Daytime Feeding Research Articles

Effects of feeding time, water temperature, feeding frequency and dietary composition on apparent nutrient digestibility in rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio

A series of experiments was conducted to evaluate the effects of feeding time (daytime vs nighttime feeding), dietary fat content (8 and 20%), feeding frequency (trout 1–3 times/day, carp 2–7 times/day), water temperature (trout 18 and 11°C, carp 25 and 17°C), on the apparent nutrient digestibility in rainbow trout and common carp. The feeding time had little effect on the macronutrient digestibility in both species. In trout, starch digestibility decreased with the decrease of water temperature and with increase of feeding frequency, but in carp, increase of the feeding frequency markedly decreased the macronutrient digestibility and phosphrrus absorption of the high fat diet. Fat digestibility of the beef tallow diet decreased relative to the pollock oil diet in carp, without affecting the phosphorus absorption. Inclusion of raw starch, the digestibility of which was lower than that of gelatinized starch, increased the phosphorus absorption in carp. These results suggest that reduction of water temperature and increase of feeding frequency notably decreased starch digestibility in trout while in carp, the effects of feeding frequency and water temperature on macronutrient digestibility and phosphorus absorption are notable for a high fat diet.

MOSQUITOES OF THE MANGROVE FORESTS OF INDIA: PART FOUR – CORINGA, ANDHRA PRADESH

Mosquitoes of 12 species belonging to 5 subgenera and 9 genera--Aedes, Anopheles, Culex, Diceromyia, Lorrainea, Rhinoskusea, Stegomyia, Toxorhynchites, and Verrallina--were recorded in the Coringa mangrove forest in Andhra Pradesh, India. Tree holes, crab holes, and swamp pools constituted the larval habitats with Lo. fumida being predominant in tree holes. Adults were found resting in tree holes, tree trunks, root bases, and in crab holes. Species involved in daytime feeding on humans were Ae. cancricomes, Cx. sitiens, Lo. fumida, Rh. wardi, and Ve. lugubris.

Influence of Ramadan-type fasting on enzymes of carbohydrate metabolism and brush border membrane in small intestine and liver of rat used as a model

During Ramadan, Muslims the world over abstain from food and water from dawn to sunset for a month. We hypothesised that this unique model of prolonged intermittent fasting would result in specific intestinal and liver metabolic adaptations and hence alter metabolic activities. The effect of Ramadan-type fasting was studied on enzymes of carbohydrate metabolism and the brush border membrane of intestine and liver from rat used as a model. Rats were fasted (12 h) and then refed (12 h) daily for 30 d, as practised by Muslims during Ramadan. Ramadan-type fasting caused a significant decline in serum glucose, cholesterol and lactate dehydrogenase activity, whereas inorganic phosphate increased but blood urea N was not changed. Fasting resulted in increased activities of intestinal lactate (+34%), isocitrate (+63%), succinate (+83%) and malate (+106%) dehydrogenases, fructose 1,6-bisphosphatase (+17%) and glucose-6-phosphatase (+22%). Liver lactate dehydrogenase, malate dehydrogenase, glucose-6-phosphatase and fructose 1,6-bisphosphatase activities were also enhanced. However, the activities of glucose-6-phosphate dehydrogenase and malic enzyme fell significantly in the intestine but increased in liver. Although the activities of alkaline phosphatase, gamma-glutamyl transpeptidase and sucrase decreased in mucosal homogenates and brush border membrane, those of liver alkaline phosphatase, gamma-glutamyl transpeptidase and leucine aminopeptidase significantly increased. These changes were due to a respective decrease and increase of the maximal velocities of the enzyme reactions. Ramadan-type fasting caused similar effects whether the rats fasted with a daytime or night-time feeding schedule. The present results show a tremendous adaptation capacity of both liver and intestinal metabolic activities with Ramadan-type fasting in rats used as a model for Ramadan fasting in people.

