to quadratically increase with Cu supplementation within RAC (p = 0.08). In vitro basal lipolytic rate tended to quadratically increase with Cu supplementation within RAC (p = 0.11), while stimulated lipolytic rate tended to linearly increase within NoRAC (p = 0.10). These data suggest lipolysis and the BA response of steers are influenced by dietary and liver Cu concentrations.

Investigating the effects of a novel rumen-protected folic acid supplement on feedlot performance and carcass characteristics of beef steers.

Angus-crossbred steers (n = 180; 292 ± 18 kg) from a single ranch were used to investigate the effects of a novel rumen-protected folic acid (RPFA) supplement on feedlot performance and carcass characteristics. On d 0, steers were blocked by body weight to pens (5 steers/pen), and pens within a block were randomly assigned to dietary treatments (n = 6 pens/treatment): target intake of 0 (CON), 30 (RPFA-30), 60 (RPFA-60), 90 (RPFA-90), 120 (RPFA-120), or 150 (RPFA-150) mg RPFA·steer-1·d-1. Steers were weighed before feeding on d -1, 0, 55, 56, 86, 87, 181, and 182. Pen average daily gain (ADG), dry matter intake (DMI), and gain:feed (G:F) were calculated for growing (d 0 to 56), dietary transition (d 56 to 87), finishing (d 87 to 182), and overall (d 0 to 182). Liver and blood samples were collected from two steers/pen before trial initiation and at the end of growing and finishing. Steers were slaughtered on d 183, and carcass data were collected after a 48-h chill. Data were analyzed as a randomized complete block design using ProcMixed of SAS 9.4 (fixed effects of treatment and block; experimental unit of pen). Liver abscess scores were analyzed using the Genmod Procedure of SAS 9.4. Contrast statements assessed the polynomial effects of RPFA. Supplemental RPFA linearly increased plasma folate at the end of growing and finishing (P < 0.01), and linearly decreased plasma glucose at the end of growing (P = 0.01). There was a cubic effect of RPFA on liver folate at the end of growing (P = 0.01), driven by lesser concentrations for RPFA-30, RPFA-60, and RPFA-150. Growing period ADG and G:F were greatest for CON and RPFA-120 (cubic P ≤ 0.03). Transition period DMI was linearly increased due to RPFA (P = 0.05). There was a tendency for a cubic effect of RPFA on the percentage of livers with no abscesses (P = 0.06), driven by a greater percentage of non-abscessed livers in RPFA-30 and RPFA-60. Despite supplementing 1 mg Co/kg DM, and regardless of treatment, plasma vitamin B12 concentrations were low (<200 pg/mL), which may have influenced the response to RPFA as vitamin B12 is essential for recycling of folate.

Effects of increasing supplemental dietary Zn concentration on growth performance and carcass characteristics in finishing steers fed ractopamine hydrochloride.

Angus-cross steers (n = 288; 427 ± 0.4 kg) were utilized in a finishing study to evaluate the influence of increasing dietary Zn concentration on growth performance and carcass characteristics of steers fed ractopamine hydrochloride (RAC). In a randomized complete block design, steers were blocked by weight (6 steers/pen) and fed a dry-rolled corn-based diet for 79 d containing no supplemental Zn (CON; n = 8), 60 mg Zn/kg from ZnSO4 and no supplemental Zn-amino acid complex (ZnAA; ZnAA0; n = 8) or ZnAA0 diet supplemented with 60 (ZnAA60; n = 8), 90 (ZnAA90; n = 7), 120 (ZnAA120; n = 8), or 150 (ZnAA150; n = 8) mg Zn/kg DM from ZnAA. Thirty-one days prior to harvest (day 48 of study) all steers began receiving RAC at 300 mg⋅steer-1⋅d-1. This study was organized as 2 groups (GRP) of steers and groups were stagger started so that GRP1 started and ended 2 wk before GRP2. Pen was the experimental unit, and the statistical model included the fixed effects of treatment and block nested within GRP. Three a priori single degree of freedom contrasts were developed: linear and quadratic effects of ZnAA supplementation (ZnAA0, ZnAA60, ZnAA90, ZnAA120, and ZnAA150), and CON vs. Zn (CON vs. ZnAA0, ZnAA60, ZnAA90, ZnAA120, and ZnAA150). Dietary Zn concentration did not affect growth performance prior to RAC supplementation (P ≥ 0.17). During the RAC-period ADG and DMI were not affected by dietary Zn (P ≥ 0.16), while there was a linear effect of dietary Zn supplementation to decrease G:F (P = 0.04). Marbling scores were greatest in CON steers (P = 0.03). Liver Cu (day 45 and 80) and meat Cu (harvest) concentrations were greater in CON steers relative to Zn-supplemented steers (P ≤ 0.05), and plasma Zn linearly increased as dietary Zn increased (P = 0.007). Warner-Bratzler shear force was not different among treatments (P ≥ 0.25), and meat total collagen was quadratically affected by dietary Zn supplementation (P ≤ 0.002) where ZnAA0 was greatest. Overall, there was no effect of dietary Zn concentration on growth performance of RAC-supplemented steers in this study.