Genetic and Maternal Factors Underlying Early Milk Production and Their Influence on Calf Health

The quality of early milk produced by dams is affected by various factors (i.e. breed, age, parity, environment, nutrition, management). The impact of these factors on the quality of milk then have subsequent effects on calf health and development. Producers are responsible for following guidelines in order to ensure that they feed calves optimal quality milk in order to produce a healthy animal. They can also regulate factors such as environment and nutrition of the dam in order to produce better quality early milk. However, even after maximizing these factors there is still high mortality rate among pre-weaned calves, therefore, other factors such as mode of birth and genetics need to be studied to determine impacts on early milk quality and make further improvements to calf health and decrease mortality. Two experiments were conducted in order to study the effects of maternal and genetic factors on early milk production and to determine relationships that exist with calf health. The objective of the first study was to determine the effects that the mode of delivery had on early milk composition, and on the rumen microbiome of calves. We hypothesized that mode of birth would impact early milk composition, and, in turn, influence the microbial phyla in the calf gut. The second study had three objectives: 1) establish phenotypic relationships between colostrum composition traits, milk production traits, and calf health, 2) determine impact of breed and season on colostrum production and 3) ) elucidate the genetic parameters (i.e. heritability, genotypic, and phenotypic correlations) among colostrum production and milk production We hypothesized that colostrum composition and production differ among breeds and by season and that individual components influence calf health. Additionally, we hypothesized that colostrum quality traits (i.e. Brix score and volume) are heritable.

For the first study Charolaise (CHAR; n = 23) and Angus (ANG; n = 15) dams were divided into two experimental groups; dams underwent vaginal (VD; n= 25) or cesarean (CD; n= 13) deliveries. Early milk samples were collected and quantified for protein, lactose, somatic cell count, and fatty acid concentrations. After parturition calves were separated based on dams experimental group. Rumen fluid was collected from calves on d 1, 3, and 28 post-partum. Extracted DNA from fluid were used for metagenomic sequencing (ANG calves, n=11; CHAR calves, n=13). Samples were run on the HiSeq 2500 platform as paired end reads according to Ilumina's standard sequencing protocol. A regression analysis was done in SAS using PROC GLM and regressing mode of birth on milk components for d 1,3, and 28. After, milk components found to be significantly impacted by mode of birth were regressed against microbial counts. Results showed that VD dams were more likely to have increased (P  0.05) protein, solids non-fat, and lactose on d 1 and 3, but decreased (P < 0.05) urea concentrations. Similarly, short, medium, and long-chain fatty acids were increased (P  0.05) in VD d 3 milk. Changes in true protein elicited a decrease (P  0.05) in rumen fluid Actinobacteria and Proteobacteria; whereas, both solids non-fat and lactose were associated with an increased (P  0.05) response in d 1 transition milk. No significant results for d 28 of sampling were observed. Based on our results we suggest that mode of birth influences protein concentrations in early milk. However, only a slight impact on the overall dynamics of the calf rumen was observed with the microbiome remaining relatively stable on the phyla level in response to changes in protein concentration.

The second study looked into relationships between colostrum composition traits, management practices, and calf health, as well as determined heritability and genetic correlations for colostrum quality traits. Values for test-day milk, protein, fat, and somatic cell count (SCS) for Holstein (HO, n= 250) and Jersey (JE, n=289) cows were obtained from the Animal Genomic and Improvement laboratory server at the USDA. Brix score, colostrum weight, dam age, parity, and 3-month season of calving were also recorded. After, colostrum samples from JE cows were sent to DHIA where compositional measurements were obtained (i.e. true protein, fat, lactose, SCS, solid non-fats). Lactoferrin concentration for JE colostrum samples was also determined via ELISA. Calf blood samples were collected within 72 h post-partum and total serum protein (TSP) quantified to determine success of passive immunity transfer. Additionally, farm staff were instructed to record colostrum source for 1st feeding (i.e. dam, mix, other), freshness for 1st feeding (frozen vs fresh), Brix score of colostrum fed, volume of colostrum fed, and birth weight. A PROC Mixed with LSMEANS was performed in SAS to determine relationships between colostrum components, test day components, and quality traits for season, breed, and the interaction between season and breed. Also, PROC Mixed with LSMEANS was used to determine relationships of calf health with environment, management, and colostrum components. Additionally, a Pearson correlation was used to determine relationships between colostrum components and quality traits. Results for Holstein and Jersey showed that both colostrum Brix and volume (P < 0.001) differed by breed. Colostrum volume (P < 0.001), lactose (P < 0.001), and lactoferrin (P = 0.002) varied significantly by season. Additionally, test day milk (P = 0.046), fat (P = 0.012), and protein (P = 0.003) varied significantly by season. Moreover, a significant season and breed interaction (P = 0.028) was observed solely for colostrum volume. Calf health models indicated that TSP, colostrum total protein and solid non-fats impacted incidence of respiratory illness, but no factor significantly impacted incidence of scours. Results for Pearson correlation indicated strong correlations between true protein and solid non-fats and Brix (r = 0.99; 0.86). Lactoferrin also had moderate negative correlations with volume and lactose (r = -0.35; -0.33). Heritability and repeatability's were calculated using BLUPF90 family of programs. A single-trait repeatability animal model was used and included a 1-vector phenotype (Brix or Colostrum weight), fixed effects (i.e. calving year, parity, 3-month season of calving, and age at calving), additive genetic variance, random permanent environment effects, and random residual effects. A series of bivariate models were used to calculate genetic correlations of Brix score and colostrum weight with test-day compositional traits. Heritability estimates results for Holstein cow Brix and colostrum weight, were 0.25 and 0.15. Jersey cow heritability estimates were 0.36 and 0.47 respectively. We also observed some significant genetic correlations with Holstein Brix score and test-day milk (-0.23), fat (0.54), and SCS (0.29) having moderate correlations. Holstein colostrum weight had a strong correlation with test-day milk (0.96). Jerseys had strong genetic correlation of Brix score with colostrum weight (-0.98). Low to moderately heritability was observed for Brix score and colostrum weight in both breeds making them receptive to genetic selection in order to improve breeding programs. In conclusion, mode of birth significantly impacted colostrum composition which had subsequent effects on abundance of rumen microbiota. Colostrum Brix and volume were impacted by breed, season, and interaction, and calf incidence of disease was impacted by colostrum composition and environment. Additionally, two factors influencing colostrum quality (Brix score and colostrum weight) were found to be low to moderately heritable and have moderate to strong genetic correlations to compositional traits. Strong significant relationships were also found between colostrum compositional traits and colostrum quality traits. Therefore, incorporating quality traits into breeding programs has the potential to influence compositional traits which, in turn, can impact calf health and development by the interactions that exist between composition and microbial abundance in the rumen.