Early Weaning of Lambs on Hill Country

New Zealand Journal of Agriculture, Volume 89, Issue 5, 15 November 1954, Page 471

Early Weaning of Lambs on Hill Country

INCREASED efficiency in the utilisation of pasture and great flexibility in stock management, especially in respect to shearing, pasture utilisation, and weed control, were two of the main advantages in early weaning of lambs on hill country that were indicated in work on this subject described by E. A. Clarke, Senior Research Officer, Department of Agriculture Animal Research Station, Ruakura, in an address to .this year's Ruakura Farmers' Conference. The results of the research into early weaning, as discussed in the following adaptation of his paper, indicate what might be expected in similar early weaning of Romney lambs under average hill-country conditions.

PROBABLY the most usual time for weaning lambs in the North Island is in late December or early January, when the lambs are approaching 4 months of age. From time to time some farmers, for various reasons, have practised earlier weaning and reports on the merits of this practice have been uncertain and opinions often conflicting. T , . , . • ls uncommon to notice m a small flock where the animals are known individually or where ewes and lambs are suitably identified that lambs which become mismothered, esneciallv later in the season frequently grow well and suffer no apparent disadvantage.

Recent studies on milk production in ewes have also suggested that earlier weaning of lambs might warrant some investigation. In Fig. 1 are shown some average lactation curves of Romney ewes subjected to varying levels of feeding before and after lambing. The effect of level of feeding on the lactation curve is clearly shown. The curve produced by ewes with single lambs, under lowplane feeding both before and after i am h; n p- fT t < i nP -i P o'i nrobablv most „ g r „ n S j n ?£ e J L-S® nearly represents the situation obtainwith hill-country ewes. _ During the fourth month of lactation the lamb receives only about 10 per cent, of the milk produced in the entire

lactation period. Lambs begin eating grass at 2 to 4 weeks and consumption rises rapidly, so that by about 2 months the lambs are becoming less dependent on milk and more dependent on grass. Milk Factor L. R. Wallace has shown, for example with individually fed ewes and lambs, that lambs in the seventh week of lactation eat as much food, other than milk, as in the whole, previous 6 weeks. The declining importance of milk and the increasing importance of other feedstuffs in the diet of the lambs with advancing age is shown in Fig. 2. Under conditions

of limited feed supply it is likely that toward the end of lactation the supplementary value of the milk received by the lamb may be offset by the increasing competition between ewe and lamb for available feed. This, it should be emphasised, is occurring at a time of the year when, even in a good season, increasing animal requirements are tending to outstrip pasture production.

Furthermore, because of the decline in the lactation curve, and to some small extent the changing composition of the milk, the gross efficiency of milk production declines as lactation advances. This decline is greatest in low-producing ewes and becomes most marked after the second month. L. R. Wallace has shown, for example, that in a low-producing ewe the gross digestible energy consumed to produce lib. of milk approximately doubles by the eighth to twelfth week.

Conversion of Feed

A further loss of efficiency results from the double conversion of grass to milk by the ewes and milk to meat by the lamb. Approximate estimates only are available, but if it is assumed that the ewe is no more efficient than the dairy cow, the conversion of grass to milk is only 30 per cent, efficient. The lamb is probably also 30 per cent, efficient in the conversion of milk to body tissues, so that as the result of the double conversion efficiency falls to about 9 per cent. At the age of 3 to 4 months, however, the lamb is about three times more efficient than this (approximately 30 per cent.) in the direct conversion of grass to meat.

Such considerations as these and a limited experience in the early weaning of lambs suggested that earlyweaned lambs might grow as well as, if not better than, lambs weaned at the normal time and at the same time ■enable greater flexibility in the utilisation of grass to be achieved as well as permit greater efficiency in stock management.

