RESUMEN
Three experiments evaluated delaying corn silage harvest, silage concentration, and source of supplemental protein on performance and nutrient digestibility in growing and finishing diets. Experiment 1 used 180 crossbred yearling steers (body weight [BW] = 428; SD = 39 kg) to evaluate corn silage dry matter (DM) (37% or 43%) and replacing corn with silage (15% or 45% of diet DM) in finishing diets containing 40% modified distillers grains with solubles. Experiment 2 used 60 crossbred steers (BW = 271; SD = 32 kg) to evaluate corn silage harvest DM (37% or 43%) and response to rumen undegradable protein (RUP) supplementation (0.5%, 1.4%, 2.4%, 3.3%, or 4.2% of diet DM) in silage growing diets. Experiment 3 used 9 crossbred lambs (BW = 30.1; SD = 4.1 kg) to evaluate nutrient digestibility of 37% or 43% DM corn silage in silage growing diets fed ad libitum or restricted to 1.5% of BW. In experiment 1, as corn silage concentration increased from 15% to 45%, average daily gain (ADG) and gain-to-feed ratio (G:F) decreased (P ≤ 0.04). Carcass-adjusted final BW and hot carcass weight (HCW) were lower (P ≤ 0.04) for steers fed 45% corn silage compared to 15% when fed for equal days. As DM of corn silage was increased from 37% to 43%, no differences (P ≥ 0.30) in dry matter intake (DMI), ADG, G:F, or HCW were observed. In experiment 2, as DM of corn silage increased from 37% to 43%, ADG and G:F decreased (P ≤ 0.04). Increasing supplemental RUP in the diet increased (P ≤ 0.05) ending BW, DMI, ADG, and G:F linearly as supplemental RUP increased from 0.5% to 4.2%. In experiment 3, there were no differences (P ≥ 0.56) in DM digestibility and organic matter digestibility between silage harvest DM and intake level. Neutral detergent fiber (NDF) intake was reduced (P < 0.01) for lambs fed the delayed harvest corn silage compared to earlier corn silage harvest. As silage harvest was delayed from 37% to 43% DM, NDF digestibility decreased (P < 0.01) from 64.39% to 53.41%. Although increasing corn silage concentration in place of corn in finishing diets reduced ADG and G:F, delayed silage harvest did not affect performance of finishing cattle. Delayed silage harvest in growing cattle resulted in lower ADG and G:F, possibly due to increased starch or maturity leading to decreased NDF digestibility. The addition of RUP to silage-based, growing diets improves performance by supplying more metabolizable protein and suggests RUP of corn silage is limiting.
RESUMEN
This study investigated bovine coronavirus (BCV) in both beef calves direct from the ranch and commingled, mixed-source calves obtained from an auction market. The level of BCV-neutralizing antibodies found in the calves varied among ranches in 2 different studies in a retained-ownership program (ROP), from the ranch to the feedlot. Calves with low levels of BCV-neutralizing antibodies (16 or less) were more likely to be treated for bovine respiratory disease (BRD) than those with higher titers. In 3 studies of commingled, mixed-source calves, BCV was recovered from calves at entry to the feedlot and the infections were cleared by day 8. The BCV was identified in lung samples [bronchoalveolar lavage (BAL) collection] as well as in nasal swabs. Calves with low levels of BCV-neutralizing antibodies at entry were most likely to be shedding BCV. Bovine coronavirus was isolated from both healthy and sick calves, but not from sick calves after 4 d arrival at the feedlot. Bovine coronavirus (BCV) should be considered along with other bovine respiratory viruses in the diagnosis of etiologies in bovine respiratory disease, especially for animals that become sick shortly after arrival. If approved vaccines are developed, it would be best to carry out vaccination programs before calves are weaned, giving them sufficient time to gain active immunity before commingling with other cattle.