Jv. Odoherty et Tf. Crosby, THE EFFECT OF DIET IN LATE PREGNANCY ON PROGESTERONE CONCENTRATION AND COLOSTRUM YIELD IN EWES, Theriogenology, 46(2), 1996, pp. 233-241
In the ewe, high level feeding is associated with low levels of circul
ating progesterone and that progesterone withdrawal is a prerequisite
for lactogenesis and the onset of copious milk secretion. A total of 1
08 ewes was allocated to a 3 x 2 factorial experiment to determine the
effect of diet on serum progesterone (P4) concentration and colostrum
yield. On D 96 of pregnancy, the ewes were offered either grass silag
e, molassed sugar beet pulp (beet pulp) silage or grass silage supplem
ented with beet pulp All ewes were given ad libitum access to silage.
From D 126 of pregnancy, half the diets were supplemented with soybean
meal with the aim of achieving a total crude protein intake of 220 g/
ewe/day. Blood samples were taken on D 142 of pregnancy and at 1, 10 a
nd 18 h post lambing for P4 determination. Metabolizable energy intake
s (Mega Joules/ewe/day) of 9.1, 11.2 and 12.1 (SEM 0.37) and crude pro
tein intakes (g/ewe/day) of 142.8, 167.4 and 162.0 (SEM 3.46) were rec
orded for grass silage, beet pulp ensiled and beet pulp supplemented s
ilages, respectively, from D 126 to D 147 of pregnancy. Soybean meal s
upplementation increased the crude protein intake from 97.1 to 217.0 g
/ewe/day (SEM 2.86) and Metabolisable Energy intake from 9.0 to 12.6 M
ega Joules/ewe/day (SEM 0.31). Supplementation with soybean meal decre
ased P4 concentration (ng/ml) on D 142 (P <0.05) and at 1 h (P <0.01),
10 h (P <0.01) and 18 h post lambing (P <0.01). Ewes offered grass si
lage had higher P4 concentrations on D 142 (P <0.01) and at 1 h after
lambing (P <0.05) than the beet pulp-supplemented ewes. There were neg
ative linear relationships between P4 concentration at D 142 and colos
trum yield at 1 h (P <0.01) and between P4 concentration at 1 h and co
lostrum yield at 1 h (P <0.001) and total yield at 18 h (P <0.001). In
conclusion, ewes which were underfed had higher P4 concentrations at
all times, and there were negative linear relationships between colost
rum yield and P4 concentrations on D 142 of pregnancy and at 1 h post
lambing.