Evidence of vitamin D synthesis in insects exposed to UVb light.

Vertebrates obtain the prohormone vitamin D primarily by endogenous cutaneous synthesis under ultraviolet b (UVb) exposure. To date, endogenous synthesis of vitamin D in insects has never been investigated. In an initial experiment, we exposed four insect species which differ in ecology and morphology (migratory locusts, house crickets, yellow mealworms and black soldier fly larvae (BSFL)) to a low irradiance UVb source. In a second experiment we exposed these species to a higher UV irradiance, and in a third we tested the effect of exposure duration on vitamin D concentrations in yellow mealworms. Low irradiance UVb tended to increase vitamin D3 levels in house crickets, vitamin D2 levels in BSFL and vitamin D2 and D3 in yellow mealworms. Higher UVb irradiance increased vitamin D3 levels in all species but BSFL. Both BSFL and migratory locusts had increased vitamin D2 levels. Longer UVb exposure of yellow mealworms increased vitamin D2 and increased vitamin D3 until a plateau was reached at 6400 IU/kg. This study shows that insects can synthesize vitamin D de novo and that the amounts depend on UVb irradiance and exposure duration.

Efficiency of lysine or threonine retention in growing rats fed diets limiting in either lysine or threonine.

Over a 21-d experiment, the efficiency of lysine and threonine retention was determined in 80 male Sprague-Dawley rats (65.9 +/- 0.3 g, means +/- SE) fed purified diets containing an amino acid mix limiting in either lysine or threonine. With additional increments of the first limiting amino acid, lysine concentration in total body protein (g/16 g N) increased (P < 0.01) in rats fed lysine-limiting diets but, when fed threonine-limiting diets, lysine concentration in body protein first increased and then decreased (P < 0.01). As increments of the first limiting amino acid were added, the threonine concentration in total body protein increased then decreased when both lysine- (P < 0.01) and threonine- (P < 0.06) limiting diets were fed. Lysine and threonine retention were calculated based on comparative slaughter. Sixteen rats were killed on d 0 to estimate the grams of amino acid in the body. Retention responses were analyzed using a logistic equation in which lysine or threonine intake was used to predict retention. The maximum marginal efficiency (dr/dI, retention/intake) was observed at <40% of maximum retention. For lysine retention, it was 81% when lysine was limiting and 70% when threonine was limiting. For threonine retention, it was 58% when threonine was limiting and 49% when lysine was limiting. The maximum cumulative efficiency (retention adjusted for maintenance relative to cumulative intake) for lysine retention was 62% when lysine was limiting or 58% when threonine was limiting. For threonine retention, it was 51% when threonine was limiting and 35% when lysine was limiting. Thus, amino acid concentration in body protein is not constant, and amino acids are used with higher efficiency when first limiting.

Energy requirements of adult female beagles.

The energy requirements of 19 intact adult female beagles were determined over a 60-wk period. The initial age of the dogs averaged 6.5 y (range 0.8-13.4) and the initial weight averaged 11.0 kg (range 8.7-13.7). Dogs were housed in groups of four in heated indoor-outdoor kennel runs. Dogs were fed daily a commercial dry dog food that contained 13.8 kJ/g. The amount offered was adjusted to maintain body weight. Daily energy intake ranged from 2227 to 3667 kJ/dog, with an average of 3061 kJ/dog. When adjusted for differences in body weight, average daily energy intake ranged from 482.6 to 803.1 kJ/kg body weight0.67 with a mean of 617.5 kJ/kg0.67. Energy intake (kJ/kg body weight0.67) declined with age and could be described by the nonlinear equation Y = 753 x age-0.1321; r = -0.802. When these data are combined with an earlier study, the energy intake (kJ/kg body weight0.67) of this group of 36 dogs could be described by the equation Y = 767 x age-0.1408; r = -0.777. These data demonstrate that canine energy requirements decline with age and that the National Research Council recommendations of 552 kJ/kg body weight0.75 overestimates the requirements of adult dogs 3 y of age and older.

