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411 Relationships between dietary composition and reproductive outcomes in cattle


 Individual experiments and recent literature summaries suggest links between reproductive outcomes in cattle and dietary composition. The objective of this meta-analysis was to evaluate the effects of dietary composition on reproductive efficiency of cows and heifers. A literature search returned 42 previously published papers containing 164 treatment means that were eligible for use in the meta-analysis. Diet composition information of interest included neutral detergent fiber (NDF), acid detergent fiber (ADF), organic matter (OM), crude protein (CP), lignin, ether extract (EE), non-structural carbohydrate (NSC) and starch percentages. For papers to be included, they needed to report reproductive outcomes, dry matter intake (DMI), experimental design details (treatments, design, number of experimental units, measurement SE or SD values, and P-values), and diets with all ingredients and inclusion percentages. Details on diet composition, intake, and reproductive outcomes were extracted from these papers and analyzed using linear mixed effects models with a random intercept for each study. When diet composition information was not reported, it was estimated from commercial feed library data and reported dietary feed inclusion rates. Days to service, days to ovulation, pregnancy at first artificial insemination, and overall pregnancy rate were the primary reproductive outcomes of interest. Significant variables were identified through a backward elimination approach. Overall pregnancy rate tended to be affected by the percentage of lignin in the diet (P = 0.078). Days to service was affected by dietary NDF (P = 0.013), ADF (P = 0.022), and starch (P = 0.027) percentages, and tended to be affected by lignin (P = 0.0768) percentage. Days to ovulation and pregnancy at first artificial insemination were not affected by the nutritional factors tested here. Additional assessment is needed to assess how dietary factors interact with other experimental and environmental variables to influence reproductive outcomes.