Book Description

The overall objective of this dissertation was to evaluate genetic parameters of dairy calf and heifer health which are important considerations for animal wellbeing and farm profitability. Despite this, little research has been conducted regarding the genetics of health in dairy youngstock. In Chapters 2 and 3, we report genetic parameters for serum total protein in calves and the genetic correlations between serum total protein and other calf health traits. In Chapter 2, we explore serum total protein as a novel trait for selection in dairy calves. Serum total protein was measured and recorded by producers on-farm and then extracted from herd management software. Failure of passive transfer of immunity was declared for serum total protein values less than 5.2 g / dL. Stayability until 365 days of age was defined as a binary trait where calves were assigned a value of 2 if they remained in the herd and 1 if they were removed from the herd for any reason. For each trait, two datasets were analyzed: one that included all Holstein sired calves (n = 16,725) and a more restrictive dataset that required Holstein sired calves to have a recorded Holstein maternal grandsire (n = 7,518). Heritability estimates for serum total protein ranged from 0.06 to 0.08, and heritability estimates for failure of passive transfer of immunity ranged from 0.04 to 0.06. Stayability heritability estimates ranged from 0.08 to 0.11. The genetic correlation estimate between serum total protein and failure of passive transfer of immunity was near 1 while the genetic correlation estimates between serum total protein and stayability ranged from 0.19 to 0.25. Approximate genetic correlations were estimated between serum total protein and predicted transmitting abilities for health, fertility, and production traits evaluated by the Council on Dairy Cattle Breeding. Serum total protein exhibited positive approximate genetic correlations with cow livability, productive life, net merit dollars, and milk yield, and favorable correlations were also found with calving traits. Our results suggest that serum total protein is heritable and favorably correlated with measures of cow health and production. After showing that serum total protein is heritable in Chapter 3, we explore the genetic relationship between serum total protein and three additional measures of calf health: respiratory disease until 365 days of age, scours until 60 days of age, and stayability until 365 days of age. Genetic correlations were generally low between serum total protein and respiratory disease, scours, or stayability and ranged from 0.010 to 0.137 for respiratory disease and scours, respectively, with large posterior standard deviations. While numerically serum total protein exhibited an unfavorable genetic correlation with scours risk, the magnitude was small. We further explored regions of the genome explaining additive variance for serum total protein, respiratory disease, scours, and stayability through a genome-wide association analysis. The results from the genome-wide association analysis suggest that these calf traits are largely polygenic and influenced by many regions of the genome. The objectives of Chapter 4 were to estimate genetic parameters of calf health in organic US Holstein calves for three calf health traits: calf respiratory disease until 365 days of age, calf scours until 60 days of age, and heifer stayability until 365 days of age. Heritability estimates were 0.100, 0.075, and 0.085 for respiratory disease, scours, and stayability, respectively. Signs were reversed when presenting correlations such that higher correlations between scours, respiratory disease and stayability were all favored and corresponded with resistance to disease rather than risk. The genetic correlation estimate between respiratory disease resistance and stayability was 0.675. However, genetic correlation estimates between respiratory disease and scours (0.148) and between scours and stayability (0.165) were low. We also estimated approximate genetic correlations of calf health traits with other traits evaluated nationally by the Council on Dairy Cattle Breeding. These were generally low to moderate in magnitude. The strongest genetic correlation estimates were with longevity, particularly between stayability and heifer livability (0.417) and between stayability and cow livability (0.475); respiratory disease was also favorably correlated with heifer (0.355) and cow (0.296) livability. Because the approximate genetic correlation between stayability and heifer livability was only moderate in magnitude, we evaluated the random interaction of herd by sire which may indicate potential genotype by environment interaction effects; results showed that herd by sire interaction accounted for approximately 2 % of total variance. Overall, results suggest there is significant genetic variation in organic calf health, and there was potential evidence of genotype by environment interaction. Finally, in Chapter 5, we estimated genetic parameters for direct treatment costs in US organic Holstein nulliparous animals (n = 17,936). Producers provided cost estimates for veterinary treatment, on-farm supplies, and on-farm labor for respiratory disease and scours. Unique events were declared if 4 and 5 days elapsed between events for scours and respiratory disease, respectively, and treatment costs for scours and respiratory disease per animal were calculated as the product of mean treatment cost and number of unique event occurrences. Total treatment cost was calculated as the sum of respiratory disease cost, scours cost, and disposal cost (fixed at $6.00) for animals that were removed from the herd. All treatment costs were summed until 18 months of age. Average treatment costs were $56.37 and $25.21 for respiratory disease and scours, respectively. The average cost per animal were $10.19, $25.03, and $25.00 for respiratory disease, scours, and total costs, respectively. Heritability estimates ranged from 0.047 for total treatment cost to 0.057 for scours treatment costs. Total treatment cost was genetically correlated with both respiratory disease cost (0.495) and scours cost (0.465). The genetic correlation estimate between respiratory disease cost and scours cost was -0.331. Because total treatment cost was semi-continuous and right-skewed, we investigated various response variables for total treatment cost; these included total treatment cost, log-transformed treatment cost, and 2-trait conditional model with response variables any treatment cost (0 = no treatment costs; 1 = treatment cost greater than $0) and log-transformed total treatment cost conditional on treatment cost being greater than $0. The model with log-transformed total treatment cost as the response variable resulted in the highest heritability and reliability estimates while the response variable in the 2-trait model had the lowest. Predicted transmitting ability correlations with traits evaluated by the Council on Dairy Breeding were low and mostly not significant. This suggests that calf and heifer treatment costs are generally not genetically correlated with current national traits in the United States. While genetic variation for youngstock heath treatment costs was detected, heritability estimates were comparable to estimates for binary disease events despite the continuous nature of treatment costs. In conclusion, significant additive variance exists for dairy calf and heifer health traits such as serum total protein, youngstock disease, and youngstock disease treatment costs. In addition, disease and disease treatment costs were generally lowly to moderately correlated with current genetic evaluations in the United States. These results suggest there is potential to improve calf and heifer health through genetic selection.