Early-weaning Trial

In 1952 a flock of 200 mixed-age ■ewes was run separately, so that an early-weaning trial could be carried out with ewe lambs. It was decided that the early-weaned group would be weaned at an average age of 12 weeks, and since lambing began in late August and extended over a period of about 9 weeks, the end of November was chosen as the time of early weaning. The late group were weaned on 7 January, 5 weeks later. At the time of early weaning the lambs averaged 49.51 b. liveweight and 83 days (12 weeks) in age, but ages ranged from about 50 days to 108 days. The early-weaned lambs were a random half of the ewe lambs of the flock and were weaned on to a paddock which had been lightly grazed by cattle and spelled from sheep for about a month. The dams of these lambs were removed from the flock and replaced by the same number of ewes with lambs at foot from another flock. Thus the total flock numbers were restored and the management of the flock continued along usual lines and at the same rate of stocking. The pasture provided was as good and as plentiful as that available to other ewes and lambs on the Station. The early-weaned lambs had ample feed of good quality 'until the

time of late weaning, after which the early-weaned and late-weaned lambs were run together as one mob. The results of this trial are shown in Fig. 3, where it will be seen that the two groups, each of 40 lambs, are almost identical in their mean growth curves. Both groups grew reasonably well until 20 March, when they were again shifted to another paddock, where they rapidly lost weight. After the lambs were shifted again about a month later the growth-rate recovered and remained satisfactory thereafter. No explanation can yet be given for such paddock effects on growth-rate. It has been found in this and other trials that such paddock effects can be very marked, but so far these have been unpredictable. The worm burdens of these lambs have been followed, the standard technique being used of counting the number of worm eggs in a known

weight of dung from each lamb. The mean values in terms of eggs/gm. of dung are also shown in Fig. 3. At the time of late weaning worm burdens were quite low in both groups. Drenching with phenothiazine was begun at this time and at no stage have the egg counts reached high levels. Throughout the trial no difference of any magnitude occurred between the two groups. The amount of scouring was slight in both groups and there was no difference between groups in this respect. There were two deaths in each group and though the causes could not be determined, it was clear that parasitism was not involved. Early Weaning Satisfactory In this trial early weaning proved very satisfactory in that the early-

weaned lambs grew as well as the late-weaned ones throughout and both groups were similar in wool clip, both as lambs and as hoggets. Lamb shearing was carried out in mid-December and was greatly simplified with earlyweaned lambs, as the lambs were already separated from their dams and were brought in from the paddock when required, shorn, and immediately returned to their paddock. The late-weaned lambs had to be drafted from their dams and could not be mothered up again and returned to their paddock until both ewes and lambs had been shorn.

The early-weaned ewes, with other dry ewes, were used to clean up a paddock where the feed was rough and unsuitable for ewes and lambs and where ragwort threatened to be a problem. Thus early weaning, in addition to sparing pastures suitable for lambs, enabled ewes to be employed some 5 weeks earlier for pasture improvement.

A further advantage of early weaning is that where bidi-bidi is troublesome in some paddocks weaning in late November before the seed ripens may enable the lambs to be concentrated on the cleaner paddocks. The “seedy” paddocks can be grazed by shorn ewes and the lambs need not be shorn until desired.

Various methods of early weaning could be devised, but it should be pointed out that where the provision of spelled pastures is difficult good results might be expected by merely removing the ewes and leaving the lambs in their paddocks. As necessary the lambs could be suitably consolidated and either set stocked or rotationally grazed to allow sufficient paddocks for the ewes. Earlier mob grazing of ewes has obvious advantages in pasture control and improvement. It is’ hoped to carry out suitable trials of such methods in the near future.

In the . 1953 season, when this earlyweaning trial was repeated, feed conditions were less favourable than in the previous year, though a suitable spelled paddock with ample feed was available for the early-weaned lambs. This pasture became somewhat stemmy in the last week of December, which probably contributed to the spread of a mild outbreak of pink eye in these lambs. It is believed that these conditions were responsible for the less favourable result (shown in Fig. 4) in the early-weaned group. Over the period 29 November to 5 January the late-weaned lambs also grew slowly, but achieved an advantage of about 31b. over the earlyweaned ones. This result is less satisfactory than in the previous season, where both groups gained about 51b. to 61b. over the same period.

After late weaning both groups were run together in a fresh pasture and grew well and at identical rates for the next month. This improved rate of growth in both groups suggests that both the early- and late-weaned lambs were inadequately fed during the previous month. The similarity in the growth curves in both groups was maintained for a considerable time, but at no time did the difference between groups exceed 31b. From 13 February both groups showed the typical picture of hogget ill-thrift.

