Effects of Post-Insemination Dam Nutrition on Longevity and Calf Performance.

Our laboratory has reported that moving heifers from a drylot to pasture at AI can negatively impact pregnancy success, but what is not known is how this nutritional stress impacts the embryos that survive. Thus the objective of this study was to evaluate the impact of moving drylot developed heifers to forage immediately following AI on their longevity and the performance and longevity of their calves. Longevity data and calving records were collected from 105 heifers that were allotted into two treatments prior to breeding; drylot or range. All heifers were fixed-time inseminated following the 7-day CO-Synch plus CIDR protocol to a single bull and were turned out to pasture together and managed as a single group. Pregnancy success to AI was determined by ultrasonography, and calving data (calving date, birth weight, sex, and weaning weight) were collected for the following five years. Thus heifers were then divided into four groups 1) AI Range 2) AI Drylot 3) Bull bred Range, and 4) Bull bred Drylot. Among drylot and range heifers that conceived the first year there was no difference in longevity (P=0.30). There was also no difference in longevity for the heifer calves that were in utero during the first year following treatment (P=0.43). However, among calves that were in utero during year 1; bull calves were heavier at birth compared to heifer calves (P=0.03; 36±0.5 vs 35±0.59 kg) and AI Range calves were heavier at birth compared to AI Drylot calves (P<0.01; 37±0.68 vs 34±0.64 kg). Bull bred calves did not differ in birth weight (P=0.44; 35±0.77 and 36±0.95 kg). Furthermore, weaning weights and ADG were greater for AI Range calves (207±4.6 and 0.8±0.02kg) compared to AI Drylot calves (P=0.02; 191±4.4 and 0.77±0.02 kg) which was greater than Bull bred Range (174±6.0 and 0.8±0.03 kg) and Bull bred Drylot (171±5.5 and 0.77±0.02 kg) which were similar. Bulls tended (P=0.06) to be heavier at weaning than heifers (191±7.5 vs 181±3.9 kg). With calves born in year 2 through 4, there was not difference between treatments in BW (P>0.33), WW (P>0.24), or ADG (P>0.31). In conclusion, moving Drylot developed heifers to pasture immediately following AI had not impact on longevity, but did result in the AI sired embryos having a decrease in BW, WW, and ADG compared to AI sired calves from the Range developed heifers.