Pregnant and Lactating Ewe

NUTRITION-THE PREGNANT AND LACTATING EWE

First two months of pregnancy:

The nutritional requirements of the ewe during the first two months are still relatively low, and the natural grazing should normally be sufficient.

Last six weeks of pregnancy and lactation

Most losses occur in the period just before birth until seven days after birth. Nearly 80% of these mortalities are related to the nutrition of the ewe during the last weeks before kidding and the first weeks after kidding. The nutritional requirement of a late pregnant Angora ewe is known to increase more than two fold (200% above standard maintenance requirements) compared to that of a dry ewe. This figure is too often forgotten or underestimated.

weeks_from_conception_crop

Nutritional requirements of the ewe during pregnancy compared to dry ewe (100%)

Effects of inadequate nutrition during late gestation include:

(i)     Abortion after day 90 of pregnancy

(ii)   Poor lactation (udder formation, low colostrum and milk production)

(iii) Low birth weight

(iv)  Foetal Programming

(v)    Poor mothering instincts

(i)     Abortion:

The nutritional requirements of the ewe are increased considerably, and energy supplementation must be increased accordingly. Trials were performed to determine blood glucose concentration in 20 pregnant ewes receiving a high and low plane of nutrition during the fourth month of gestation (Wentzel, Le Roux and Botha). They concluded a drop in blood glucose levels due to nutritional stress to be the likely trigger for the onset of hormonal changes related to abortion in Angora goat ewes. In addition, the stress of sub-nutrition during the experimental period increased the incidence of perinatal mortality.

In a ewe which is energy deficient there is a decrease in blood glucose level which is passed on to the foetus.  This triggers a stress-response by the foetus, causing a rise in cortisol (steroid) production.  As these steroids are oestrogen precursors, this has the ultimate effect of increasing oestrogen production.  This causes the regression and eventual destruction of the Corpus Luteum (CL), the area of the ovary responsible for progesterone production. In goats the CL is the only source of progesterone and is solely responsible for maintaining pregnancy, whereas in sheep, progesterone is also produced by the placenta. For this reason, sheep are significantly less likely to abort during energy shortages.

The aborted foetus is usually well formed, normal in appearance and sometimes still alive when aborted. When energy is supplemented appropriately, abortions will typically stop within two weeks.

It is important that care should be taken when the ewe is moved to a new type of grazing during this time (e.g. to cultivated pastures or lucerne lands). When such a move takes place the ewe takes time to adapt to the altered diet, and the temporary deficiency created by this can lead to abortions even in the midst of plenty. During such a movement an energy supplement should be supplied, or lucerne hay provided a week before the move until several days after introduction to the lands

During cold snaps it is important to remember cold stress also increases glucose consumption by up to 66% which is aggravated by restricted grazing at times when goats are housed in sheds. Abortions typically then occur 1-5 days later. Pregnant ewes should therefore when possible be given supplementary feeding when housed.

(ii)   Lactation:  

The feeding requirements of the goat ewe in lactation are higher than at any other time during the reproduction cycle. Should these requirements not be satisfied, milk production, and consequently the growth of the kid, will be adversely influenced. Although sufficient energy supplementation can normally give the desired results on natural grazing, it may be necessary during droughts, and in the case of ewes having twins, to give a limited protein supplementation as well.

(iii)    Low birth weight:

Birth weight largely determines the survival prospects of the kid.  Eighty percent of the kids that die do so in the first month due to decreased colostrum and hence maternal antibody intake, poor milk intake and poor mothering (excluding predation).

The effect of birth weight of the kid relative to its survival prospects (M.Sheldon)

      (iv) Foetal programing:

Foetal Programming is a recent development in the research field. Research has shown that whatever happens to the foetus in the uterus can have an influence on production later in life.  This has proven to have both intra-generation (mother-progeny) as well as inter-generation (grandmother-mother-progeny).

Nutritional shortfall in late gestation programmes the foetus to be born into a nutritionally stressed environment and thereby results in slow growth rates.

In sheep it has been proven that decreasing feed during day 30-50 of gestation (the period during which the foetal udder is formed) results in that ewe lamb having a higher milk production during its lifetime. More research in this field is required.

(iv) Poor mothering instinct:

Links are known to exist between mothering instinct and the progesterone/ oestrogen status of the ewe at kidding. This in turn can be linked to the nutritional status (see above).

 

Dr Mackie Hobson

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