Energetic Costs of Lactation with and without Simultaneous Pregnancy in the White-Toothed Shrew Crocidura russula monacha

Abstract

Milk composition, gas exchange, and energy intake in food were measured in whitetoothed shrews, Crocidura russula monacha, in lactating females (LF) and in simultaneously lactating and pregnant females (LPF). Milk contained 51.2% ± 11.3 SD solids and 9.4% ± 1.0 SDproteins. Milk fat increased from 28.5% ± 0. 46 SD on day 2 of lactation to 42.6% ± 3.5 SD on day 20. Lactose decreasedfrom 3%-8% during the first week of lactation to 2%-4% at the end. Energy content of milk paralleled fat concentration, increasing from 14.86 kJ. g⁻¹ + 0. 4 SD to 17.92 kJ. g⁻¹ ± 1.04 SD. Mass-specific oxygen consumption rate (Mspo₂) of the LF reached apeak value of 3. 68 mL. (g . h)⁻¹ ± 0.58 SD on days 6-8 of lactation, then declined to the nonreproductive value on day 16 (2. 48 mL. [g . h]⁻¹). The Mspo₂ of the LPF remained unchanged throughout lactation at 2. 75 mL. (g . h)⁻¹ ± 0.47 SD. Energy intake in food in both LF and LPF increased daily depending on litter size. In a onepup litter it increased from 31.4 kJ. d⁻¹ ± 4.4 SD to 62.3 kJ. d⁻¹ ± 11.2 SD on day 10, whereas in a four-pup litter it increased from 53.0 kJ. d⁻¹ ± 7.5 SD to 119.3 kJ . d⁻¹ ± 19.2 SD on day 10. The milk with moderate protein and high fat content suits the fast growth rate and heat loss of the pups. Although lactation imposes a severe energy load on the LF, this burden is mainly expressed by the up to fivefold increase in energy intake in food where Mspo₂ increases only up to 1.5 times the normal value. The energy requirements of simultaneous lactation and pregnancy are not simple additives. They seem to overlap partially and thus are energetically less demanding