Reduced Feed Efficiency Research Articles

Dietary supplementation of tetradecylthioacetic acid increases feed intake but reduces body weight gain and adipose depot sizes in rats fed on high‐fat diets

The pan-peroxisome proliferator-activated receptor (PPAR) ligand and fatty acid analogue tetradecylthioacetic acid (TTA) may reduce plasma lipids and enhance hepatic lipid metabolism, as well as reduce adipose tissue sizes in rats fed on high-fat diets. This study further explores the effects of TTA on weight gain, feed intake and adipose tissue functions in rats that are fed a high-fat diet for 7 weeks. The effects on feed intake and body weight during 7 weeks' dietary supplement with TTA ( approximately 200 mg/kg bw) were studied in male Wistar rats fed on a lard-based diet containing approximately 40% energy from fat. Adipose tissue mass, body composition and expression of relevant genes in fat depots and liver were measured at the end of the feeding. Despite higher feed intake during the final 2 weeks of the study, rats fed on TTA gained less body weight than lard-fed rats and had markedly decreased subcutaneous, epididymal, perirenal and mesenteric adipose depots. The effects of TTA feeding with reduced body weight gain and energy efficiency (weight gain/feed intake) started between day 10 and 13. Body contents of fat, protein and water were reduced after feeding lard plus TTA, with a stronger decrease in fat relative to protein. Plasma lipids, including Non-Esterified Fatty Acids (NEFA), were significantly reduced, whereas fatty acid beta-oxidation in liver and heart was enhanced in lard plus TTA-fed rats. Hepatic UCP3 was expressed ectopically both at protein and mRNA level (>1900-fold), whereas Ucp1 mRNA was increased approximately 30-fold in epididymal and approximately 90-fold in mesenteric fat after lard plus TTA feeding. Our data support the hypothesis that TTA feeding may increase hepatic fatty acid beta-oxidation, and thereby reduce the size of adipose tissues. The functional importance of ectopic hepatic UCP3 is unknown, but might be associated with enhanced energy expenditure and thus the reduced feed efficiency.

Comparing differential tolerance of native and non-indigenous marine species to metal pollution using novel assay techniques

Recent research suggests anthropogenic disturbance may disproportionately advantage non-indigenous species (NIS), aiding their establishment within impacted environments. This study used novel laboratory- and field-based toxicity testing to determine whether non-indigenous and native bryozoans (common within marine epibenthic communities worldwide) displayed differential tolerance to the common marine pollutant copper (Cu). In laboratory assays on adult colonies, NIS showed remarkable tolerance to Cu, with strong post-exposure recovery and growth. In contrast, native species displayed negative growth and reduced feeding efficiency across most exposure levels. Field transplant experiments supported laboratory findings, with NIS growing faster under Cu conditions. In field-based larval assays, NIS showed strong recruitment and growth in the presence of Cu relative to the native species. We suggest that strong selective pressures exerted by the toxic antifouling paints used on transport vectors (vessels), combined with metal contamination in estuarine environments, may result in metal tolerant NIS advantaged by anthropogenically modified selection regimes.

Haploinsufficiency of the retinoblastoma protein gene reduces diet-induced obesity, insulin resistance, and hepatosteatosis in mice

Brown adipose tissue activity dissipates energy as heat, and there is evidence that lack of the retinoblastoma protein (pRb) may favor the development of the brown adipocyte phenotype in adipose cells. In this work we assessed the impact of germ line haploinsufficiency of the pRb gene (Rb) on the response to high-fat diet feeding in mice. Rb(+/-) mice had body weight and adiposity indistinguishable from that of wild-type (Rb(+/+)) littermates when maintained on a standard diet, yet they gained less body weight and body fat after long-term high-fat diet feeding coupled with reduced feed efficiency and increased rectal temperature. Rb haploinsufficiency ameliorated insulin resistance and hepatosteatosis after high-fat diet in male mice, in which these disturbances were more marked than in females. Compared with wild-type littermates, Rb(+/-) mice fed a high-fat diet displayed higher expression of peroxisome proliferator-activated receptor (PPAR)gamma as well as of genes involved in mitochondrial function, cAMP sensitivity, brown adipocyte determination, and tissue vascularization in white adipose tissue depots. Furthermore, Rb(+/-) mice exhibited signs of enhanced activation of brown adipose tissue and higher expression levels of PPARalpha in liver and of PPARdelta in skeletal muscle, suggestive of an increased capability for fatty acid oxidation in these tissues. These findings support a role for pRb in modulating whole body energy metabolism and the plasticity of the adipose tissues in vivo and constitute first evidence that partial deficiency in the Rb gene protects against the development of obesity and associated metabolic disturbances.

