From a biological perspective, it is natural that some inseminations will be unsuccessful, so the cows/heifers have to be inseminated again. Impregnation failure can either be due to follicular or luteal cysts, or that the embryo is lost, in other words, that the cow actually became pregnant, but that the foetus is lost early in the pregnancy. It is well documented that early embryo loss is one of the most significant factors in pregnancy rates. An early loss of pregnancy (loss of embryo before day 42) is mostly attributed to management related conditions and not infections. Cows that lose > 1 body condition score in the space of the first 30 days of lactation, have a 2.4 times greater risk of embryo loss.
Investigations indicate that infectious diseases outside the reproductive organs (mastitis) can lead to unsuccessful fertilisation or loss of embryos.
Classifying the problem
The gap between the first and second insemination performed in the period is calculated. The gaps are shown in a graph, where you can see, for example, the percentage in the 18-24 day range. If this is a high percentage, this suggests that insemination has failed, and that the cows / heifers will come into heat again during the next cycle. If there are several insemination gaps that e.g. range from 25-45 days, this indicates that insemination was successful but that a high proportion resulted in early embryo loss. When the insemination gaps are even greater, this can be due to follicular or luteal cysts that cause irregular heat – BUT, this can also be because you have missed some estrus periods. Body condition ought to be systematically recorded, so you can identify if this is a problem.
To avoid embryo loss, it is important that the embryo develops sufficiently in the first period after impregnation. A well-developed embryo secretes sufficient amounts of a protein that acts locally in the uterus and prevents the secretion of the reproduction hormones that trigger a new cycle. It has been discovered that embryonic survival is negatively affected by a temperature rise in the cow in association with mastitis. However, the most significant factors for continued pregnancy are: body condition at calving, the degree and rate of loss of body condition in early lactation and stress.
Stress can be physiological (very high performing cows), physical (e.g. pain from hoof and limb problems) or psychologically related (high stocking density), or can be due to heat from the external environment.
Points for action plan
Minimise stress levels in the herd, the proportion of cows with udder inflammation or body condition loss in the first 30 days after calving.
- Cows / heifers with a body condition score < 3.0 at calving and score < 2.5 at insemination
- Cows that lose ≥ 1 body condition score in the first 30 days of lactation
- Stress (physiological, physical, psychological, heat)