Lack of Food Anticipation in Per2 Mutant Mice

Predicting time of food availability is key for survival in most animals. Under restricted feeding conditions, this prediction is manifested in anticipatory bouts of locomotor activity and body temperature. This process seems to be driven by a food-entrainable oscillator independent of the main, light-entrainable clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus . Although the SCN clockwork involves self-sustaining transcriptional and translational feedback loops based on rhythmic expression of mRNA and proteins of clock genes , the molecular mechanisms responsible for food anticipation are not well understood. Period genes Per1 and Per2 are crucial for the SCN's resetting to light . Here, we investigated the role of these genes in circadian anticipatory behavior by studying rest-activity and body-temperature rhythms of Per1 and Per2 mutant mice under restricted feeding conditions. We also monitored expression of clock genes in the SCN and peripheral tissues. Whereas wild-type and Per1 mutant mice expressed regular food-anticipatory activity, Per2 mutant mice did not show food anticipation. In peripheral tissues, however, phase shifts of clock-gene expression in response to timed food restriction were comparable in all genotypes. In conclusion, a mutation in Per2 abolishes anticipation of mealtime, without interfering with peripheral synchronization by feeding cycles.

Diel vertical migration of Euphausia pacifica (crustacea, euphausiacea) in relation to molt and reproductive processes, and feeding activity

We investigated the diel vertical migration of Euphausia pacifica in relation to molt and reproductive processes and feeding activity in April and September 2001 at fixed stations off northeastern Japan. The vertical distribution of this species was shallower in April than in September during both day and night, which was partly explained by a high surface temperature (19°C) and the existence of a subsurface chlorophyll maximum in September. It has been demonstrated for the first time that diel vertical migration of this species is influenced by molt processes because upward migration of molting individuals was restricted compared with non-molting ones. Feeding activity of molting individuals was reduced throughout the day, being lower than or similar to the daytime feeding activity of non-molting ones. The percentage of molting individuals was least (2–4%) among the gravid females, which suggests that gravid females molt less frequently than other stages of females and males. Molt and reproductive processes therefore seemed to be coupled in this species.

Prediction of bird‐day carrying capacity on a staging site: a test of depletion models

1. The carrying capacity of a site for migratory water birds, expressed in bird-days, can be of particular conservation value. Several attempts have been made to model this carrying capacity using ideal free distribution models such as, for instance, depletion models, in which the distribution is fully determined by exploitative competition. 2. In the tests of depletion models carried out so far, no alternative models were compared; rather, one specific model was tested. We tested whether bird-days were more in accordance with birds depleting the food resource (a1) until a critical food density which just enabled survival or (a2) until a threshold food density which renders the site as profitable as an alternative site; and birds (b1) satisfying their daily requirements or (b2) maximizing daily intake. 3. We studied Bewick's swans feeding on below-ground tubers of fennel pondweed in one part of an autumn staging site. In most years between 1995 and 2005, we measured tuber biomass densities around September, November and March, and counted swans daily during their stopover in October. 4. The best fit between observed and predicted bird-days was obtained by assuming that the swans were maximizing their daily intake and depleting the tubers until a threshold biomass density (which yielded the same energetic return as the alternative food source after accounting for a small part of the initial tuber biomass being out of reach of the swans). Also in line with daily intake maximization, the daily feeding time did not differ from 10 h day(-1), the value predicted for Bewick's swans based on their feeding costs. 5. Our results suggests that the applicable model to calculate carrying capacity may depend strongly on whether birds use a site to stopover or to winter, because it determines whether the birds are more likely to use a threshold or critical food density, and to behave as energy maximizers or satisficers.