Efficiency of facultative frugivory in the nectar-feeding bat Glossophaga commissarisi: the quality of fruits as an alternative food source

The efficiency of food exploitation correlates positively with the extent of dietary specialization. Neotropical nectar-feeding bats (Glossophaginae) have one of the most specialized diets among mammals, as floral nectar constitutes a sugar-rich and highly digestible but protein and fiber depleted food source. However, dietary constraints, such as a temporary scarcity of nectar, or protein demands may sometimes require the uptake of alternative food items. We investigated the influence of a diet switch from nectar to fruit on intestinal morphology, body mass, and energy budget in the nectar-feeding bat Glossophaga commissarisi and quantified feeding efficiency. We hypothesized that these nectar specialists depend on a constant supply of nectar, if they were lacking the ability for morphological and physiological plasticity in response to a fiber-rich diet. Although capable of harvesting infructescences of Piper hispidum, G. commissarisi was less efficient in extracting energy from fruits (48% digestive efficiency of total fruit energy content) than from nectar (c. 99% digestive efficiency). The intestinal morphology and organ masses did not change after bats were switched from nectar to fruits. Captive bats exhibited lower daily energy expenditures and flight activity when feeding on fruits than during nectarivory. Possibly, this may have been a deliberate regulation to balance reduced feeding efficiency, or simply the consequence of extended digestive pauses. The low digestibility of Piper, in combination with slow digestion and the bats' inability for morphological and physiological plasticity may cause nectar-feeders to reduce their maximum energy expenditure when feeding on fruits. We argue that although fruits may substitute for nectar, they may cause restricted maximum energy assimilation compared with nectar.

The nutritional value of zero-tannin faba bean for grower-finisher pigs

The nutrient profile of zero-tannin faba bean and its effects on performance and carcass characteristics of grower-finisher pigs was investigated. In exp. 1, chemical characteristics were analyzed. Faba bean contained (as fed) 27.5% crude protein (CP), 1.75% lysine, 0.88% threonine, and 0.21% methionine. Twelve 55-kg barrows were fitted with an ileal cannula and fed twice daily at 3 x maintenance either a 96% faba bean diet or a 62% faba bean diet containing cornstarch to measure apparent total tract energy and ileal amino acid (AA) digestibility, respectively, and calculate standardized ileal digestible (SID) AA and net energy (NE) content. After a 6-d acclimation, faeces were collected for 2 d and ileal digesta for 2 d. Apparent total tract energy digestibility, and digestible energy and NE content were 88.5%, and 3.47 and 2.27 Mcal kg-1 (as fed), respectively. Apparent ileal digestibility was 85.9, 76.1, and 74.1%, and SID AA content was 1.54, 0.70, and 0.16% (as fed), for lysine, threonine, and methionine, respectively. In exp. 2, 100 grower pigs in 20 pens were fed either a soybean or faba bean-based diet regimenfrom 35 to 115 kg. Diets were formulated to equal NE and SID [Grower (35 to 60 kg), 2.40/3.95; Finisher 1 (60 to 90 kg), gilts 2.38/3.15, barrows 2.38/2.76; Finisher 2 (90 to 115 kg), gilts 2.38/2.92, barrows 2.35/2.55; Mcal kg-1 NE/g SID lysine Mcal-1 NE, respectively] using determined NE and SID values for faba bean. Pigs were weighed, feed intake was measured, and carcass measurements were obtained. From 35 to 115 kg, average daily feed intake (ADFI; 2.58 and 2.56 kg d-1, respectively) and gain (0.96 and 0.98 kg d-1) did not differ between faba bean and soybean meal. Feed efficiency was 0.02 higher for soybean meal than for faba bean in the Grower phase (P < 0.05). At slaughter, back fat thickness did not differ; however, loin depth was 4.0 mm thicker for soybean meal than for faba bean (P < 0.05). In summary, zero-tannin faba bean has an attractive nutrient profile and does not alter ADFI or average daily gain (ADG) of grower-finisher pigs at inclusion rates up to 30%.The reduced feed efficiency in the Grower phase and reduced lean thickness for pigs fed faba bean indicate that dietary AA supply might have been limiting for the faba bean diets early in the study. In conclusion, the zero-tannin faba bean is a worthwhile energy and protein feedstuff to consider in swine feed formulation. Key words: Digestibility, energy, faba bean, growth performance, nutritional value, pig

