Research Accomplishment Reports 2009

Grading-Up to Hair Sheep Genetics in a Low-Input Production System

D.K. Aaron, D.G. Ely
Department of Animal and Food Sciences

 

Non-Technical Summary

The sheep industry must reduce labor requirements and improve efficiency of lean lamb production if it is to remain economically viable. Easy-care traits that affect labor requirements include hardiness, parasite tolerance, and shedding of hair and wool to eliminate shearing. Traits contributing to production efficiency include fertility, prolificacy, ewe and lamb vigor, maternal ablity, and post-weaning lamb growth. This project will evaluate lean lamb production of hair sheep in a low-input or "easy-care" (pasture) system.

2009 Project Description

Hair sheep germplasm was initially incorporated into a flock of Polypay (PP) ewes through White Dorper (WD) rams. This has been ongoing since 2005 via a grading-up mating scheme. A contemporary group of PP ewes, bred to PP rams, is being maintained as a control. Each year, ewes are exposed to rams for a 3-wk period beginning Nov 15. Ewes and lambs are maintained as a single flock, on pasture, until lambs are weaned at 70 d. Following weaning, lambs remain on pasture and are supplemented with a concentrate mix at 2% of their body weight until entrance into the breeding flock, marketing, or harvest (55 kg) at the University of Kentucky Abattoir.

Multiple studies have been conducted in Phase I of this project to answer questions regarding maternal performance, parasite resistance or tolerance, coat characteristics, lamb growth and carcass merit of percentage WD sheep.

Results of these studies have been presented to producers and industry personnel at the following: Kentucky Small Ruminant Grazing Conference (Lexington, Jan 6, 2009), National Sheep Industry Association Covention (San Diego, CA, Jan 21-24, 2009), 40th Annual Kentucky Sheeprofit Day (Versailles, May 21, 2009) Joint Annual Meeting of the Kentucky Sheep and Wool Producers Association and Kentucky Goat Producers Association (Frankfort, Oct 17, 2009), American Dorper Sheep Breeders' Society Annual Meeting, Louisville, KY, Nov 19, 2009.

In addition, sheep were used to for producer education at three Eweprofit Schools. "Purebred" WD rams and ewes generated from the grading-up process were also made available, via sales, to producers for improving hair sheep germplasm in flocks throughout the U.S.

2009 Impact

The following conclusions are drawn from results of maternal and growth/carcass studies completed during this reporting period:

1) Incorporation of White Dorper (WD) breeding into a Polypay (PP) flock can result in ewes that are almost as productive as ewes of the foundation breed, and that eventually do not have to be sheared. Pregnancy rates are similar across ewe genetic types but lambing rates decrease as percent WD breeding increases, litter weaning weights are heaviest for 1/2 WD ewes (51 kg) but decrease as percent WD increases, and ewe weights and body condition scores are similar (69 kg, 2.4/5.0)across genetic types. When differences in age and parity are considered, percentage WD ewes (younger) may be comparable to PP ewes (older). However, PP will remain the more productive maternal breed.

2) Postweaning performance of 1/2 WD lambs is superior to PP lambs. Higher percentage WD lambs grow slower; however, this is likely the result of a loss of heterosis.

3) Indicators of Hamonchus contortus (stomach worm or barber pole worm) infection are influenced by characteristics of the ewe, which may mean susceptibility or tolerance to infection is dependent on her genetic type and production status. Higher percentage WD ewes are less susceptible to infection based on lower fecal egg counts, higher packed cell volumes, and lower FAMACHA scores.

4) Carcasses of WD cross lambs are superior to PP lambs; they yield the highest amount of lean meat and have heavier loins and racks. Fat thickness is similar for PP and WD lambs but longissimus area is 4.1 sq cm larger (18.7 vs. 14.6) for WD lambs. This adds evidence to the assumption that WD is a meaty, carcass breed.

Overall, these results imply producers who have existing wool flocks, but desire to switch to hair sheep to eliminate shearing, can do so by breeding rams of a hair breed to existing wool ewes in a grading-up mating scheme. This scheme allows a pasture-based operation to be ongoing during the grading-up process. Conversion to a WD flock from a wool flock results in ewes that do not have to be sheared, can be as productive as the parent flock, and may offer some resistance to stomach worm infestation. Lambs produced by these ewes are heavy at weaning, perform as well after weaning as parental flock lambs, and produce carcasses that are heavily muscled. Continued selection for growth rate and carcass merit will be important as the percentage of WD genetics increases.

2009 Publications

Aaron, D. K., Ely, D. G., Fink, E., and Burden, B. T. 2009. Grading-up to hair sheep genetics in a pasture-based production system. Page 50 to 52 in Proc. U.S. Sheep Research Programs, American Sheep Industry Assoc. Conv., San Diego, CA.

Aaron, D. K., Ely, Ely, D. G., Fink, E., and Burden, B. T. 2009. Factors affecting indicators of Haemonchus contortus infection in Polypay and percentage White Dorper ewes. J. Anim. Sci. J. Anim. Sci. (E Suppl. 3):36.