The Effects of Early Health and Genetic Background on Organic Dairy Calf Growth

open_access
Open Access
Author:
Schultz, Alexandra
Area of Honors:
Animal Sciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Chad Daniel Dechow, Thesis Supervisor
William Burton Staniar, Thesis Honors Advisor
Keywords:
Calves
Organic
Growth
Scours
Serum Total Protein
Abstract:
Organic dairy producers face greater challenges in raising calves due to organic antimicrobial regulations compared to their conventional counterparts. This thesis aims to evaluate relationships among serum total protein (STP), health, and growth in the first year of life, and whether these traits are genetically distinguishable. From June 2024 through January 2025, we sampled calves on 2 organic dairy farms at weekly or bi-weekly intervals, collecting body weight (BW) during the first two weeks after birth (n=165 calves), and 1 (n=168), 2 (n=159), 3 months (n=162), and 1 year (n=128) of age. We collected blood from 47 calves to measure serum total protein (STP). Average daily gain (ADG) from birth to 3 months of age was derived. Correlations between growth outcomes and health measures, and genomic predicted transmitting abilities (gPTA) to select traits when available, were evaluated. Growth traits were evaluated with mixed models to estimate the effect of farm, STP, and health measures, with sample date treated as a random effect; parasite egg counts were evaluated with a mixed model that included the random effects of farm and calf. Results showed highly significant differences in growth and health between the two farms, with one farm exhibiting significantly lower weights and an average STP level (5.4 ± 0.81g/dL) near the failure of passive transfer threshold (< 5.2 g/dL). Lower STP was positively associated with weight at one month (W1M; P<0.1), emphasizing the lasting impact of early immunity. Birth weight was a highly significant predictor for all subsequent weight measures (P<0.01). While parasite counts sometimes showed unexpected positive correlations with weight, higher natural logarithm of Eimeria and Other egg counts significantly reduced FDM (scours severity; P<0.05), confirming the parasites' role in disease development. Importantly, lower FDM was strongly correlated with reduced ADG (P<0.01) and lower weight at three months, especially on the farm with lower STP, suggesting that scours incidence, often triggered by parasite burden, is the primary mechanism by which health negatively impacts growth. Finally, W1Y was significantly predicted by gPTA for Stature and Strength (P<0.01). These findings demonstrate that successful heifer development in organic systems is critically dependent on effective passive immunity transfer and management strategies that mitigate scours incidence. Integrating specific health metrics like FDM and STP with genomic selection for traits like STA and STR offers organic producers robust avenues for improving calf health and growth, reducing reliance on restricted treatments.