Until recently, use of antibiotics to enhance terrestrial animal growth performance was a common, U.S. Food and Drug Administration (FDA)-approved, but controversial practice. There are no FDA-approved production claims for antibiotic drug use in fish, but it is a common misconception that antibiotics are widely used for this purpose in U.S. aquaculture. Antibiotics are not thought to be effective growth promoters in fish, but there is little quantitative data available to address whether there are growth-promoting effects that might incentivize the use of antibiotics in this way, despite legal prohibitions. Therefore, this study was conducted to determine if oral administration of oxytetracycline, an antibiotic with known growth-promoting effects in terrestrial livestock, has a similar effect when applied to channel catfish Ictalurus punctatus, hybrid striped bass Morone chrysops × M. saxatilis, Nile tilapia Oreochromis niloticus, or rainbow trout Oncorhynchus mykiss. Oxytetracycline products with production claims are typically applied at doses substantially lower than the approved therapeutic doses for the same products. Medication (0, 0.24, or 1.2 g oxytetracycline dihydrate kg-1 feed) and feeding rates (3% BW d-1) were selected to achieve target daily doses of 0, 16, or 80 mg kg-1 fish representing control, subtherapeutic, and therapeutic treatments. Replicate groups of fish (N = 4) were fed accordingly for 8 wk. Overall, oral administration of oxytetracycline did not affect survival or promote growth of the selected taxa, with no significant differences observed for weight gain, feed conversion ratio, or specific growth rate (P > 0.05 in all cases). Few differences were observed in organosomatic indices and in the frequency of tissue abnormalities; where present, these differences tended to suggest a negative effect of long-term dietary exposure to oxytetracycline. These data demonstrate that there is no benefit to dietary supplementation with oxytetracycline for nontherapeutic purposes in a range of economically important finfish species. As such, our results indicate there is little incentive to misuse oxytetracycline products for purposes of growth promotion in U.S. aquaculture.

Our goal was to determine if relative bioavailability values (RBV) for fats and oils (lipids) determined in adult roosters are different than RBV determined with young broiler chickens. Lipids that were expected to have widely varying ME content were evaluated using a slope-ratio approach in adult roosters (Exp. 1) via the precision-fed rooster assay (PFRA) and broiler chicks via a growth assay (Exp. 2). The same lipids were tested in both experiments and were refined corn oil (RCO), a 2:1 blend of stearic acid (C18:0) with RCO (SAB1), a 1:1 blend of C18:0 with RCO (SAB2), tallow (TW), poultry fat (PF), and corn oil from a corn ethanol plant (DDGSCO). In Exp. 1, roosters were tube-fed diets containing 0, 5, and 10% of supplemental lipid in ground corn. In Exp. 2, diets consisted of 0, 5, and 10% supplemental lipid in an amino-acid fortified corn-soybean meal diet. Chicks were limit-fed test diets from 10 to 20 d posthatch to maintain energy as the growth-limiting factor. The TMEn of diets or BW gain of chicks were regressed on supplemental lipid level. The RBV were calculated as the regression coefficient of the test lipid divided by that of RCO. For Exp. 1 a non-linear response was observed for SAB2; however, the RBV for SAB1 (22%), TW (72%), PF (96%), and DDGSCO (90%) were as expected. The RBV of SAB1 and TW were lower (P < 0.001) than RCO, while PF and DDGSCO were not different than RCO. For Exp. 2, BW increased linearly in proportion to the energy content of the lipid sources. The RBV of SAB1 (22%), SAB2 (46%), and TW (76%), were lower (P < 0.001) than RCO, while PF (96%) and DDGSCO (97%) were not different than RCO. Excellent agreement was obtained for RBV between the two assays, with rooster and chick values being similar and the ranking of the lipids being the same for the two assays.

The precision-fed rooster assay (PFRA) frequently yields TME values for fats and oils in excess of their gross energies. Six experiments were conducted to determine if the PFRA could be combined with a slope-ratio type assay to yield more useful lipid TME values. In experiment (EXP) 1, refined corn oil (RCO) was fed to conventional and cecectomized roosters at zero, 5, 10, 15, and 20% of a ground corn diet. In EXP 2 through 6, lipids were fed to conventional roosters at zero, 5, and 10% in a ground corn diet. Palomys (a novel lipid), high stearidonic acid soybean oil (SDASO), 2 animal-vegetable blends (AV1, AV2), a vegetable-based oil blend (VB), and corn oil from an ethanol plant (DDGSCO) were evaluated and compared to refined soybean oil (RSO) or RCO as the reference lipid. Multiple linear regression of diet TME on supplemental lipid level generated regression coefficients that were used to calculate relative bioavailability values (RBV). In EXP 1, RCO was a suitable reference material as TME linearly increased up to 20% RCO inclusion. There were some minor differences in TME of RCO between conventional and cecetomized bird types. In EXP 2, Palomys was found to have a lower (P < 0.05) RBV (87%) than RCO. In EXP 3, there were no significant differences between SDASO and RSO. In EXP 4, the RBV of AV2 (79%) was lower (P < 0.05) than RCO, while the RBV of AV1 was not different from RCO. The RBV of DDGSCO (116%) was higher (P < 0.05) than RCO in EXP 5. The RBV of VB (84%) was lower (P < 0.001) than RCO in EXP 6; however, this may be an underestimation for low levels of VB, as there was an interaction (P < 0.01) between lipid type and lipid supplementation level. These results indicate that the precision-fed slope-ratio rooster assay can detect differences among lipids and yields practically useful lipid TME values.

