This article forms part of the proceedings from the Red Cow Symposium 2005 that took place in South Africa.
The cow that survives
The average cow enrolled in milk recording in the USA completes between two and three lactations during her lifetime. Supply of replacement heifers plays a role in decisions to keep or cull older cows in herds. At this time, replacement heifers in the USA are costly (> US$2,000) because of tremendous demand for them. Dairy producers have less opportunity to voluntary cull cows for low production than in years past, because more cows are culling themselves from
herds due to death, infertility, and assorted health problems.
Good data is hard to get on survival of cows; however, there is general agreement that Holstein cows are calving fewer times during their lifetimes in the 2000s than previously in most places in the world. Also, evidence suggests that the death rate of dairy cows on farms has increased in recent years in most places. Furthermore, the fertility of cows is declining in most countries of
the world, and more than 10% of Holstein calves are stillborn.
Genetic Evaluation for Productive Life in the USA
Productive Life is the genetic trait evaluated and published by the Department of Agriculture in the USA that predicts the survival of dairy cows. Productive Life is different than total days in the herd, because it measures only the days that a cow is milking during her lifetime to a maximum of 84 months (7 years) of age. The Productive Life of a cow begins when she calves the first time and ends when she leaves the herd; however, cows are allowed only 305 days in
milk for each lactation, so cows with long calving intervals are not rewarded for poor fertility.
Genetic relationship of Productive Life and cow fertility is substantial and estimated at approximately +0.60 (on a +1 to –1 scale). Most of the major sires of sons and grandsons of the current A.I. Holstein bulls around the world transmit poor daughter fertility, so the negative observed trends, as well as underlying genetic trends, for cow fertility in the Holstein breed aren’t surprising.
Relationship of Productive Life with Other Traits
Table 1 has genetic relationship of Productive Life with milk production and type traits of Holsteins from two studies that looked at birth years of cows that differed by 15 years in the USA. One study looked at cows born in the early 1980s and the other study examined cows bornin the middle to late 1990s. During the 15 years separating the two data files, genetic relationship of Productive Life with production changed drastically (from more than +0.40 to
less than - 0.10). Over the 15-year period of time, milk production lost its powerful predictive power for survival of cows in USA dairy herds. Therefore, non-production factors, especially cow fertility, are now explaining a higher percentage of Productive Life of Holstein cows.
“Sharpness” had a drastic change in relationship with survival of cows during the 15-year period of time. In the early 1980s, sharpness had a strongly positive relationship with Productive Life; however, by the late 1990s, the relationship between Productive Life and sharpness had become decidedly antagonistic (- 0.25 on the +1 to –1 scale). Perhaps dairy producers will need to learn to appreciate dairy cows that milk heavily, yet maintain adequate body condition during lactation to permit cows to reproduce.
The results of the two studies reviewed in Table 1 suggest that rumps should have some slope from hips to pins; however, rumps with extreme slope might not be as helpful to cow fertility and health as hypothesized by some. A steep foot angle appears to be of some predictive value for survival of cows, as do rear legs that lean toward straightness from the side view.
Among udder traits, udder depth has become the trait that consistently predicts survival of dairy cows. Other udder traits seem to have lost some of their genetic relationship with survival, and that is particularly true for rear udder width. Rear udder width has a positive relationship with rump width, which in turn has an antagonistic relationship with survival.
Table 1. Genetic relationships of Productive Life with other traits of Holsteins in USA (on a scale of +1 to –1).
|
Birth year
of cows |
|
| Trait |
1980-82* |
1995-97** |
| Milk production |
+0.43 |
-0.11 |
| Dairy form (“sharpness”) |
+0.41 |
-0.25 |
| Stature |
+0.05 |
-0.13 |
| Strength |
-0.13 |
-0.20 |
| Body depth |
-0.07 |
-0.29 |
| Rump angle (slope) |
+0.09 |
+0.03 |
| Rump width |
-0.04 |
-0.20 |
| Rear legs-side view (straight) |
-0.02 |
-0.10 |
| Foot angle |
+0.07 |
+0.12 |
| Udder depth |
+0.24 |
+0.37 |
| Udder cleft |
+0.28 |
+0.14 |
| Teat placement |
+0.22 |
+0.03 |
| Fore udder |
+0.29 |
+0.27 |
| Rear udder height |
+0.32 |
+0.12 |
| Rear udder width |
+0.31 |
+0.03 |
* Weigel et al. (1998) J. Dairy Sci. 81:2040.
** Tsuruta et al. (2005) J. Dairy Sci. 88:1156.
Body size
For many years, we have known that large Holstein cows were less likely to survive in dairy herds than more moderate-sized Holsteins. However, it appears that the relationship of Productive Life with the body size traits has become more unfavorable as Holstein cows have continued to become larger (Table 1). All of the routinely recorded body dimension traits of Holsteins (width of chest floor, depth of body behind the shoulders, width of rump) have
negative relationships with Productive Life of cows, despite the testimonials of some dairy producers that cows need to be wide and deep to survive in herds.
