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Association among serum IgG concentrations in newborn dairy heifers and fertility, milk yield, and survival to first lactation.

A. Velasquez Munoz

T156
Association among serum IgG concentrations in newborn dairy heifers and fertility, milk yield, and survival to first lactation.
A. Velasquez Munoz*1, P. Pinedo1, C. Shivley2, N. Urie2, J. Lombard2. 1Colorado State University Fort Collins, CO, 2USDA–APHIS–Veterinary Services Fort Collins, CO.

The objective was to analyze the associations between serum IgG concentrations in newborn Holstein heifer calves (mean ± SE = 3.7 ± 1.7 d old) and fertility, milk yield, and survival to first and second lactation. A retrospective study was performed with data from calves (n = 193) born in 4 farms in CO over a 12-mo period (June 2014 to June 2015). Calves were enrolled to evaluate pre-weaned heifer health and productivity as part of a national study where serum IgG concentrations, health events, and ADG were analyzed. Calves were categorized by serum IgG concentrations into 4 categories: A = ≥25.0 g/L (n = 79); B = 18.0—24.9 g/L (n = 57); C = 10.0—17.9 g/L (n = 36); and D = <10.0 g/L (n = 21). Data were analyzed using SAS. Season and year of birth were included as covariates in the analyses. Outcome variables included survival to 1st and 2nd calving, age at 1st calving, 305d milk yield for lactation 1, and days to conception after 1st calving. Binary outcomes (survival) were analyzed by logistic regression, while ANOVA regression was used for continuous outcomes. Models included serum IgG category, season and year of birth as fixed effects and farm as random effect. Overall, 143 (74.1%) calves reached 1st calving (A = 81.0%; B = 70.1%; C = 69.4%; D = 66.6%; P = 0.3) and 105 (54.4%) started a second lactation (A = 64.5%; B = 47.3%; C = 44.4%; D = 52.3%; P = 0.1). No difference was observed in the odds of culling in the 1st lactation by IgG category (P = 0.4). A significant difference in age at 1st calving (mean ± SE) for A (715 ± 8 d) vs. C (760d ± 12 d), and D (695 ± 16) vs C (760d ± 12 d; P = 0.005) was established. Milk yield was not associated with serum IgG category (P = 0.3). Average 305d milk production (±SE) in 1st lactation was A = 8,750 ± 706 kg; B = 7,626 ± 847 kg; C = 7,345 ± 1,050 kg; and D = 8,517 ± 1,469 kg. Days to conception after 1st calving (±SE) did not differ among IgG categories (A = 113 ± 13 d; B = 152 ± 19 d; C = 131 ± 23 d; and D = 169 ± 31 d; P = 0.6). In conclusion, status of passive immunity, indicated by serum IgG concentration early in life, affected age at first calving but did not impact fertility, 305d milk yield, or survival to or through the first lactation.

Keywords: heifer, immunity, survival.