Impact of Shearing on ReproductionWednesday, 17th April 2019
By Dr Mackie Hobson
Shearing Angora goat ewes at different times may impact on the fertility and kid survival rate.
Shearing prior to pregnancy
Shearing causes a rapid increase in plasma cortisol concentrations. Stress before mating can result in a delay in the onset of oestrus and a reduction in ovulation rates.
Stressors, even common management procedures such as shearing suppress normal oestrus behaviour and reduce ewe fertility. All these events are co-ordinated by endocrine interactions, which are disrupted in stressful situations. This disruption is short lived when conditions return to normal after shearing.
It would in theory be expected that shearing would stimulate the metabolic rate, feed intake and thus increased ovulation (flush effect). However shearing sheep ewes prior to mating tended to improve lamb birth weight by 0.31kg and increased weaning weight by 2kg but had no effect on number of lambs reared per ewe joined.
Shearing during early pregnancy.
The majority of prenatal mortality occurs in embryos and not in foetuses (during the interval from fertilization to attachment). About 20‑30% of all fertilized ova in sheep ewes are lost in the first month and very few losses occur after about day 35. Ewes return to oestrus after 16‑18 days (sheep) 19-21 days (goats) after the loss.
It is therefore advised not to stress ewes immediately after mating prior to implantation of the ovum as this is a sensitive time.
Shearing during mid- pregnancy
Shearing during mid-pregnancy can be used to improve productivity and reduce perinatal mortality of kids.
Studies on sheep have demonstrated the effect of shearing at about 74 days of pregnancy resulted in:
- Increased birth weight at lambing
- Increased weaning weight
- Increased milk production
It is well known that the birth weight of Angora goat kids effects survival rates.
Birth weight of the kid
- kids below 2.0 kg only had a survival rate of 50%
- Kids above 3.5kg had a survival rate of 90%.
The nutritional requirements of the Angora ewe increase dramatically between days 90-150 of pregnancy. The impact of nutrition over this period has significant impact on birth weight, udder development, colostrum and milk production and mothering instincts. Poor milk production of the dam accounts for 8.7% cause of kid deaths. Shearing Angora goats increases the metabolic rate as well as increasing food and water intake so is the reason for the increased kid birth weight.
Shearing during gestation alters the metabolism and the placenta of ewes and increases lamb survival rate by up to 17% due to increasing the weight at birth.
It has been suggested the best time for shearing ewes (sheep) in order to obtain the higher placenta development in ewes is around 74 days of pregnancy. A probable explanation for the effect of shearing is the stimulus for a greater food intake by the sheep exposed to cold temperature
Better milk yield has been observed in sheep sheared at 100 days of pregnancy compared to non-sheared sheep.
Shorn Angora ewes (shorter hair) also tend to seek shelter during periods of cold and so may increase the survival rate of kids born in the veld due to an improved microclimate.
The shorn Angora ewe (or crutched ewe) may also enable the kid to suckle more easily and hence improve survival rates.
The pros and cons must be taken into consideration when planning shearing dates considering the impact on birth mass, ovulation, environmental temperatures (hypothermia) and farm management.
The importance of feeding pregnant ewes during shearing
Goat ewes are much more susceptible to nutritionally related abortions (1-5 days after the nutritional stress) than sheep. This is why it is important not to starve Angora goat ewes during shearing time. In an Angora 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.
AN ANALYSIS OF PRE-WEANING KID MORTALITY IN SOUTH AFRICAN ANGORA GOATS
Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900
Effects of stress on reproduction in ewes.
Dobson H1, Fergani C, Routly JE, Smith RF
EFFECT OF SHEARING DURING PREGNANCY ON PRODUCTIVE PERFORMANCE IN THE POST-PARTUM PERIOD OF EWES ON EXTENSIVE HUSBANDRY
Viviane Marques Guyoti1
Mariana de Souza Farias1
Magnus Larruscaim Dalmolin1
César Henrique Poli2
Felix Diaz Gonzalez2
1Pós-graduandos da Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
2Professores Doutores da Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
Teagasc project team:
Dr. Tim Keady (PI) Dr. Seamus Hanrahan Noel McNamara
Effect of shearing on oestrus and ovulation in sheep
- A. Parr , I. F. Davis and A. J. Tilbrook
Sheep Health & Production
Chapter 7. Reproductive management and diseases in naturally mated flocks