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Estimated breeding values of dairy sires regarding colostrum traits
Soufleri, A., Banos, G., Panousis...
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Objectives
Colostrum administration provides newborn calves with important nutrients (fat, protein, lactose) and immunity (IgG). Significant heritability estimates have been reported on colostrum traits ranging from 0.15 to 0.27, suggesting the traits can be improved with selective breeding based on estimated breeding values (EBVs) of selection candidate. The objective of this study was to derive and examine EBVs of Holstein sires for colostrum traits.
Materials and Methods
The study examined daughter of 67 Holstein sires, raised in 6 commercial dairy herds in Northern Greece. Number of daughters (purebred Holsteins with full pedigree) for each sire ranged from 5 to 49; the total number of cows with records in the study was 699. These cows calved between February 2015 and September 2016. Cows were milked completely after calving and a colostrum sample was collected. Fat, protein and lactose content (%) were determined with Milkoscan. Colostrum total solids (TS) were assessed with a digital Brix refractometer and expressed in % Brix values. Sire EBVs for colostrum traits (TS, fat, protein and lactose content) were derived with univariate statistical analyses based on a mixed model. The model included the effects of farm, parity number, calendar season, age at calving, colostrum yield, time interval between calving and colostrum collection, dry period length, cow body condition score at calving and milk yield of previous lactation, and the random animal additive genetic effect. The ASREML software was used for all statistical analysis.
Results
Sire EBVs were normally distributed. The EBV for colostrum TS ranged from a -4.05 to +3.47 (average EBV reliability 0.42). The EBV difference between the 10th and the 90th percentiles was 3.20% (-1.50 and +1.70, respectively). The phenotypic difference in % Brix values between daughters of sires in the 10th and 90th percentiles was 5.6% (22.6 and 28.2, respectively). The EBV for colostrum fat content ranged from a -2.60 to +1.29 (average EBV reliability 0.29). The EBV difference between the 10th and the 90th percentiles was 2.23% (-1.56 and +0.67, respectively). The phenotypic difference of fat content between daughters of sires in the 10th and 90th percentiles was 3.7% (4.2 and 7.9, respectively). The EBV for colostrum protein content ranged from a -2.76 to +2.04 (average EBV reliability 0.34). The EBV difference between the 10th and the 90th percentiles was 2.32% (-0.92 and +1.40, respectively). The phenotypic difference of protein content between daughters of sires in the 10th and 90th percentiles was 4.4% (15.7 and 20.1, respectively). The EBV for colostrum lactose content ranged from a -0.34 to +0.38 (average EBV reliability 0.24). The EBV difference between the 10th and the 90th percentiles was 0.33% (-0.21 and +0.12, respectively). The phenotypic difference of lactose content between daughters of sires in the 10th and 90th percentiles was 0.9% (1.7 and 2.6, respectively). Three bulls had positive EBVs and 5 had negative EBVs for all four traits studied. When considering TS, fat and protein content only, 13 bulls had positive EBVs and 19 had negative EBVs for all three traits. Mean EBVs for the 13 "positive" bulls were 1.05, 0.44 and 0.61, for TS, fat and protein content, respectively. Mean EBVs for the 19 "negative" bulls were -1.10, -0.66 and -0.67, for TS, fat and protein content, respectively.
Conclusions
Variability in sire EBVs regarding colostrum traits supports the concept of genetic selection leading to trait improvement. A synthetic colostrum quality index could be potentially developed comprising sire EBVs on individual traits. This index could be eventually included in an overall performance index that will drive future breeding programs.
Keywords: Breeding values, sire, cow, colostrum.
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