The Department of Physiology, Veterinary College of Norway1), Oslo and the Department of Animal Nutrition, Agricultural College of Norway, As2), Norway
PLASMA INSULIN AND GROWTH HORMONE CONCENTRATIONS IN PREGNANT SHEEP II:
Post-absorptive levels in mid-
and late pregnancy
By Anne Kristine Blom1), Knut Hove1)3) and Jon J. Nedkvitne2)
ABSTRACT The pregnant ewe compensates the reduced carbohydrate availability in late pregnancy by increased fat combustion. The purpose of the present study was to examine the adaptation of plasma growth hormone (GH) and insulin levels to this change in energy substrate metabolism. Two groups of ewes were bled in the post-absorptive state at different stages of pregnancy. One group (7 animals) was fed adequately throughout pregnancy, while the other received a maintenance ration for non-pregnant sheep
(28 animals).
Plasma GH increased from averages from 2\p=n-\3 to 8\p=n-\14 ng/ml during the last month before lambing. Shearing of the wool combined with a cold stress resulted in a clearly detectable peak in plasma GH in the underfed sheep. No significant difference in plasma GH attributable to differences in diet could be detected in late pregnancy. Plasma insulin decreased steadily the last 5 weeks towards lambing, most in mothers with 3 lambs. Plasma free fatty acid levels (FFA) increased
3) Present address: Institute of Medical
Norway.
Biology, University 553
of Tromso, Tromso,
the last 2 months of pregnancy, most in the underfed sheep. GH and FFA were positively correlated (r 0.50 and 0.30 in the two groups). It is concluded that the adaptation of the maternal metabolism to reduced carbohydrate and eventually energy-availability in late pregnancy included lowering of insulin and enhancement of plasma GH levels. These adaptations were detectable under the present conditions the last 5\p=n-\6 weeks before term. =
-
As pregnancy progresses the metabolism of ewes changes from one of carbo¬ hydrate adequacy to one of carbohydrate sparing and increased fat combustion (Reid 1968). Hove 8c Blom (1976) found increased growth hormone and lowered insulin levels in plasma of sheep the last week of pregnancy. These changes were particularly obvious in an ewe carrying 3 lambs and were thought to be due to lowered carbohydrate availability in late pregnancy. The present study was undertaken to investigate the development of these endocrine changes during the last half of the gestation period. Maintenance rations were fed to most of the animals throughout pregnancy in order to augment changes in the maternal metabolism induced by the metabolic demands of the foetal lambs.
ANIMALS AND METHODS
relationship between plasma concentrations of GH, insulin and some energy sub¬ were investigated in two groups of ewes of local breed at various stages of pregnancy. Group 1 was fed adequately, while the group 2 animals were kept on a maintenance ration for non-pregnant sheep throughout the pregnancy. All animals of group 2 were in addition cold-stressed by shearing of the wool. The animals were mated at approximately the same time in late October after synchronization of the heat. All animals were shorn at this time of the experiment. Throughout the preg¬ nancy they were kept in an open barn where the temperature changed with the outdoor temperature. Blood samples were taken from the jugular vein before morning feeding. Heparinized plasma was kept at -20°C until analyzed. The
strates
1 included 7 animals which all gave birth to twins. An adequate nutrition obtained by feeding 3.5 kg grass ensilage, 0.5 kg hay and 0.2 kg concentrates (15 °/o crude protein) daily. To increase the energy supply moderately, 0.1 kg con¬ centrates were substituted for 0.5 kg silage 2 weeks before lambing. The animals were in good condition at the time of lambing. Blood samples were taken on nine dates in the course of a 95 day's period, the last about 5 days before parturition.
