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Ractopamine hydrochloride (RH) alters protein metabolism and improves growth performance in Bos taurus cattle with high carcass fat. Our objective was to evaluate the effects of RH, dietary CP and RH×CP interaction on performance, blood metabolites, carcass characteristics and meat quality of young Nellore bulls. A total of 48 bulls were randomly assigned to four treatments in a 2×2 factorial arrangement. The factors were two levels of dietary CP (100% and 120% of metabolizable protein requirement, defined as CP100 and CP120, respectively), and two levels of RH (0 and 300 mg/animal·per day). Treated animal received RH for the final 35 days before slaughter. Animals were weighed at the beginning of the feedlot period (day 63), at the beginning of ractopamine supplementation (day 0), after 18 days of supplementation (day 18) and before slaughter (day 34). Animals were slaughtered and hot carcass weights recorded. After chilling, carcass data was collected and longissimus samples were obtained for determination of meat quality. The 9–11th rib section was removed for carcass composition analysis. Supplementation with RH increased ADG independently of dietary CP. There was a RH×CP interaction on dry matter intake (DMI), where RH reduced DMI at CP120, with no effect at CP100. Ractopamine improved feed efficiency, without RH×CP interaction. Ractopamine had no effect on plasma creatinine and urea concentration. Greater dietary CP tended to increase blood urea, and there was a RH×CP interaction for plasma total protein. Ractopamine supplementation increased plasma total protein at CP120, and had no effect at CP100. Ractopamine also decreased plasma glucose concentration at CP100, but had no effect at CP120. Ractopamine increased alkaline phosphatase activity at CP120 and had no effect at CP100. There was a tendency for RH to increase longissimus muscle area, independently of dietary CP. Ractopamine did not alter fat thickness; however, fat thickness was reduced by greater CP in the diet. Supplementation with RH decreased meat shear force, but only at day 0 of aging, having no effect after 7, 14 or 21 days. Greater dietary protein increased meat shear force after 0 and 7 days of aging, with no effect after 14 or 21 days. These results demonstrate for the first time the efficacy of ractopamine supplementation to improve gain and feed efficiency of intact Bos indicus males, with relatively low carcass fat content. Ractopamine effects were not further improved by increasing dietary protein content above requirements. [ABSTRACT FROM PUBLISHER]

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Copyright of Archives of Veterinary Science is the property of Archives of Veterinary Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cancer vaccines can be utilized in combination with checkpoint inhibitors to optimally stimulate the anti-tumor immune response. Uptake of vaccine antigen by antigen presenting cells (APCs) is a prerequisite for T cell priming, but often relies on non-specific mechanisms. Here, we have developed a novel vaccination strategy consisting of cancer antigen-containing liposomes conjugated with CD169- or DC-SIGN-specific nanobodies (single domain antibodies) to achieve specific uptake by APCs. Our studies demonstrate efficient nanobody liposome uptake by human and murine CD169 + and DC-SIGN + APCs in vitro and in vivo when compared to control liposomes or liposomes with natural ligands for CD169 and DC-SIGN. Uptake of CD169 nanobody liposomes resulted in increased T cell activation by human APCs and stimulated naive T cell priming in mouse models. In conclusion, while nanobody liposomes have previously been utilized to direct drugs to tumors, here we show that nanobody liposomes can be applied as vaccination strategy that can be extended to other receptors on APCs in order to elicit a potent immune response against tumor antigens., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)