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Limits to sustained energy intake : III. Effects of concurrent pregnancy and lactation in 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



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  		Fig. 1. Mean daily food intake of the control (filled circles) and experimental (open circles) mice throughout the first lactation (A), second pregnancy (B) and second lactation (C). In the experimental animals, the second pregnancy occurred concurrent with the first lactation; in the control animals, the second pregnancy occurred after completion of the first lactation. Values are means ± S.E.M. N=19 for the controls and N=24 for the experimental mice in A, and N=21 for experimental females in C. In B, the sample size for the experimental mice varied over time depending on when pregnancy was initiated relative to when the male was removed. Sample sizes for sequential points are 1, 1, 1, 3, 5, 8, 11, 16, 19, 21 and 21.

 


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  		Fig. 2. Comparison of the mean pup mass of the litters of the control females (filled circles, N=19) and the experimental females (open circles, N=24 for lactation 1 and N=21 for lactation 2) during the first (A) and second (B) lactation. Values are means ± S.E.M.

 


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  		Fig. 3. Mean maternal resting metabolic rate (RMR, kJday-1) prior to breeding, at the peak of the first lactation and at the peak of the second lactation for the control (filled columns, N=19) and experimental (open columns, N=21) females. Values are means ± S.E.M.

 


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  		Fig. 4. Relationship between maternal resting metabolic rate (RMR) and body mass at the peak of the first lactation in the control (filled circles) and experimental (open circles) females. The relationships are described by y=1.92x-38.0 and y=0.48x+24.4 for the control and experimental females, respectively.

 


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  		Fig. 5. Frequency distribution of the length of the second pregnancy of the experimental (concurrently pregnant and lactating) females. The normal gestation length of females that go through pregnancy when not lactating is 19 days.

 


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  		Fig. 6. Relationship between the delay in implantation at the start of the second pregnancy in the experimental females and (A) the litter size at the peak of the first lactation (y=0.42x+8.3), (B) the mean pup mass at the end of the first lactation (y=-0.3x+10.3) and (C) the asymptotic daily food intake at the peak of the subsequent (second) lactation (y=-0.6x+25.1).

 




© The Company of Biologists Ltd 2001