Role Of Oestrogens In Plants

Press, Volume CVI, Issue 31119, 23 July 1966, Page 10

Role Of Oestrogens In Plants

Farmers are well aware by now of the excellent lamb fattening qualities of white clover and lucerne as shown by Dr. J. W. McLean on the pure species trials at Lincoln College.

Speaking to the Canterbury branch of the New Zealand Institute of Agricultural Science this week Dr. McLean recalled that lambs weaned at seven weeks had, after nine weeks on white clover, reached live-weights of about the 1001 b mark. Similar results had been obtained on lucerne.

But the problem with white clover and also lucerne is the oestrogens that they contain and the part that they may play on the one hand in stimulating growth and on the other hand in possibly interfering with fertility. An oestrogen is a female sex hormone type of substance.

Dr. McLean said that a high growth rate was associated with a high intake of digestible organic matter and rate of intake was governed by the rate of fermentation of the food in the rumen—the more rapidly this occurred the sooner the animal was ready to take more. Work with lambs off the pure pasture species trial had shown that the rumen fill or weight of the rume?. of lambs on clover, and particularly lucerne, was much less than with the grasses. The point he made here was that the quality of this food was so high from the point of view of the rumen microflora or bacteria, that the animal was getting all the food that it required without filling its rumen, but he suggested that in clover and lucerne some other factor was involved in determining the rate of intake.

Referring to trials in which it has been shown that with the introduction of synthetic oestrogen, by injection of stilboestrol, a reduction in the fat content of the carcase has been achieved, Dr. McLean said that the so-

called demand for lightweight lambs in the United Kingdom was spurious. It was not a demand for lightweight lambs but for lambs that were not fat. If heavy lambs could be produced with

the carcase characteristics of a 311 b lamb then he believed that the English would take th«m. At the college they had grown lambs to 501 b dressed weight with a fat content nowhere near the level where they would be graded out for being overfat. They had to have a fat content of 35 to 40 per cent before they were rejected on this account. Highlighting the rather uncertain situation as far as oestrogens in plants was concerned, Dr. McLean said that plants could be high in oestrogens, as determined by chemical analysis, yet exhibit low oestrogenic activity and the reverse could be the case, which implied that there might be oestrogens present in plants of which they were not aware. Oestrogens, he said, could disturb the reproductive functions of the female and also under special circumstances of the male. The reproductive functions of the female sheep could be affected in three weeks and lambing percent-

■ age had been reduced by 30 per cent experimentally, but this was temporary and the • reproductive system could ; return to normal in five weeks. A permanent effect had,

however, been shown to exist in Western Australia associated with the ingestion of oestrogens over a long period and a change in the lining of the uterus. Here lambing percentage could drop from a normal 80 per cent to 20 or 30 per cent. But Dr. McLean pointed out that progesterone that was present in the ovary could have a protective action against oestrogens injected or derived from the pasture. If increased production over the whole year was the objective in New Zealand, he said, it would be necessary to change the quality of the pastures. He would not suggest that that they go over solely to lucerne and clover and discount grasses. What they wanted to find out precisely was what it was in clover and lucerne that enabled animals to utilise it so rapidly. If this could be ascertained, then it could be made available to the plant breeders to produce plants for any particular [purpose.