Lipid metabolite responses to diet and training in sled dogs.

Two groups of Alaskan Huskies were fed either a high fat (HFD) or a high carbohydrate diet 4 wk before and during an 8-wk conditioning program. Aerobic bouts of exercise were performed before and after conditioning. Blood samples taken before and after each exercise test were analyzed for serum concentrations of free fatty acids (FFA), triglycerides (TG), vitamin E, glucose and serum lipase activity. The post-exercise FFA and TG values were greater in the HFD group both before and after training. There were no significant differences in plasma vitamin E or in serum lipase activity between diet groups. It is concluded that after an adequate period of adaptation, prolonged feeding of a HFD safely enhances the availability of local and peripheral lipid stores during exercise. Although the elevated levels of FFA and TG associated with HFD suggest enhanced potential for performance, further study of more prolonged and possibly more intense exercise is necessary to confirm this theory.

Use of a four-parameter logistic equation to evaluate the response of growing rats to ten levels of each indispensable amino acid.

Over a 21-d period, 400 [four rats/level, 10 levels/amino acid, 10 indispensable amino acids (IAA)] male weanling rats (65.9 +/- 0.3 g; mean +/- SEM) were fed diets with one of 10 levels of each of the 10 IAA. In addition, four rats were fed an amino acid-free diet and 16 rats were killed on d 0 for individual body composition. With the exception of the limiting amino acid (LAA), an increment (35% of the requirement) of each IAA was added to the mixture to insure that the LAA remained first limiting. A four-parameter logistic equation was used to describe the nitrogen and weight gain responses of rats to each IAA. Conservation of nitrogen, defined as a predicted y-intercept value greater than the value observed for rats fed an amino acid-free diet (-0.304 +/- 0.023 g N/21 d), was seen when diets devoid of total aromatic amino acids or lysine (-0.062 +/- 0.013 g N/21 d) or histidine, leucine, tryptophan or valine (-0.115 +/- 0.011 g N/21 d) were fed. When total sulfur amino acids were first limiting, diminishing returns (a decrease in the first derivative) was evident from zero intake to Rmax (estimated asymptotic response maximum). In contrast, when other IAA were limiting, diminishing returns were apparent after approximately the first third of the full response. Based on the first derivative of the response curves, the efficiency of nitrogen gain depends on the LAA. The dietary LAA would be expected to influence the shape of the response curve and therefore influence the quantitative aspects of diminishing returns.

Evaluation of the energy requirements of adult kennel dogs.

The objective of this experiment was to compare the energy requirements of healthy adult kennel dogs to those recommended by the National Research Council (NRC). The energy requirements of six beagles, six Siberian huskies and six Labrador retrievers were determined over a 54-wk period. Dogs were housed in groups of three in heated indoor-outdoor runs and fed a complete and balanced commercial dry dog food. Beagles had an average daily energy intake of 3414 kJ/dog with monthly averages ranging from 3146 to 3740 kJ/dog. Siberian huskies had an average daily energy intake of 5021 kJ/dog. Average monthly energy intakes ranged from 4715 to 5238 kJ/dog. Labrador retrievers had an average daily intake of 5611 kJ/dog with monthly averages ranging from 5063 to 6623 kJ/dog. Seasonal variation appeared to affect the breeds differently, with long-haired Siberian huskies showing less seasonal variation than the shorter-haired breeds. For all dogs energy intake (kJ/kg body weight 0.75) declined with age. The energy intake of each group of dogs was considerably below that recommended by the NRC. The reason for this discrepancy is unknown, although these data suggest that environmental conditions, breed and/or age play an important role.

Use of a four-parameter logistic model to evaluate the quality of the protein from three insect species when fed to rats.