Feed Stalls Affect the Social and Feeding Behavior of Lactating Dairy Cows

The first objective of this study was to study the effects of increased bunk space on the frequency of aggressive behavior at the feed bunk and on feed access. The second objective was to determine whether the addition of partitions (feed stalls) between adjacent cows would provide additional protection while feeding, particularly for subordinate cows. Twenty-four lactating Holstein cows were subjected to each of 3 treatments in 3 successive 10-d treatment periods using a 3×3 Latin square design. The treatments tested were: 1) 0.64m of feed bunk space/cow, 2) 0.92m of feed bunk space/cow, and 3) feed stalls (0.87m of feed bunk space/cow with feed stall partitions separating adjacent cows). Time-lapse video was used to quantify the feeding and standing behavior, as well as the aggressive behavior (displacements) displayed by the cows at the feed bunk. To meet our first and second objectives, we compared data from the 0.64 m/cow treatment with that from the 0.92 m/cow treatment, and data from the 0.92 m/cow treatment with that from the feed-stall treatment, respectively. Total daily feeding time increased when feed bunk space was increased from 0.64 to 0.92 m/cow. Further, the time spent standing in the feeding area while not feeding and the frequency of aggressive interactions at the feed bunk decreased when more bunk space was provided. The addition of feed stalls resulted in more pronounced effects compared with when cows had 0.92 m/cow of bunk space. The feed stalls also forced cows to change the strategy by which they displaced others from the feed bunk, forcing them to also initiate contact at the rear of the animal they were displacing rather than only from the front and side, as in the other 2 treatments. Further, when the cows were provided with additional feeding space, particularly when combined with feed stalls, those cows with lower social status at the feed bunk experienced the greatest decreases in the number of times they were displaced per day. The results indicated that providing increased feed bunk space, particularly when combined with feed stalls, will improve access to the feed and reduce competition at the feed bunk, particularly for subordinate cows.

House Finch Carpodacus mexicanus roosting behaviour during the non‐breeding season and possible effects of mycoplasmal conjunctivitis

We studied House Finch Carpodacus mexicanus roosting behaviour during the non‐breeding season using radiotracking and direct observations in Ithaca, NY, USA. In contrast to what has been reported in the literature and in contrast to what should be expected from Newton's European studies of cardueline finches, House Finches roost in small groups (mean 3.5; maximum 11) and do not display at roost sites. Seventy‐seven per cent of the birds re‐used the same tree on successive observations. In winter, birds re‐used the same roost tree more often than in the autumn, and birds with mycoplasmal conjunctivitis tended to move more between roost trees than did birds without conjunctivitis. A small number of radiotagged birds that roosted in the same tree were observed together in the daytime more often than by chance, suggesting the existence of social bonds between birds (some same sex) during the non‐breeding season. In the autumn the birds often roosted in leafed deciduous trees and closer to their daytime feeding locations than they did in winter. In winter all birds roosted in evergreen trees. It is possible that the reliable and predictable food sources at feeding sites offered by the public might have changed House Finch roosting behaviour.

Effects of starvation and recovery on the survival, growth and RNA/DNA ratio in loliginid squid paralarvae

The ability of Loligo opalescens paralarvae to resist and recover from starvation was examined by measuring their survival, growth rate and RNA/DNA ratios during starvation and refeeding. Paralarvae were fed Artemia sp. nauplii, zooplankton and mysid shrimp. Fourteen days after hatching they were separated into five feeding treatments: a control treatment (food was always available) and treatments starved for 2, 3, 4 and 5 days, and then refed. Each day, 5–7 paralarvae from each treatment were anesthetized to measure mantle length and wet weight (WW), and then RNA and DNA were extracted using an ethidium bromide fluorometric technique. Paralarvae did not survive 4 and 5 days of starvation, showing that at 15 days of age and at 16 °C the limit to recovery was 3 days of starvation. Paralarvae starved for 2 and 3 days showed compensatory growth that mitigated the effects of starvation, in that at the end of the experiment (10 days), they attained mean final body weights similar to the control treatment. Differences in the RNA/DNA ratios between control and starved paralarvae were detected within 2 days of food deprivation. For paralarvae starved 2 and 3 days, it took 1 day after refeeding to attain RNA/DNA ratios not significantly different from the control treatment. Additionally, RNA/DNA ratios were highest during the day (0800, 1200, 1600 h) and lowest at night (0000, 0400 h), suggesting daytime feeding activity. Growth rates ranged from − 14% to 21% WW day − 1 and the resulting equation between RNA/DNA ratio and growth rate (GR) of paralarvae was GR = 1.74 RNA/DNA − 11.79 ( R 2 = 0.70). After starvation, there was a reduction in growth variability in all starved treatments, while growth variability remained high in the control treatment. Findings from the present study indicate that nucleic acids are a valid indicator of nutritional condition and growth in squid paralarvae.

