Factors Involved In Post-Weaning Thrift

Press, Volume CI, Issue 29744, 10 February 1962, Page 7

Factors Involved In Post-Weaning Thrift

Today Mr AL K. Hill, who up until last week was a scientific officer on the staff of the Department of Agriculture’s irrigation research station at Winchmore,'continues his review of stock health investigations at the station. It embraces studies of times of weaning and feeding levels, an explanation for the incidence of ill-thrift on abundant feed, experiments with cobalt, parasitism and responses to phenothiazine, effects of selenium and factors involved in the ideal feed for young stock. Mr Hill is about to take up a position on the staff of the University of New England in New South Wales.

Post-weaning Effects.— After weaning, lamb growth rate was governed entirely by the quantity of feed available, its composition, worm burden, and the rate at which food was ingested. An important feature of post-weaning lamb thrift was lamb age or weight at separation from its mother. Station trials had shown that by early January under good feed conditions unweaned lambs might weigh 41b to 71b more than lambs weaned at eight weeks of age. More detailed experiments had been conducted in an attempt to define feed supply levels which would make seven, 10, 13, or 16week weaning profitable. For this purpose lamb groups had been run on paddocks containing varying levels of feed and they had been progressively weaned from these on to good pastures nearby. The results of this season’s trials with weights recorded at January 11 are:—

Considering this and earlier trials, Mr Hill said it was likely that under conditions of feed shortage weaning at 10 to 17 weeks of age was prudent management, but weaning at less than 10 weeks of age had never been found beneficial even with extremely low levels of feeding. In conditions of feed abundance, however, weaning at less than a mean age of 13 weeks would cause a substantial reduction in rate of growth. Another factor which markedly influenced postweaning weight gains was, of course, the level of feed and this aspect of the station trials had often given spectacular results. Though the post lambing level of feeding was largely dependent on the vagaries of nature, it was important to know the extent to which feed supply dictated ’rowth rate. In every trial in every season growth rate had been proportional to feed supply, maximum growth being obtained on hay type pasture.

Thus, depending on the quantity of feed available, lambs had gained by 30 to 401 b during the 10-week period following weaning while others had actually lost weight in the same period. Hay-type pasture was, of course, generally only seen on adequately stocked areas in very growthy seasons but the significant finding had been that successive increments of feed were accompanied by successive increments in growth rate and only at impossibly high levels of feeding did further increases in growth cease. Exceptions But as with all rules there were exceptions and in the present case there were instances of high growth rate on apparently bare pastures and actual ill-thrift on abundant pasture. The high growth rate on bare pasture had the same basis as chisel mouthed sheep on tussock country. That was the low stocking rate and variety of grasses, clovers and weeds permitted a high degree of feed selectivity ensuring a high intake of high quality feed. Under these conditions lamb health was invariably good but peracre production was low. There was also a rational explanation for instances of ill-thrift on abundant pasture, which incidentally was the form experienced in Ashburton county in the spring and summer of 1956-57. Station trials and North Island plant analysis had shown that rapid pasture growth resulted in a low selenium concentration and as herbage maturity advanced mineral concentration declined still further. This was the probable reason for selenium deficiency being of greatest importance in abnormally growthy springs and dry summers. Deficiencies of other minerals, internal parasites and unpalatable or toxic pasture could also cause ill-thrift on abundant feed, but the commonest cause of this condition was found to be selenium deficiency. Selenium responses in lambs were generally greater after weaning than before and selenium treated lambs commonly grew 0.2 to 0.51 b per week faster than their untreated mates. As was the case with unweaned lambs, copper, cobalt, iron, manganese and zinc were almost invariably found to be without effect. Though relatively unimportant in

Canterbury cobalt deficiency was important in the north and south of the South Island and the volcanic plateau of the North Island and the use of cobalt bullets for the correction of this disease was now standard practice.

Very recently, however, it had been found that quite frequently these bullets not only failed to give a growth stimulation burt actually induced a growth depression. In one of this season’s trials cobalt topdressing, weekly dosing and single bullet methods of cobalt administration were being compared. Steel bullets of identical shape to their cobalt counterparts were included in order to distinguish chemical effects of the bullets from their physical effects of possible intestinal blockage. This trial with 160 lambs had now been in progress at Winchmore for about three weeks and similar trials were being conducted at Wallaoeville and Invermay.

Weaning High Lowage plane plane 7 weeks ., ... 3548 38 2 10 weeks . ... 46.0 40.0 13 weeks ... 52.0 41.4 16 weeks .. ... 57.6 42.2