Selenium Digestibility and Bioactivity in Dogs: What the Can Can, the Kibble Can't.

There is a growing concern for the long-term health effects of selenium (Se) over- or underfeeding. The efficiency of utilization of dietary Se is subject to many factors. Our study in dogs evaluated the effect of diet type (canned versus kibble) and dietary protein concentration on Se digestibility and bioactivity. Canned and kibble diets are commonly used formats of dog food, widely ranging in protein concentration. Twenty-four Labrador retrievers were used and four canned and four kibble diets were selected with crude protein concentrations ranging from 10.1 to 27.5 g/MJ. Crude protein concentration had no influence on the digestibility of Se in either canned or kibble diets, but a lower Se digestibility was observed in canned compared to kibble diets. However, the biological activity of Se, as measured by whole blood glutathione peroxidase, was higher in dogs fed the canned diets than in dogs fed the kibble diets and decreased with increasing crude protein intake. These results indicate that selenium recommendations in dog foods need to take diet type into account.

In vitro selenium accessibility in pet foods is affected by diet composition and type.

Se bioavailability in commercial pet foods has been shown to be highly variable. The aim of the present study was to identify dietary factors associated with in vitro accessibility of Se (Se Aiv) in pet foods. Se Aiv is defined as the percentage of Se from the diet that is potentially available for absorption after in vitro digestion. Sixty-two diets (dog, n 52; cat, n 10) were in vitro enzymatically digested: fifty-four of them were commercially available (kibble, n 20; pellet, n 8; canned, n 17; raw meat, n 6; steamed meat, n 3) and eight were unprocessed (kibble, n 4; canned, n 4) from the same batch as the corresponding processed diets. The present investigation examined if Se Aiv was affected by diet type, dietary protein, methionine, cysteine, lysine and Se content, DM, organic matter and crude protein (CP) digestibility. Se Aiv differed significantly among diet types (P< 0·001). Canned and steamed meat diets had a lower Se Aiv than pelleted and raw meat diets. Se Aiv correlated positively with CP digestibility in extruded diets (kibbles, n 19; r 0·540, P =0·017) and negatively in canned diets (n 16; r - 0·611, P =0·012). Moreover, the canning process (n 4) decreased Se Aiv (P =0·001), whereas extrusion (n 4) revealed no effect on Se Aiv (P =0·297). These differences in Se Aiv between diet types warrant quantification of diet type effects on in vivo Se bioavailability.

Quantitation of Maillard reaction products in commercially available pet foods.

During processing of pet food, the Maillard reaction occurs, which reduces the bioavailability of essential amino acids such as lysine and results in the formation of advanced Maillard reaction products (MRPs). The aim of this study was to quantitate MRPs (fructoselysine (FL), carboxymethyllysine (CML), hydroxymethylfurfural (HMF)) and the cross-link lysinoalanine (LAL) in commercial pet foods. Sixty-seven extruded, canned, and pelleted dog and cat foods for growth and maintenance were analyzed using UPLC-MS. Canned pet foods contained on average the most FL, CML, and HMF (4534, 37, and 1417 mg/kg dry matter, respectively) followed by pelleted and extruded foods. Average daily intake (mg/kg body weight(0.75)) of HMF is 122 times higher for dogs and 38 times higher for cats than average intake for adult humans. As commercial pet foods are most often the only source of food for dogs and cats, future research focus should be on the bioavailability and long-term health implications of MRP consumption by dogs and cats.

Reactive lysine content in commercially available pet foods.

The Maillard reaction can occur during processing of pet foods. During this reaction, the ε-amino group of lysine reacts with reducing sugars to become unavailable for metabolism. The aim of the present study was to determine the reactive lysine (RL; the remaining available lysine) to total lysine (TL) ratio of commercial pet foods and to evaluate whether RL levels meet minimal lysine requirements (MLR). Sixty-seven extruded, canned and pelleted commercially available dog and cat foods for growth and maintenance were analysed for proximate nutrient composition, TL and RL. RL was expressed on a metabolisable energy basis and compared with the MLR for maintenance and growth. In dog foods, average RL:TL ratios were 0·87 (se 0·02) for extruded, 0·97 (se 0·02) for canned and 0·85 (se 0·01) for pelleted foods, with the lowest ratio of 0·77 in an extruded diet for growing dogs. In extruded and canned cat foods, the average ratio was 0·91 (se 0·02) and 0·90 (se 0·03), respectively, with the lowest ratio being 0·67 in an extruded diet for growing cats. Variation in the RL:TL ratio between and within processing type indicate that ingredients rather than processing might be the key factor influencing RL content in pet foods. Eight dry foods for growing dogs had RL contents between 96 and 138 % of MLR, indicating that RL has to be between 62 and 104 % digestible to meet the MLR. Considering the variability in RL digestibility, these foods could be at risk of not meeting the MLR for growing dogs. Ingredients and pet foods should be characterised with respect to the RL content and digestibility, to avoid limitations in the lysine supply to growing dogs.

