Research Accomplishment Reports 2011

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.

2011 Project Description

The overall objective of this long-term grading-up project was to track changes in production traits as breed composition of the flock changed from Polypay (a traditional wool breed) to White Dorper (a hair breed).

During the lifetime of the project, Polypay, 1/2 White Dorper x 1/2 Polypay, 3/4 White Dorper x 1/4 Polypay, 7/8 White Dorper x 1/8 Polypay, 15/16 White Dorper x 1/16 Polypay and White Dorper (genetic composition greater than 15/16 White Dorper)offspring were produced. Replacement ewes were subsequently selected from these six genetic types. Maternal and growth performance were measured and a random sample of lambs of each genetic type were harvested to evaluate carcass composition.

In the final year of the project, ewes of each genetic type were mated to a third breed (Hampshire, a terminal sire breed) to evaluate lamb growth and carcass composition. Over the lifetime of the project, maternal, growth and carcass data were combined and final statistical analyses are in progress. Data (FAMACHA scores, fecal egg counts and packed cell volumes) collected for evaluation of interal parasite tolerance or resistance were analyzed. Results have been shared with researchers participating in a multi-state coordinating committee (NCERA-214) and were shared with producers from Kentucky and adjoining states through five field days, four producer schools each year, grazing workshops and radio programs.

Also, data collection and analyses provided opportunities to train three graduate students and four undergraduate students. Two undergraduate research projects were conducted in association with this project. Animals of the resulting "new" breed were exhibited at state and national livestock shows and were made available for producers to purchase.

2011 Impact

Efficient lean lamb production is the goal of commercial sheep producers. An important objective of this project was to compare carcass characteristics of wether lambs randomly selected for harvest from all those produced during the period 2003 through 2010.

Percentage White Dorper breeding in the harvested lambs ranged from 0 (Polypay, n = 50), 50 (1/2 White Dorper, n = 50), 75 (3/4 White Dorper, n = 50), 87.5 (7/8 White Dorper, n = 35) to 93.75% or higher (White Dorper, n = 48). Each year lambs were born in April, creep fed on pasture, and weaned at 70 days of age. Postweaning, lambs were managed on pasture and supplemented with grain at 2 to 3% of body weight. Lamb carcasses were harvested at a live target weight of 54 kg.

Weaning weights were heaviest for Polypay, 1/2 White Dorper and 3/4 White Dorper lambs and lightest for 15/16 White Dorper lambs. Postweaning average daily gain decreased as percent White Dorper breeding increased. There were no lamb genetic type differences in age at harvest but Polypay and 1/2 White Dorper lambs were heaviest (55.8, 56.2, 55.3, 54.4 and 50.8 kg for the 0, 50, 75, 97.5 and 93.75% or higher White Dorper, respectively) and had the heaviest carcasses (25.9, 26.9, 26.4, 26.2 and 25.4 kg, respectively). Rack weight increased as percent White Dorper breeding increased. There were no differences in leg or shoulder weights. Carcasses from 7/8 White Dorper lambs were fattest while carcasses from 15/16 White Dorper lambs were leanest. Longissimus muscle area was largest from 15/16 White Dorper and smallest for Polypay lambs. Yield grades were lowest for 15/16 White Dorper lambs.

Results from this long-term project indicated carcasses of White Dorper lambs compare favorably with those of Polypay lambs for most traits. During the final year of the project, productivity of Polpay, White Dorper and White Dorper x Polypay ewes bred to Hampshire rams was evaluated. Lambing rates were lowest for White Dorper ewes. Total weight of lambs weaned was heaviest for Polpay (57.8 kg) and White Dorper x Polpay (52.6 kg) and lightest for White Dorper (46.7 kg). Polypay and White Dorper x Polypay ewes had higher condition scores than White Dorper ewes. Indicators of internal parasites (FAMACHA scores, packed cell volumes and fecal egg counts) were similar for all ewes.

Lamb production of Polypay, White Dorper and F-1 cross ewes can be increased by using Hampshire rams. Lower production of the smaller White Dorper ewes may be offset by their natural shedding, which eliminates the need for shearing.

2011 Publications

Aaron, D. K., D. G. Ely, E. Fink, B. T. Burden, M. E. Hoar, M. M. Simpson, and A. K. Lundsford. 2011. Lean lamb production during the process of grading-up to hair sheep genetics. J. Anim. Sci. 89 (E-Suppl. 1):698.