Stair-step strategy and immunomodulatory feed ingredient supplementation for grazing heat-stressed Bos indicus-influenced beef heifers.

On day 0 of years 1 and 2, 64 Brangus crossbred heifers per year were stratified by initial body weight (BW) and age (mean = 257 ± 20 kg and 271 ± 22 d) and allocated into 16 bahiagrass (Paspalum notatum) pastures (4 heifers per pasture per yr). Treatments were randomly allotted to pastures in a 2 × 2 factorial arrangement of treatments (4 pastures per treatment per yr). Treatments consisted of concentrate dry matter (DM) supplementation at 1.50% of BW from days 0 to 100 (CON) or concentrate DM supplementation at 1.05% of BW from days 0 to 49 and 1.95% of BW from days 50 to 100 (SST). Then, each respective supplementation strategy was added or not with immunomodulatory feed ingredients from days 0 to 100 (OMN; 4 g/45 kg of BW). Heifers were assigned to an estrus synchronization protocol from days 100 to 114. Heifers detected in estrus from days 111 to 114 were inseminated (AI) 12 h after estrus detection. Heifers not detected in estrus were timed AI on day 114. All heifers were exposed to Angus bulls from days 120 to 210 (1 bull per pasture). Effects of supplementation strategy × OMN inclusion × hour were detected (P < 0.0001) only for intravaginal temperature from days 26 to 30, which were the least (P ≤ 0.03) for SST heifers offered OMN supplementation and did not differ (P ≥ 0.17) among all remaining treatments from 0830 to 1600 hours. Effects of supplementation strategy × OMN inclusion and OMN inclusion were not detected (P ≥ 0.12) for any variable, except for the percentage of heifers detected in estrus, which was greater (P = 0.01) for heifers supplemented with vs. without OMN. Total concentrate DM offered from days 0 to 100 and heifer BW on days 0 and 56 did not differ (P ≥ 0.49) between CON and SST heifers, but SST heifers were heavier (P ≤ 0.01) on days 100 and 210 compared with CON heifers. Body surface temperature on day 25 and plasma IGF-1 concentrations on day 75 were greater (P ≤ 0.04) for SST vs. CON heifers. Percentage of pubertal heifers, heifers detected in estrus, and pregnancy to AI did not differ (P = 0.36) between SST and CON heifers but the final pregnancy percentage was greater (P = 0.04) for SST vs. CON heifers. Thus, OMN supplementation decreased the intravaginal temperature of SST heifers but failed to improve their growth and reproduction, whereas the SST strategy improved body thermoregulation, growth, and final pregnancy percentage of heat-stressed Bos indicus-influenced beef heifers compared with a constant concentrate supplementation strategy.

In Bos taurus beef heifers, altering the timing of body weight (BW) growth pattern either reduced feed costs without decreasing reproduction or enhanced reproduction without increasing feed costs. Moreover, supplementation of OmniGen-AF (OMN, a patented immunomodulatory feed ingredient) decreased internal body temperature in dairy and beef B. taurus cattle, with variable impacts on growth and reproduction. Combining both nutritional strategies for Bos indicus-beef heifers developed under heat stress conditions of tropical and subtropical environments has not been reported in the literature yet and was the main objective of the present study. For 100 d before the breeding season, heifers received either a constant supplementation amount or stair-step (SST) supplementation strategy (50 d of low followed by 50 d of high supplement amount), with or without OMN inclusion. Overall, OMN supplementation alleviated the internal body temperature of heifers but did not improve their growth and reproduction, whereas the SST strategy increased BW gain and final pregnancy percentage of B. indicus-influenced beef heifers under heat stress conditions.

Yeast cell wall supplementation alters the metabolic responses of crossbred heifers to an endotoxin challenge.

This study examined the effect of feeding yeast cell wall (YCW) products on the metabolic responses of newly-received feedlot cattle to an endotoxin challenge. Heifers were separated into treatment groups receiving either a Control diet, YCW-A or YCW-C, and were fed for 52 d. Heifers were weighed on d 0, 14, 36, 38 and 52. On d 37 heifers were challenged i.v. with LPS [0.5 µg/kg body weight (BW)] and blood samples were collected relative to LPS challenge. Heifer BW increased from d 0 to 36 and from d 38 to 52, but was not affected by treatment. Post-LPS, glucose concentrations increased and were less in YCW-A than Control and YCW-C heifers. Pre-LPS, insulin concentrations were greater in YCW-A and YCW-C than Control heifers. Post-LPS, insulin concentrations increased with YCW-C having greater insulin than Control heifers. Pre-LPS, NEFA concentrations tended to be less in YCW-C than Control heifers. Post-LPS non-esterified fatty acids (NEFA) concentrations were less in YCW-C than Control and YCW-A heifers. Post-LPS, blood urea nitrogen (BUN) concentrations were greater in YCW-A than Control and YCW-C. These data indicate, based on NEFA and BUN data, that certain YCW products can enhance energy metabolism during an immune challenge without causing lipolysis or muscle catabolism.

