7 Awardee Talk: Muddy Environmental Conditions Increase Net Energy Requirements and Decrease Cow and Heifer Body Weight and Body Condition During Late Gestation

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Abstract Winter and spring precipitation are expected to increase 20-30% by the end of the century in the Midwest, U.S. As a result, cows in this region are exposed to muddy conditions in pastures during late gestation. Two experiments were completed with multiparous cows and primiparous heifers to determine the energetic cost of mud during late gestation. In the first experiment, multiparous Angus cows (n = 8/treatment) were paired based on initial body weight (BW). One cow from each pair was randomly assigned to either the mud (MUD) or control (CON) treatment. Cows were housed and fed individually from d 213 to 269 of gestation. Each pair was fed to meet requirements for maintenance and gestation. In the second experiment, primiparous Angus heifers (n = 9/treatment) were paired based on initial BW. One heifer from each pair was randomly assigned to either the MUD or CON treatment. Heifers were housed and fed individually from d 196 to 266 of gestation. Each pair was fed to meet requirements for maintenance, growth, and gestation. Data in both experiments were analyzed as randomized complete block designs with repeated measurements (SAS 9.4). Although cows consumed the same amount of dry matter, cows in the MUD treatment weighed 37.4 kg less than the CON treatment (P < 0.01) and were 1.5 body condition score (BCS) units less (P < 0.01) by d 269 of gestation. Similarly, heifers in the MUD treatment weighed 43.5 kg less than the CON treatment (P < 0.01) and were 1.8 BCS units less (P < 0.01) by d 266 of gestation. In both experiments, however, calf birth weight was similar (P = 0.34). Although cows and heifers housed in mud were in a negative energy balance, they prioritized fetal growth and mobilized body tissues to meet the energetic demands of gestation.