Throughout the trial parasitism was kept at a very low level with regular drenching with phenothiazine and at

no time was there any marked difference in the mean egg counts of the two groups (Fig. 5). , „ . n , „ ~ In this season a random half of the male lambs from this flock were also weaned early. The result with these lambs was similar to that for the ewe lambs at the time of late weaning, when the male lambs were withdrawn from the trial. This year also an early-weaning trial was carried out with another small flock. In this trial a random half of lambs of both sexes were weaned on to a well-spelled, leafy

pasture and the dams of these were also withdrawn from the flock but not replaced with ewes with lambs at foot. In this trial the 45 early-weaned iambs, irrespective of sex, averaged about 51b. heavier than the 45 lateweaned lambs at the time of late weaning. The result of this trial for the two groups of 20 ewe lambs each j s shown in Fig. 6. The resus o these trials have been presented in terms of group means, The records of individual animals, however, showed no serious anomalies, and in general the younger and lighter animals grew and behaved relatively

the same as the older and heavier animals. Though the results of the trials presented are not perfectly consistent, it can be said that differences in the growth pattern between late- and early-weaned lambs are either nil or small. It is most probable that the small differences seen are entirely due to feed conditions. When early- and late-weaned lambs were grazed separately every effort was made to provide each with the best feed available. With this in mind, it is believed that these results indicate the sort of result to be expected in similar early weaning of Romney lambs under average hill-country conditions. Advantages of Early Weaning The main points arising from this study may be summarised as follows:

1. Early weaning of lambs may be expected to result in increased efficiency in the utilisation of pasture. 2. In two seasons lambs weaned in early December were, [on the average, very similar in liveweight and rate of growth to lambs weaned in early January or 5 weeks later. 3. The slight inferiority in one group of early-weaned lambs in one season was most likely due to unsuitable feed rather than a deficiency in quantity of feed. 4. Differences between early- and lateweaned lambs at the time of late weaning tend to persist for some months thereafter, irrespective of rate of growth. 5. Early weaning confers great flexibility in stock management, especially in respect to shearing, pasture utilisation, and weed control.

Preventing Damage by Potato Tuber Moth

IN dry seasons in the North Island and especially in Hawkes Bay severe damage is caused to main crop potatoes by the caterpillar of the potato tuber moth. Crops growing in the lighter soils and those which dry out rapidly are attacked with much greater severity than crops on the heavier soils, which retain moisture. If no precautionary measures are taken, the whole crop can become affected and its commercial value reduced. It is not uncommon for a crop to be a complete loss.

The caterpillar does not thrive under damp conditions, so that in a wet season damage to crops is practically negligible.

The potato tuber moth is a small, brownish-grey moth about Jin. long. In a growing. crop the female lays its eggs in the eyes of any exposed tubers or at the bases of the stems. The larvae then burrow into the tubers, making them useless for commercial purposes and for seed.

The first precaution to be taken is to plant the tubers at least 7in. to Sin. deep. Rows should be not less than 30in. apart so that periodical moulding can be done throughout the growing season. The wider the rows are the better it is, as more soil is available for complete coverage of the tubers. This coverage is essential, because once the tubers are exposed they are open to direct attack by the moths. Widely spaced rows also allow for only a minimum amount of damage to the foliage when moulding is done.

The first ridging should be delayed until the foliage is well grown, though cultivation between rows is necessary to keep weed growth down. The reason for delaying the first ridging is to retain the moisture content as long as possible.

The moth is generally on the wing in mid-January, but in a very dry spring it may be noticed somewhat earlier. Spraying with lindane has been found to be most effective in controlling moth attacks. The first spraying must be undertaken as soon as the moth makes its appearance. To keep the crop free of moth damage spraying every 2 weeks is necessary. Moulding must also be done at intervals during the spraying period. In the event of rain applications of spray must begin again after the topsoil dries out.

After digging, the bags should be sewn up immediately and at no time should the foliage or haulms be placed over the mouths of the bags.

Pitted potatoes should be well covered with straw before they are sprayed. Finally, it is essential that the lindane should not come into contact with the potato tubers; otherwise a taint will be noticed after they are cooked.

—F. H. COLLIN,

Fields Instructor, Department of Agriculture, Hastings