Review/Oorsig Volume 23, Issue 02 - Page 20

Oorsig/Review either just use hybrid vigour in crossbreeding systems or start developing a new breed for intensive systems utilizing the best animals existing in our local breeds? 8. Methods of selecting for fertility and fecundity after the use of “modern synchronization programs” and the use of hormones, also needs a “re-look”. Now that we are not afraid of raising multiple-birth lambs any more, fecundity can be raised artificially by using higher dosage rates of PMSG. As stated above, we should maybe then put more emphasis on repeatability of conception than on litter size per se? 9. When selecting replacement ewes Magee and Hogue used the same principles as with the selection of flock sires, with some additional traits: - - - - They looked at “maternal-line selection” primarily, as opposed to sire-line selection. Once a “ram mother” was identified, those genes were multiplied in the flock predominantly via the rams. This is in direct contrast to what I see is being done on most SA farms where things are being done the other way around i.e. by selecting rams with little emphasis on maternal lines! They also noted that the season in which a ewe lamb was born, had a significant influence on her lifetime performance. The majority of their replacement lambs came from mature ewes who had “proven themselves” and who lambed down in spring. These lambs were then mated for the first time at the age of 9 months to lamb down at 14 months of age. Here in SA this will mean that the majority of replacement ewes will come from the November lambing period. If they are then mated at the age of 9 months, that would be in August to lamb down 5 months later in January. We have the same principle that we find in cattle where heifers calving for the first time, or in this case young maiden ewes who have lambed down for the first time, have lower re-conception rates. The main reason being that they are still growing and therefore need additional food levels for this, plus for production. By re-mating during the “season of best conception” i.e. during the autumn mating season in 20 April, we increase the chances of getting better conception as well as better fecundity in these ewes and thereby an increase in “lifetime performance”! - - There is definitely “method in their madness”! By using their records they “fine-tuned” their overall performance! Replacement ewe selection is therefore also done on maternal performance but season of birth, age at first mating as well as the number of lambs born after “natural synchronisation” with teaser rams, are added… (This paragraph contains a lot of “nuggets” needing extra time to be “digested properly”!) Que vadis (where to now)? It is time to climb out of the box and to look back into it – instead of just thinking outside the box! We cannot keep on doing the things in the same way as we have been doing and then expect a different outcome… If you still believe that a ewe should be raising her own offspring and/or recommend to your clients to go the “Intensive sheep farming route”, you need not look any further – the STAR Management Program is the way to go. BUT – not the way Magee and Hogue originally did it. I usually start with 5 x 21 day cycles giving 105 “high intensity days”. Ewes that “skip” rest slightly longer and mostly conceive early in the next cycle, after which they usually remain in the STAR cycle. A ewe that skips once after 2 x 219 day cycles still lambs 3 times in 2 years - 219 + 219 + 292 = 730 ÷ 2 = 365 days. 730 days equals 2 years… It is now 2019 – implement new technology and new approaches. The sky is the limit! References: Hogue, D. (2019). STAR Management | Cornell Sheep Program. [online] Blogs.cornell.edu. Available at: http://blogs.cornell.edu/newsheep/management/ reproduction/star-management