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First published online October 27, 2003

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Limits to sustained energy intake VI. Energetics of lactation in laboratory mice at thermoneutrality

E. Król^1,* and J. R. Speakman^1,2

¹ Aberdeen Centre for Energy Regulation and Obesity (ACERO), School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK
² ACERO, Division of Appetite and Energy Balance, Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK

View larger version (19K): [in a new window]   Fig. 1. Mean body mass (A) and food intake (B) of reproductive female mice (filled circles; N=12) throughout pregnancy and lactation at 30°C. Parturition is day 0. Data for non-reproductive females (open circles, N=28) are also shown. Error bars indicate 1 S.D.

View larger version (15K): [in a new window]   Fig. 2. Food intake as a function of body mass for lactating (filled circles, y=-2.11+0.36x; N=67) and non-reproductive (open circles, y=-0.15+0.11x; N=28) female mice at 30°C. Food intake is the mean value for days 9-13 of lactation (reproductive females) or the mean value for 8 consecutive days (non-reproductive females). Body masses are the mean values for the same days as for food intake.

View larger version (10K): [in a new window]   Fig. 3. Asymptotic food intake of lactating female mice exposed to 30°C (N=67) as a function of litter size. Asymptotic food intake is the mean value for days 9-13 of lactation. Litter size is that on day 14 of lactation. Females with 6 pups ate more food than those with 1-3 pups. For litter size increasing from 6 to 15, no further increase in asymptotic food intake was observed (for statistical details, see Results).

View larger version (15K): [in a new window]   Fig. 4. Litter mass (A) and pup body mass (B) as a function of litter size for mice at 30°C raising 6-15 pups (filled circles; N=61). Data for mice raising 1-5 pups are also shown (open circles; N=6). All parameters are those on day 14 of lactation. Pup body mass is the litter mass divided by litter size. The relationships are described by y=39.58+1.89x (A) and y=10.48-0.44x (B).

View larger version (17K): [in a new window]   Fig. 5. Litter size (A), litter mass (B) and pup body mass (C) as a function of maternal body mass for mice at 30°C raising 6-15 pups (filled circles; N=61). Data for mice raising 1-5 pups are also shown (open circles; N=6). Litter size, litter mass and pup body mass are those on day 14 of lactation. Pup body mass is the litter mass divided by litter size. Maternal body mass is the mean value for days 9-13 of lactation. The relationships are described by y=6.40+1.33x (B) and y=-0.31+0.15x (C).

View larger version (16K): [in a new window]   Fig. 6. Litter mass (A) and pup body mass (B) as a function of asymptotic food intake for mice at 30°C raising 6-15 pups (filled circles; N=61). Data for mice raising 1-5 pups are also shown (open circles; N=6). Litter mass and pup body mass refer to day 14 of lactation. Pup body mass is the litter mass divided by litter size. Asymptotic food intake is the mean value for days 9-13 of lactation. The relationships are described by y=4.58+4.33x (A) and y=1.25+0.36x (B).

View larger version (16K): [in a new window]   Fig. 7. Residual litter mass (A) and residual pup body mass (B) as a function of residual asymptotic food intake for mice at 30°C raising 6-15 pups (N=61). Litter mass (g) and pup body mass (g) refer to day 14 of lactation. Pup body mass is the litter mass divided by litter size. Asymptotic food intake (g day-1) is the mean value for days 9-13 of lactation. Both correlations (A and B) are significant (for statistical details, see Results).

View larger version (12K): [in a new window]   Fig. 8. Maternal body mass on day 0 of lactation (A), increase in maternal body mass over days 0-13 of lactation (B), maternal body mass on day 13 of lactation (C) and maternal food intake on day 13 of lactation (D) in mice at hot (30°C), warm (21°C) and cold (8°C) temperatures. The cold group was transferred from 21°C to 8°C on day 10 of lactation. Bars are means + 1 S.D. (N as in text). Different letters above bars indicate significant differences between the temperatures (P<0.05), as assessed by ANOVA followed by Tukey pairwise comparisons.

View larger version (12K): [in a new window]   Fig. 9. Litter size (A), pup body mass (B), litter mass (C) and litter mass increase between days 13 and 14 of lactation (D) in mice lactating at hot (30°C), warm (21°C) and cold (8°C) temperatures. Litter size, pup body mass and litter mass refer to day 14 of lactation. Bars are means + 1 S.D. (N as in text). Different letters above bars indicate significant differences between the temperatures (P<0.05), as assessed by ANOVA followed by Tukey pairwise comparisons.