Scanning essential to detect the threat of late embryo death
Published 17/06/2015 | 02:30
The MONTH of May will be remembered as one of the harshest on record. Temperatures reduced grass growth rates and cows had to be rehoused by night in many wetland areas.
Farmers had to resort to increasing concentrate supplementation to maintain milk yields and avoid body condition score loss. Unfortunately, in many cases the required interventions did not occur.
With increased stress on cows at a critical period of spring calving breeding programmes, reports of poorer heat detection or inordinately high non-return rates to first service were the first signs of a lurking bogeyman!
Embryo development encompasses, in the first instance fertilisation 24 to 36 hours after the onset of heat. The sperm that fertilises the egg has to be in the oviduct at the point of fertilisation for a minimum period of six hours. The latter is known as capacitation.
A sample analogy of this process is the equivalent of a motorcyclist covering a distance of 100 miles in 20 minutes and a period of six hours to take off his helmet at the finish line.
If both oocyte and sperm are competent, fertilisation takes place in approximately 90pc of cows. The early development of the embryo incorporates cell divisions to form two, four, eight, 16 and 32 cells.
The early divisions are dependent on nutrient reserves of the oocyte. Some embryos fail to get through these early stages and referred to as four to 12 cell stage blocks to development. It is noteworthy that the individual cells of these young embryos are totipotent. This means that each of the individual cells of an eight cell embryo can be transferred to other empty zygotes to form identical offspring.
Early embryo mortality with death prior in the two to 32 cell stage is primarily associated with events prior to breeding. Therefore, stressors associated with nutrient quality and supply will impact negatively on egg quality.