Sprinkling coarse marble powder during the afternoon, toward the end of the laying period, may increase eggshell quality

ABSTRACTThe aim of this study was to investigate the effects of time, particle size (PS) and level of calcium supplementation above the requirements toward the end of the laying period on egg production and eggshell quality. A total of 675 Isa‐Brown layer hens were distributed in a completely randomized factorial arrangement of 3×3×3, using three sprinkling times (08.00, 12.00, 16.00 hours), PC (mash, granular and large size) and amounts (0 g control, 0.75 g/day/h, 1.50 g/day/h) of marble sprinkling as a calcium source. All hens were fed a commercial layer diet from 55 to 67 weeks of age. Sprinkling of 1.50 g marble reduced (P < 0.05) egg production compared to 0.75 g marble, and feed efficiency (FE) compared to that of 0 and 0.75 g marble. Sprinkling of 0.75 and 1.50 g marble increased (P < 0.01) eggshell weight, shell strength and shell thickness compared to that of 0 g marble. The interaction of sprinkling time‐by‐PS‐by–quantity of marble was significant for egg production (P < 0.05), FE and shell strength (P < 0.01). Results showed that sprinkling of coarse marble powder to complete diet increased shell strength without reduction in egg production and FE.

Protein Kinase Cβ Deficiency Increases Fatty Acid Oxidation and Reduces Fat Storage

Metabolic syndrome is common in the general population, but there is little information available on the underlying signaling mechanisms regulating triglyceride (TG) content in the body. In the current study, we have uncovered a role for protein kinase Cbeta (PKCbeta) in TG homeostasis by studying the consequences of a targeted disruption of this kinase. PKCbeta(-/-) mutant mice were considerably leaner and the size of white fat depots was markedly decreased compared with wild-type littermates. TG content in the liver and skeletal muscle of PKCbeta(-/-) mice was also significantly low. Interestingly, mutant animals were hyperphagic and exhibited higher food intake and reduced feed efficiency versus wild type. The protection from obesity involves elevated oxygen consumption/energy expenditure and increased fatty acid oxidation in adipose tissue with concurrent increased mitochondria genesis, up-regulation of PGC-1alpha and UCP-2, and down-regulation of perilipin. The ability of PKCbeta deficiency to promote fat burning in adipocytes may suggest novel therapeutic strategies for obesity and obesity-related disorders.

Confinement exposure induces glucose regulated protein 75 (GRP75/mortalin/mtHsp70/PBP74/HSPA9B) in the hepatic tissue of gilthead sea bream (Sparus aurata L.)

Glucose regulated protein 75 (GRP75/mortalin/mtHsp70/PBP74/HSPA9B) is a molecular chaperone that was partially cloned and sequenced in gilthead sea bream (Sparus aurata L.) using a RT-PCR and 3'RACE approach. The deduced amino acid sequence supported the early vertebrate divergence of the heat shock protein 70 family into cytoplasmic Hsp70/Hsc70 group, endoplasmic reticulum-resident group and the mitochondrial-type group of GRP75. The tissue-specific regulation of GRP75 was analyzed by real-time PCR and Western blot after acute (24 h, 120 kg/m(3)) and prolonged confinement exposure (3 weeks-trial, 45-50 kg/m(3)). In both experiments, GRP75 gene expression was not significantly altered in brain, head kidney and gills. By contrast, hepatic transcripts of GRP75 were up-regulated and the magnitude of the response was dependent on the intensity of stressor. Furthermore, similar increments in hepatic transcripts and protein levels of GRP75 were found after prolonged confinement exposure. In addition, these stressed animals exhibited a 10% reduction in feed efficiency, significantly increased glycaemia and plasma peroxidases, and their plasma transaminases and respiratory burst of circulating leucocytes were significantly decreased. This stress-mediated response may act in concert with the increased production of hepatic GRP75 to protect metabolically active tissues against oxidative damage.