The effects of feeding resistant starch on apparent total tract macronutrient digestibility, faecal characteristics and faecal fermentative end-products in healthy adult dogs.

The benefits of whole grain consumption have been studied in human subjects, but little research exists on their effects in dogs. The objective of the present study was to test the effects of resistant starch (RS) in the diet of healthy adult dogs. Twelve adult Miniature Schnauzer dogs (eight males, four females; mean age: 3·3 (1·6) years; mean body weight: 8·4 (1·2) kg; mean body condition score: D/ideal) were randomly allotted to one of three treatment groups, which consisted of different amounts of RS supplied in a biscuit format. Dogs received either 0, 10 or 20 g biscuits per d (estimated to be 0, 2·5 or 5 g RS per d) that were fed within their daily energetic allowance. A balanced Latin square design was used, with each treatment period lasting 21 d (days 0-17 adaptation; days 18-21 fresh and total faecal collection). All dogs were fed the same diet to maintain body weight throughout the study. Dogs fed 5 g RS per d had lower (P = 0·03) fat digestibility than dogs fed 0 gRS per d, but DM, organic matter and crude protein digestibilities were not affected. Faecal fermentative end-products, including SCFA and branched-chain fatty acids, ammonia, phenols and indoles, and microbial populations were not affected. The minor changes observed in the present study suggest the RS doses provided to the dogs were too low. Further work is required to assess the dose of RS required to affect gut health.

The Maillard reaction and pet food processing: effects on nutritive value and pet health.

The Maillard reaction, which can occur during heat processing of pet foods or ingredients, is known to reduce the bioavailability of essential amino acids such as lysine due to the formation of early and advanced Maillard reaction products (MRP) that are unavailable for utilisation by the body. Determination of the difference between total and reactive lysine by chemical methods provides an indication of the amount of early MRP present in foods, feeds and ingredients. Previous research reported that the difference between total and reactive lysine in pet foods can be up to 61.8%, and foods for growing dogs may be at risk of supplying less lysine than the animal may require. The endogenous analogues of advanced MRP, advanced glycation endproducts, have been associated with age-related diseases in humans, such as diabetes and impaired renal function. It is unknown to what extent advanced MRP are present in pet foods, and if dietary MRP can be associated with the development of diseases such as diabetes and impaired renal function in pet animals. Avoidance of ingredients with high levels of MRP and processing conditions known to favour the Maillard reaction may be useful strategies to prevent the formation of MRP in manufactured pet food. Future work should further focus on understanding the effects of ingredient choice and processing conditions on the formation of early and advanced MRP, and possible effects on animal health.

Theoretical evaluation of risk for nutritional deficiency with caloric restriction in dogs.

BACKGROUND: Risk of nutrient deficiency in dogs during caloric restriction is not currently known, while obesity is a growing concern. OBJECTIVES: To determine nutrients that might require further evaluation for the risk of deficiency during caloric restriction. ANIMALS AND METHODS: Five commercially available canine diets, representing a range of caloric density (2900-4240 kcal/kg metabolizable energy), were assessed for potential nutrient inadequacy if fed to a hypothetical overweight dog. Caloric density and typical nutrient analysis for protein, amino acids, fat, fatty acids, minerals, and vitamins were obtained from the manufacturer. Nutrient intake was calculated using ideal body weight for caloric intakes including 87, 79, 70, 61 and 52 kcal/kg(0.75) and compared with National Research Council recommended nutrient allowances (NRC-RA) for ideal weight. RESULTS: No diets were less than NRC-RA when compared to NRC-RA (/1000 kcal). The five evaluated diets varied in terms of which nutrients were less than NRC-RA and the degree of restriction required for this to occur. All diets had at least one essential nutrient less than NRC-RA at 79 kcal/kg(0.75)/day and multiple nutrients less than NRC-RA at 70 kcal/kg(0.75)/day. Choline and selenium were the nutrients most often affected by caloric restriction but others were less than the NRC-RA with caloric restriction. CONCLUSIONS: Further research is needed to determine actual nutrient requirements in overweight dogs, and whether clinical nutrient deficiencies actually arise in vivo. CLINICAL IMPORTANCE: Weight loss plans for overweight dogs (particularly those with very low-energy requirements) should include consideration for nutrient adequacy.

