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1722
Genetic and non-genetic effects on performance traits in a U.S. population of dairy sheep
There are relatively few dairy sheep operations in the U.S., but the industry is growing. Genetic improvement in dairy flocks has come through “breeding-up” ewes of common meat and wool breeds to European dairy breeds with imported rams and semen. This process has led to a crossbred domestic dairy sheep population consisting of East Friesian (EF), Lacaune (LA), and non-dairy (Meat) breeds. The objectives of this research were to: 1) determine the non-genetic factors affecting ewe performance, 2) estimate genetic parameters of and among traits, and 3) evaluate the genetic trends in traits of economic importance. Data were obtained from flock records collected at the Spooner Ag Research Station, University of Wisconsin-Madison from 1995-2015. There were 5,438 records on number of lambs born per ewe lambing (NLB) and 4,763 records on 180-d adjusted milk (MY), fat (FY), and protein (PY) yield, and percentage fat (%F) and protein (%P). There were 1,969 and 1,688 ewes with NLB and lactation records, respectively. The two multiple trait repeatability models jointly analyzed NLB, MY, FY, and PY or NLB, MY, %F, and %P. The significant fixed effects were trait dependent but included proportion of EF and LA breeding, EFxLA and LAxMeat specific retained heterosis coefficients, age of ewe at lambing, and production year. The estimated heritabilities were 0.08 ± 0.02, 0.30 ± 0.04, 0.26 ± 0.04, 0.29 ± 0.04, 0.53 ± 0.04, and 0.61 ± 0.04 for NLB, MY, FY, PY, %F, and %P, respectively. NLB had a negative genetic correlation with %F (-0.25 ± 0.12). However, all other estimates of genetic correlations between NLB and lactation traits were low. The yield traits had high genetic correlations with each other (0.90 ± 0.02 between MY and FY, 0.96 ± 0.01 between MY and PY, and 0.93 ± 0.01 between FY and PY). There were unfavorable genetic correlations of -0.29 ± 0.08 between MY and %F and -0.35 ± 0.08 between MY and %P. The genetic correlation between %F and %P was high (0.60 ± 0.05). The regression of MY predicted breeding value on ewe year of birth revealed an average genetic improvement of 2.60 ± 0.12 kg yr-1 from 1995 to 2014 in this population. Due to the current restrictions and difficulties surrounding importation of foreign germplasm, a national dairy sheep genetic evaluation program is key to the continued improvement of U.S. flocks.
Keywords: genetic parameters, dairy sheep, crossbreeding