Energetic efficiency of rats fed low or high protein diets and grown at controlled rates from 80 to 205 grams.

Energetic efficiency of protein and lipid deposition was estimated based on the data from 53 rats fed purified diets. Intercepts of equations relating energy gain to metabolizable energy intake were different (P less than 0.002) for rats fed diets that contained 10 and 20% casein, so that metabolizable energy for maintenance was 118 and 108 kJ/day, respectively. Surprisingly, in view of the supposedly greater efficiency of lipid deposition, energetic efficiency above maintenance was constant at 0.38 +/- 0.02. Part of the reason is that composition of body gain was much less rigidly tied to daily energy intake--even across the wide range of data in this experiment--than is necessary to quantify reliably such an effect. Two methods of quantifying partial energetic efficiencies of protein and lipid deposition gave results that were comparable to previous estimates of about one-third and two-thirds, respectively. One of the methods used a more biological model but failed to fit data for rats fed the 10% casein diet. Because traditional statistical methods are unlikely to be extended much further to account for the many unsolved problems associated with estimating partial efficiencies, systems based at tissue and cellular levels are necessary to model detailed differences in energy utilization.

Use of quantitative testicular histology to assess the effect of dibromochloropropane (DBCP) on reproduction in rabbits.

Dibromochloropropane (DBCP) was administered orally to 36 sexually mature male Dutch Belted rabbits assigned at random to one of six groups to receive 0, 0.94, 1.88, 3.75, 7.5, or 15.0 mg DBCP per kilogram of body weight daily 5 days per week during a 69-day treatment period. Animals were euthanized and necropsied on Day 70. Body weights and weights of the kidneys, liver, epididymides, and accessory sex glands were not influenced by DBCP treatment. The highest dosage reduced mean paired testes weight to 45% of control values (p less than 0.01). Mean seminiferous tubular diameter was reduced by 15 and 29% with the two highest dosages of DBCP, respectively (p less than 0.01), and the percentage of seminiferous tubules containing elongating and round spermatids, as the most advanced cell type present, was decreased (p less than 0.01). The number of leptotene primary spermatocytes per Sertoli cell, and the numbers of spermatogonia, young and old primary spermatocytes, and Step 1 spermatids per Stage I seminiferous tubular cross section likewise indicated a general depression (p less than 0.01) of spermatogenesis. Based upon the number of Step 1 spermatids per cross section at Day 70, production of sperm at this time by rabbits receiving the highest dose of DBCP was estimated to be less than one-fourth of control values. No significant effect (p greater than 0.05) of 0.94 mg DBCP/kg on any parameters was found, so this could be considered to be the no effect dose. However, the regressions and mean values are interpreted to indicate that the no effect level of DBCP may be less than 0.94 mg DBCP/kg of body weight. It is suggested that the most sensitive tests described here be included in future screening tests for potential effects of agents on male reproduction.

The measurement of liquid and solid digesta retention in ruminants, equines and rabbits given timothy (Phleum pratense) hay.

1. Digesta passage and retention were measured in heifers, sheep, goats, equines and rabbits of varying body-weights when given timothy (Phleum pratense) hay. 2. Two passage markers were compared, cobalt (III) ethylene diamine tetraacetate (CoEDTA) and chromiummordanted timothy fibre for liquid and solid phase respectively. Both markers were injected into the rumen of the ruminants and into the caecum of the equines and rabbits. 3. In ruminants, two different sets of rate constants (k1 and k2) were derived from a two-pool model for marker passage, using a graphical approach and a computer-based non-linear least-squares curve-fitting technique. 4. Retention times, due to unidirectional flow through the gastrointestinal tract (transit time) and due to pool effects (mean retention time, MRT), were calculated. 5. Curve fitting was only successful for the excretion of liquids in ruminants. The two-pool model was not applicable to the passage of solids. 6. Apparent retention of liquid was always shorter than for solids in all species, except in rabbits. However, absorption of CoEDTA was too large in the rabbits to determine liquid retention accurately. Times for first appearance of the two markers were similar within animal groups. 7. MRT values were lowest in the rabbit, intermediate in equines and high in the ruminants. The MRT values (h) of solids and liquids respectively were: large heifers 65, 18; small heifers 48, 20; goats 41, 28; sheep 57, 26; equines 23, 18; rabbits 5.3, not determined. 8. Liquid retention seemed to decrease somewhat with increasing body-weight in the ruminants. Solids retention decreased with decreasing body-weight in the ruminants, but sheep had longer retention times than goats of similar size. Equines exhibited large individual variation in retention of the liquid or solid markers, seemingly unrelated to size. No effect of size was seen in the retention of solids in the rabbits.