Obese humans as economically designed feed converters: Symmorphosis and low oxidative capacity skeletal muscle

Human obesity is considered a consequence of a thrifty or economic metabolism. In this hypothesis, we apply an established economic design theory, called symmorphosis, to help explain the known association between obesity and low oxidative capacity skeletal muscle. Symmorphosis reflects an engineering principle, and predicts that physiological systems are most economically designed when unnecessary spare capacity is eliminated. This is because the structural/functional adaptations accounting for spare capacity themselves bear energetic costs of construction, maintenance and load. As oxidation of feed energy occurs in mitochondria, and because skeletal muscle accounts for 30% of resting metabolism, we focus on skeletal muscle mitochondria. In the same way that the most economically designed elevator is supported by a cable that is strong enough, but not too strong, symmorphosis predicts that the most economically designed feed converters should have enough, but not too much mitochondrial oxidative (fuel burning) capacity. While ATP demand is clearly more efficiently met by oxidative (38 molecules of ATP) rather than glycolytic (2 molecules of ATP) metabolism, symmorphosis predicts that having excess oxidative capacity actually reduces feed efficiency. This inefficiency is manifest by having to maintain, ultimately using feed energy, the expensive inner mitochondrial proton gradient in the superfluous mitochondria. On this basis, we predict that established molecular controllers of mitochondrial biogenesis and oxidative capacity such as eNOS, SIN3 co-repressor, TFAM and PPARgamma may yield useful DNA markers and therapeutic targets for issues relating to frugal energetics, namely predisposition to obesity and starvation resilience.

A novel method to determine larval mandibular wear of the African stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae)

The African stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae), is the most significant indigenous pest on sugarcane in South Africa (Atkinson 1980; Conlong 2001). Currently, crop management and cultivar resistance in sugarcane remain the most widely accepted control methods for E. saccharina in South Africa (Nuss & Atkinson 1983; Keeping 2006). Following emergence, E. saccharina larvae graze up and down the sugarcane stalk or disperse onto dead leaf sheaths for several days until old enough and, presumably, with sufficiently strong mandibles to bore into the plant (Leslie 1993). As young larvae use their mandibles to chew through the sugarcane stalk, abrasion of the mandibles’ chewing surface is inevitable and could ultimately reduce feeding efficiency. It is recognized that fertilization with silicon (Si) can enhance the resistance of plants to insect attack, including that of sugarcane to E. saccharina (Keeping & Meyer 2002, 2006; Kvedaras et al. 2007). Testing the effects of this treatment highlighted a need to measure the extent of wear on larval mandibles. While there have been studies that have reported wear of chewing mouthparts of insects, they have either failed to describe the method (Djamin & Pathak 1967), used a method which can only be applied to mandibles of the same size (Raupp 1985) or have not accounted for differences in mandibular size between individuals (Kokko et al. 1993). The objective of this study was to develop an accurate and repeatable method to measure the mandibular wear experienced by E. saccharina larvae fed on commercial sugarcane. It is anticipated that the method will be useful in quantifying mandibular wear in other adult and larval chewing insects. A method is described that uses a simple image analysis technique to determine the loss of feature on the chewing edge of the mandible. Ten third instar E. saccharina larvae were randomly sampled from commercial sugarcane cultivars N26 and N11 grown at the South African Sugarcane Research Institute (SASRI), Mount Edgecombe, KwaZulu-Natal. Larvae were placed directly into 70 % alcohol until required. Prior to analysis, the larvae were removed from the alcohol, allowed to air dry for 10 min and their heads removed under a light microscope. The labrum was removed and using a fine tipped dissecting needle, the mandibles were carefully pried apart to avoid chipping and air-dried for 1 h. The heads were mounted with their mandibles in a horizontal position using black, double-sided carbon tape (12 mm × 20 m, Structure Probe Inc., West Chester, U.S.A.), on standard aluminium scanning electron microscopy (SEM) stubs. Debris on the mandibles was removed using a fine dissection needle and a fine camel hair brush. The specimens were gold coated for 3.5 min (approx. 6 nanometres thickness) using a gold sputtercoater (Polaron E5100 coating unit and E5500 film thickness moniter, Polaron Equipment Limited, Watford Hertfordshire, U.K.). Specimens were viewed using a scanning electron microscope (Leo 1450 Scanning Electron Microscope, Cambridge, U.S.A.) and the images captured digitally. Each mandible has two scissorial teeth and a proximal tooth, the mola. The degree of wear of a mandible was quantified using an algorithm to obtain a mean square error (MSE), as follows. The (x,y) coordinates (x = horizontal, y = vertical) of the pixels in the digital image that represent the chewing edge of the mandible, from the distal to the proximal convex protrusion (distal scissorial teeth and mola tooth) (Fig. 1), were subjected to linear regression. As the chewing edge of each mandible is carefully orientated under a microscope in a vertical direction, the deviation in the X-axis is the most relevant measurement, hence the best-fitting straight line is calculated as:

Palaeopathology in late Pleistocene and early Holocene Central Plains bison: dental enamel hypoplasia, fluoride toxicosis and the archaeological record

Multiple formative agents are cited for dental enamel hypoplasia (DEH) in modern and fossil mammals. Here, four late Pleistocene-early Holocene bison assemblages from the Central Great Plains are analyzed for DEH and other bone pathologies to investigate the possible influence of chronic fluoride toxicosis, a condition that may have presented a long-term source of duress for prehistoric bison and devalued them as nutritional resources to human hunters. Although DEH is present in all the analyzed assemblages, the lack of corroborating dental and post-cranial anomalies consistent with chronic fluoride toxicosis speaks against it as a primary factor of DEH formation or general ill health in these bison. Rather, maternal nutritional stress, weaning, and seasonal forage condition are invoked as probable promoters of DEH formation. Other identified abnormalities are discussed in reference to their contribution to reduced feeding efficiency and lameness, as are their roles in developing palaeoecological models applicable to archaeological questions about ancient human lifeways.

Re-feeding rapidly restores protection againstHeligmosomoides bakeri(Nematoda) in protein-deficient mice

This study determined whether the timing of re-feeding of protein-deficient mice restored functional protection against the gastrointestinal nematode, Heligmosomoides bakeri. Balb/c mice were fed a 3% protein-deficient (PD) diet and then transferred to 24% protein-sufficient (PS) diet either on the day of primary infection, 10 days after the primary infection, on the day of challenge infection, or 7 days after the challenge infection. Control mice were fed either the PD or PS diet. Onset of challenge, but not primary, infection caused short-term body weight loss, anorexia and reduced feed efficiency. Weight gain was delayed in mice when re-feeding commenced on the day of challenge infection; alkaline phosphatase (ALP) was also elevated in these mice on day 28 post-challenge. In contrast, other re-feeding groups attained similar body weights to PS mice within 4 days and had similar ALP at day 28. Serum leptin was higher in PD than PS mice and positively associated with food intake. As expected, worm survival was prolonged in mice fed the PD diet. However, egg production and worm burdens were similar in all re-feeding groups to the PS mice, indicating that protein re-feeding during either the primary or challenge infection rapidly restored normal parasite clearance.

GGEx regulates body weight gain, hyperphagia and adipose tissue mass in obese and diabetic Otsuka Long‐Evans Tokushima fatty (OLETF) rats.

To investigate whether Gyeongshingangjeehwan (GGEx), an herbal medicine widely used in oriental medicine, regulates body weight and adiposity, we measured body weight, adipose tissue mass, feeding efficiency ratio, liver and fat histology, and the computerized tomography (CT) on abdomen of them in obese and diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats. Rats treated with GGEx not only significantly decreased body weight gain and adipose tissue mass, but also reduced feeding efficiency ratio compared with controls. Hepatic lipid accumulation was also inhibited by GGEx treatment. Moreover, the administration of GGEx significantly decreased adipocyte size, as evidenced by results for histological analysis. Concomitantly, fat area, such as subcutaneous fat and visceral fat, were statistically decreased by GGEx. Therefore, these results suggest that GGEx effectively suppresses obesity and hyperphagia in OLETF rats.

