Effect of feeding rumen-protected lysine through the transition period on postpartum uterine health of dairy cows

Feeding rumen-protected methionine as an indispensable amino acid source has been shown to improve reproductive performance in dairy cows, but the effect of feeding rumen-protected lysine (RPL) during the peripartum period on reproductive performance is not well explored. Therefore, we aimed to determine the effects of feeding RPL (AjiPro-L Generation 3, Ajinomoto Heartland Inc.) prepartum, postpartum, or both on follicular dynamics, uterine health, and mRNA gene expression of the endometrium. Seventy-five multiparous Holstein cows were assigned to 1 of 2 dietary treatments with or without RPL in a randomized, complete block design. A 2 × 2 factorial arrangement of treatments was used. Prepartum (–28 d to calving), animals were fed a diet (68% of dietary DM from forage) with RPL [PRE-L; 0.54% RPL of dietary dry matter intake] or without RPL (PRE-C). After calving, half of the cows from each prepartum treatment group were assigned to a diet (56% forage) with RPL (PRE-L POST-L; PRE-C POST-L; 0.40% RPL of dietary dry matter intake) or without RPL (PRE-C POST-C; PRE-L POST-C) until 28 d in milk (DIM). Vaginal discharge was detected with a Metricheck device (Simcro) to detect metritis, and at 28 DIM polymorphonuclear leukocytes were evaluated as a percentage of the epithelial cells using a cytology brush (Andwin Scientific) and an endometrial tissue biopsy was collected for mRNA expression and histology. The first postpartum follicular growth cycle was monitored at 7, 10, 11, 13, 15, 17, 19, 21, 23, 25, 27, and 28 DIM via transrectal ultrasonography. Time to first ovulation did not differ between treatments and averaged 18 ± 1.6 DIM. Follicular diameter at first ovulation was not affected by the treatments, but the growth rate of dominant follicle before first ovulation tended to be lower for cows in POST-L in comparison with cows in POST-C. Prevalence of fetid vaginal discharge and metritis did not differ between treatments. Cows in PRE-L POST-L had lower polymorphonuclear leukocytes percentage at 15 and 28 DIM than cows in PRE-L POST-C, PRE-C POST-L, and PRE-C POST-C. Feeding RPL prepartum downregulates the expression of TLR4, SLC7A6, EHMT2, and tends to downregulate the expression of PTGES3 in uterine tissues at 28 DIM. Additionally, it upregulates the expression of APOL3 and NFKB1, and tends to upregulate the expression of AHCY and MAT2A. In conclusion, feeding RPL pre- and postpartum improved indicators of uterine immune status, but did not change days to first ovulation postpartum.