Heritability and Genetic Correlations of Test Day Milk Yield and Composition, Individual Laboratory Cheese Yield, and Somatic Cell Count for Dairy Ewes

Abstract

Genetic parameters for milk yield, contents of fat, total protein, casein and serum protein, individual laboratory cheese yield, and somatic cell counts (SCC) were estimated from 7492 monthly test-day records of 1119 Churra ewes. Estimates were from multivariate REML using analytical gradients (AG-REML) procedures. Except for fat content, estimates for the other routinely recorded traits (milk yield, protein content, and SCC) agreed with those previously obtained in this and other dairy sheep populations. Protein content and composition had the highest heritabilities and repeatabilities. Heritabilities for protein and casein contents were very similar (0.23 and 0.21, respectively), and genetic correlation between the traits was close to unity (0.99). Accordingly, casein content is not advisable as an alternative to protein content as a selection criterion in dairy ewes; it does not have any compelling advantages and costs more to measure. Individual laboratory cheese yield (ILCY) obtained with Churra ewes had a low heritability (0.08), suggesting that potential for selection for this parameter would be possible but is not recommended. All correlations with ILCY were high and positive except for milk yield. A high SCC was accompanied by an increase in serum protein content and involved a loss in milk yield.

Genetic selection for reduced somatic cell counts in sheep milk: A review

“…Heritability estimates, based on repeatability test-day models, range from 0.04 to 0.16 for several breeds including the Churra (Baro et al, 1994;El-Saied et al, 1998;Othmane et al, 2002), the Manchega (Serrano et al, 2003), the East Friesian (Hamann et al, 2004) and the Valle del Belice sheep breeds (Riggio et al, 2007). Other studies reported similar or slightly higher heritability estimates (from 0.11 to 0.18) for the average SCS during lactation, for Chios (Mavrogenis et al, 1999), Lacaune (Barillet et al, 2001;Rupp et al, 2003a), Latxa (Legarra and Ugarte, 2005) and Manech Red Faced ewes (Barillet et al, 2008).…”

Detection of QTL Underlying Milk Traits in Sheep: An Update

“…On a lactation basis, moderate heritabilities for milk yield have been reported in Lacaune (0.30; Barillet, 1997) and Sarda (0.30;Sanna et al, 1997), whereas the estimates are slightly lower in Spanish breeds such as Manchega (0.18;Serrano et al, 1996), Latxa (0.21; Legarra & Ugarte, 2001) and Churra (0.26; Othmane et al, 2002). Protein and fat yield heritabilities range from 0.16-0.18 (Latxa; Legarra & Ugarte, 2001) to 0.32-0.35 (Manech).…”

Estimation of genetic parameters and evaluation of test-day milk production in sheep

“…The models of Serrano et al (2001) and Othmane et al (2002) were identical in their application to our data. The coefficients of determination of the validated models ranged from 0.7600 (P-LDIM) to 0.7999 (P-FLTY).…”

“…Relationships between the milk production and the fecundity traits (litter size, number of weaned lambs) should be further analyzed by including a multi-trait approach. The milk-component effects could be used to optimize BV for milk product yield, as the dry matter content and the milk yield are negatively correlated (Othmane et al, 2002;Komprej et al, 2009), and product yield depends on both the parameters. When more records are available and the data have better connectedness, which can be facilitated by broader production recording, the random regression of days-in-milk should be tested as well.…”

“…Milk-yield breeding values for sheep are estimated using the test-day model (Othmane et al, 2002;Oravcová et al, 2006) rather than the older lactation model, because the test-day model is more accurate in accounting for the environmental variations associated with lactation.…”