Variations in the Yield and Composition of the Milk During Lactation in the Rabbit and the Galactopoietic Effect of Prolactin

Abstract

The daily milk yields and the concentrations of fat, protein and lactose in the milk were studied throughout lactation in New Zealand White (NZW) and Dutch rabbits. The highest daily milk yields, 270 g. in the NZW and 140 g. in the Dutch rabbits, occurred at the end of the third week of lactation; on a body weight basis the yields were similar being 61\m=.\0and 62\m=.\3 g. milk/kg. body weight for the NZW and Dutch rabbits respectively. Over a 6-week period the total milk yields were 6940 g. for the NZW and 3820 g.for the Dutch rabbits.In both breeds considerable changes occurred in the composition of the milk after the third week of lactation. During the first 3 weeks the concentrations of fat, protein and lactose were approximately 15\p=n-\17, 11 and 1\ m=. \ 8\ p=n-\ 2\ m=. \ 0 g./100 ml. milk respectively, but during the fourth to the sixth week the values for fat and protein increased to 25\p=n-\30 and 18\p=n-\20 g./100 ml. respectively, while lactose declined to 0\m=.\5 g./100 ml. or less.Sheep prolactin (25 i.u. injected s.c. twice daily for 2 days) in late lactation was galactopoietic, augmenting both the daily milk yield and the concentration of lactose in the milk.From days 9 to 31 of lactation the NZW litters gained 0\m=.\45g. body weight/g. of milk consumed, the Dutch litters gained 0\m=.\38 g./g. of milk. This difference in weight increment was highly significant (P < 0\m=.\001) and was apparently due not to a higher calorie content of the milk of the NZW does but to a greater efficiency of milk utilization by the NZW litters.

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

“…The rabbit mammary-tissue weight can be calculated as a function of body weight at the various stages of lactation from the data of Lu & Anderson (1973). Applying these values to the present study the rate of lactose synthesis by the tissue slices (Table 2) is virtually identical with the yields of rabbit milk lactose at the various stages of lactation which have been reported by Cowie (1969) and by Hall (1971).…”

“…The reasons for this asychrony are unclear, although results from the studies in vitro are consistent with measurements in vivo. The daily yield of lactose in lactating rabbits decreased linearly with time from approximately 4.Og on day 15 postpartum to 0.6g by 27 days postpartum, whereas the yield of fat and percentage of fat in the milk continued to increase over the same period (Cowie, 1969;Hall, 1971).…”

“…Purina rabbit chow was fed ad libitum during pregnancy and lactation. An average litter of 7 (range 6-8) pups was maintained with the lactating rabbits to assure complete milk removal (Cowie, 1969).…”

“…In addition, Cowie (1969) and Hartmann & Jones (1970) have reported that the yield of lactose in vivo decreased approx. 50 % from 15-24 days post partum.…”

Immediate postnatal sucking in the rabbit: Its influence on pup survival and growth

“…The present study suggests, however, that the ability of rabbit mothers to provide, and of the pups to gain, colostrum after parturition contributes to pup survival, at least in first litters. From birth onwards, colostrum is rich in proteic and lipidic compounds, contains more lactose than later in lactation [6,26], and is rich in immunoglobulins [2,37,42]. It is thus well suited to serve as fuel and antigen defense in the newly born rabbit.…”