by Dr Charlie Blackwood
Over the last couple of months, we have undertaken the first round of pregnancy testing to detect cows in calf to AI in many of our clients’ herds. In the next couple of months, we will do the second-round tests to detect bull matings in these herds. One of the frustrating aspects of the modern dairy cow is the loss of pregnancies after they have been confirmed pregnant. Across the world, the proportion of cows identified as early pregnant, who then fail to calve or calve to a later conception date is increasing. It is a trend we have noticed in the herds we service.
At a recent seminar organised by the InCalf team at Dairy Australia, a presentation was given by Dr Richard Shephard on pregnancy losses after confirmed diagnosis in four Gippsland dairy herds. A total of 1756 cows were available for analysis. All herds were owned by a single owner and management across the herds was very similar. The study was done in 2015.
Of 1149 cows confirmed pregnant following a spring mating program, there were 90 pregnancy losses between day 35 and 140 of pregnancy. This equates to a loss of 7.8% of pregnancies!
Two factors were significantly associated with pregnancy loss:
- Milk production in litres – cows producing 30 litres of milk at peak lactation had the lowest loss of pregnancy. Cows producing both more, and less than 30 litres had greater losses of pregnancy than cows producing 30 litres. The risk was higher the further away from 30 litres a cow’s production was.
- Clinical mastitis – cows with clinical mastitis after conception were 2.77 times more likely to lose a pregnancy than cows without a clinical mastitis event. In fact, by the end of the trial only 79% of cows with clinical mastitis were pregnant compared to 93% of cows without clinical mastitis.
The reasons for the first finding are speculative, and the authors suggested that inadequate energy intake was part of the reason for loss of pregnancy. Cows producing 40 litres of milk may not be able to match energy requirements in a pasture based system, while cows producing 20 litres of milk may not be achieving production potential because of inadequate energy in the diet.
There are numerous international studies linking mastitis and loss of pregnancy, and the main reason for loss is due to the toxic effects of inflammation on pregnancy.
Strategies to reduce pregnancy loss are difficult to implement but implementing practices that reduce the amount of clinical mastitis in a herd will assist. Long-term, selection for cows which are better adapted to pasture based systems will reduce pregnancy losses due to energy imbalances.
Pre-dry-off pregnancy diagnosis (PDPD)
Feeding empty dry cows is a waste of money. A service we use on a number of clients is to undertake pregnancy diagnosis just before dry-off. This final pregnancy tests detects cows which have lost pregnancies so that they can either be milked on, or sold. We only have to find two or three empty cows that were previously called pregnant for the service to pay for itself.
If you would like more information on this research, or using the PDPD, feel free to contact one of our vets on 5561 7666.