Whole-body amino acid composition of adult fancy ranchu goldfish (Carassius auratus).

Aqua feeds should be formulated to provide complete and balanced nutrition to achieve optimal health and growth in fish, including adequate levels of essential amino acids (EAA). There are few or no data relating to the EAA requirements for ornamental fish species, with the majority of quantitative data for these nutrients being available for commercially farmed fish. The determination of EAA requirements is usually established through dose-response studies, which can be costly and time consuming, especially if determining the requirement for many amino acids (AA). An alternative method for predicting the EAA of fish, which is also relatively fast and inexpensive, is the assessment of whole-body AA composition. A total of eight goldfish with a mean wet weight of 34.2 (SEM 1.4) g were obtained as a result of a routine cull by breeders. The fish were freeze-dried and AA was content analysed by hydrolysis or performic 'acid' oxidation. EAA values ranged between 0.97 (SEM 0.02) for tryptophan and 7.9 (SEM 0.14) for lysine (g/100 g AA). Compositional data were also used to estimate the essential amino acid ratios of these fish. The findings are in agreement with those for juvenile common goldfish, suggesting that there are no differences in whole-body AA composition between juvenile and adult, or fancy and common goldfish. However, these indices do not provide a quantitative total amount of each AA required by the fish, but can be used proportionally to provide guidelines to formulate diets for ornamental species.

Haematology and plasma chemistry of the red top ice blue mbuna cichlid (Metriaclima greshakei).

Clinical haematology and blood plasma chemistry can be used as a valuable tool to provide substantial diagnostic information for fish. A wide range of parameters can be used to assess nutritional status, digestive function, disease identification, routine metabolic levels, general physiological status and even the assessment and management of wild fish populations. However to evaluate such data accurately, baseline reference intervals for each measurable parameter must be established for the species of fish in question. Baseline data for ornamental fish species are limited, as research is more commonly conducted using commercially cultured fish. Blood samples were collected from sixteen red top ice blue cichlids (Metriaclima greshakei), an ornamental freshwater fish, to describe a range of haematology and plasma chemistry parameters. Since this cichlid is fairly large in comparison with most tropical ornamental fish, two independent blood samples were taken to assess a large range of parameters. No significant differences were noted between sample periods for any parameter. Values obtained for a large number of parameters were similar to those established for other closely related fish species such as tilapia (Oreochromis spp.). In addition to reporting the first set of blood values for M. Greshakei, to our knowledge, this study highlights the possibility of using previously established data for cultured cichlid species in studies with ornamental cichlid fish.

Effects of neutering on food intake, body weight and body composition in growing female kittens.

To understand the effects of neutering on food intake, body weight (BW) and body composition in kittens, data from an unrelated study were subjected to post hoc analysis. A total of twelve pairs of 11-week-old female littermates were randomly assigned to either a neutered group (neutered at 19 weeks old) or an entire group (kept entire) and offered free access to a dry diet until the age of 1 year. Neutered kittens exhibited increased food intake and increased BW after neutering (both P < 0.00 001). Food intake (per kg BW) peaked 10 weeks after neutering; the mean intake of neutered kittens was 17 (95 % CI 8, 27) % more than entire littermates (P = 0.00 014). The intake was then reduced until there was no significant difference between the groups 18 weeks post-neutering. By 52 weeks of age, the neutered kittens were 24 (95 % CI 11, 39) % heavier than entire littermates (P < 0.0001) with a body condition score (BCS) 16.6 (95 % CI 0.9, 34.8) % higher (P = 0.0028). Neutered kittens continued to grow significantly fatter after neutering (all P < 0.0014), while entire kittens showed no significant change after 18 weeks of age. As neutered kittens consumed similar amounts of energy to their entire littermates from 18 weeks post-neutering, while their BW, BCS and percentage fat continued to increase, we suggest that neutered kittens have a reduced metabolisable energy requirement, and should therefore be fed to maintain an ideal BCS rather than ad libitum. Moreover, to maintain an ideal BCS, entire kittens consumed 93 (95 % CI 87, 100) % of their theoretical intake at 26 weeks of age, and 79 (95 % CI 72, 87) % at 52 weeks of age, suggesting that the current energy recommendation is inappropriate for these kittens.

