BY: TREVOR COOK
The lamb crop recently weaned is an outcome of several factors that started last summer. There are some key points of influence that can make that outcome less exposed to chance. Less exposed to what the weather does. That lambing outcome begins with how many lambs get conceived. While we do not get paid for a pregnancy scanning result, it does set the potential for how many lambs can be weaned.
The single most common cause of a lower than the potential pregnancy scanning is at mating time there are too many ewes below body condition score three. Interestingly for all of our key breeding systems, dairy, sheep, beef cows and deer, too many dams being too light at mating is the most common failing. It sounds easy to manage this, but it requires an intervention plan to be certain there are minimal ewes too light at mating. Just feeding the flock better does not do it. I advise that it requires two events between weaning and six weeks before mating that the flock is condition scored and those below three are given feeding priority. The scanning percentage is largely driven by how many ewes are too light. So it is not about flock averages. It is about identifying all ewes below three and feeding them to get their body condition up. I put six weeks before mating as the last date to be able to rescue light ewes because late summer pastures are often not that flash and those light ewes require priority time on those pastures to gain condition. Of course if they go onto specialist feeds that time can be a lot shorter.
There are many guidelines on the Beef + Lamb NZ website about condition scoring ewes. The single site one I use to enable fast condition scoring is demonstrated there. Visually condition scoring ewes will leave up to 50% behind of those that will benefit from being given preferential feed. The return on the feed required to bring a condition score two ewe up to mate in condition score three is about 45 cents/kg DM. It is the most profitable use of feed. Compare that with summer lambs or weaner bulls which are at best 20 cents. Manually condition scoring is an imprecise process but it is better than visually doing it.
Weighing can be a substitute for condition scoring but is hampered by variations in frame size influencing the weight. Age classes can have different frame sizes due to the summer they were a ewe lamb. A drought summer often sets a ceiling on the frame size of a ewe lamb. If there has been the introduction of rams from different sources, differing frame sizes can result. The wool cover contributes to the weight. Of course gut fill can have a big impact on the weight recorded.
Body weight also important
For two-tooth ewes the importance of condition score still applies. But actual body weight is also influential. A fat but light two-tooth will not scan as well because of it being heavier but having less fat. I like to see rising two-tooth ewes weighed twice from hogget weaning to six weeks before mating and light ones taken out. The target for them is to have a minimum mating weight that is 90% of mature ewe weight. So for a flock that has an average mature weight of 70kg, the two-tooth ewes need to mate at 63kg or more. A common reason for a big difference between the two and mixed age scanning is because too many two-tooth ewes are too light at mating. That scanning difference should be less than 10%.
It is about identifying all ewes below three and feeding them to get their body condition up.
In dry summers it is very important to start prioritising feed early. Most ewes will go into the summer with condition on board. They do not have to be fed well to maintain that. But to gain condition does require being fed better. Often in a dry summer that means getting first choice of not much. Getting ewes that are condition score three or more better brings much less gain than that feed being allocated to light ewes. Condition score drafting to ensure that the lights get fed rather than the heavier ones getting heavier can be necessary to create the feed needed. Condition score of ewes at mating is so important that it requires a plan to minimise the number that are behind. Leaving it to what the summer delivers is just leaving it to chance.
Feeding levels
The other management bit that underpins the pregnancy scanning is feeding levels coming into mating. At the very least ewes need to maintain condition coming into mating and for the first part of mating. At almost all costs, preventing ewes losing any condition around mating needs to be avoided. Feed planning to have the pasture available, or embarking on providing supplements, are used by many to avoid ewes being underfed at that crucial time. But even when the summer dry has not been so limiting, pasture quality can be low. This can result in ewes being underfed unless they are given choice. I like to set up a 20-day window starting 10 days before mating and extending at least for 10 days into mating in which ewes are shifted frequently. Even on poor quality pasture, given choice they can select the best, which reduces the chances of being underfed. Along with having that pasture grazing choice they might avoid consuming some of the fungal nasties that reside in our hill country pastures.
Other management actions can be important. Creating mating mobs well before mating, mixing age classes, having a sound and sufficient ram team, and not being selenium-deficient are in that list.
Looking beyond the next lambing, recognise the importance of having heavy ewe lambs before the winter and its big influence on subsequent pregnancy scannings in the young ewe classes. Being heavier means more will reach puberty. That target is 60% of mature ewe weight. A very common cause of two-tooth ewes not scanning well, other than too many being less than 90% of mature weight at mating, too many are too light going into their first winter. These two factors are interrelated, but a two-tooth that had got to the 90% but was light as a ewe hogget will scan less than if she had been heavy the previous autumn. The return on the feed to get ewe lambs heavier and reaching puberty is 40% more profitable than that feed finishing a summer lamb.
The key points of influence to maximise lamb survival will be in the next installment.
