Environmental effects on water intake and water intake prediction in growing beef cattle

Water is an essential nutrient, but there are few recent studies that evaluate how much water individual beef cattle consume and how environmental factors affect an individual’s water intake (WI). Most studies have focused on WI of whole pens rather than WI of individual animals. Thus, the objective of this study was to evaluate the impact of environmental parameters on individual-animal WI across different seasons and develop prediction equations to estimate WI, including within different environments and management protocols. Individual daily feed intake and WI records were collected on 579 crossbred steers for a 70-d period following a 21-d acclimation period for feed and water bunk training. Steers were fed in 5 separate groups over a 3-yr period from May 2014 to March 2017. Individual weights were collected every 14 d and weather data were retrieved from the Oklahoma Mesonet’s Stillwater station. Differences in WI as a percent of body weight (WI%) were analyzed accounting for average temperature (TAVG), relative humidity (HAVG), solar radiation (SRAD), and wind speed (WSPD). Seasonal (summer vs. winter) and management differences (ad libitum vs. slick bunk) were examined. Regression analysis was utilized to generate 5 WI prediction equations (overall, summer, winter, slick, and ad libitum). There were significant (P \u3c 0.05) differences in WI between all groups when no environmental parameters were included in the model. Although performance was more similar after accounting for all differences in weather variables, significant (P \u3c 0.05) seasonal and feed management differences were still observed for WI%, but were less than 0.75% of steer body weight. The best linear predictors of daily WI (DWI) were dry mater intake (DMI), metabolic body weights (MWTS), TAVG, SRAD, HAVG, and WSPD. Slight differences in the coefficient of determinations for the various models were observed for the summer (0.34), winter (0.39), ad libitum (0.385), slick bunk (0.41), and overall models (0.40). Based on the moderate R2 values for the WI prediction equations, individual DWI can be predicted with reasonable accuracy based on the environmental conditions that are present, MWTS, and DMI consumed, but substantial variation exists in individual animal WI that is not accounted for by these models

OFF ganglion cells cannot drive the optokinetic reflex in zebrafish

Whereas the zebrafish retina has long been an important model system for developmental and genetic studies, little is known about the responses of the inner retinal neurons. Here we report single-unit ganglion cell recordings from 5- to 6-day-old zebrafish larvae. In wild-type larvae we identify at least five subtypes of ganglion cell responses to full-field illumination, with ON-OFF and ON-type cells predominating. In the nrc mutant retina, in which the photoreceptor terminals develop abnormally, we observe normal OFF responses but abnormal ON-OFF responses and no ON responses. Previously characterized as blind, these mutants lack an optokinetic reflex (OKR), but in another behavioral assay nrc mutant fish have near-normal responses to the offset of light and slow and sluggish responses to the onset of light. Pharmacological block of the ON pathway mimics most of the nrc visual defects. We conclude that the abnormal photoreceptor terminals in nrc mutants predominantly perturb the ON pathway and that the ON pathway is necessary to drive the OKR in larval zebrafish

Test duration for water intake, ADG, and DMI in beef cattle

Water is an essential nutrient, but the effect it has on performance generally receives little attention. There are few systems and guidelines for collection of water intake (WI) phenotypes in beef cattle, which makes large-scale research on WI a challenge. The Beef Improvement Federation has established guidelines for feed intake (FI) and ADG tests, but no guidelines exist for WI. The goal of this study was to determine the test duration necessary for collection of accurate WI phenotypes. To facilitate this goal, individual daily WI and FI records were collected on 578 crossbred steers for a total of 70 d using an Insentec system at the Oklahoma State University Willard Sparks Beef Research Unit. Steers were fed in five groups and were individually weighed every 14 d. Within each group, steers were blocked by BW (low and high) and randomly assigned to one of four pens containing approximately 30 steers per pen. Each pen provided 103.0 m2 of shade and included an Insentec system containing six feed bunks and one water bunk. Steers were fed a constant diet across groups and DMI was calculated using the average of weekly percent DM within group. Average FI and WI for each animal were computed for increasingly large test durations (7, 14, 21, 28, 35, 42, 49, 56, 63, and 70 d), and ADG was calculated using a regression formed from BW taken every 14 d (0, 14, 28, 42, 56, and 70 d). Intervals for all traits were computed starting from both the beginning (day 0) and the end of the testing period (day 70). Pearson and Spearman correlations were computed for phenotypes from each shortened test period and for the full 70-d test. Minimum test duration was determined when the Pearson correlations were greater than 0.95 for each trait. Our results indicated that minimum test duration for WI, DMI, and ADG were 35, 42, and 70 d, respectively. No comparable studies exist for WI; however, our results for FI and ADG are consistent with those in the literature. Although further testing in other populations of cattle and areas of the country should take place, our results suggest that WI phenotypes can be collected concurrently with DMI, without extending test duration, even if following procedures for decoupled intake and gain tests

