7.4. Fertility and reproduction

The reproductive health of the herd is a great indicator of how a management system is working, by highlighting the profit or losses seen financially. With dairy cattle, these results can be seen from the view point of reproduction (calving interval, dry period, and services per conception) and milk production (milk yield and fat and protein %).

Ideally, every farmer would like his herd increase every year, with each cow having at least one calf, and in turn increase the milk yield with every subsequent lactation. In reality, multiple births come with unwanted problems. Unfortunately, more calves per cow do not automatically mean more profits seen.

From higher incidence of abortions, reduced birth weight or higher numbers of stillbirths, mastitis, and problems related to dystocia, the increase in costs in the case of multiple births adds up to 40% per cow [64].

There is a higher incidence of pregnancy loss, with number of fertile heifers' herd replacement [15].

Increase of calf mortality is 18% [30] and fertility of the cows was shown to deteriorate after multiple pregnancies, with the most unfavorable indicators of fertility found in triplet births [14].

Other studies show that twinning increases open days and services per conception on average and therefore decreases reproductive performance of the dam during subsequent lactations [21].

There is a longer regeneration time of the uterus and this in turn causes the elongation of the resting period after calving‑these were increasing with the number of lactations, relating to twin calving and shorter gestation. This was more evident with calving in the summer period.

Cows with dead twins also had increased time to conception, compared with live twins. The natural incidence of multiple births in cattle is largely due to multiple ovulations and is around 1–5%, depending on breed, parity, and environmental conditions [65].

Analysis of bovine pregnancy–associated glycoprotein (bPAG-1) can also be used to determine the nature of the pregnancy from about day 90 [66]. Dissemination of twin and singleton pregnancies is not possible before day 85, so prevention or early identification of twinning is not possible with this measurement. To achieve diagnostic test with both high sensitivity and specificity, further studies such as ultrasound are required.
