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Growth and development of rats artificially reared on rats' milk or rats' milk/milk-substitute combinations
Insights
Artificial rearing (AR) of rat pups using gastric infusion proved successful, with optimized milk substitute regimens preventing bloat and supporting growth comparable to mother-reared (MR) pups. Heart weight was a notable exception, consistently lower in AR groups.
Area of Science:
- Animal Science
- Developmental Biology
- Comparative Physiology
Background:
- Artificial rearing (AR) is crucial for studying developmental processes without maternal influence.
- Traditional AR methods often face challenges like 'bloat' and suboptimal growth.
- Developing effective AR protocols is essential for reliable animal research.
Purpose of the Study:
- To evaluate the efficacy of artificial rearing (AR) in rat pups using intermittent gastric infusion.
- To compare growth parameters of artificially reared (AR) rat pups with mother-reared (MR) controls.
- To investigate the impact of different feeding regimens, including milk substitutes, on AR pup development.
Main Methods:
- Rat pups were artificially reared (AR) from post-natal day 5 via gastric infusion.
- Control groups were mother-reared (MR).
- Experiments involved using only expressed rat milk and later, milk substitutes, with varying transition timings.
Main Results:
- Early AR with insufficient rat milk led to reduced growth but normal organ weights relative to body weight.
- Later AR with adequate milk or milk substitutes supported growth comparable to MR pups.
- No 'bloat' (gastrointestinal distention) occurred with optimized milk substitute regimens.
- Lower heart weight was observed in all AR groups; adrenal weight was lower in one AR group.
- Stomach, caecum weights, and small intestine length were increased in AR pups.
Conclusions:
- Artificial rearing of rat pups is feasible using gastric infusion and optimized milk substitute protocols.
- Successful AR requires careful management of nutrition and feeding schedules to avoid complications like bloat.
- While overall growth can be normalized, specific organ weights (e.g., heart) may differ between AR and MR rats, requiring consideration in research.
Abstract:
Rat pups were artificially reared (AR) from post-natal day 5 by intermittent gastric infusion. Mother-reared (MR) siblings served as controls. Fourteen measures of body and organ growth were taken at the end of each experiment. In Expt 1, two batches of pups were given rats' milk only, obtained by manual expression from anaesthetized dams. The first batch, reared to 12 d, grew less well than the MR group, probably because they received too little milk. However, relative to body-weight, organ weights were as great or greater than those of MR pups, except for heart weight. The second batch, given more milk and reared to 20 d, showed no deficits in organ or body-weights, but excesses in kidney, gastrocnemius muscle, stomach and caecum weights. There were no losses from 'bloat', a condition of gastrointestinal distention often encountered in artificial rearing with milk substitutes. Obtaining rats' milk is extremely labour-intensive and in Expt 2, more economical regimens were devised in which pups were started off on expressed rats' milk and then changed to a milk substitute resembling rats' milk in composition, either abruptly at 12 d or gradually between 8 and 17 d. Both regimens were successful, in that there were no losses from bloat and most measures of growth were at least as great as in the MR group. Only heart weight was lower in both AR groups and adrenal weight in the abruptly changed AR group. The weights of the stomach and caecum and the length of the small intestine were all high in both AR groups.(ABSTRACT TRUNCATED AT 250 WORDS)