Introduction
Several questions commonly come up among dairy producers who practice management intensive rotational grazing when the topic of sire selection arises:
Should I use bulls that were tested under confinement feeding conditions?
Should I use bulls from countries where grazing is common, such as New Zealand?
Should I consider crossbreeding? If so, which breeds should I choose?
Hundreds of bulls from a dozen different breeds are at your disposal, and each has predicted transmitting abilities (PTA) for traits such as milk yield, milk composition, physical appearance, udder health, calving performance, fertility, and longevity. This is good news, right?
It can be good news, if you can sort through this mountain of genetic information, but it isn’t an easy task. A fair amount of research has been done on grazing and sire selection in New Zealand, which is the most “extreme” managed grazing environment (in terms of the proportion of nutrients coming from pasture). Some work has been done in Ireland and Australia as well, but research on this topic in North America has been limited. Therefore, the goal of this article is to provide some background information that will help you make informed and effective decisions about your herd’s breeding program.
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Genotype by environment interaction occurs whenever the performance of an animal for a specific trait, such as milk yield, somatic cell count, or fertility, varies from one environment or production system to another. We usually think of this as a change in sire rankings. For example, daughters of bull A may give more milk in a confinement feeding system, whereas daughters of bull B may give more milk in a managed grazing system. Fortunately, changes in sire rankings between environments are often relatively minor, although some sire families move up a few spots on the list and others move down a few spots. Because many bulls have daughters in both confinement feeding and managed grazing systems, we can estimate the genetic correlation between milk yield in these two environments. Research in Wisconsin, Indiana, Ireland, Australia, and New Zealand has shown that this correlation ranges from +0.7 to +0.9 (+1.0 would indicate perfect agreement, -1.0 would indicate complete disagreement, and 0.0 would indicate no relationship), which indicates that sire rankings for this trait change only modestly from one production system to another. This is not too surprising, given that we have basically selected for animals that can consume large quantities of feed, whether it be forage or concentrate. On the other hand, these same studies showed that the response to selection is slightly lower in managed grazing systems. On average, a 1.0 lb increase in sire PTA for milk will give 1.0 lb of additional lactation yield by each daughter. However, intensely managed confinement feeding operations often achieve 1.1 or 1.2 lb of additional milk per 1.0 lb of sire PTA, whereas managed grazing operations typically achieve only 0.8 or 0.9 lb. This means that the economic gain due to selection of superior sires will be slightly lower in a grazing system.
Differences in economic values occur whenever the importance of one trait relative to another, such as the value of fertility relative to milk yield, varies from one environment or production system to another. Such differences are quite common and can be large. For example, the economic value of milk volume is greater in a fluid market, whereas the value of fat or protein percentage is greater in a cheese yield market. In the case of managed grazing, several traits take on much greater importance. The most obvious is female fertility, which is vastly more important in herds that attempt to maintain a seasonal calving pattern. Another is longevity, as it is difficult to keep production costs low if you’re constantly replacing “broken” cows with new home-grown or purchased heifers. Small frame size may be desirable, as the enormous Holstein cows that win blue ribbons at shows may be too large for your facilities. Avoiding calving problems is another key consideration because this will reduce labor and veterinary costs. Adequate body condition (as measured by low PTA for dairy form) may be desirable, in terms of fewer health problems and enhanced reproductive performance, and mobility traits might be important if cows are forced to walk long distances between paddocks.
To identify example bulls whose daughters would be expected to excel in a managed grazing system, we screened the list of sires available to U.S. dairy producers using the following criteria:
- Top 20% for within-breed ranking based on Lifetime Net Merit
- Stature PTA less than 0.0 (Holsteins, Brown Swiss)
- Service Sire and Daughter Calving Ease PTA less than 8% (Holsteins, Brown Swiss)
- Dairy Form PTA less than +1.0 (Jerseys) or less than +0.50 (Holsteins)
- Udder Composite PTA greater than 0.0 (Holsteins)
- Feet and Legs Composite PTA greater than 0.0 (Holsteins)
- Minimum of 50 daughters in at least 30 herds
- Maximum retail price of $25 per unit.
Then we converted all breeds to the U.S. Holstein genetic base and applied the following criteria:
- Productive Life PTA greater than +1.5 months
- Daughter Pregnancy Rate PTA greater than +1.5%
- Somatic Cell Score PTA less than 3.20.
This gave us the following list of potential bulls for a managed grazing system, along with their corresponding Lifetime Net Merit values (on their original breed-specific genetic bases):
| Bull | NAAB Code | Source | Lifetime Net Merit |
|---|---|---|---|
| ISNZ BOURKES NIMROD | 190JE32 | New Zealand Jersey | +$434 (US Jersey base) |
| SUNSET CANYON MAXIMUS | 7JE620 | US Jersey | +$432 (US Jersey base) |
| ISNZ PARKWOOD CASPER | 190JE12 | New Zealand Jersey | +$425 (US Jersey base) |
| MORNINGVIEW DURHAM JINX | 7HO7287 | US Holstein | +$452 (US Holstein base) |
| CO-OP MNFRD TIGER | 1HO5678 | US Holstein | +$451 (US Holstein base) |
| ISDK Q IMPULS | 236JE3 | Danish Jersey | +$406 (US Jersey base) |
| D-K-DANDY HERCULES | 1HO5518 | US Holstein | +$427 (US Holstein base) |
| NORZ-HILL FORM WIZARD | 1HO6360 | US Holstein | +$410 (US Holstein base) |
| BOTANS | 249SR3829 | Swedish Red | +$538 (US Ayrshire base) |
| PETERSLUND | 249SR1213 | Swedish Red | +$420 (US Ayrshire base) |
Although these bulls represent a mix of breeds and countries of origin, they were selected with one goal in mind: profitability in a managed grazing system. There are certainly other breeds or individual bulls that will do a good job, but we hope these criteria and the corresponding list can serve as a useful starting point. Remember, whether you’re crossbreeding or maintaining a pure breed, the key to effective sire selection is to determine the traits that are most important for the management conditions on your farm and to select the best available bulls from one or more breeds for those traits. There are no shortcuts or “magic pills” when it comes to breeding a good herd of cattle; it is a long-term process that requires focus, patience, and discipline.
Author Information
Kent Weigel and Jon Schefers
University of Wisconsin – Madison