Technical note: using an automated head chamber system to administer an external marker to estimate fecal output by grazing beef cattle.

The objective of this experiment was to determine if titanium dioxide (TiO2) dosed through an automated head chamber system (GreenFeed; C-Lock Inc., Rapid City, SD, USA) is an acceptable method to measure fecal output. The GreenFeed used on this experiment had a 2-hopper bait dispensing system, where hopper 1 contained alfalfa pellets marked with 1% titanium dioxide (TiO2) and hopper 2 contained unmarked alfalfa pellets. Eleven heifers (BW = 394 ± 18.7 kg) grazing a common pasture were stratified by BW and then randomized to either 1) dosed with TiO2-marked pellets by hand feeding (HFD; n = 6) or 2) dosed with TiO2-marked pellets by the GreenFeed (GFFD; n = 5) for 19 d. During the morning (0800), all heifers were offered a pelleted, high-CP supplement at 0.25% of BW in individual feeding stanchions. The HFD heifers also received 32 g of TiO2-marked pellets at morning feeding, whereas the GFFD heifers received 32 g of unmarked pellets. The GFFD heifers received a single aliquot (32 ± 1.6 g; mean ± SD) of marked pellets at their first visit to the GreenFeed each day with all subsequent 32-g aliquots providing unmarked pellets; HFD heifers received only unmarked pellets. Starting on d 15, fecal samples were collected via rectal grab at feeding and every 12 h for 5 d. A two-one sided t-test method was used to determine agreement and it was determined that the fecal output estimates by HFD and GFFD methods were similar (P = 0.04). There was a difference (P < 0.01; Bartlett's test for homogenous variances) in variability between the dosing methods for HFD and GFFD (SD = 0.1 and 0.7, respectively). This difference in fecal output variability may have been due to variability of dosing times-of-day for the GFFD heifers (0615 ± 6.2 h) relative to the constant dosing time-of-day for HFD and constant 0800 and 2000 sampling times-of-day for all animals. This research has highlighted the potential for dosing cattle with an external marker through a GreenFeed configured with two (or more) feed hoppers because estimated fecal output means were similar; however, consideration of the increased variability of the fecal output estimates is needed for future experimental designs.

Effects of supplementary selenium source on the blood parameters in beef cows and their nursing calves.

Over 2 years, 32 beef cows nursing calves in southwest Arkansas were randomly selected from a herd of 120 that were managed in six groups and were assigned to six 5.1-ha bermudagrass (Cynodon dactylon [L.] Pers.) pastures. Treatments were assigned to pastures (two pastures/treatment) and cows had ad libitum access to one of three free-choice minerals: (1) no supplemental selenium (Se), (2) 26 mg of supplemental Se from sodium selenite per kilogram, and (3) 26 mg of supplemental Se from seleno-yeast per kilogram (designed mineral intake = 113 g/cow daily). Data were analyzed using a mixed model; year and pasture were the random effects and treatment was the fixed effect. At the beginning of the calving and breeding seasons, cows supplemented with Se had greater (P < 0.01) whole blood Se concentration (WBSe) and glutathione peroxidase activities (GSH-Px) than cows receiving no supplemental Se; cows fed seleno-yeast had greater (P ≤ 0.05) WBSe than cows fed sodium selenite, but GSH-Px did not differ (P ≥ 0.25) between the two sources. At birth and near peak lactation (late May), calves from cows supplemented with Se had greater (P < 0.01) WBSe than calves from cows fed no Se and calves from cows fed seleno-yeast had greater (P ≤ 0.01) WBSe and GSH-Px than calves from cows fed sodium selenite. Thyroxine (T4), triiodothyronine (T3), and the T4:T3 ratio in calves did not differ among treatments (P ≥ 0.35). At birth, insulin-like growth factor 1 (IGF-1) was greater (P = 0.02) in calves nursing cows with no supplemental Se than in ones with supplemental Se; in calves nursing cows with supplemental sodium selenite, IGF-1 did not differ (P = 0.96) from ones offered supplemental seleno-yeast. Selenium supplementation of gestating beef cows benefited cows and calves by increasing WBSe and GSH-Px. The use of seleno-yeast as a Se supplement compared to sodium selenite increased the WBSe of both cows and their calves without affecting the T4 to T3 conversion or IGF-1 concentrations.