@conference {40634,
	title = {Determining the number of calves in early pregnancy using real-time ultrasound imaging in beef cows induced to twin.},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {54},
	year = {1994},
	month = {Jan},
	pages = {353-356},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Details of the timing of pregnancy loss following induced twinning are  
unknown.  The aim of this study was to evaluate real-time ultrasound as a  
method of determining early pregnancy status (0, 1 or 2 foetuses) in beef cows  
induced to twin using AI and ET.  A 7.5 Mhz ultrasound probe was used intra- 
rectally to count foetuses in 2 experiments.  In Exp. 1, 57 heifers were  
examined between 25 and 60 days of pregnancy and then slaughtered.  In Exp.  
2, up to 103 cows were examined between Day 25 \& 60 of pregnancy, and final  
pregnancy status was confirmed using calving records.  In Exp. 1, the accuracy  
of Day 25, Day 45 and Day 60 predictions of 2 foetuses was 100\%, 20\% and  
100\%, and 1/24, 5/33 and 1/33 twin pregnant heifers were predicted.  The  
accuracy of correctly predicting twin outcomes was 33, 50 and 33\% at the same  
3 stages of pregnancy, but only 3, 2 and 3 twin pregnancies occurred,  
respectively. In Exp. 2, there was generally little difference between the  
accuracy of predicting twin pregnancies and the accuracy of the prediction.   
Thus, at Day 25, 35 and 45 and 60, the accuracies were approximately 20, 47,  
52 and 45\%.  Twenty recipients eventually calved twins.  We conclude that  
real-time ultrasound imaging up to Day 60 is not an accurate technique for  
determining twin pregnancy status of cows.  Loss of concepti between scanning  
and term did contribute substantially to this poor result in Exp. 2, but not in  
Exp. 1. 
 },
	issn = {1176-5283},
	author = {McMillan WH and Oakley AP and Hall DRH}
}