Oxidative profile varies with personality in European greenfinches.

Where behavioural responses differ consistently between individuals, this is termed 'personality'. There is the suggestion, but with little supporting data, that personality traits reflect underlying variation in physiology. Here, we tested whether greenfinches Carduelis chloris differing in personality traits differed in various plasma indices of oxidative profile: antioxidant capacity (OXY), pro-oxidant status (reactive oxygen metabolites, ROMs), oxidative stress (OS) and an end-product of oxidative damage: malondialdehyde (MDA). We measured two personality traits: neophobia (latency to approach food near novel objects) and object exploration (latency to approach novel objects). These traits were uncorrelated. ROMs, OXY, OS and MDA were also uncorrelated with each other. Highly neophobic birds had lower OXY, higher ROMs and higher OS than less neophobic birds. Fast exploring birds had higher OXY than slow explorers, but did not differ in ROMs or OS. Variation in MDA was described by a quadratic relationship with neophobia: birds with extremely high or low neophobia had lower MDA than birds with intermediate neophobia, despite highly neophobic birds exhibiting lower OS than intermediately neophobic birds. Additively in that model, fast explorers had lower MDA than slower explorers. To conclude: first, personality types can differ in oxidative profile. Second, although physiological differences (e.g. hormonal stress responsiveness) between personality types generally range along a linear continuum, physiological costs may not. Finally, relationships with oxidative profile differed between neophobia and object exploration. Understanding how oxidative profile and thus physiological costs vary within and between personality traits may explain how differences in personality traits can predict fitness.

Colour cues or spatial cues? Context-dependent preferences in the European greenfinch (Carduelis chloris).

Using featural cues such as colour to identify ephemeral food can increase foraging efficiency. Featural cues may change over time however; therefore, animals should use spatial cues to relocate food that occurs in a temporally stable position. We tested this hypothesis by measuring the cue preferences of captive greenfinches Carduelis chloris when relocating food hidden in a foraging tray. In these standardised associative learning trials, greenfinches favoured colour cues when returning to a foraging context that they had encountered before only once ("one-trial test") but switched to spatial cues when they had encountered that scenario on ten previous occasions ("repeated-trial test"). We suggest that repeated encounters generated a context in which individuals had a prior expectation of temporal stability, and hence context-dependent cue selection. Next, we trained birds to find food in the absence of colour cues but tested them in the presence of visual distracters. Birds were able to learn spatial cues after one encounter, but only when visual distracters were identical in colouration. When a colourful distracter was present in the test phase, cue selection was random. Unlike the first one-trial test, birds were not biased towards this colourful visual distracter. Together, these results suggest that greenfinches are able to learn both cue types, colour cue biases represent learning, not simply distraction, and spatial cues are favoured over colour cues only in temporally stable contexts.

Dietary antioxidants, lipid peroxidation and plumage colouration in nestling blue tits Cyanistes caeruleus.

Carotenoid pigments are responsible for many of the red, yellow and orange plumage and integument traits seen in birds. One idea suggests that since carotenoids can act as antioxidants, carotenoid-mediated colouration may reveal an individual's ability to resist oxidative damage. In fact, there is currently very little information on the effects of most dietary-acquired antioxidants on oxidative stress in wild birds. Here, we assessed the impacts on oxidative damage, plasma antioxidants, growth and plumage colouration after supplementing nestling blue tits Cyanistes caeruleus with one of three diets; control, carotenoid treatment or α-tocopherol treatment. Oxidative damage was assessed by HPLC analysis of plasma levels of malondialdehyde (MDA), a by-product of lipid peroxidation. Contrary to predictions, we found no differences in oxidative damage, plumage colouration or growth rate between treatment groups. Although plasma lutein concentrations were significantly raised in carotenoid-fed chicks, α-tocopherol treatment had no effect on concentrations of plasma α-tocopherol compared with controls. Interestingly, we found that faster growing chicks had higher levels of oxidative damage than slower growing birds, independent of treatment, body mass and condition at fledging. Moreover, the chromatic signal of the chest plumage of birds was positively correlated with levels of MDA but not plasma antioxidant concentrations: more colourful nestlings had higher oxidative damage than less colourful individuals. Thus, increased carotenoid-mediated plumage does not reveal resistance to oxidative damage for nestling blue tits, but may indicate costs paid, in terms of oxidative damage. Our results indicate that the trade-offs between competing physiological systems for dietary antioxidants are likely to be complex in rapidly developing birds. Moreover, interpreting the biological relevance of different biomarkers of antioxidant status represents a challenge for evolutionary ecology.

