Naslov
Effect of fat-protein ratio on somatic cell count in milk

Autori
Luštrek, Barbara ; Kaić, Ana ; Štepec, Miran ; Krsnik, Jurij ; Potočnik, Klemen

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Proceedings of the 42nd ICAR Conference: Cooperation, networking and global interactions in the animal production sector / Bryant, J., Burke, M., Cook, R., Harris, B., Mosconi, C., Wickham, B. - Auckland : ICAR Technical Series, 2018, 89-89

ISBN
92-95014-19-7

Skup
42nd Conference Cooperation, networking and global interactions in the animal production sector (ICAR 2018)

Mjesto i datum
Oakland (CA), Sjedinjene Američke Države, 10.02.2018. - 11.02.2018

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Fat-protein ratio ; somatic cell count ; milk

Sažetak
International genetic trend study in Brown Swiss bulls has revealed the largest changes in genetic trend direction for somatic cell count (SCC) (Gorjanc et. al., 2011). Somatic cells in milk are represented by epithelial cells and leukocytes (immune cells), where the latter predominate and in case of udder inflammation (mastitis) increase to extreme extent. The relation between increase of SCC and immune response is confirmed by several studies (e.g. Concha, 1986 ; Burvenich et al., 1994). Due to the low economic value of milk fat in the last decades, high selection pressure on the protein content (PC) has been applied. At the same time no selection pressure, or in some populations even negative one, has been applied on fat content (FC). Taking into account also the fact that precursors of milk components enter the mammary system from the blood, the hypothesis is that milk composition changes expressed as narrow fat - protein ratio (FPR) affect cow’s immune response and result in higher SCC. Hypothesis was tested on Slovenian Brown Swiss dairy cattle population included in national milk recording scheme. Test day records (TD) from years 2004 to 2017 were used. Data set included 862, 780 TD of 44, 821 cows. Distribution of raw SCC values was right skewed hence the data were transformed using binary logarithm and the resulting values were almost normally distributed afterwards. To estimate variance and covariance parameters animal TD models were used. Two-trait model (model 1) included SCC and FPR while three-trait model (model 2) included SCC, FC and PC. Statistical model was the same as the model in the routine national genetic evaluation. Results of described models were compared with results of variance component estimates from routine single-trait evaluation for SCC, FC and PC. Heritability estimates for SCC were almost the same for all three evaluations (0.36). Heritability for FC increased for 0.01 in model 2 in comparison to national evaluation whereas heritability for PC decreased for 0.01. Estimated heritability was lower for FPR than for the other traits (0.17). Estimated phenotypic correlation between SCC and FPR in model 1 was negative and very low (-0.001) while genetic correlation among these traits was higher though still negative (-0.100). In model 2, phenotypic correlations were low for all three trait combinations (0.062 - 0.065) but genetic correlations showed to be quite different. Genetic correlation between FC and PC was moderate and positive (0.541), between SCC and PC was low and positive (0.064) whereas genetic correlation between SCC and FC was low and negative (-0.043). Moderate and positive genetic correlation between FC and PC indicates opposite orientation compared to the estimated genetic correlations between SCC and each of these two traits. This difference is supported Effect of fatprotein ratio on SCC in milk by negative genetic correlation between SCC and FPR. The results show the complexity of the relations between considered traits. Especially traits with low and negative genetic correlations could on long term result in unexpected negative (unwanted) consequences. These results will also be tested on the other two Slovenian dairy cattle breeds. More conservative approach will have to be taken when making selection pressure changes on individual traits in breeding programs if the hypothesis is confirmed.

Izvorni jezik
Engleski

Znanstvena područja
Poljoprivreda (agronomija)

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