Frozen-thawed boar sperm (FTS) has reduced in vitro and in vivo life span compared to liquid semen. Experiments tested whether extenders, thawing procedures, and storage temperatures could extend the fertile life span of FTS. Experiment 1 tested the effect of six extenders on postthaw motility (MOT) and viability (VIA). Straws from boars (n = 6) were thawed, diluted into each extender, and evaluated at 20, 60, and 120 minutes. There was a trend (P = 0.08) for an extender-by-time interaction for MOT and effect of extender and time for MOT (P < 0.0001) and extender (P = 0.10) and time (P < 0.0001) for VIA. Experiment 2 evaluated the effect of temperature and time of thawing on in vitro fertility at intervals after thawing. Straws (0.5 mL) from different boar ejaculates (n = 15) were thawed at 50 °C for 10, 20, or 30 seconds or at 70 °C for 5, 10, or 20 seconds and evaluated at 5, 30, and 60 minutes. There was an effect of thawing treatment on MOT, VIA, and ACR (viable sperm with intact acrosomes, P < 0.0001) and an effect of time of evaluation (P < 0.0001) on MOT and ACR. Thawing at 70 °C for 20 seconds reduced (P < 0.05) MOT, VIA, and ACR compared to other treatments. Experiment 3 tested the effects of storage temperature and time after thawing using 20 ejaculates. Samples were thawed, diluted, and allotted to storage at 17 °C, 26 °C, or 37 °C with evaluation at 2, 6, 12, and 24 hours. There was a storage temperature and time effect and an interaction for MOT and VIA (P < 0.0001). Storage at 17 °C and 26 °C increased (P < 0.05) MOT over all times (38.5%) compared to 37 °C (26%), whereas MOT was reduced at intervals. Viability was also greatest with 17 °C and 26 °C compared to 37 °C and was also affected by time and decreased with time. These results indicate that FTS can be held at 17 °C or 26 °C for up to 2 hours before use and would allow for preparation of multiple doses. These data suggest in vitro fertility of FTS is affected by extenders, thawing, and storage.

Feed consumption increases body temperature and may delay a return to euthermia and exacerbate intestinal injury following acute hyperthermia recovery in pigs. The study objective was to evaluate the effects of feed removal on body temperature, feeding behavior, and intestinal morphology in pigs exposed to acute hyperthermia and then cooled. Twenty-four gilts (78.53 ± 5.46 kg) were exposed to thermoneutrality (TN; n = 12 pigs; 21.21 ± 0.31°C) for 6 h, or heat stress (HS; 38.51 ± 0.60°C) for 3 h followed by a 3-h recovery period of cooling (HSC; n = 12 pigs; water dousing and TN conditions). Within each temperature treatment, half the pigs were provided feed (F; n = 6 pigs/temperature treatment) and half were not provided feed (NF; n = 6 pigs/temperature treatment). Gastrointestinal (TGI) and vaginal (TV) temperature were recorded every 15 min and pigs were video-recorded to assess feeding behavior. Immediately following the 6 h period pigs were euthanized, and intestinal samples were collected for histology. During the HS period, Tv and TGI were increased overall (P < 0.01; 1.63°C and 2.05°C, respectively) in HSC vs. TN pigs, regardless of feeding treatment. A temperature by feeding treatment by time interaction was detected during the recovery period where TGI was greater (P = 0.03; 0.97°C) for HSC+F compared to HSC+NF pigs from 45–180 min. Feeding behavior was greater overall (P = 0.02; 223.14%) in F vs NF pigs, regardless of temperature treatment. A decrease (P < 0.01) in jejunum and ileum villus height (24.72% and 26.11%, respectively) and villus height to crypt depth ratio (24.40% and 25.52%, respectively) was observed in HSC vs TN pigs, regardless of feeding treatment. Ileum goblet cells were reduced (P = 0.01; 37.87%) in HSC vs TN pigs, regardless of feeding treatment. No other differences were detected for any parameter. In summary, TGI decreased more rapidly following acute hyperthermia when feed was removed.