Passive immunity in calves is evaluated or quantified by measuring serum or plasma IgG or serum total protein within the first 7 d of age. While these measurements inform about circulating concentrations of this important protein, they are also a proxy for evaluating all of the additional benefits of colostral ingestion. The current individual calf standard for categorizing dairy calves with successful passive transfer or failure of passive transfer of immunity are based on serum IgG concentrations of ≥10 and 40, 30, 20, and <10% of calves in the excellent, good, fair, and poor categories, respectively. Because serum IgG concentrations are not practical for on-farm implementation, we provide corresponding serum total protein and %Brix values for use on farm. With one-third of heifer calves in 2014 already meeting the goal of ≥25 g/L serum IgG at 24 h of life, this achievable standard will require more refinement of colostrum management programs on many dairy farms. Implementation of the proposed standard should further reduce the risk of both mortality and morbidity in preweaned dairy calves, improving overall calf health and welfare.

Highly pathogenic avian influenza virus of the H5N1 subtype has been infecting U.S. dairy cattle and spreading among dairy operations since March 2024. H5N1 surveillance systems for dairies are needed, but information on whether environmental sampling can inform these systems is lacking. To guide a surveillance framework, we determined the environmental sites with Influenza A virus (IAV) detection on H5N1-affected dairies (n = 25) in four states (California, Colorado, Michigan, and Ohio) and explored sample characteristics that may have influenced detection. A total of 581 samples from dairy environmental sites were characterized for IAV RNA via rRT-PCR, and classified into six categories. A total of 94 samples (16.2%) had IAV detected, and the Ct values measured from these samples were typically higher than those measured in bulk tank milk from a subset of sampled herds. A majority of IAV detections were made from the following site categories: milking equipment/personal protective equipment, parlor surfaces, and wastewater/lagoons/manure. These results suggest that environmental sites most likely to be contaminated with IAV on dairies are those with exposure to milk. Meanwhile, mixed effect logistic modeling showed that days into an outbreak that samples were collected was associated with IAV detection. These results provide a framework within which to continue the assessment of environmental sampling as a surveillance tool for dairy H5N1. This framework can be strengthened by studies that perform further IAV viral characterization and collect samples from sites prior to, during, and after H5N1 outbreak periods.

Summary:This investigation evaluated the presence of influenza A virus RNA on dairy transport vehicles during the 2024 to 2025 H5N1 outbreak. A total of 298 samples were collected from 52 vehicles, including milk trucks, tankers, and livestock service vehicles operating in Michigan (MI), Colorado (CO), and California (CA). Samples were tested using real-time reverse-transcription polymerase chain reaction (RT-PCR). Overall, influenza A RNA was identified in 1.3% (4/298) of samples and on 7.7% (4/52) of vehicles. Of the 4 samples with RT-PCR detections, 2 were from tires on a livestock hauler and a deadstock trailer in MI. The other 2 RT-PCR detections were from a milk cabinet sample from a milk tanker in MI and a tanker milk sample from CA. Although detections were infrequent and viral loads were low, the results demonstrate that vehicles can carry detectable influenza A virus RNA. These findings highlight the importance of sanitation practices for dairy transport. Ct = cycle threshold; NAHLN = National Animal Health Laboratory Network.