Food ingestion and circadian rhythmicity

Feeding is organised within the 24-h of the light – dark (LD) cycle. Food is ingested in a circadian manner in nature and in laboratory animals kept under constant conditions. The circadian rhythmicity in food ingestion is driven by a biological clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The circadian organisation of food ingestion not only allows animals to live in harmony with their environment but food intake could also act as a zeitgeber for other rhythmic functions. Lesions in the area of the SCN result in the loss of most rhythmic functions as well as to a disrupted circadian rhythmicity of food and water intake. These findings, together with observations from daytime feeding experiments conducted in nocturnal animals, suggest that food intake may serve as a temporal signal for some peripheral organs to oscillate in phase with the SCN. This paper overviews and discusses how food intake interacts with the circadian system.

Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum

Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5–10 cm) and sub-adult (10–15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (±5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00–10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30–18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder.

Eating and drinking activity of newly weaned piglets: Effects of individual characteristics, social mixing, and addition of extra zinc to the feed1

In production systems, piglets usually fast for a period after weaning, thereby increasing the risk of diarrhea and a reduction in growth. The low level of eating may relate to insufficient drinking activity, as solid feed intake must be accompanied by water intake. Mixing of newly weaned piglets is a well-known stressor and a common procedure in pig production. The effect of mixing on the temporal development of eating and drinking activity in newly weaned piglets has not been elucidated. High concentrations of zinc (Zn) in the feed improve the health and performance of piglets after weaning, but the underlying mechanisms are still obscure. One possibility is that Zn affects eating and drinking behavior. The effects of mixing 4 littermates from each of 2 litters and adding zinc oxide (ZnO; 2,500 ppm of Zn) to the feed were studied in a 2 x 2 factorial experiment using 123 piglets weaned at 27 d of age. Individual eating and drinking times during the initial 48 h after weaning were analyzed on 2 levels of aggregation, day and hour. The piglets spent less time eating on the first day after weaning compared with the second day (20 +/- 5 vs. 98 +/- 10 min, respectively; P < 0.001), whereas they spent more time drinking on the first day compared with the second day (13 +/- 1 vs. 9 +/- 0.5 min, respectively; P < 0.001). Eating and drinking times were positively associated (P < 0.001). Females ate for longer than males (61 +/- 8 vs. 44 +/- 7 min/24 h, respectively, P = 0.002), whereas sex did not affect drinking time. Drinking time increased (P = 0.003) and eating time decreased (P = 0.001) with increasing preweaning growth rate and weaning weight. Neither mixing nor addition of ZnO affected the daily eating time. However, nonmixed piglets given 2,500 ppm of Zn as ZnO in the feed spent more time drinking per day (12 +/- 1 min) than did nonmixed piglets offered 100 ppm of Zn as ZnO (10 +/- 1 min; P = 0.002). Mixing also affected the hourly distribution of the drinking activity (P < 0.05). In conclusion, the drinking behavior of newly weaned piglets was more affected by the external factors, mixing and addition of ZnO to the feed, than the eating behavior. As eating and drinking are strongly associated, more focus should be paid to the water intake and the interplay between eating and drinking behavior in future studies aiming to reduce weaning problems.

Stocking Density and Feed Barrier Design Affect the Feeding and Social Behavior of Dairy Cattle

