OBSERVATIONS, TRIALS TO AID IN LAMBING

Press, Volume CIII, Issue 30342, 18 January 1964, Page 6

OBSERVATIONS, TRIALS TO AID IN LAMBING

Canterbury farmers should be more aware of what makes their ewes come into season because a knowledge of this can make early lambing a success or even expedite the progress of any lambing, Mr J. E. Wolff, farm advisory officer, Department of Agriculture, Timaru, said this week.

Observations and trials carried out in South Canterbury have provided knowledge on how new techniques should be put into action, he said.

The breeding season of sheep in New Zealand begins in larte summer and extends over the autumn and early winter. At other times of the year they are not sexually active.

The reproductive cycle begins when one or more of the (collides in, the ovary grows and ruptures or ovulates during the 36-hour oestrus or “heat” period. The tiny egg contained therin is released and begins its journey down the fallopian tube. Should the ewe be mated, spermatozoa travels up the uterus and one of them will fuse with the egg to begin the development of the foetus. A new gland, the corpus luteum, grows in the cavity of the follicle and if mating is successful it will provide the hormones necessary for the retention and growth of the foetus. However, if fusion of egg and spermatozoa failed to occur, the corpus luteum would degenerate to allow a separate follicle to rupture 17 days after the earlier one. With no corpus luteum to precede the first ovulation of each breeding season, the animal is not sensitised with hormones from this gland. As a result the ewe fails to display oestrus or show signs of being in season. This ovulation, normally unmaited, is commonly called the “silent heat.’’

During the last three years Dr. D. G. Edgar, at Ruakura, has been carrying out trials to demonstrate the effect that rams have on the onset of the breeding season. The first

information came from Australia and Ruakura trials are providing useful information on what promises to be an invaluable technique for achieving an earlier lambing or eliminating the slow start to a lambing which some farmers are cursed with year by year. “To give us some information about the onset of the breeding season in South Canterbury Romney ewes, we examined the ovaries of about 4000 Romney or Romney Cross ewes from 40 different properties in the district. These were all old ewes and as they were being slaughtered in the freezing works we stood on the chain and collected the ovaries. Each pair of ovaries was

examined visually and if a corpus luteum was present the ewe was classified as being in season. (Figure 2),” Mr Wolff says. Hence they could determine the percentage of each flock that had been in season by the date of slaughter. But it is also necessary to remember that virtually all ewes undergo a silent heat at the beginning of the breeding season. It is not until the second ovulation has occurred, 17 days later, that the ewe can be mated and it is necessary to transpose the date of examination by 17 days to determine how many can be mated by a given date, he says. Figure 3 shows a pattern for the onset of the breeding season in aged Romney ewes in South Canterbury. Each point on the graph represents a flock and the line drawn through the scatter of points represents an average for the district. The large variation from farm to farm makes it difficult to predict the position on any one farm, unless tupping dates and normal lambing spread are known. But the obvious point is, that for most flocks, it is pointless to turn out the ram before March 15. With only 20 per cent of the flock likely to be mated in the fortnight before this date, a slow start to lambing is the inevitable result. Farmers who have turned out their rams in early March in the hope of achieving an early lambing will now realise why their efforts were largely in vain. For the rams to have any influence on the onset of the breeding season, they must be turned out before the ewes have come into season of their own accord, i.e. before the bulk of the flock has experienced the “silent heat.”

Thanks to the technique developed by Dr. Edgar, farmers can take heart and overcome most of the former difficulties. Rams can be used to make the ewes come into season at will, if they are joined at the correct time, Mr Wolff says. Provided the ewes and the rams are kept well apart throughout January it is found that by bringing them

together for about 10 days in February will initiate the first ovulations in most of the flock. For about a month before they normally come into season, the ewes go through a susceptable period, during which the sound and/or smell of rams nearby can trigger off the first cycle. Between two and eight days after the rams are turned out most ewes have their “silent heat” and they can be mated from the eighteenth day. A peak in tupping will occur after about 22 days and up to 70 per-cent of the flock may be mated within a week. Figure 3 illustrates the effect.

Farmers wishing to start tupping during early March will be able to mate their ewes on the first cycle following the "silent heat,’’ but those tupping later, who wish to avoid the delayed start to their lambing, will have to mate on the second or perhaps even the third cycles after they have induced the “silent heat.”

Mr Wolff says that the following table shows the dates when rams should be turned out to give an immediate peak in tupping after the nominated date.

The aspects to be covered next week include the advantages of the use of the technique and the precautions necessary.

* Where a cycle is allowed to elapse between the first joining and tupping, it will be imperative to Withdraw the rams after 10 days, to avoid having unwanted early lambs. A sound fence will be needed to contain the rams during this interval.

Tupping Rams Turned Out Lambing Begins 24 Feb. 6 Feb. 19 July 2 March 13 Feb. 27 July 9 March 20 Feb. 4 Aug. * 16 March 10 Feb. 11 Aug. * 23 March 18 Feb. 18 Aug. * 30 March 8 Feb. 25 Aug. * 6 April 14 Feb. 1 Sept. * 13 April 21 Feb. 8 Sept.