Size-dependent male mating behaviour and sexual harassment in a population of Atlantic mollies (Poecilia mexicana) from a sulphur creek

The Atlantic molly Poecilia mexicana inhabits a variety of habitats. In previous studies, small males from clear-water populations showed considerably more sexual behaviours than large males. Males from a sulphur creek, the El Azufre, or from a sulphur cave (cave molly) showed comparatively low sexual activity, and typical size-dependent mating behaviour was either absent or large males showed even more sexual behaviour than smaller ones. Sexually deprived cave molly males increased their sexual activity, but small males still did not show more sexual behaviour than large ones, suggesting that the genetic basis for typical size-dependent mating behaviour has been lost. Likely, the extreme abiotic conditions (hypoxia and toxic hydrogen sulphide) have selected against energetically costly behaviours. In this paper, we examined how El Azufre males would respond to sexual deprivation. We found these males to also increase their sexual activity after sexual deprivation but, unlike cave mollies, small males now showed more sexual behaviour than large ones, suggesting that the genetic basis for this behaviour is not lost in this population. Differences between populations may be due to the less harsh characteristics of El Azufre (e.g. less H2S), resulting in weaker selection against energy-consuming behaviours. Furthermore, we tested for potential costs of male sexual harassment for females in terms of reduced feeding efficiency in the presence of a male, as was shown for P. mexicana from a clear-water population, but was not found in cave mollies or the El Azufre fish. Test females were either starved for 1 week to increase hunger levels or male sexual deprivation and female starvation were combined; however, we found no evidence for male sexual harassment even after these treatments. Our results parallel previous findings in the cave molly and suggest that El Azufre males have lost specific behavioural traits that cause sexual harassment.

Differential effects of exercise on body weight gain and adiposity in obesity-prone and -resistant rats

To determine the effect of exercise on weight gain and adiposity in obesity-prone and -resistant rats. Body weight gain, fat pad weights, food intake, plasma leptin and insulin levels were assessed in outbred male Sprague-Dawley rats, which remained sedentary or were given unrestricted access to running wheels either before or after they developed diet-induced obesity (DIO) or diet-resistance (DR) on a high energy (HE; 31% fat) diet. When fed a low fat (4.5%) chow diet, rats which would later develop DIO (n=6) after 3 weeks on HE diet ran the same amount as DR rats (n=6). Other rats were first made DIO (n=12) or DR (n=12) after 10 weeks on HE diet and then either kept sedentary or given running wheels for 4 weeks on HE diet. DIO and DR rats ran comparable amounts but only the DIO rats reduced their body weight gain, fat pad relative to body weights and plasma leptin levels significantly, compared to their sedentary controls. Exercise had no effect on food intake in either DIO or DR rats but reduced feed efficiency (weight gain/caloric intake) in both. Although DIO and DR rats ran similar amounts, the greater reduction in body weight gain and adiposity of exercising DIO rats suggests that they are more sensitive to some metabolic or physiologic system that prevents them from increasing their intake sufficiently to compensate for their net reduction in energy stores.

Distribution, Feeding and Body Condition of Four Small Fish Species in the Near-shore and Central Areas of Liangzi Lake, China

Small fish abundance is usually high in heavily vegetated habitats in Yangtze lakes, China. Visual and swimming barriers created by dense macrophytes beds could reduce feeding efficiency and growth of small fishes. We tested the hypothesis that small fishes in habitats with dense macrophytes would show decreased feeding efficiency and reduced growth rates by comparing feeding efficiency (measured as the relative weight of fore-gut contents), total length, and condition factor of four small young-of-the-year fishes collected in the near-shore (heavily vegetated) and central (less vegetated) areas of Liangzi Lake. Feeding efficiency, total length, or condition factor were each significantly reduced in the near-shore area compared with the central area for Ctenogobius giurinus, Pseudorasbora parva and Carassius auratus auratus. This supports our hypothesis that vegetation abundance may mediate feeding efficiency and growth of small fishes. Although Hypseleotris swinhonis did not show significant decreases in feeding efficiency or growth in the near-shore area, there was not any reversed tendency, i.e. increased feeding rate or growth in the near-shore area compared to the central area.

