Thursday, 20 May 2021 14:55

Managing ewes when covers are low

Written by  Professor Paul Kenyon
Farmers facing poor feeding levels going into winter need to be planning and considering their options. Farmers facing poor feeding levels going into winter need to be planning and considering their options.

The dry in some regions of New Zealand has resulted in sheep farmers wondering how they will get through the coming winter and the impacts this may have one the number and weight of lambs weaned. Massey University's Professor Paul Kenyon looks into the issue.

It is well established that poor feeding levels and thin ewes in late pregnancy and in lactation results in decreased colostrum and milk production, lighter lamb birth weights and reduced lamb vigour, brown fat levels and bonding behaviours between ewes and their lambs.

Combined, these result in lower lamb survival and lighter lambs at weaning. Therefore, farmers facing poor feeding levels going into winter need to be planning and considering their options.

Information is the key and this needs to be focused on feed availability and predicted ewe demand. Farmers need to determine, even if it's just an estimate, current feeding covers and winter supplement reserves, including winter crops, and predicted pasture growth. Ewe information needed includes, ewe body condition, number of fetuses carried and indicators of early versus late lambing ewes, whether this is through mating harnesses or via pregnancy scanning.

The folllowing outlines what farmers may wish to consider during the early-and-mid-pregnancy period.

In early pregnancy ewes can be returned to maintenance feeding levels to allow pasture covers to recover - if it is still warm enough for growth. This can be achieved with allowances in the range of 1.2 to 1.5kg DM per day, depending on ewe size or by grazing down to approximately 700kg DM/ha. The group of ewes that farmers may wish to feed above maintenance levels are thin ewes to allow them to gain condition. This should be considered in a highly fecund flock, as most ewes will be carrying multiples, and it's the thinnest 15 to 20% of ewes that likely have the biggest negative impact on overall ewe flock performance.

In late pregnancy, multiple bearing ewes cannot eat enough herbage to meet their nutritional needs. They try to meet this demand by utilising their body reserves. Thin ewes could be in the winter rotation before the majority of the flock, in a truck-and-trailer approach. It may be tempting for some farmers to offer good condition ewes slightly below maintenance levels, as a means of saving feed. However, farmers need to be careful with this approach if ewes' loose excessive condition.

If mating harnesses have been used, ewes without tup marks should be sold to save feed. If covers are extremely low, farmers who traditionally breed hoggets should consider not breeding them this year. In mid pregnancy, farmers need to get their flock scanned obtaining information on dry, single-, twin- and triplet-bearing ewes and data on early or late lambing. This - combined with body condition - will allow for targeted feeding for the remainder of the pregnancy period. Farmers may be concerned about the cost of this information. However, Australian modelling has shown that if best practise feeding guidelines in pregnancy and lactation are followed, based on the previously mentioned scanning information, for every dollar spent up to five dollars can be returned. Non pregnant ewes should be sold, saving feed. If pregnant ewes need to be sold, due to low pasture covers, there are three options to consider – late lambing ewes, singleton bearing ewes or older ewes. Late lambing ewes will on average result in lighter lambs at weaning time, which are often less valuable. Singleton bearing ewes can never wean as much total lamb weaning weight, compared to a multiple bearing ewe that successfully rears more than one lamb.

Mid-pregnancy is the period to utilise winter crops such as brassicas as a means of ensuring ewes are well fed and to save pasture for later in pregnancy and in lactation. In the last few weeks of pregnancy, bulb-based brassicas can limit ewe intake due to their high-water content and should be avoided.

Post pregnancy scanning, if herbage levels are still below where they should be, the amount of feed individual ewes are offered in the mid-to-late-pregnancy period should be based on the hierarchy of need.

Ewes can be divided into four groups. Ewes that need the most feed post scanning are thin first cycle multiple bearing ewes. Followed by better condition, first cycle multiple bearing ewes. Then the first cycle singletons – and lastly – all of the late lambing ewes. Remember these later lambing, second cycle ewes, which might be 20 to 25% of the ewe flock, are in an earlier pregnancy stage at scanning and therefore can be offered lower feeding levels and pushed a bit harder. Further for these ewes, their late pregnancy period will be in the early spring period, hopefully when pasture covers are rising and therefore, they can cope with being pushed a bit harder in winter.

Whether farmers have their pregnant ewes in two, three or four management nutritional groups in the winter rotation post scanning, should be based on feed availability. When covers are low holding the less demanding ewe groups back and focusing any spare feed on first cycle, multiple bearing ewes – especially thin ones – is the optimal approach when using targeted feeding.

Better condition multiple bearing ewes and singleton bearing ewes can be offered slightly lower allowances and be forced to graze down to slightly lower post grazing covers. However, during the last three ewes of pregnancy, post grazing covers and allowances will need to be increased further.

It is also important in the mid-to-late-pregnancy period that farmers consider the order of paddock grazing for their winter rotation. They need to ensure those paddocks that are best for lamb survival and growth are grazed easiest in the rotation. This means these paddocks have the longest time to regain covers prior to set stocking and have multiple bearing ewes in them for lactation performing at a high level.

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