Group
was
Group
2 included 28
ewes.
non-pregnant sheep and
The animals
were
fed maintenance ration sufficient for
consequently in an increasing energy deficit as preg¬ nancy progressed. The sheep were fed individually according to weights when they were 1 month pregnant. Daily rations of 0.1 kg concentrates were given together with hay at a rate of 0.045 kg dry matter per kg metabolic weight (this equals 1.2 kg dry matter in a 80 kg sheep). These ewes weighed after lambing averagely 4 kg less than at mating, and were in a rather poor condition. All ewes were shorn 43 days before expected lambing. During the first 14 days after the shearing morning temperatures were
554
3-1500
PLASMA INSULIN AND GROWTH HORMONE CONCENTRATIONS IN PREGNANT SHEEP II:
Post-absorptive levels in mid-
and late pregnancy
By Anne Kristine Blom1), Knut Hove1)3) and Jon J. Nedkvitne2)
ABSTRACT The pregnant ewe compensates the reduced carbohydrate availability in late pregnancy by increased fat combustion. The purpose of the present study was to examine the adaptation of plasma growth hormone (GH) and insulin levels to this change in energy substrate metabolism. Two groups of ewes were bled in the post-absorptive state at different stages of pregnancy. One group (7 animals) was fed adequately throughout pregnancy, while the other received a maintenance ration for non-pregnant sheep
(28 animals).
Plasma GH increased from averages from 2\p=n-\3 to 8\p=n-\14 ng/ml during the last month before lambing. Shearing of the wool combined with a cold stress resulted in a clearly detectable peak in plasma GH in the underfed sheep. No significant difference in plasma GH attributable to differences in diet could be detected in late pregnancy. Plasma insulin decreased steadily the last 5 weeks towards lambing, most in mothers with 3 lambs. Plasma free fatty acid levels (FFA) increased
3) Present address: Institute of Medical
Norway.
Biology, University 553
of Tromso, Tromso,
the last 2 months of pregnancy, most in the underfed sheep. GH and FFA were positively correlated (r 0.50 and 0.30 in the two groups). It is concluded that the adaptation of the maternal metabolism to reduced carbohydrate and eventually energy-availability in late pregnancy included lowering of insulin and enhancement of plasma GH levels. These adaptations were detectable under the present conditions the last 5\p=n-\6 weeks before term. =
-
As pregnancy progresses the metabolism of ewes changes from one of carbo¬ hydrate adequacy to one of carbohydrate sparing and increased fat combustion (Reid 1968). Hove 8c Blom (1976) found increased growth hormone and lowered insulin levels in plasma of sheep the last week of pregnancy. These changes were particularly obvious in an ewe carrying 3 lambs and were thought to be due to lowered carbohydrate availability in late pregnancy. The present study was undertaken to investigate the development of these endocrine changes during the last half of the gestation period. Maintenance rations were fed to most of the animals throughout pregnancy in order to augment changes in the maternal metabolism induced by the metabolic demands of the foetal lambs.
ANIMALS AND METHODS
relationship between plasma concentrations of GH, insulin and some energy sub¬ were investigated in two groups of ewes of local breed at various stages of pregnancy. Group 1 was fed adequately, while the group 2 animals were kept on a maintenance ration for non-pregnant sheep throughout the pregnancy. All animals of group 2 were in addition cold-stressed by shearing of the wool. The animals were mated at approximately the same time in late October after synchronization of the heat. All animals were shorn at this time of the experiment. Throughout the preg¬ nancy they were kept in an open barn where the temperature changed with the outdoor temperature. Blood samples were taken from the jugular vein before morning feeding. Heparinized plasma was kept at -20°C until analyzed. The
strates
1 included 7 animals which all gave birth to twins. An adequate nutrition obtained by feeding 3.5 kg grass ensilage, 0.5 kg hay and 0.2 kg concentrates (15 °/o crude protein) daily. To increase the energy supply moderately, 0.1 kg con¬ centrates were substituted for 0.5 kg silage 2 weeks before lambing. The animals were in good condition at the time of lambing. Blood samples were taken on nine dates in the course of a 95 day's period, the last about 5 days before parturition.
Group
was
Group
2 included 28
ewes.
non-pregnant sheep and
The animals
were
fed maintenance ration sufficient for
consequently in an increasing energy deficit as preg¬ nancy progressed. The sheep were fed individually according to weights when they were 1 month pregnant. Daily rations of 0.1 kg concentrates were given together with hay at a rate of 0.045 kg dry matter per kg metabolic weight (this equals 1.2 kg dry matter in a 80 kg sheep). These ewes weighed after lambing averagely 4 kg less than at mating, and were in a rather poor condition. All ewes were shorn 43 days before expected lambing. During the first 14 days after the shearing morning temperatures were
554
3-1500