Feedlot cattle diets based on barley or corn supplemented with dry corn gluten feed evaluated using the NRC and CNCPS beef models

A study was conducted to evaluate the effects of supplementing feedlot finishing corn diets with dry corn gluten feed (CGF). Animal performance and carcass traits were compared with those obtained by feeding a barley-based diet typical of diets fed commercially in western Canadian feedlots. The second objective of the experiment was to evaluate the diets using the 1996 National Research Council (NRC) Beef (level 1 and 2) and Cornell Net Carbohydrate and Protein System (CNCPS, version 5.0) models to determine how well the models predict animal response. Crossbred beef steers (248) weighing 423 ± 20.5 kg were allocated to 24 pens and then six pens were assigned to each of four diets: (1) barley grain (13.8% crude protein, CP), (2) corn grain (9.2% CP), (3) corn grain supplemented with a low level (7%, DM basis) of CGF (CGF-low, 9.7% CP), and (4) corn grain supplemented with a high level (23%) of CGF (CGF-high, 11.7% CP). The barley grain was steam-rolled and the corn grain was dry-rolled. All diets contained 8% barley silage (DM basis). The cattle were adapted from a backgrounding diet to the experimental diets over a period of 28 d and then fed for a period of 136 d. During the adaptation phase cattle fed unsupplemented corn grew slower (P < 0.05) than the cattle fed the other diets (1.23 vs. 1.52 kg d-1). However, after day 42 of the study, cattle fed unsupplemented corn grew very rapidly such that gain for the entire feeding period was similar for cattle fed unsupplemented corn and barley diets (1.62 vs. 1.58, P > 0.05). Furthermore, growth rate was higher (P < 0.05) for cattle fed barley or unsupplemented corn than for cattle fed low or high levels of CGF (1.48 and 1.45 kg d-1, respectively). The dry matter intake (DMI) averaged 11.4 kg d-1 during the feeding period and was not affected (P > 0.05) by diet. Feed:gain ratio (kg DM:kg gain) was similar (P > 0.05) for cattle fed barley (7.09) and unsupplemented corn (7.38), but was higher (P < 0.05) for cattle fed CGF-high (7.92), and intermediate (P > 0.05) for those fed CGF-low (7.52). There were no differences in carcass composition between barley and corn-fed cattle, but those fed low and high levels of CGF had carcasses that were fatter with lower lean meat yield. The three models underestimated DMI of all four diets. When DMI was set to observed intake in the models, CNCPS accurately predicted ADG and F:G ratio for cattle fed corn diets, but all models underestimated ADG of cattle fed barley. All models correctly predicted that gain during the feeding period was not limited by protein supply. The results from this study indicate that rolled-corn diets containing about 9.5% CP, with 50% of the CP as DIP are adequate for feedlot cattle weighing more that 500 kg. Substituting dry CGF for corn grain reduces feed efficiency and gain due to the lower digestible energy content of CGF. Key words: Grain, barley, corn, corn gluten feed, feedlot cattle, protein, models