The objectives of this study were to: 1) evaluate how stocking density at the feed bunk affects feeding and social behavior of dairy cows; and 2) determine if this effect is further influenced by the type of feed barrier used. Thirty-six lactating Holstein cows, allotted to 4 groups, were subjected to each of 4 stocking density treatments and 2 feed barrier treatments. Initially, 2 groups were assigned to a headlock barrier, and 2 groups to a post-and-rail barrier. Each group was then exposed to 4 stocking density treatments (0.81, 0.61, 0.41, and 0.21 m/cow, corresponding to 1.33, 1.00, 0.67, and 0.33 headlocks/cow), in 4 successive 10-d treatment periods. After these periods, the feed barriers were switched between groups and the 4 stocking density treatments were readministered. Time-lapse video was used to quantify feeding, standing, and aggressive behavior at the feed bunk. Daily feeding times were greater and duration of inactive standing in the feeding area was less when using a post-and-rail compared with a headlock feed barrier. Feeding time decreased and inactive standing increased for both barrier designs as stocking density increased at the feed bunk. Cows were displaced more often from the feeding area when the stocking density was increased, and this effect was greater for cows using the post-and-rail feed barrier. Cows ranked lower in the social hierarchy at the feed bunk were displaced more often when feeding at a post-and-rail barrier, particularly at high stocking densities. Therefore, we recommend avoiding overstocking at the feed bunk to increase feeding activity and reduce competition. Use of a barrier that provides some physical separation between adjacent cows, such as a headlock feed barrier, can be used to further reduce competition at the feed bunk.

Circadian rhythm orchestrates the cell cycle of rat renal epithelial cells: A novel mechanism to regulate the cell cycle

The nephron is composed of various types of differentiated cells, each of which is located at the right place at the right time to exert its specific function. During nephrogenesis and physiologic turnover of cells in mature nephron, the cell cycle of differentiated cells and its stem/progenitor cells should be orchestrated, otherwise the morphologic and functional integrity of the kidney would be deranged. Based on this concept, we hypothesized that circadian rhythm, which is maintained by an intrinsic time-keeping system regulating behavior and physiologic functions of organisms, might organize the proliferation of cells in the kidney. In fact, daily administration of 5-bromo-2′-deoxyuridine (BrdU) to pup or adult Sprague-Dawley rats at a specific clock time revealed that renal tubular epithelial cells in cortical and corticomedullary segments of the nephron proliferated rapidly in a synchronized manner but cells in the rest of segments and glomeruli were quiescent or proliferate slowly without apparent synchronization. We confirmed that the activity of cell cycle-related protein molecules such as extracellular signal-regulated protein kinase (ERK)1 and 2 oscillated with a synchronized 24-hour cycle. Restricted daytime feeding, a well-established manipulation to dissociate the circadian clock of peripheral organs from that of suprachiasmatic nucleus (SCN) (the master clock of the body), clearly shifted the phase of the synchronized cell cycle. It means that the clock not in SCN but in the kidney somehow releases a cue for the growth of tubular epithelial cells at the specific segments. Generally, the existence and oscillating phase of the circadian clock can be perceived by the oscillating expression of clock genes such as Per 1 and Per 2. Because Per 1 and Per 2 existed throughout the nephron, including glomeruli and oscillated with a 24-hour cycle, it is intriguing that cells only in the limited area of the kidney proliferate in accordance with the circadian rhythm.

Effects of Daily Feeding Time and Frequency on Channel Catfish, Ictalurus punctatus Production in Earthen Ponds

A pond study was conducted to evaluate effects of daily feeding time and frequency on channel catfish, Ictalurus punctatusproduction, feed efficiency, processing yield, and body composition. Channel catfish fingerlings (initial weight = 22 g/fish) were stocked into eighteen, 0.4-ha ponds at a rate of 24,700 fish/ha. The fish were fed to apparent satiation with a commercial 28% protein diet once daily in the morning or afternoon, or twice daily in both morning and afternoon for two growing seasons. On average, fish on the twice-a-day feeding regime were fed about 2,000 kg/ha more diet than fish fed once daily, but due to the large variation in diet input among ponds there were no significant differences in the amount of diet fed among treatments. No differences were observed in weight gain per fish, estimated survival, net production, visceral fat, or fillet proximate composition among treatments. Feed conversion ratio decreased in fish fed once daily in the morning compared to fish fed once daily in the afternoon or twice daily. Fish fed twice daily had higher carcass and fillet yields than fish fed once daily in the afternoon. However, whether the differences in feed conversion ratio and processing yield are true biological responses needs further investigation. Results from this study indicate that there are few, if any, advantages in feeding food-sized channel catfish twice daily or at a certain time of day. Therefore, we recommend that food-fish in grow-out ponds be fed once daily to apparent satiation but not exceeding what an individual pond can “metabolize,” and feeding should begin early in the morning as soon as dissolved oxygen levels begin to increase.

