1402
Physiological characteristics of cows with divergent genetic merit for fertility traits during the transition period
Cows with similar genetic merit for milk production, but with extremes of good (Fert+; n = 15) or poor (Fert-; n = 10) genetic merit for fertility traits were monitored. DMI was recorded daily from wk -2 to 5 relative to calving. Blood metabolites and metabolic hormones were measured from wk -2 to 8 relative to calving. Vaginal mucus (VM) was scored weekly on a scale 0 (no pus) to 3 (≥ 50% pus) from parturition to wk 6. Uterine polymorphonuclear neutrophil count was measured at wk 3 and 6. Continuous data were analyzed using mixed model procedures. PROC NPAR1WAY was used to analyse VM score data. Logistic regression was carried out to analyse the proportion of animals classified as having endometritis or to have resumed cyclicity by wk 6 postpartum. Prepartum DMI was similar between genotypes, but during the postpartum period, Fert+ cows had greater DMI than Fert- cows (19.7 vs. 16.8 kg DM/d, P = 0.02). Energy balance at wk 1 was greater in Fert+ cows than Fert- cows (2.3 vs. -1.12 UFL/d, P = 0.02). Fert+ cows had greater milk solids production (1.89 vs. 1.74 kg/d, P = 0.05). Fert+ cows had greater mean circulating insulin-like growth factor-I (102.62 vs. 56.85 ng/mL, P = 0.001) and tended to have greater mean circulating insulin (3.25 vs. 2.62 μIU/mL, P = 0.08) compared with Fert- cows from wk -2 to 8 relative to parturition. Mean circulating glucose (3.40 vs. 3.01 mmol/L, P = 0.04) concentrations were greater in Fert+ cows compared with Fert- cows from wk -2 to 3 relative to parturition. Fert+ cows maintained greater mean BCS throughout lactation compared with Fert- cows (2.98 vs. 2.74 units, P < 0.0001). Fert+ cows had better uterine health compared with Fert- cows as evidenced by lower weekly VM scores during wk 2 to 6 postpartum, and based on uterine cytology a smaller proportion were classified as having endometritis at wk 3 (0.42 vs. 0.78, P = 0.09) and 6 (0.25 vs. 0.75, P = 0.04). A greater proportion of Fert+ cows had resumed cyclicity by wk 6 postpartum (0.86 vs. 0.20, P = 0.009) compared with Fert- cows. These results indicate that good genetic merit for fertility traits is associated with a more favourable bioenergetic and uterine health status, earlier resumption of cyclicity and greater BCS, without antagonizing milk production.
Keywords:
genetic merit for fertility
transition period
endometritis