A TWO-GENERATION REPRODUCTIVE TOXICITY STUDY OF 4-NITROTOLUENE IN RATS

4-Nitrotoluene (4-NT) was administered orally at doses of 0, 40, 80, or 160 mg/kg/day by gavage to 24 Crj:CD (SD)IGS rats of each sex per group over two successive generations, and the effects on reproductive capacity in the parental animals and growth and development of the offspring were investigated. In the F0 and F1 parents, increased hepatic and/or renal weights were observed at the doses of 40 mg/kg or more in both generations, with lowered body weights in the F1 case and reduced feeding efficiency, histopathological changes in the kidney and spleen at doses of 80 and 160 mg/kg, as well as worsening of clinical signs and death during the perinatal period at 160 mg/kg in both generations. With regard to effects on the reproductive capacity, reduced vaginal opening was observed at 160 mg/kg in the F1 generation. However, no abnormalities were observed in the endocrine and reproductive organs or in serum hormone levels. In the F1 and F2 offspring, decrease in body weight gain and brain weights was observed at the doses of 80 and 160 mg/kg and reduced viability, with elongation or a tendency for elongation of the male anogenital distance at 160 mg/kg. Thus, the possibility that 4-NT exerted endocrine disrupting effects seems to be very low under the conditions of this study, and when the substance was administered to rats over two generations, doses less than 160 mg/kg/day did not induce any marked adverse effects on the reproductive capacity in the parental animals, with the no observed effect level (NOEL) and the no observed adverse effect (NOAEL) on growth and development in the offspring concluded to be 40 mg/kg/day.

Age‐0 Black Crappie Abundance and Size in Relation to Zooplankton Density, Stock Abundance, and Water Clarity in Three Florida Lakes

AbstractCrappies Pomoxis spp. are popular sport fishes but are often difficult to manage due to highly variable recruitment. To assess the factors influencing recruitment, we investigated the size and abundance of age‐0 black crappie P. nigromaculatus in relation to zooplankton density, adult stock abundance, and water clarity in three productive Florida lakes. Age‐0 black crappies were collected at Lakes Wauberg, Lochloosa, and Tarpon by use of surface and bottom trawls during the spring, summer, and fall of 2000 and 2001. Zooplankton abundance was measured concurrently with trawl sampling. Early‐summer juvenile abundance was positively related to stock abundance during the previous fall among lakes, indicating a relationship between stock size and juvenile black crappie abundance. Early‐summer juvenile abundance was positively related to juvenile abundance in the fall (i.e., at the end of the first summer), suggesting that year‐class strength was set by early summer in all lakes. Lake Lochloosa had the highest crustacean zooplankton abundance in both years, but this lake had the smallest age‐0 black crappie size and intermediate age‐0 fish abundance. Thus, we found no relationship between crustacean zooplankton density and black crappie size across lakes. Reduced Secchi depths due to high chlorophyll‐a values and wind resuspension of sediments may have reduced feeding efficiency for age‐0 black crappies at Lake Lochloosa relative to the other lakes. Age‐0 black crappie abundance and size during fall were not predicted solely by food availability, stock abundance, or water clarity, suggesting that these factors interacted to influence recruitment through the first year of life.

Effect of Daily Feed Intake on Feed Efficiency of Juvenile Channel Catfish

AbstractPond‐raised channel catfish Ictalurus punctatus fed to satiation typically have lower feed efficiency (the ratio of weight gain to feed consumption) than fish fed a restricted ration. It is not clear whether the reduction in feed efficiency of fish fed to satiation is caused by wasted feed or by less efficient feed utilization. Two studies were conducted using 110‐L flow‐through aquaria to evaluate the relationship among the feed intake, growth rate, and feed efficiency of juvenile channel catfish. In experiment 1, 20 fish averaging 46 g were fed once daily at 0.5% to 3.0% of body weight (BW) or to satiation for 2 weeks. In experiment 2, 15 fish averaging 37 g were fed once daily at 1.0% to 3.0% BW or to satiation for 4 weeks. Fish in the satiation group were fed as much as they would consume within 40 min, and the remaining feed pellets were removed and counted to determine the amount of feed consumed. In both experiments, weight gain increased as feed intake increased. Feed efficiency improved as feed intake increased and peaked at feeding rates of 100% and 89% satiation for experiments 1 and 2, respectively. The daily feeding rates required to maintain a constant BW were about 0.5–0.8% BW. The results from this study indicated that under controlled conditions, channel catfish most efficiently utilized feed when fed to satiation or close to satiation (without feed waste). This suggests that the reduction in the feed efficiency of fish fed to satiation in ponds is probably caused by wasted feed rather than by less efficient feed utilization by the fish. Pond‐raised channel catfish should be fed at a rate slightly below satiation without overfeeding to achieve optimum feed efficiency. Severe feed restriction may result in poor feed efficiency because a higher proportion of ingested feed would be used for maintenance in heavily stocked ponds.