Reproductive Efficiency in Dairy Cows: Change in Trends!

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department of Animal Reproduction, INIA, Avda Pta. de Hierro s/n, 28040 Madrid, Spain

  • 2 School of Veterinary Medicine and Zootechnics, Faculty of Agricultural Sciences, University of Cuenca, Avda. Doce de Octubre, Cuenca, Ecuador
  • *Corresponding author. E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it


Daily cattle industry has gone through a series of changes during the last decades to improve competitiveness. However, this has correlated to a detriment in reproductive parameters. Efforts in improving and understanding this situation have meant in practice changes in many fields. Milestones have been: (1) a deeper study and understanding of the estrus cycle of the cow, with the development of synchronization and resynchronization protocols more and more detailed and with improving fertility results after insemination; (2) better insight of how cow’s parity affects reproduction; (3) the consideration of the length of the voluntary waiting period as an essential decision in order to maintain an optimal reproductive efficiency in farms; (4) the understanding of the process and relevance of the pregnancy loss during the early fetal phase; (5) improvement in estrus detection rates through novel technologies. These advances in technology have resulted also in earlier and more precise pregnancy diagnoses.

But reproduction control alone is not enough. Nutrition, genetics, and welfare have a deep effect on reproductive performance. A better understanding of the energy during the production cycle and its effects have been pivotal in the improvement of dairy cattle fertility in high-yielding animals. In recent years, fertility has been added as a trait to be taken into account in selection programs, since they are fundamental for maintaining farm’s profitability. Annual welfare, with growing importance in animal production, has been focused on an increase of published studies, studying the effect of stress (social, environmental) on reproduction, helping to give strategies to minimize it or even to void it.

All in all, changes in veterinary advice in farms have been accomplished by this better understanding of the dairy production systems, transforming the trend of reproductive efficiency up to figures even better than the historically 50% fertility after artificial insemination.


In the last decades, there has been a major change in dairy cattle industry. In order to be more competitive, this sector has developed into an economy of scale, looking for high production, higher profitability of the investments, and reducing the production costs (European Commission, 2013). This can be seen in the changes suffered by herd size and milk yield. By 1950, the herd size was on average of 6.5 dairy cows per farm (Stevenson and Britt, 2017), but since then it has increased exponentially. In the European Union (EU) average herd size has increase from 24 lactating animals in 1997 in the EU-15 (van Arendonk and Liinamo, 2003) to 55 in 2010 (European Commission, 2013). In the United States, the number of lactating cows per herd is even larger, being on average of 180 in 2015 (NMPF Centennial Booklet, 2016). Not only the number of animals has risen, but also the average milk production per cow, incrementing the annual yield from 5000 kg/cow (van Arendonk and Liinamo, 2003; NMPF, 2016) to 7000 kg/cow in EU from 1997 to 2010 (EU Dairy Farms 2010 Report, 2013) (Fig. 5.1).

These two factors imply a total transformation of the management of the herd at different levels, being especially important in bigger farms, since individual cows that produce more milk are usually found in them (Lucy, 2001). For example, during the early half of the 20th century, most of the dairy cattle grazed pastures, being housed in tie-stalls or stanchion barns (Fig. 5.2) only during winters (Stevenson and Britt, 2017). However, nowadays the more coimnon installations are freestalls (Fig. 5.3) and dry-lot systems (NAHMS, 2009), although in recent years loose-housing methods with compost or straw bedding are increasingly being used (Barberg et al., 2007). These new ways of keeping the cattle mean a drastic modification in the herd nutrition and feeding systems (NAHMS, 2009). Other change can be seen in the number of cows managed by a single daily worker (Stevenson and Britt, 2017). The greater number of animals under the control of a worker is extremely important in different factors in the farm. For instance, the volume of milk managed by each person is larger (Stevenson and Britt, 2017), as it is the number of cows milked per minute per operator (Progressive Dairy Operators, 2016). Related to the reproductive management, these new farm situations affect it at various levels. For example, it limits drastically the capacity to observe estrus, which has stimulated the study of different strategies to make easier and more efficient the estrus detection (Palmer et al., 2010), or even that makes unnecessary estrus detection to be able to inseminate the cows by the implementation of timed artificial insemination (TAI) (Stevenson, 2016). Another factor affected by the changes in dairy cattle industry is the increased numbers of calves per worker. Some studies reported increases in calf mortality risk according to herd size (Gulliksen et al., 2009; Mellado et al., 2014; Seppa-Lassila et al., 2016), which could be caused by the increase care in management of fewer and more valuable annuals in smaller farms (Seppa- Lassila et al., 2016).