Yeast cell wall supplementation alters aspects of the physiological and acute phase responses of crossbred heifers to an endotoxin challenge.

A study was conducted to determine the effect of feeding yeast cell wall (YCW) products on the physiological and acute phase responses of crossbred, newly-received feedlot heifers to an endotoxin challenge. Heifers (n = 24; 219 ± 2.4 kg) were separated into treatment groups receiving either a control diet (n = 8), YCW-A (2.5 g/heifer/d; n = 8) or YCW-C (2.5 g/heifer/d; n = 8) and were fed for 52 d. On d 37 heifers were challenged i.v. with LPS (0.5 µg/kg body mass) and blood samples were collected from -2 h to 8 h and again at 24 h relative to LPS challenge. There was an increase in vaginal temperature in all heifers post-LPS, with YCW-C maintaining a lower vaginal temperature post-LPS than control and YCW-A heifers. Sickness behavior scores increased post-LPS in all heifers, but were not affected by treatment. Cortisol concentrations were greatest in control heifers post-LPS compared with YCW-A or YCW-C heifers. Concentrations of IFN-γ and TNF-α increased post-LPS, but were not affected by treatment. Serum IL-6 concentrations increased post-LPS and were greater in control heifers than YCW-A and YCW-C heifers. These data indicate that YCW supplementation can decrease the physiological and acute phase responses of newly-received heifers following an endotoxin challenge.

Enhancement of the acute phase response to a lipopolysaccharide challenge in steers supplemented with chromium.

The study examined the effect of chromium supplementation on the response of steers to an LPS challenge. Steers received a premix that added 0 (control; n = 10) or 0.2 mg/kg of chromium (n = 10) to the total diet on a dry matter basis for 56 d. Steers were fitted with jugular catheters and rectal temperature (RT) recording devices on d 52. Blood samples were collected and sickness behavior scores assigned to each steer relative to an LPS challenge (0.5 µg/kg) on d 55. Pre-LPS RT were greater in chromium-supplemented than in control steers. Post-LPS RT increased in both treatments, with control steers producing a greater change in RT than chromium-supplemented steers. Sickness behavior scores were greater in control than in chromium-supplemented steers post-LPS (P = 0.03). Cortisol concentrations did not differ between treatments pre-LPS. Post-LPS cortisol concentrations increased but did not differ due to treatment. Concentrations of IL-4 increased post-LPS but were not affected by treatment pre- or post-LPS. Treatment did not affect pre-LPS TNF-α or IFN-γ. Post-LPS TNF-α and IFN-γ increased in both treatments, with chromium-supplemented steers producing greater TNF-α (P = 0.005) and IFN-γ (P = 0.004) than control steers. Pre-LPS IL-6 was greater (P = 0.027) in chromium-supplemented steers than in control steers. Post-LPS IL-6 increased in both treatments and was greater (P < 0.001) in chromium-supplemented than in control steers. These data suggest that chromium supplementation enhances the acute phase response of steers to an LPS challenge, which may expedite recovery.

Effect of dietary lipoic acid on metabolic hormones and acute-phase proteins during challenge with infectious bovine rhinotracheitis virus in cattle.

OBJECTIVE: To determine the effect of dietary supplemental lipoic acid (LA) on serum concentrations of metabolic hormones and acute-phase proteins of steers challenged with infectious bovine rhinotracheitis virus (IBRV). ANIMALS: 32 steers. PROCEDURES: Steers were randomly assigned to 4 treatments: negative control (NC; no LA, no IBRV challenge), control (CON; no LA, IBRV challenge), 16 mg of LA/kg of body weight (BW)/d plus IBRV challenge (LA16), and 32 mg of LA/kg of BW/d plus IBRV challenge (LA32). Following a 21-day adaptation period, CON, LA16, and LA32 steers received IBRV (2 mL/nostril [day 0]); NC steers received saline (0.9% NaCl) solution. Blood samples, nasal swab specimens, BW, and rectal temperatures were obtained 0, 1, 3, 5, 7, 14, and 21 days after challenge. Serum was analyzed for concentrations of haptoglobin, amyloid-A, leptin, and anti-IBRV antibodies. RESULTS: Steers fed LA32 began gaining BW by day 7, whereas BW of CON and LA16 steers declined. Serum haptoglobin concentration of LA32 steers was lower than that of CON and LA16 steers on day 7. Serum neutralization titers for 30 of 32 steers were negative for anti-IBRV antibodies before challenge; however, all steers (including NCs) had antibodies on day 21. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that LA supplementation augmented certain aspects of the immune response; LA32 steers had a more rapid recovery from IBRV viral challenge than did others.