Short-Term Impact of Oxytetracycline Administration on the Fecal Microbiome, Resistome and Virulome of Grazing Cattle.

Antimicrobial resistance (AMR) is an important public health concern around the world. Limited information exists about AMR in grasslands-based systems where antibiotics are seldom used in beef cattle. The present study investigated the impacts of oxytetracycline (OTC) on the microbiome, antibiotic resistance genes (ARGs), and virulence factor genes (VFGs) in grazing steers with no previous exposure to antibiotic treatments. Four steers were injected with a single dose of OTC (TREAT), and four steers were kept as control (CONT). The effects of OTC on fecal microbiome, ARGs, and VFGs were assessed for 14 days using 16S rRNA sequencing and shotgun metagenomics. Alpha and beta microbiome diversities were significantly affected by OTC. Following treatment, less than 8% of bacterial genera had differential abundance between CONT and TREAT samples. Seven ARGs conferring resistance to tetracycline (tet32, tet40, tet44, tetO, tetQ, tetW, and tetW/N/W) increased their abundance in the post-TREAT samples compared to CONT samples. In addition, OTC use was associated with the enrichment of macrolide and lincosamide ARGs (mel and lnuC, respectively). The use of OTC had no significant effect on VFGs. In conclusion, OTC induced short-term alterations of the fecal microbiome and enrichment of ARGs in the feces of grazing beef cattle.

Influence of inclusion of low doses of tannin blends in beef cattle dietary supplements on in vitro and in situ digestibility of nutrients in some feedstuffs / Influência da inclusão de baixas doses de taninos em suplementos para bovinos de corte sobre a digestibilidade in vitro e in situ dos nutrientes de alguns alimentos

The objective of this study was to evaluate the effects of the daily supplementation with a low dosage of a blend of condensed and hydrolysable tannins on the in vitro and in situ digestibility of protein and fibrous feedstuffs. In situ ruminal incubation assays were conducted on seven protein and five roughage feedstuffs with and without tannin supplementation (1 g kg-1 DM intake). From these same cattle, rumen Mundim, A. T. et al.1146Semina: Ciênc. Agrár. Londrina, v. 44, n. 3, p. 1145-1166, maio/jun. 2023fluid was collected for in vitro incubations of the same feedstuffs. In vitro assays we evaluated the gas production (GP) up to 24 h and, sequentially, digestibility of dry matter (IVDMD), crude protein (IVCPD), fiber (IVNDFD), and ammonia nitrogen (NH3-N). For in situ assays, the disappearance curves were modeled and then the potentially degradable (B), digestion rate (kd), and undegradable (U) fractions were estimated. Of all the variables studied, only IVCPD of soybean meal showed effect (P<0.05) with the addition of dose of tannins. The supplementation of tannin affected only B of the DM and CP of the cottonseed meal. The kd of DM and CP increased with the supplementation of the tannin blend only for Marandu (dry season), soybean and cottonseed meal. Additionally, the kd of the DM of corn silage was reduced. The U of CP was affected by the increase of tannin supplementation for soybean and cottonseed meal. Daily supplementation with a low dose of tannin blend for grazing cattle affects for grazing cattle affects the ruminal digestibility of some of the evaluated feedstuffs, which are soybean and cottonseed meal.(AU)

O objetivo com este estudo foi avaliar os efeitos da inclusão de uma mistura de taninos condensados e hidrolisáveis em suplementos sobre a digestibilidade in vitro e in situ de alguns alimentos proteicos e volumosos. Sete alimentos proteicos e cinco volumosos foram avaliados in situ no rúmen de bovinos de corte em pastejo recebendo suplementos com e sem taninos (dose de taninos = 1g kg-1 MS). Destes mesmos animais, foi coletado líquido ruminal para incubação in vitro dos alimentos. Nos ensaios in vitro avaliou-se a produção de gás (PG) até 24 h e, sequencialmente, a digestibilidade da matéria seca (DMS), proteína bruta (DPB), fibra (DFDN) e nitrogênio amoniacal (N-NH3). Para os ensaios in situ, as curvas de desaparecimento foram modeladas e, em seguida, as frações potencialmente degradáveis (B), taxa de digestão (kd) e indigestível (U) foram estimadas. De todas as variáveis estudadas, apenas a DPB do farelo de soja apresentou efeito (P<0,05) com a adição de taninos. A suplementação com taninos afetou apenas a fração B da MS e PB do farelo de algodão. O kd da MS e PB aumentaram com a inclusão de taninos para o capim Marandu (estação seca), farelo de soja e farelo de algodão. Adicionalmente, o kd da MS da silagem de milho foi reduzido. A fração indisgestível (U) da PB do farelo de soja e farelo de algodão foram afetadas pela suplementação com taninos. A inclusão de baixas doses de um blend de taninos em suplementos para bovinos em pasto afeta a digestibilidade ruminal de alguns dos alimentos avaliados, notadamente em farelo de soja e farelo de algodão.(AU)

Incidence and risk factors for ketosis in grazing dairy cattle in the Cundi-Boyacencian Andean plateau, Colombia.

Ketosis is a metabolic disorder that has an important impact on health and productivity in dairy cattle during early lactation. In Colombia, the incidence and risk factors for ketosis development have not been studied. The objectives of the present study were to determine the incidence of subclinical (SCK) and clinical ketosis (CK) and to determine the risk factors associated with ketosis within the first 6 weeks of lactation in dairy cattle in Colombia. A prospective cohort study was carried out. A convenience sample of 150 lactating dairy cows from ten commercial dairy farms in the Cundi-Boyacencian Andean plateau were tested weekly using a point of care device to measure ß-hydroxybutyrate during the first 6 weeks of lactation. Incidence of SCK and CK was calculated. Risk factors were evaluated using a survey for each animal and for each farm. Potential risk factors were evaluated using a X2 test, Relative Risk was calculated for significant variables by the X2 test (P ≤ 0.05) and these variables were included in the logistic regression model. Cumulative incidence of SCK was 25.33%, 3.33% for CK, and overall incidence of ketosis was 26%. In the logistic regression model, parity 3 or more, herd size > 150 animals, body condition score ≥ 3, retained placenta, and metritis were determined as risk factors for ketosis. The results of this study confirm previous reports in which a high body condition score, increased parity, herd size, retained placenta, and metritis are associated with an increased risk of ketosis in stabled and grazing cattle.