The quality of three insect protein sources [Mormon cricket meal (MCM), house cricket meal (HCM) and Eastern tent caterpillar meal (TCM)] was evaluated relative to that of lactalbumin (LA) and soy protein (SP) by using both amino acid analysis and a rat bioassay. The amino acid pattern of the three insect meals indicated that methionine should be the first limiting amino acid for growing rats. In the rat bioassay, weanling Sprague-Dawley rats were fed graded levels of the five proteins in purified diets and the response (weight or nitrogen gain) evaluated as a function of nitrogen intake. The individual nitrogen intake-animal response results could be described by a series of curves using a four-parameter logistic model. The use of parameter sharing permitted the full range of responses to be described so that statistical differences between the dose-response curves could be identified. When used for either weight maintenance, nitrogen equilibrium, maximum weight gain or maximum nitrogen retention, the five protein sources could be ranked in the following order: LA greater than HCM greater than MCM = SP greater than TCM. Relative to lactalbumin, the value of all four protein sources decreased with increasing nitrogen intake. The low values obtained for TCM may have been related to factors other than protein quality. The results of this study indicate that some insect proteins are equivalent or superior to soy protein as a source of amino acids for growing rats.

Use of simultaneous curve fitting and a four-parameter logistic model to evaluate the nutritional quality of protein sources at growth rates of rats from maintenance to maximum gain.

A four-parameter logistic model was used to describe the dose-response relationship of rats fed diets containing 12 levels of casein, peanut meal or wheat gluten. The model was capable of accurately describing the entire response curve of rats fed diets containing each of the three protein sources. Incorporation of a technique known as parameter sharing into the curve-fitting process facilitated convergence of the parameter estimates for b (the response of rats fed a protein-free diet) and Rmax (maximum response) for all curves when compared with the values observed experimentally. Parameter sharing also provided a method by which the curves could be differentiated on a statistical basis. These data indicate that the relative value of a protein source is dependent on the concentration of the protein in the diet. The application of nonlinear models combined with parameter sharing provides a technique by which protein values can be evaluated at levels of animal response from maintenance to maximum growth.

Use of a four-parameter logistic model to evaluate the protein quality of mixtures of Mormon cricket meal and corn gluten meal in rats.

Weanling Sprague-Dawley rats were fed diets containing corn gluten meal (CGM), Mormon cricket meal (MCM), MCM supplemented with methionine (MCM + Met) or CGM-MCM mixtures as the sole source of dietary protein in purified diets. Animal response (weight or nitrogen gain) was analyzed as a function of nitrogen intake and described by a series of curves using a four-parameter logistic model. Parameter sharing was used to differentiate statistically between the response curves. When used for maximum nitrogen retention the quality of the protein sources could be ranked as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. When used for maximum weight gain the ranking was as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. The rankings of the protein sources when used for weight maintenance or nitrogen equilibrium were similar to those seen for maximum weight or nitrogen gain except for the ranking of MCM, which changed from fifth to first. These results show MCM to be a good quality protein source and that methionine is the first limiting amino acid when used for growth but not for maintenance. The shape of the response curves was dependent upon the response criteria as well as the source of dietary protein. The factors that may affect the shape of the dose-response curves and the application of nonlinear models toward animal feeding programs are discussed.

The contributions of larval growth and pupal duration to protandry in the black swallowtail butterfly, Papilio polyxenes.

Shorter male larval and pupal durations were sufficient to produce the protandrous emergence pattern of the black swallowtail butterfly. In 9 broods observed under natural conditions, the first male was seen 7.1±6.5 days before the first female, although the peak of captures relative to the first capture was similar in both sexes. The field data supported only weakly the predictions of the Wiklund-Fagerstrom model for protandry. Some prereproductive period was necessary for males, and they were limited in how frequently they could mate. A third of the females mated more than once.Males were significantly smaller in size and weight than females in both diapausing and non-diapausing broods. Feeding experiments indicated that male larvae ate less and converted their food into biomass more efficiently than females. Female pupae contained higher proportions of fat and protein than male pupae. Differential body composition may be involved in sexual dimorphism differences in both larval and pual developmental rates. Thus, in addition to size, chemical differences in composition or metabolism may contribute to the observed natural protandry.