Genetic Evaluation of Brown Swiss Cattle in the United States
Open Access
- Author:
- Gibson, Keith Daniel
- Graduate Program:
- Animal Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 08, 2015
- Committee Members:
- Chad Daniel Dechow, Thesis Advisor/Co-Advisor
- Keywords:
- dairy cattle
Brown Swiss
genetic evaluation
Data Envelopment Analysis - Abstract:
- Genetic parameters were estimated for Brown Swiss dairy cattle using a population from the United States born in 2000 and later. The data set consisted of 108,633 first through fifth lactation records from 45,464 cows for yield, somatic cell score, days open, and productive life. Approximately half of the records also had observations for 18 linear type traits and 41,074 had observations for milking speed. Heritabilities and correlations amongst yield, fitness, and type traits were evaluated with 3-trait models in ASREML with fixed effects for lactation, age, and herd-calving cluster, and random effects for animal, permanent environment, and residual. The heritabilities of milk, fat, and protein yield were 0.30, 0.20, and 0.20, respectively. The heritabilities of productive life, days open, SCS, and milking speed were 0.11, 0.03, 0.12, and 0.26, respectively. Milk, fat, and protein yield had strong positive correlations with productive life (0.67 to 0.71), days open and SCS had strong negative correlations with productive life (-0.69 and -0.60, respectively), and milking speed had a positive correlation with productive life (0.26). All three yield traits were slightly unfavorably correlated with days open, but there was little relationship found between yield traits and SCS or milking speed. Correlations of body traits with yield and fitness traits tended to be small, though dairy form was positively correlated with yield (0.31 to 0.40) and negatively correlated with days open (0.36 to 0.67). Of the feet and leg traits, mobility was most favorably correlated with yield (0.26 to 0.27) and productive life (0.50). For udder traits, yield traits were positively correlated with rear udder height and rear udder width, ranging from 0.19 to 0.48, and negatively correlated with udder depth and fore udder attachment, ranging from -0.04 to -0.40. However, udder depth and fore udder attachment were more favorably correlated with SCS (-0.26 and -0.14, respectively) than rear udder height and rear udder width (-0.02 and 0.18, respectively). Productive life was most strongly correlated with fore udder attachment, rear udder width, udder depth, and rear udder height (0.44, 0.40, 0.35, and 0.33, respectively). Due to the importance of the relationship between udder traits with yield and fitness traits, an additional analysis was performed using the same data set to create an “udder efficiency” trait for Brown Swiss cows using Data Envelopment Analysis (DEA). The DEA assigned units, individual cows in this case, with an efficiency measure ranging from 0 to 1 based on their ability to minimize inputs and maximize outputs relative to other cows in the same herd. The sole input was the inverse of milking speed and the outputs were defined as milk, fat, and protein yield, and the inverse of somatic cell score. The most efficient cows would be those that milked quickly and produced large volumes of milk, fat, and protein with a low somatic cell score. The 40,960 udder efficiency records were derived and evaluated using 3-trait ASREML models as previously described. The heritability of udder efficiency was estimated to be 0.23 ± 0.0133. Genetic correlations with udder efficiency were positive and moderate for yield traits (0.40 to 0.42), favorable with SCS (-0.21), and strongly positive for milking speed (0.86). Udder efficiency was also strongly correlated with productive life (0.69). Of the udder traits, rear udder height (0.30), teat length (-0.28), fore udder attachment (0.25), and rear udder attachment (0.21) were most favorably correlated to udder efficiency. The correlation of udder depth with udder efficiency was 0.16. Based on these findings, DEA could be a useful and novel method for evaluating udder efficiency, helping to identify traits that enable selection for mastitis resistance without compromising yield. Results from the estimation of genetic parameters for U.S. Brown Swiss will allow for improved genetic selection for the breed.