Evolution of number of milk cows, milk per cows and fertility from 1990 to 2017

FIGURE 5.1 Evolution of number of milk cows, milk per cows and fertility from 1990 to 2017. Data combined coming from Lopez-Gatius et al., 2002; Norman et al., 2009; Huang et al., 2009; Feijoo et al., 2018, USDA, 2019.

A dairy cattle herd in a typical barn, nowadays

FIGURE 5.2 A dairy cattle herd in a typical barn, nowadays.

All in all, there has been a shift in the way we understand dairy cattle medicine. As veterinarians, we find ourselves as health professionals with no patients, not even with just a group of patients. As in other species, like swine or poultry, we are dealing with a very complex system, that includes the cow itself, the herd, the farm staff, the livestock facilities, etc. (Astiz et al., 2018a). We are no longer working in the traditional individual medicine, but in production medicine, also called “herd health medicine” (Van der Leek, 2015).

A dairy cattle herd in a typical stall, nowadays

FIGURE 5.3 A dairy cattle herd in a typical stall, nowadays.

The development of the dairy cattle industry has driven to modifications in its productivity, not always leading to an optimal situation, especially regarding the reproductive efficiency of our herds. The trend in the increase of milk production has been concomitant with a decrease in fertility, since in some systems cows with the greatest milk yields have the highest incidence of infertility (Lucy, 2001). The first service conception rate has declined from approximately 65% in 1951 (Butler, 1998) to 40% in 1996 (Lucy, 2001), with an average of 1.5-2.5 artificial insemination (AIs) per conception being necessary (van Arendonk and Liinamo, 2003). The decline of fertility when AI is used can also be found, that could be up to 30% in the case of TAI (Pursley et al., 1997a,b; Schmitt et al., 1996). The reproductive physiology of dairy cattle has evolved over the past 50 years to cope with the high milk production, which could explain some (but not all) of the reproductive problems that have been common in the industry until 2000 (Lucy, 2001). It is important to highlight that, even though benefits of improving reproduction are obvious, specific causes of poor reproductive performance are hard to identify and resolve (Stevenson, 2016).

However, in the last decade has occurred a great increase of approximately 5% in daughter pregnancy, even though the milk yield is still boosting (Stevenson, 2016). What has happened? Is this change random? Is it the consequence of one certain factor or of several strategies and circumstances?

In this chapter, the authors try to briefly review, resume and explain this change in tendency of the reproductive efficiency of our high yielding dairy cow, assuming its health (we will not cover specific health issues, but the reproductive difficulties when dealing with healthy dairy adult cows). In this transformation, it has been vital the effort of a variety of professionals that includes advisors, scientists, practitioners, fanners, etc. With then- work, it has been possible to understand the high producing daily cow in its different aspects: reproductive physiology, immunology, health, welfare, herd medicine, and genetic selection (Astiz et al., 2018a.; Weigel, 2006). Thanks to this deeper knowledge, we can conclude that the decrease in fertility was not only caused by the increasing milk yield, but by many other factors as well (Lucy, 2001; Stevenson, 2016). It is impossible to improve reproduction with unhealthy and not well-being annuals, so it is important to take care of feeding, care, management, facilities, etc. (Astiz et al., 2018b). Being aware of and optimizing all of them have caused the recent change in reproduction traits.

Therefore, factors affecting the healthy daily cattle reproduction will be explained, as well as the different strategies used nowadays to keep reproductive efficiency at a satisfactoiy level at farms. These factors will be organized in four major categories: reproductive management, nutrition, genetics and welfare, especially focusing on the first one.

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