Long-term effect of minor genetic changes of milk components on somatic cell count
2018
Barbara Luštrek | Ana Kaić | Miran Štepec | Jurij Krsnik | Klemen Potočnik
Selection pressure on protein content (PC), and thus milk composition changes have manifested as an increasingly narrow fat - protein ratio (FPR). In addition, higher somatic cell count (SCC) in milk has been observed in recent years, and that is why it is hypothesized that milk composition changes affect cow’s immune response resulting in higher SCC. 2,459,250 test day (TD) records of 127,499 Slovenian Simmental (SIM) cows from years 2004 to 2017 were used for this study. For the estimation of (co)variance components two multiple trait animal TD models were used (M1, M2). M1 included SCC and FPR while M2 included SCC, fat content (FC) and PC. For comparisson of results parameters from the routine single-trait national genetic evaluation were used. Heritability estimates (h²) for SCC, FC and PC from M2 (0.34, 0.29 and 0.38, respectively) were very similar to those form national evaluation; h² for FPR was lower than for the other traits (0.22). Both, estimated genetic correlation ("r" _"g" = 0.1) and estimated phenotypic correlation ("r" _"p" = 0.007) among SCC and FPR in M1 were negative and low. "r" _"p" in M2 were positive, but low for all three trait pairs (0.062 0.076) and "r" _"g" for SCC PC was similar (0.069). Conversely, FC PC "r" _"g" (0.502) was positive and moderate whereas SCC FC "r" _"g" ( 0.046) was negative and low. Results confirm the hypothesis by suggesting the possibillity of unpredicted and unwanted long term cumulative effect of seemingly irrelevantly small genetic changes of individual trait.
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