Environmental effects on water intake and water intake prediction in growing beef cattle

Water is an essential nutrient, but there are few recent studies that evaluate how much water individual beef cattle consume and how environmental factors affect an individual’s water intake (WI). Most studies have focused on WI of whole pens rather than WI of individual animals. Thus, the objective of this study was to evaluate the impact of environmental parameters on individual-animal WI across different seasons and develop prediction equations to estimate WI, including within different environments and management protocols. Individual daily feed intake and WI records were collected on 579 crossbred steers for a 70-d period following a 21-d acclimation period for feed and water bunk training. Steers were fed in 5 separate groups over a 3-yr period from May 2014 to March 2017. Individual weights were collected every 14 d and weather data were retrieved from the Oklahoma Mesonet’s Stillwater station. Differences in WI as a percent of body weight (WI%) were analyzed accounting for average temperature (TAVG), relative humidity (HAVG), solar radiation (SRAD), and wind speed (WSPD). Seasonal (summer vs. winter) and management differences (ad libitum vs. slick bunk) were examined. Regression analysis was utilized to generate 5 WI prediction equations (overall, summer, winter, slick, and ad libitum). There were significant (P \u3c 0.05) differences in WI between all groups when no environmental parameters were included in the model. Although performance was more similar after accounting for all differences in weather variables, significant (P \u3c 0.05) seasonal and feed management differences were still observed for WI%, but were less than 0.75% of steer body weight. The best linear predictors of daily WI (DWI) were dry mater intake (DMI), metabolic body weights (MWTS), TAVG, SRAD, HAVG, and WSPD. Slight differences in the coefficient of determinations for the various models were observed for the summer (0.34), winter (0.39), ad libitum (0.385), slick bunk (0.41), and overall models (0.40). Based on the moderate R2 values for the WI prediction equations, individual DWI can be predicted with reasonable accuracy based on the environmental conditions that are present, MWTS, and DMI consumed, but substantial variation exists in individual animal WI that is not accounted for by these models

Zebrafish larvae lose vision at night

Darkness serves as a stimulus for vertebrate photoreceptors; they are actively depolarized in the dark and hyperpolarize in the light. Here, we show that larval zebrafish essentially turn off their visual system at night when they are not active. Electroretinograms recorded from larval zebrafish show large differences between day and night; the responses are normal in amplitude throughout the day but are almost absent after several hours of darkness at night. Behavioral testing also shows that larval zebrafish become unresponsive to visual stimuli at night. This phenomenon is largely circadian driven as fish show similar dramatic changes in visual responsiveness when maintained in continuous darkness, although light exposure at night partially restores the responses. Visual responsiveness is decreased at night by at least two mechanisms: photoreceptor outer segment activity decreases and synaptic ribbons in cone pedicles disassemble

Retinal function and morphology in two zebrafish models of oculo-renal syndromes.

We characterized visual system defects in two recessive zebrafish mutants oval and elipsa. These mutants share the syndromic phenotype of outer retinal dystrophy in conjunction with cystic renal disorder. We tested the function of the larval visual system in a behavioural assay, eliciting optokinetic eye movements by high-contrast motion stimulation while recording eye movements in parallel. Visual stimulation did not elicit eye movements in mutant larvae, while spontaneous eye movements could be observed. The retina proved to be unresponsive to light using electroretinography, indicative of a defect in the outer retina. Histological analysis of mutant retinas revealed progressive degeneration of photoreceptors, initiated in central retinal locations and spreading to more peripheral regions with increasing age. The inner retina remains unaffected by the mutation. Photoreceptors display cell type-specific immunoreactivity prior to apoptotic cell death, arguing for a dystrophic defect. Genomic mapping employing simple sequence-length polymorphisms located both mutations on different regions of zebrafish linkage group 9. These mutants may serve as accessible animal models of human outer retinal dystrophies, including oculo-renal diseases, and show the general usefulness of a behavioural genetic approach to study visual system development in the model vertebrate zebrafish