Factors affecting ewe's milk fat and protein content and relationships between milk yield and milk components

Abstract

Test-day records of purebred Tsigai, Improved Valachian and Lacaune ewes were used to analyse the effect of environmental factors on milk fat and protein content. There were 121 424 and 121 158 measurements of fat and protein content for Tsigai, 247 742 and 247 606 measurements of fat and protein content for Improved Valachian and 2 194 measurements of fat and protein content for Lacaune ewes lambing between 1995 and 2005. Overall means and standard deviations for fat and protein content were 7.77 ± 1.606% and 5.94 ± 0.690% for Tsigai, 7.48 ± 1.446% and 5.82 ± 0.620% for Improved Valachian, and 6.97 ± 1.514% and 5.62 ± 0.692% for Lacaune. For fat content, analyses showed a highly significant (P < 0.01) effect of flock-test day and a highly significant (P < 0.01) or significant (P < 0.05) effect of the month of lambing, with the only exception of the month of lambing in Lacaune. The effect of litter size was highly significant (P < 0.01) or significant (P < 0.05) in Improved Valachian and Lacaune. For protein content, analyses showed a highly significant (P < 0.01) effect of flock-test day and a highly significant (P < 0.01) or significant (P < 0.05) effect of the month of lambing. The effect of litter size was highly significant (P < 0.01) in Tsigai and Improved Valachian. Covariates of days in milk which modelled the shape of lactation curves were insignificant, except for Improved Valachian fat content (Ali-Schaeffer regression adopted for sheep). The model explained about 50% of fat and protein variation in the breeds, with coefficients of determination between 0.517 and 0.587 for fat content and between 0.495 and 0.527 for protein content. Fat and protein content were almost equally correlated with milk yield in the three breeds. Lactation curves were constructed on the basis of solutions of a statistical model employed in the analyses.

Covariance components by a repeatability model in Slovenian dairy sheep using test-day records

“…The average DMY of the Bovec (1 090 g), Improved Bovec (1 010 g) and Istrian Pramenka (731 g) sheep population in our study was much lower than DMY of East Friesian dairy breed (2 330 g) reported by Hamann et al (2004). Daily milk yield in breeds B and IB was comparable to DMY in Churra (1 008 In general, the average FC and PC in all three Slovenian breeds were lower in comparison to the previously mentioned sheep breeds observed by Ploumi et al (1998), Carta et al (2001 and Oravcová et al (2007). Contrary, all three observed breeds had higher FC and PC in milk than East-Friesian sheep reported by Hamann et al (2004).…”

The effect of stage of lactation on daily milk yield, and milk fat and protein content in Tsigai and Improved Valachian ewes

“…In contrast to previous studies of Oravcová et al (2006Oravcová et al ( , 2007, coefficients of Ali and Schaeffer (1987) lactation curve were not considered nested within parities and only one lactation curve for each milk trait in each breed was estimated here. This approach appeared to describe milk traits according to stage of lactation sufficiently, though some limitations to describe the beginning and the end of lactation curves occurred.…”

“…The AC method stands for corrected monthly test for evening/morning differences, taking into account the total volume of milk produced by the whole flock over the two milkings concerned (ICAR, 2011). Milk fat and protein content were determined using the automated infrared method and apparatus calibrated against known sample standards (Oravcová et al, 2007). The analysis of daily milk yield was based on 188403 (Tsigai) and 352094 (Improved Valachian) test-day records; at least three test-days per lactation and four flock-test-day measurements were required.…”

“…Covariance components were estimated using the REML (Restricted Maximum Likelihood) method as applied in VCE 6 (Groeneveld et al, 2010). The main effects were described in previous studies of Oravcová et al (2005Oravcová et al ( , 2006Oravcová et al ( , 2007Oravcová et al ( and 2008. The model used here was aimed to estimated only one lactation curve for each trait in each breed (i.e.…”

“…Therefore, there is growing interest in increase of milk yield and efficiency of milking. Studies analyzing the factors affecting ewe's milk yield and milk composition (Margetín et Antonič et al, 2013) such as breed, age at lambing, parity, litter size as well as studies estimating lactation curves (Oravcová et al, 2006(Oravcová et al, , 2007 were performed. Among factors that affect variation of daily milk yield, milk fat and protein content, the effect of stage of lactation was reported important by Gonzalo et al (1994), Pavic et al (2002), Komprej et al (2012).…”