A calm Merino ewe and lamb.

CALM Merino ewes have been shown to wean 10-19 percent more lambs than nervous mothers in Western Australian research.

A calm temperament in ewes improves ovulation rate and successful pregnancies, the study published by the University of Western Australia has found.

In 1990, two different selection lines of Merino sheep were established for low behavioural reactivity or calm temperament,  and high behavioural reactivity or nervous temperament, at the University of Western Australia. In the early years of the selection, a calm temperament was more strongly correlated with improved maternal behaviour and greater lamb survival than in nervous ewes.

After 10 to 13 years of selection, the differences in maternal behaviour and lamb survival between the two lines had dissipated, but breeding records of the two lines obtained over four years showed that 10-19pc more lambs (to mated ewes) were weaned from the calm ewes than from the nervous ewes. The higher reproductive success of the ewes of the calm line compared with those of the nervous line could be explained by diverse impacts of behavioural reactivity on the reproductive biology of each line, the researchers found.

Previous investigations have shown that 32 hours after the withdrawal of progesterone sponges, calm ewes are more active in seeking males and more receptive to approaches by males than nervous ewes. Also colostrum produced by calm ewes has more lactose, less fat and is less viscous than that from nervous ewes. Calm dairy ewes produce more milk than nervous ewes and milk from calm ewes has more protein than that of nervous ewes.

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. In fact, the analysis showed that ewes in the calm line carried more foetuses compared with nervous ewes and the calm ewes carried a higher proportion of twins, 35.4pc compared with 14.6pc for the nervous ewes.

The study, which was conducted in collaboration with researchers from Uruguay, the Department of Primary Industries and Regional Development WA and UWA, has implications for the impact of stress in human reproduction.

The team investigated the reproductive outcomes of 200 Merino ewes known to have either a calm or a nervous temperament. They found the ovulation rate and rate of successful pregnancies to be higher in the calm ewes.

Associate Professor Dominique Blache from UWA’s School of Agriculture and Environment and Institute of Agriculture who led the study said temperament affects ovulation rate, 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.

“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,” Professor Blache said.

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, a statement from The University of Western Australia said.

The paper, Calm Merino ewes have a higher ovulation rate and more multiple pregnancies than nervous ewes was published in the journal Animal and the research was supported by Meat and Livestock Australia.

Source: UWA.