Constitutive expression of EIL-like transcription factor partially restores ripening in the ethylene-insensitive Nr tomato mutant.

Climacteric fruit ripening is regulated by the phytohormone ethylene. ETHYLENE-INSENSITIVE3 (EIN3) is a transcription factor that functions downstream from the ethylene receptors in the Arabidopsis ethylene signal transduction pathway. Three homologues of the Arabidopsis EIN3 gene have been identified in tomato, Lycopersicon esculentum, EIN3-like or LeEIL, LeEIL1, LeEIL2, and LeEIL3. These transcription factors have been proposed to be functionally redundant positive regulators of multiple ethylene responses. In order to test the role of such factors in the ethylene signal transduction pathway during ripening, EIL1 fused to green fluorescent protein (GFP) has been over-expressed in the ethylene-insensitive non-ripening Nr mutant of tomato. Increased levels of LeEIL1 compensated for the normally reduced levels of LeEIL1 in the Nr mutant, and transgenic Nr plants that exhibited high-level constitutive expression of LeEIL1GFP phenotypically resembled wild-type plants, the fruit ripened and the leaves exhibited epinasty, unlike Nr plants. The EIL1GFP fusion protein was located in the cell nuclei of ripe tomato fruit. The mRNA profile of these plants showed that the expression of certain ethylene-dependent ripening genes was up-regulated, including polygalacturonase and TOMLOX B. However, not all ripening genes and ethylene responses, such as seedling triple response, were restored. These results demonstrate that expressing candidate genes in the Nr ethylene-insensitive background is a valuable general approach for testing the role of putative downstream components in the ethylene-signalling pathway.

Ethylene biosynthesis and action in tomato: a model for climacteric fruit ripening.

Elucidating the mechanisms involved in ripening of climacteric fruit and the role that ethylene plays in the process are key to understanding fruit production and quality. In this review, which is based largely on research in tomato, particular attention is paid to the role of specific isoforms of ACC synthase and ACC oxidase in controlling ethylene synthesis during the initiation and subsequent autocatalytic phase of ethylene production during ripening. Recent information on the structure and role of six different putative ethylene receptors in tomato is discussed, including evidence supporting the receptor inhibition model for ripening, possible differences in histidine kinase activity between receptors, and the importance of receptor LeETR4 in ripening. A number of ethylene-regulated ripening-related genes are discussed, including those involved in ethylene synthesis, fruit texture, and aroma volatile production, as well as experiments designed to elucidate the ethylene signalling pathway from receptor through intermediate components similar to those found in Arabidopsis, leading to transcription factors predicted to control the expression of ethylene-regulated genes.

Characterization and modelling of the hydrophobic domain of a sunflower oleosin.

The oleosins are a group of hydrophobic proteins present on the surface of oil bodies in seeds, where they are thought to prevent coalescence. They contain a central hydrophobic domain of 68-74 residues that is thought to form a loop into the triacylglycerol matrix of the oil body, but the conformation adopted by this sequence is uncertain. We have therefore expressed an oleosin cDNA from sunflower (Helianthus annuus L.) in Escherichia coli as a fusion with maltose-binding protein (MBP) and isolated a peptide corresponding to the hydrophobic domain by sequential digestion with factor Xa (to remove the MBP) followed by trypsin and Staphylococcus V8 protease to remove the N- and C-terminal domains of the oleosin. Circular dichroism spectroscopy of the peptide in two solvent systems chosen to mimic the environment within the oil body (trifluoroethanol and SDS) demonstrated high proportions of alpha-helical structure, with no beta-sheet. A model was therefore developed in which the domain forms an alpha-helical hairpin structure, the two helices being separated by a turn region. We consider that this model is consistent with our current knowledge of oleosin structure and properties.