Sheep reproduction - 2015 in review
For many sheep producers across the region, 2015 has been a roller coaster ride. The journey so far has seen an excellent joining period with high conception rates followed by a long, cold, winter where the combination of high pregnancy rates, poor feed quality, over-fat stock and worms caused headaches for some. Now that lambing is finished for most flocks, I think there are some really valuable lessons that we can take away.
The value of body condition at joining
One of the biggest things this year has highlighted (or perhaps reminded us about) is the impact of body condition on reproduction, or more specifically, conception rates. Comments from a number of producers and scanning contractors was that scanning rates were generally well up as a result of more twin-bearing ewes. This was a direct result of summer rainfall and ewes being in top condition at joining. Maiden ewes also joined up particularly well thanks to the excellent growing season in 2014.
I get the feeling that there is still come confusion among producers when it comes to ewe management prior to joining. Some producers aim to have their ewes on a "rising plane"; while others say as long as they are in good condition they'll be right. So, what's the correct answer?
To answer this question it's important to understand the two different ways that nutrition and liveweight (body condition) affect ewe fertility – these are known as the 'static' effect and the 'dynamic' effect.
The static effect is where ewes of superior condition (i.e. 'heavier ewes') have higher ovulation rates than lighter ewes of the same frame size. This relationship has been consistent across many experiments over the years. Research from the NSW Lifetime Wool project in the early 2000s showed that a 1 score increase (fat score) at joining results in 12-13 more foetuses scanned per 100 ewes (Figure 1). This increase in reproduction efficiency is a result of more twin-bearing ewes.
The other critical thing to note from the NSW Lifetime Wool project is that change (loss or gain) in liveweight or fat score in the month prior to joining did not have a significant influence on conception rate, provided that they were at the target fat score when the rams went out. In other words, it doesn't matter if ewes are on a 'rising plane' or losing weight prior to joining, as long as they are in good condition at joining you can expect to get a good result. This was evident in 2015 where ewes were probably losing a bit of condition during joining, but were coming off a high base as a result of summer rainfall.
Figure 1: The positive relationship between fat score and the number of foetuses scanned/100 ewes joined (source: Hatcher et al 2007, Primefact 151 Fat score of ewes at joining: the benefits of optimal nutrition)
The dynamic effect, also known as 'flushing', involves giving ewes, which are in relatively poor condition, an improved diet for a short period prior to and during joining so that they are rapidly rising in condition when they meet the ram. The 'rising plane' approach that we commonly hear about is
more applicable when sheep are coming from a relatively low base. This is where we can use nutrition to 'trick' the ewe's internal feedback system that she is in better condition than she actually is. Historically producers have used lupin grain to 'flush' ewes, however recent research has shown that
high quality pasture can do the same trick.
While 'flushing' can be highly effective at stimulating ovulation rates (and hence conception rates), research suggests the response isn't as consistent as having ewes in good body condition (i.e static effect).
- Aim to have ewes in fat score 3 for joining. Replenish lost fat reserves immediately after weaning. It is much easier to put weight on at this stage before pasture quality declines.
- Absolute body condition (static effect) gives the most consistent result in terms of conception rate. Once fat score targets are met, ewe condition can simply be maintained.
- The 'rising plane' rule doesn't apply if ewes are in good condition at joining. In fact, ewes can even be losing weight, as long as they are still in good condition at joining.
- A 'rising plane' is more applicable when sheep are coming from a relatively low base prior to joining (e.g. fat score 2 – 2.5). This strategy can work quite well in difficult seasons when ewes are in lighter condition. However, this should be seen as 'Plan B' as this method isn't as reliable as having ewes in good condition.
- For maiden ewes the focus should be on achieving critical mating weights, not fat score targets.
Don't let summer rain catch you out
One of the downsides of summer rainfall and growing a lot of feed early in the year is that we tend to pay the price later on in terms of winter growth rates as a lot of nitrogen has been used up. Pasture quality (i.e. digestibility) also suffers if it is not actively managed. This year we had a number
of heavy frosts that hit our pastures hard, particularly pastures that were carrying a lot of feed from the summer rain. Frosts not only slow down pasture growth, but they also have a negative impact on pasture quality (digestibility). A number of producers were caught out by this – pastures that
visually looked okay but were not providing enough energy to meet ewe demand. This was particularly evident on the Monaro with ewes losing a lot of weight during pregnancy due to poor quality feed combined with high worm counts. Lambing percentages and lamb growth rates were hit hard in some flocks as
a result of ewe deaths and ewes lambing down in poor condition with poor milk supply.
Not surprisingly, pregnancy toxaemia also raised its head this year and was generally the result of twin bearing, over fat ewes eating low quality feed. Interestingly, pregnancy issues are much more common in over-fat ewes compared to their lighter contemporaries. Over-fat ewes tend to deposit a lot of fat in the abdominal area, further restricting feed intake and increasing the risk of pregnancy toxaemia. Over-fat ewes are also more likely to have difficult births and feet issues (i.e. foot abscess).
- In years where we experience good growing conditions in late summer/ early autumn grazing management in autumn becomes critical, especially paddocks that are earmarked for lambing. Grazing these paddocks in autumn will help plants become 'frost hardened' as we move towards winter, reducing the impact of frost on pasture quality.
- Pregnancy issues are much more common in over-fat ewes. The key to managing body condition is acting early - if ewes hit the last 6-7 weeks of pregnancy and they are too fat then we are in real trouble as we can't restrict their diet in the last trimester. The first 100 days is your only opportunity to control weight gain.
- Fat scoring ewes at the end of joining helps to identify future management:
FS 2.5 = aim to achieve slight weight gain in the lead up to birth.
FS 3.0 = manage ewes to maintain weight during pregnancy.
FS > 3.5 = aim for slight weight loss (1/3 of a fat score) in the first 100 days.
Watch out for worms!
While providing adequate nutrition during pregnancy and lactation is essential in maximising production, a lot of the 'nutritional' benefit can be lost or nullified if worms are not kept to a reasonable level. A number of producers were caught out this year - over estimating the impact of the cold, frosty conditions on scour worms. Unfortunately the main scour worms (black scour, brown stomach) and barbers pole worm are able to survive quite well against frosts, especially if they are protected by a large overburden of pasture, and can quickly cause significant damage.
A number of properties across the south east region lost ewes due to the combination of malnutrition and/or high worm burdens. Lamb performance also suffers when worm burden is high due to scouring and reduced milk supply from the ewe. Implementing a sound worm management program is essential. Worm management should focus on using a range of tools such as strategic grazing to prepare low-worm pastures in lambing paddocks, using faecal egg testing in combination with an effective drench, weaning early (i.e. 12 -14 weeks from the start of lambing) and where possible selecting rams with a favourable WEC breeding value. The WormBoss website is a fantastic resource loaded with great information on managing worms: www.wormboss.com.au
- Keeping the worm population in check is an ongoing battle and needs to be actively managed to reduce significant economic loss.
- A worm management program that uses a range of tools (not than just relying on drenching) will be the most effective in controlling worms.