Debunking the Dogma: A Fresh Look at Reprodcutive Efficiency of High Producing Cows
Nora Bello & Rob Tempelman, Dept. of Animal Science
Long story short. Our results provided solid evidence that it is an over-simplification to think that “one-size-fits-all” describes the relationship between milk yield and reproductive performance of dairy cows. Instead, we found the production-reproduction relationship to be highly variable and differing with management practices and characteristics of the herd. This is certainly good news as it implies that it might be possible to enhance or fine-tune farm management to jointly optimize both milk yields and dairy cow reproduction.
In particular, highly specialized management practices that typically characterize intensive production systems, such as rbST supplementation and 3X milking frequency, were associated with a favorable link between milk yield and reproduction. In other words, under intensive management, high milk yields did not necessarily match up with poor reproduction. In some cases, the opposite was actually true and high milk yield went hand in hand with good reproductive performance. For example, among herds that used rbST extensively, calving intervals shortened by 1.3 days for approximately every 200-pound increase in herd 305-d milk yield. Similarly, high producing cows milked 3X were getting pregnant sooner than high yielding cows milked twice daily. Please note: We are not stating that rbST or increased milking frequency were the direct causes for enhanced reproductive performance of high producing cows; nor should Michigan herds all be moving to more frequent milking and hoping to have rbST back on our shelves. Instead, consider rbST and 3X milking as more general indicators of intensive farm management, noting that both practices imply more frequent opportunities for observing cows. Thus, intensive management practices that encourage higher milk productivity also may facilitate better than average reproductive performance if the same level of management leads to more attentive and responsive observation of cows. Further investigation certainly will be required to better describe these conditions our group is already working on it.
Our New research Approach
Clearly, the delicate intricacies of a cow’s physiology were not mirroring the management mechanisms of the production system in which the cow was living. Previous research had failed to make this cow vs. herd distinction. Such omission may have resulted in the general assumption that does not necessarily apply to all cows in all herds. Moreover, we should realize that we cannot just look at the connection between milk production and reproduction without accounting for other potential confounding factors such as genetics, nutrition, energy balance, body condition, presence of infectious diseases, metabolic diseases, and seasonal effects. Our research statistical methods are more comprehensive than anything used in this field before. They were recently published in a leading biological statistics research journal. These methods allow us to jointly evaluate milk production and reproduction while accounting for numerous other variables. This is a powerful new tool that provides a fresh perspective on the long-misunderstood issue of fertility of high producing cows.
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