Frequency of Feed Delivery Affects the Behavior of Lactating Dairy Cows

The objectives of this study were to examine how frequency of feed delivery affects 1) the behavior of group-housed and group-fed dairy cows and 2) the extent of feed sorting. These objectives were tested in two experiments. In each experiment, 48 lactating Holstein cows, split into groups of 12, were subjected to each of 2 treatments (over 10-d periods) in a cross-over design. The treatments for the first experiment were 1) delivery of feed once per day (1×) and 2) delivery of feed twice per day (2×). Treatments for the second experiment were 1) delivery of feed 2× and 2) delivery of feed four times per day (4×). For the 1×, 2×, and 4× treatments, feed was pushed up 3, 2, and 0 times per day, respectively. For both experiments, cows had 0.6m of feeding space; one cows was allowed per lying stall. Time-lapse video was used to quantify the feeding and lying behavior, as well as the aggressive behavior displayed at the feed bunk by the cows. Changes in NDF content of the TMR throughout the day were used to determine the extent of feed sorting by the cows. In both experiments, increased frequency of feed provision increased, as well as changed, the distribution of daily feeding time. The changes in distribution of feeding time resulted in cows having more equal access to feed throughout the day. Frequency of feed delivery had no effect on the daily lying time of the cows or the daily incidence of aggressive interactions at the feed bunk. However, subordinate cows were not displaced as frequently when fed more often. For all treatments, in both experiments, the NDF content of the TMR present in the feed bunk increased throughout the day, indicating that sorting of the feed had occurred. Further, the amount of sorting of the feed was reduced by increasing the frequency of feed delivery from 1× to 2×. These results indicate that frequent delivery of feed improves access to feed for all cows, particularly during peak feeding periods when fresh feed is provided, and reduces the amount of feed sorting.

Feeding Behavior Identifies Dairy Cows at Risk for Metritis

Dairy cows experience a high incidence of disease and metabolic disorders in the weeks immediately following calving, but early and accurate diagnosis remains a challenge. Cows suffering from metritis, one common disease following calving, exhibit reduced milk yield and reproductive performance. However, afflicted cows show few overt signs of illness and frequently go unnoticed in the absence of veterinary examination. To determine whether changes in feeding behavior could be used to identify animals at risk for metritis, attendance at the feed alley was monitored continuously for 26 Holstein cows during the transition period, beginning 2 wk before and ending 3 wk after calving. Every 3±1 d, cows were examined for metritis based on rectal body temperature and condition of vaginal discharge. Over the 3 wk of observations after calving, 69% of cows showed some signs of metritis. These cows spent on average 22min/d less time at the feed alley during the transition period than did non-metritic cows. For every 10-min decrease in average daily feeding time, cows were twice as likely to be diagnosed with metritis. A threshold of 75min of average daily feeding time was 89% sensitive and 62% specific for detection of acute metritis. In conclusion, reduced time at the feeder can be used to identify dairy cows at risk for metritis. More research is required to determine how soon before calving at-risk cows can be identified and whether these behavioral differences can also be used in the early diagnosis of other diseases or metabolic disorders.

Short Communication: Effect of Feed Barrier Design on the Behavior of Loose-Housed Lactating Dairy Cows

The objective of this study was to evaluate the effects of 2 feed barrier systems on feeding and social behavior of dairy cows. Forty-eight lactating Holstein cows were subjected to each of 2 treatments in a cross-over design. The treatments were 2 types of feed-line barriers: 1) post-and-rail, and 2) headlock. Time-lapse video was used to quantify the feeding behavior and incidence of aggressive displacements of the cows at the feed bunk. Average daily feeding time did not differ when cows used the headlock barrier compared with the post-and-rail barrier. However, there were certain changes in feeding time during periods of peak feeding activity: cows that had lower feeding times relative to group mates when using the post-and-rail barrier showed more similar feeding times to group mates when using the headlock barrier. There were 21% fewer displacements at the feed bunk when cows accessed feed by the headlock barrier compared with the post-and-rail barrier. These results suggest that using a headlock barrier reduces aggression at the feed bunk and improves access to feed for socially subordinate cows during peak feeding periods.

