Genetic Parameters for Mycoplasma Ovipneumoniae Nasal DNA Copy Number Provide Progress to Promote Domestic and Bighorn Sheep Coexistence on Public Lands

Authors: Wilson, Carrie - Welsh; Taylor, Joshua - Bret; Mousel, Michelle; White, Stephen; Piel, Lindsay; Wilmer, Hailey; MURDOCH, BRENDA - University Of Idaho

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Conflict between domestic sheep producers and bighorn sheep conservationists primarily involves concerns over the transmission of Mycoplasma ovipneumoniae between sheep. Mycoplasma ovipneumoniae is a respiratory bacterium that can cause subclinical disease, mild clinical disease, such as coughing, or pneumonic disease, and was reported in 85 percent of domestic sheep flocks that were tested. A genetic solution utilizing an existing phenotype, M. ovipneumoniae nasal DNA copy number (MONCN), was explored in the Rambouillet breed to evaluate if selection for reduced MONCN would be effective. The objectives of this research were to determine if measurable additive genetic variation exists in sheep with MONCN and to determine the heritability and repeatability for this trait. The level of MONCN was measured at least three times per year at the U.S. Sheep Experiment Station (USSES) from ewes ranging from 1 to 7 years of age. Repeated measures animal models were evaluated from 320 ewes with a total of 1,223 samples. Of the models evaluated, the categorical model had the highest heritability (0.12 ± 0.09) and repeatability (0.60 ± 0.05). Outcomes from this research resulted in heritability estimates from which breeding values can be estimated to select USSES rams for reduced MONCN.

Technical Abstract: Discord between domestic sheep producers and bighorn sheep conservationists primarily involves concerns over the transmission of Mycoplasma ovipneumoniae between sheep. A genetic solution utilizing an existing phenotype, M. ovipneumoniae nasal DNA copy number (MONCN), was explored in the Rambouillet breed to evaluate if selection for reduced MONCN would be effective. The objectives of this research were to determine if measurable additive genetic variation exists in sheep with MONCN and to determine the heritability and repeatability for this trait. The level of MONCN was measured at least three times per year at the U.S. Sheep Experiment Station (USSES) from ewes ranging from 1 to 7 years of age. Repeated measures animal models were evaluated from 320 ewes with a total of 1,223 samples (x ¯ = 3.8 per ewe). The MONCN values ranged from 0 to 71,654 copies per 2 µl of extracted DNA. Since the data were right skewed, with 37.5 percent of the data being 0, data were transformed, and a constant (+5) was added to remove zero values. Models were evaluated using the BLUPF90 suite and included 1) untransformed MONCN, 2) ln10 transformed MONCN, 3) Box-Cox power transformed MONCN, and 4) categorical MONCN (1 is < 100, 2 is 100 - 1,000, and 3 is > 1,000 MOCN). Fixed effects included season/year (n = 9) and ewe age (n = 7). The categorical model had the highest heritability (0.12 ± 0.09) and repeatability (0.60 ± 0.05). Outcomes from this research resulted in heritability estimates from which breeding values can be estimated to select U.S. Sheep Experiment Station rams for reduced MONCN.