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Limits to sustained energy intake : I. Lactation in the laboratory mouse MUS MUSCULUS

M. S. Johnson, S. C. Thomson and J. R. Speakman^*

Aberdeen Centre for Energy Regulation and Obesity (ACERO), Department of Zoology, University of Aberdeen, Aberdeen AB24 2TZ, Scotland, UK

View larger version (15K): [in a new window]   Fig. 1. (A) Mean female body mass and (B) mean daily food intake of female mice throughout pregnancy and lactation in mice raising natural litters (filled symbols, N=71) and manipulated litters (open symbols, N=37). Error bars represent ±1 S.E.M. Parturition is day 0.

View larger version (15K): [in a new window]   Fig. 2. Histogram of the litter sizes at weaning (day 18) of natural (filled columns) and manipulated (open columns) litters.

View larger version (16K): [in a new window]   Fig. 3. The difference (observed minus expected) in food intake of mice raising manipulated litters in relation to the numbers of pups added to or subtracted from the natural litter sizes. The line represents the relationship fitted to the data for subtractions (y=0.66x-0.12). There was no significant relationship for additions.

View larger version (14K): [in a new window]   Fig. 4. Maternal asymptotic daily food intake per pup (food intake averaged over days 13–16 of lactation) in relation to litter size in females raising natural (filled symbols) and manipulated (open symbols) litters. Each point is one litter. The relationship is described by y=-0.18x+4.18 for the control females and by y=-0.19x+4.41 for those with manipulated litters.

View larger version (15K): [in a new window]   Fig. 5. Mean individual pup mass as a function of litter size in natural (filled symbols) and manipulated (open symbols) litters. The least-squares regression lines for the two sets of data are also shown. The relationships are described by the equations: y=-0.54x+13.97 for the natural, control litters and y=-0.59x +16.3 for the manipulated litters.

View larger version (10K): [in a new window]   Fig. 6. (A) Daily energy expenditure (DEE) of mouse litters as a function of litter mass. The least-squares relationship explained 45.5% of the variation in DEE and was described by y=1.6x -38.0. (B) Predicted DEE and (C) predicted total energy requirement (TER) for natural litters in late lactation. The relationships between predicted DEE (B) and predicted TER (C) and litter size were described by y=3.77x+38.9 and y=3.15x +74.03 respectively.

View larger version (8K): [in a new window]   Fig. 7. Maternal milk production in relation to (A) litter mass and (B) litter size. The line represents the best-fit curvilinear relationship between milk production and litter mass, described by y=1.91e0.025x.

View larger version (9K): [in a new window]   Fig. 8. (A) Relationship between litter mass and the percentage of fat in the milk. (B) Energy content of milk in relation to the volume of milk produced. Lines in both cases are the least-squares regressions and are described by (A) y=-0.24x+45.95 and (B) y=-3.03x+50.59.