Identification of Bunyamwera and Possible Other Orthobunyavirus Infections and Disease in Cattle during a Rift Valley Fever Outbreak in Rwanda in 2018.

In 2018, a large outbreak of Rift Valley fever (RVF)-like illness in cattle in Rwanda and surrounding countries was reported. From this outbreak, sera samples from 157 cows and 28 goats suspected to be cases of RVF were tested to confirm or determine the etiology of the disease. Specifically, the hypothesis that orthobunyaviruses-Bunyamwera virus (BUNV), Batai virus (BATV), and Ngari virus (NRIV)-were co-circulating and contributed to RVF-like disease was tested. Using reverse transcriptase-polymerase chain reaction (RT-PCR), RVFV RNA was detected in approximately 30% of acutely ill animals, but in all cases of hemorrhagic disease. Seven cows with experienced abortion had positive amplification and visualization by gel electrophoresis of all three segments of either BUNV or BATV, and three of these were suggested to be coinfected with BUNV and BATV. On sequencing, five of these seven cows were conclusively positive for BUNV. However, in several other animals, sequencing was successful for some but not all segments of targeted viruses BUNV and BATV. In addition, there was evidence of RVFV-orthobunyavirus coinfection, through RT-PCR/gel electrophoresis and subsequent Sanger sequencing. In no cases were we able to definitely identify the specific coinfecting viral species. This is the first time evidence for orthobunyavirus circulation has been molecularly confirmed in Rwanda. Furthermore, RT-PCR results suggest that BUNV and BATV may coinfect cattle and that RVFV-infected animals may be coinfected with other orthobunyaviruses. Finally, we confirm that BUNV and, perhaps, other orthobunyaviruses were co-circulating with RVFV and contributed to the burden of disease attributed to RVFV in Rwanda.

Elevated concentrations of crude glycerin in diets for beef cattle: feedlot performance, carcass traits, and ruminal metabolism1.

Three experiments were conducted to evaluate the inclusion of crude glycerin (CG) in diets for beef cattle. In Exp. 1, 4 ruminally cannulated steers were fed diets with 0 or 15% CG (DM basis), to evaluate DM disappearance, VFA profiles, and gas production. There was a tendency for an interaction (P = 0.06) between diet fed to donor animals and substrate fed to in vitro system, and digestion was increased when CG was added to cultures with ruminal fluid from CG-fed animals. Total VFA were unaffected by diets or by substrate incubated. The CG increased production of propionate, butyrate, and valerate (P < 0.01) while the gas production was unaffected (P = 0.16). In Exp. 2, 24 crossbred heifers (334.4 ± 0.9 kg BW) were fed the same diets as Exp. 1, for 35 d. Fecal grab samples were collected 3 times daily on day 7, 21, and 35, to evaluate total tract digestibilities of DM, OM, and NDF. The CG improved digestibility of diet OM (P = 0.04), and DM followed a similar trend (P = 0.06), while the NDF digestibility was unaffected (P = 0.29). In Exp. 3, crossbred heifers (n = 374; 375.8 ± 36.1 kg BW) were used to evaluate feedlot performance and carcass traits when fed diets with 0, 7.5, or 15% CG, with or without added 0.3% salt. Heifers were assigned to 25 pens and were harvested on day 125. Removing salt from CG-based diets did not impact performance (P = 0.50). The CG did not influence average daily gain (P = 0.27), but decreased DM intake (P = 0.003), USDA Yield Grade (P = 0.01), and improved feed efficiency (P = 0.03), while tended to decrease USDA prime carcasses (P = 0.10). Carcass weight (P = 0.24), Longissimus muscle area (P = 0.63), and kidney, pelvic, heart fat (P = 0.59) were unaffected by CG. Twelfth-rib fat was less for heifers fed 15% CG without salt compared with the other treatments (P = 0.005), while marbling was less for heifers fed CG diets compared with the control-fed animals (linear, P = 0.004; quadratic, P = 0.02). In conclusion, GC can replace dry-rolled corn in diets for beef heifers when fed at 15% of diet DM, improving OM digestion, increasing ruminal propionate and butyrate without affecting greenhouse gas emissions. Feeding up to 15% CG improves feed efficiency but depresses marbling and tends to decrease Quality Grade. Removing supplemental salt from CG-diets has no impact on performance or carcass traits.