KEEP calm and get pregnant.
That’s the advice from a study published by The University of Western Australia (UWA) after researching the reproductive outcomes of 200 Merino ewes known to have either a calm or a nervous temperament.
The study, ‘Calm Merino ewes have a higher ovulation rate and more multiple pregnancies than nervous ewes’, revealed that ewes increased their likelihood of carrying more foetuses, getting pregnant, carrying twins and producing more milk (for dairy ewes) if they were calm.
Conducted in collaboration with researchers from Uruguay, the Department of Primary Industries and Regional Development, the study has implications for the impact of stress in human reproduction.
UWA’s School of Agriculture and Environment and Institute of Agriculture associate professor Dominique Blache, who led the study, said temperament affected the ovulation rate in ewes but not the occurrence of ovulation.
“Differences in reproductive outcomes between the calm and nervous ewes were mainly due to a higher ovulation rate in calm ewes,” Dr Blache said.
“Even when the ovulation rate is maintained some of the nervous ewes have problems in maintaining their pregnancy, possibly because of the quality of the eggs and subsequent embryos, and perhaps the quality of the uterine environment during the first two weeks of pregnancy.”
The results also suggest that reproduction in nervous ewes is compromised by factors leading up to ovulation and conception, or in the uterine environment during early pregnancy, which reflects differences in energy utilisation.
Understanding why the reproductive outcome of these ewes is different will help to breed sheep better suited for the production system, improving their welfare.
The study reveals that in 1990, two different selection lines of Merino sheep were established for low and high behavioural reactivity (also called calm and nervous temperament) at UWA.
Breeding records of the two lines obtained over four years showed that 10 per cent to 19pc more lambs (to mated ewes) were weaned from the calm ewes than from the nervous ewes.
The higher ovulation rate in calm ewes was possibly due to the effects of metabolic hormones.
Previous investigations have shown that calm ewes were more likely to seek males and receptive to approaches by males than nervous ewes.
Colostrum produced by calm ewes has more lactose, less fat and is less viscous than that from nervous ewes.
The study found that calm dairy ewes produced more milk than nervous ewes and milk from calm ewes had more protein.
An analysis of two years of data from routine ultrasound scanning of the two selection lines during mid pregnancy (60 to 90 days post mating) suggested that selection for behavioural reactivity could influence fertility and prolificacy.
The analysis showed that ewes in the calm line carried more foetuses.
The calm ewes carried a higher proportion of twins, 35.4pc compared with 14.6pc for the nervous ewes.
The paper was published in the journal Animal and the research was supported by Meat and Livestock Australia.