North American Holsteins have been selected for increased body size for many years, so dairy producers are milking larger cows today than they were previously. Notably, the Holstein Association USA dramatically altered its “Ideal Holstein Cow” in 1977. The replacement ideal cow was much taller, much deeper, much longer, and much sharper than the previous cow that
the breed considered ideal since 1922.
 |
 |
Probable reasons that Holstein cows have increased in body size include: 1) scoring of type traits by the Holstein Association USA, especially since 1977, has placed more favorable ratings on cows with larger body size, 2) some dairy producers believe that larger cows have more body capacity to consume more feed, which in turn might allow cows to produce greater volumes of milk, and 3) dissatisfaction with body size of heifers at first calving because of poor heifer
growth has led some dairy producers to attempt to compensate for substandard heifer management by selecting for increased genetic potential for mature body size.
Unfortunately, no research has documented that large Holstein cows have functional or economic advantages over Holstein small cows on a genetic basis in the USA. On the other hand, studies have indicated that smaller Holstein cows (due to genetics, not to poor management) have longer survival, are more feed efficient, have fewer health problems, and have better fertility than larger Holstein cows.
The major justification given for including type traits in selection programs of breed associations is to improve the longevity of cows. No evidence with USA Holsteins exists to support continued selection for larger body size of cows; therefore, in late 2004, stature (height) of dairy cows was de-emphasized in scoring of cows for type by the Holstein Association USA.
However, if anything, the Holstein Association USA has begun placing even more weight on traits related to width of Holstein cows. Unfortunately, the width traits (strength and rump width) have even greater antagonistic relationships with Productive Life than does tall stature.
Research Herd of Large and Small Holsteins
An experimental herd of Holstein cows at the Northwest Research and Outreach Center, Crookston, of the University of Minnesota has been selected since 1966 for large versus small body size. To initiate the study, cows in the experimental herd of Holsteins were paired by sire 5 and/or producing ability and randomly assigned to one of two genetic lines -- large or small. Daughters were assigned to the same genetic line as their dams. Except for sire selection,
animals have been housed and managed alike since 1966. Milking cows are housed in a tie-stall barn with very large stalls to accommodate large cows.
Service sires are required to be among the top 50% of active A.I. Holstein sires available in the U.S. for transmitting high production. The actual production traits for selection changed over the years of the study and, in time order, were 1) milk (kg), 2) milk-fat dollar value, and 3) fat (kg) plus protein (kg). All other selection was based on body size of daughters, either large or small. Selection of sires is based on genetic evaluations for body size traits with the index: 0.5(stature) + 0.25(strength) + 0.25(body depth). The three most extreme sires for transmitting large and small body size are selected once each year from the summer genetic evaluations of USDA for production and the Holstein Association USA for body size. Cows within line are randomly mated to sires, except inbreeding is not allowed to surpass 6.25%, if possible, with use of the three sires selected annually for each body size line.
Cows in the large line and small line that were born from January 1, 1983 to April 30, 1991 were compared for results reported here. All cows were weighed immediately after calving, as were their calves. Body dimensions were recorded one month after calving. Reasons for disposal of cows were assigned to twelve categories and cows could be culled for up to three reasons.
Direct Response to Selection for Body Size
Table 2 has the numbers and ranges of observations for body weights at calving and wither height at one month postpartum. The ranges of observations in Table 2 indicate that there was considerable overlap across the two genetic lines. Table 3 has the averages for body weight and dimensions and the differences for the genetic lines. Cows in the small line had average body weight of 558 kg immediately after calving. Most dairy producers probably would not regard this average weight as extremely small. On the other hand, cows in the large line had average body weight of 609 kg after first calving, which would be regarded as quite large by most dairy producers, especially when the average age of first calving of only 25.5 months is considered.
Table 2. Number and ranges (minimum and maximum) of observations for direct response to selection for body size.
|
LACTATION |
Small Line |
Large Line |
| Trait |
Number |
Number |
Min. |
Max. |
Number |
Min. |
Max.
|
| Body weight |
|
|
(kg) |
(kg) |
|
(kg) |
(kg) |
|
1 |
217 |
416 |
720 |
159 |
450 |
822 |
|
2 |
126 |
488 |
731 |
93 |
514 |
834 |
|
3 |
70 |
515 |
784 |
53 |
580 |
885 |
| Wither height |
|
|
(cm) |
(cm) |
|
(cm) |
(cm) |
|
1 |
210 |
120 |
142 |
145 |
127 |
147 |
|
2 |
135 |
121 |
141 |
93 |
128 |
146 |
|
3 |
80 |
123 |
138 |
51 |
130 |
150 |
Cows in both lines increased in body weight with lactation number; however, the difference of body weight became more pronounced with increased lactation number. In other words, the cows that were bred to be large continued to grow more after first calving than the cow that were bred to be small. Immediately after third calving, cows in the small line had average body
weight of 641 kg, which is a good-sized cow. In comparison, cows in the large line had average body weight of 720 kg lb after third calving. At time of dry off, cows in both size lines weighed much more than they did immediately after calving; in fact, some cows in the large line surpassed 900 kg at the time of dry off. Once dairy cows reach an acceptable body size, continued growth beyond that body size might not be desirable, especially for survival.
