A recent study published in JDS explored the effects of survival, milk production, body size characteristics and inbreeding on Jersey cows. Before we discuss the results of the study, consider the changes in cattle survival over the past two decades.
Figure 1 shows the percentage of Jersey cattle that survive to the next lactation period or are sold to other farms to continue lactating. As you can see, the survival rate of cattle has decreased by about 10% since 2000. Much of this change is likely due to increased use of sex-controlled semen and more gilts on the farm to replace.
Figure 1. The tendency of Jersey cattle to survive to the next lactation period
Changes in herd size, other management factors, and changes in the genetic level may also play a role. Many farms are reducing the size of their replacement herds by using beef cattle semen, which may increase the average survival rate of the herd, but this is not yet reflected in the data at the national level.
Lay the groundwork
In a recent study, researchers at the University of Wisconsin-Madison considered the proportion of cows that survive to the age of 36, 48, 60, 72 or 84 months, and how yield, size and inbreeding affect survival at each age. Figure 2 shows the percentage of cows that survived in their study and the heritability to survive to a given age.
Figure 2.Survival and heritability of Jersey cattle at different ages
However, it is clear that most cattle that successfully survive to the first lactation can also live to 36~48 months. Survival rates in older cattle decline rapidly, with about 60% of cattle surviving to 60 months and only 10% surviving to 84 months.
Interestingly, the heritability of survival increases dramatically with age. The authors speculate that this is because cows have more opportunities to express the genetic potential for viability.
More production, less inbreeding
Cows with higher yields live longer, regardless of the point in time they survive. This difference is less pronounced in younger herds that only survive to 36 months of age.
The difference in survival rates between the top quartile (top 25%) and the bottom quartile is one or two percentage points, suggesting that most producers are willing to give younger cows with lower milk production a second chance. This is not the case with older cows. Considering cattle that survive to 60 or 72 months, the difference between the highest and lowest quartile of survival is 20%.
The level of inbreeding also showed correlation, with higher levels of inbreeding being associated with lower survival rates, regardless of the cow's milk production. The effect of inbreeding on survival becomes more severe as the degree of inbreeding increases. For example, the results showed that a cow with a 10% inbreeding rate was 1.25% less likely to survive to 60 months than a cow with a 5% inbreeding rate. Correspondingly, the inbreeding rate of cattle increased from 10% to 15%, and the survival rate decreased by 2.75%.
Body shape traits need to be balanced
Finally, the authors explored how cattle's conformation traits and the interaction between conformation traits and milk production affect survival. The study collected data on the size scores of first-born cattle because there was less data on older cattle.
Overall, cows with higher body size scores live longer, regardless of milk production. However, there was an interaction between body size scores and yield levels, with cows with high scores and yields surviving longer than cows with low scores and poor yields. The highest-scoring cows with the highest milk production were nearly 70 percent more likely to survive to 60 months of age than the lowest-rated cows with the lowest milk production.
The authors also analysed the relationship between individual body type traits and survival rates, and as shown in Table 1, perhaps the most valuable information about body type traits is that the extreme manifestations of most body type traits are not the highest survival rates. We expect traits to be in the middle of the best, for example, a low Shiri angle score is associated with too high ischium, while a high score means that the angle is too steep. Similarly, a medium score for hindlimb sideways vision was associated with a less straight or sickle-shaped leg. There is also an intermediate optimum for body height, but the strength of this relationship is usually less than for other traits.
Table 1.Body shape traits and best scores on survival rates
However, many traits with intermediate optimal values are generally considered to be preferred for high-scoring traits, including strength, breast width, and shiri width. Cows with above-average dairy characteristics and hoof angles survived longer, but those with very high scores fared worse. We know that cows with extreme dairy characteristics have poor fertility and disease resistance, so it's no surprise that extreme cows have lower survival rates.
The relationship between breast depth and anterior breast attachment and survival depends in part on milk production. If the cow has a high milk production, shallow udder depth and tight attachment to the front udder are advantageous. However, cows with poor milk production and very shallow udder depth are less likely to survive, and perhaps such cows are simply the worst of the worst in terms of milk production.
Posterior breast height is the only trait that scores the highest is the best. Cow hind udders are tall and wide and usually have good udder capacity without necessarily needing a deeper udder depth.
Choosing cows with good udder structure and controlling inbreeding can prolong survival. When it comes to traits such as height, strength, and dairy traits, we do need to protect some traits from extremes, but I think these findings validate the expectations of many breeders.