- Preliminary results of selection for resistance / resilience to Haemonchus contortus in a South African Dohne Merino sheep flock
PRELIMINARY RESULTS OF SELECTION FOR RESISTANCE / RESILIENCE TO HAEMONCHUS CONTORTUS IN A SOUTH AFRICAN DOHNE MERINO SHEEP FLOCK
M.A. Snyman1# & A. Fisher2
1 Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa
2 Queenstown Provincial Veterinary Laboratory, Private X7093, Queenstown, 5320, South Africa
#Corresponding author: Gretha Snyman
Background: The farm Wauldby, in the Stutterheim district, has a well-documented history of heavy Haemonchus contortus challenge and of Haemonchus resistance to all five major anthelmintic groups on the market prior to 2011. At the end of 2011, a project aimed at selection for resistance to Haemonchus was implemented in the Dohne Merino stud on this farm.
Aim: The aim of this study was to evaluate the progress made in selecting for resistance / resilience to Haemonchus contortus in the Wauldby Dohne Merino flock to date.
Selection in the stud was aimed at increasing resistance to Haemonchus contortus, while maintaining reproductive performance, body weight, wool weight and fibre diameter and improving wool quality traits. A select flock was established in 2012. The aim with this flock was to create a line in which the most resistant ewes were mated to the most resistant rams. Only ram and ewe lambs that were never drenched were considered for selection into the select flock. Selection for resistance to Haemonchus contortus was based on a selection index incorporating faecal egg counts (FEC), Famacha© score (FAM) and body condition score (BCS), as well as BLUP-EBV for FEC. FEC, FAM and BCS of all lambs were recorded annually from January until July for the 2011- to the 2015-born lambs. FAM was recorded weekly and FEC and BCS every 14 days. Lambs were only drenched when they had a FAM of 2.5 or more, in conjunction with a BCS of less than 1.5. Body weight was recorded monthly.
Results and Discussion: During the first year of the trial, 43% of the ram lambs and 68% of the ewe lambs were not dosed after weaning. A total of 57% and 32% were dosed from one to three times during the 2012 recording period. In 2014, 58% of the ram lambs and 80% of the ewe lambs did not need dosing after weaning, while these percentages further increased to 81% for the ram lambs and 83% for the ewe lambs for the 2015-born lambs. One of the most significant results of the trial to date was the increase in percentage offspring of the sires that did not need dosing. The best performing sire used during 2011 had 53% lambs that did not need dosing, while 74% lambs of the poorest sire needed dosing. In 2015, 39% lambs of the poorest performing sire needed dosing, while 93% of the best sire did not need dosing. Furthermore, 70% of the offspring of the ewes in the selection line did not need dosing, while 50% of the offspring of the unselected ewes did not need dosing. Of the offspring of the unselected ewes, 37% were dosed once, 10% were dosed twice and 3% were dosed three times during the recording period between January and July. The corresponding percentages for the selected ewes were 24.5%, 5% and 0.5%. Body weight of the ram and ewe lambs that were not dosed after weaning was higher than the body weight of those lambs that were dosed.
Conclusions: The preliminary results indicated that progress was made when selecting for resistance / resilience to Haemonchus contortus in the Wauldby Dohne Merino flock.
Proc. 50th Congr. S. Afr. Soc. Anim. Sci. Port Elizabeth, September 2017