Estimates of genetic parameters for feed intake, feeding behavior, and daily gain in composite ram lambs1,2

Our objective was to estimate genetic parameters for feed intake, feeding behavior, and ADG in composite ram lambs ((1/2) Columbia, (1/4) Hampshire, (1/4) Suffolk). Data were collected from 1986 to 1997 on 1,239 ram lambs from approximately 11 to 17 wk of age at the U.S. Meat Animal Research Center near Clay Center, NE. Feeding equipment consisted of an elevated pen with an entrance chute that permitted access to the feeder by only one ram lamb at a time, with disappearance of feed measured by an electronic weighing system. Ram lambs were grouped 11 per pen from 1986 to 1989, and nine per pen from 1990 to 1997. Data were edited to exclude invalid feeding events, and approximately 80% of the data remained after edits were applied. Traits analyzed were daily feed intake (DFI), event feed intake (EFI), residual feed intake (RFI), daily feeding time (DFT), event feeding time (EFT), number of daily feeding events (DFE), and ADG. Feed intake traits of DFI and EFI had estimated heritabilities of 0.25 and 0.33, respectively, whereas estimated heritability of RFI was 0.11. Heritability estimates for feeding behavior traits, including DFT, EFT, and DFE, ranged from 0.29 to 0.36. Average daily gain had an estimated heritability of 0.26. Genetic correlations were positive between all pairs of traits, except for RFI and ADG, and that estimate was essentially zero. Phenotypic correlations were generally similar to genetic correlations. Genetic correlations were large (0.80) between DFI and ADG, intermediate between DFI and RFI (0.61) and between DFT and DFE (0.55), and low (0.17 to 0.31) for the other pairs of traits, with the exception of RFI and ADG (-0.03). Genetic correlations between behavioral traits were greater than correlations between behavioral traits and measures of feed intake or ADG; however, selection for ADG and/or feed intake would be expected to cause some changes in feeding behavior.

TESTS OF THEORY FOR DIEL VARIATION IN SALMONID FEEDING ACTIVITY AND HABITAT USE

For many animals, selecting whether to forage during day or night is a critical fitness problem: at night, predation risks are lower but feeding is less efficient. Habitat selection is a closely related problem: the best location for nocturnal foraging could be too risky during daytime, and habitat that is safe and profitable in daytime may be unprofitable at night. We pose a theory that assumes animals select the combination of daytime and night activity (feeding vs. hiding), and habitat, that maximizes expected future fitness. Expected fitness is approximated as the predicted probability of surviving starvation and predation over a future time horizon, multiplied by a function representing the fitness benefits of growth. The theory's usefulness and generality were tested using pattern-oriented analysis of an individual-based model (IBM) of stream salmonids and the extensive literature on observed diel behavior patterns of these animals. Simulation experiments showed that the IBM reproduces eight diverse patterns observed in real populations. (1) Diel activity (whether foraging occurs during day and/or night) varies among a population's individuals, and from day to day for each individual. (2) Salmonids feed in shallower and slower water at night. (3) Individuals pack more tightly into the best habitat when feeding at night. (4) Salmonids feed relatively more at night if temperatures (and, therefore, metabolic demands) are low. (5) Daytime feeding is more common for life stages in which potential fitness increases more rapidly with growth. (6) Competition for feeding or hiding sites can shift foraging between day and night. (7) Daytime feeding is more common when food avail- ability is low. (8) Diel activity patterns are affected by the availability of good habitat for feeding or hiding. We can explain many patterns of variation in diel foraging behavior without assuming that populations or individuals vary in how inherently nocturnal or diurnal they are. Instead, these patterns can emerge from the search by individuals for good trade- offs between growth and survival under different habitat and competitive conditions.