Artificial insemination in cattle
Recent research from the UK confirmed the "AM:PM Rule" for AI in cows, i.e. if a acow starts bulling in the morning, AI her in the afternoon and vice versa.
Also pregnancy rates are reduced in cows with somotic cell counts over 200,000 in the four weeks prior to insemination. However if these cows are AI'd again 8 to 12 hours later the pregnancy rates are improved.
(Original paper is vet record (2015) 176 PJ 411)