Recent studies on nutritional factors affecting reproductive efficiency in U.S. dairy herds

Reproductive efficiency is declining on U.S. dairy herds. There are numerous factors that affect reproductive efficiency on individual farms. These include heat detection rate, heat stress, semen quality, bull fertility, AI technique, nutrition, body condition score, clinical and subclinical mastitis, cow comfort, and many other factors related to whole farm management, individual farm managers and laborers, and individual cows. This manuscript will briefly summarize 2 recent research areas. The first section of the manuscript discusses a recent study on body condition score. This study was part of a larger study that evaluated numerous factors simultaneously to determine the management factors most related to reproductive performance (Caraviello et al., 2006). This study used a machine learning technique to simultaneously evaluate numerous factors (341 different variables) that may be affecting reproductive efficiency on U.S. dairies. Interestingly, one of the top factors that was found to be closely associated with reproductive performance was the amount of bunk-space per cow in the breeding pen. The predicted percentage of cows that were pregnant by 150 days tended to increase linearly as bunk space increased from 30 to 60 cm (from 35% to 70%). Thus, cows that were overcrowded (<36 cm of bunk space/cow) had a much lower percentage of cows that were pregnant at 150 days in milk than cows with more bunk space.