The magnitude of difference (kg and cm) in average body size in Table 3 might seem fairly small. However, the greater body weight of cows in the large line -- 9% (1st lactation), 11% (2nd lactation), and 12% (3rd lactation) -- seemed considerable based on eyeball inspection. Although the increase in stature (height at the withers) was less pronounced than body weight on a percentage basis (5% to 6%), the difference of about 7 cm also seemed to be magnified on casual observation. A point to be made from this is that published breeding values for stature, strength, and body depth might lead dairy producers to believe that extreme sires for these traits will uniformly transmit extremely small or large size to their daughters. Actually, the differences in observed body sizes of daughters of sires with extreme breeding values will likely be much more modest than anticipated. In this study, consistent use for over 25 years of the most extreme sires for small body size resulted in cows that would be considered of adequate size by most dairy producers internationally.
Table 3. Average for response to selection for body size.
| Trait |
Number |
Small |
Large |
Difference |
| Body weight |
|
(kg) |
(kg) |
(kg) |
|
1 |
558 |
609 |
51 |
|
2 |
596 |
664 |
68 |
|
3 |
641 |
720 |
79 |
| Wither height |
|
(cm) |
(cm) |
(cm) |
|
1 |
129.0 |
136.1 |
7.1 |
|
2 |
130.4 |
137.4 |
7.0 |
|
3 |
130.9 |
138.6 |
7.7 |
| |
|
|
|
|
| Depth of chest |
1 |
67.1 |
70.9 |
3.8 |
|
2 |
68.2 |
72.6 |
4.4 |
|
3 |
69.5 |
74.2 |
4.7 |
| Chest circumference |
1 |
186.2 |
195.1 |
8.9 |
|
2 |
190.1 |
200.5 |
10.4 |
|
3 |
194.0 |
205.7 |
11.7 |
Body weights were immediately postpartum and body dimensions were one-month postpartum.
Across years of this study, body weights did not change with year for cows in the small line, but body weights had a significant increase with year for the large line. Because of the continued emphasis on larger body size of Holsteins, the cows in the small line in this study have not changed in body size with time; however, cows in the large line have continued to become larger. The small genetic line in this research herd might reflect the body size of the earlier Ideal
Holstein Cow, which was developed in 1922.
Response for Milk Production, Number of Services, Calving Ease, and Calf Weight
The 305-day mature equivalent (5-8 years) milk production of the two body size lines differed only for cows during their first lactations. Cows in the small line averaged 11,013 kg milk and cows in the large line averaged 10,280 kg milk, for a difference of 733 kg milk favoring cows in the small line. Herd average production throughout the years of the study has tended to favor the
small line, but differences have not been significantly different.
Table 4 has averages for number of services, calving ease, and calf weight. Although differences were statistically different only for first lactations, all differences in the genetic lines for number of services favored the small line. No obvious explanation exists for the difference in reproductive performance for the body size lines. The lines did not differ for calving ease; however, both lines had high levels of calving difficulty at first calving, with an average score of approximately 3.1 on a scale of 1 (good) to 5 (bad). Average calf weight at birth differed for all three lactations, and the average difference was about 2.5 kg.
Table 4. Averages for number of services, calving ease, and calf weight.
|
LACTATION |
Small Line |
Large Line |
| Trait |
Number |
No. |
Average |
No. |
Average |
Difference
|
| Number of services |
Virgin heifer |
233 |
1.54 |
164 |
1.67
|
0.13 |
|
|
1 |
141 |
1.79 |
98 |
2.08
|
0.29* |
|
|
2 |
88 |
1.91 |
59 |
2.08 |
0.17 |
|
|
3 |
48 |
2.02 |
25 |
2.24 |
0.22 |
|
|
|
|
|
|
|
|
|
Calving ease |
1 |
228 |
3.2 |
163 |
3.1 |
-0.1
|
|
|
2 |
130 |
1.5 |
96 |
1.4 |
-0.1 |
|
|
3 |
77 |
1.4 |
56 |
1.5 |
0.1 |
|
|
|
|
|
|
|
|
|
Calf weight (kg) |
1 |
222 |
39.4 |
163 |
42.0 |
2.6* |
|
2 |
126 |
42.4 |
95 |
44.7 |
2.3* |
|
3 |
73 |
43.0 |
54 |
45.5 |
2.5* |
*Difference is statistically significant.
Response for Reasons for Disposal
Reproduction has been an ongoing management problem of this research herd, which is reflected in the approximately one-third of cows in both body size lines culled due to reproductive problems (Table 5). Mastitis was the only other reason for disposal that surpassed 15%, and the two lines did not differ for this reason for disposal. Averages for body size differed significantly for three reasons for disposal -- udder conformation, legs and feet, and a miscellaneous category.
Table 5. Reasons for disposal.
| Reason |
Small cows% |
Large cows % |
Difference
% |
| Low production |
5 |
6 |
1 |
|
Reproduction |
35 |
33 |
-2 |
|
Calving complications |
9 |
8 |
-1 |
|
Abortion |
8 |
4 |
-4 |
|
Mastitis |
15 |
16 |
1 |
| Udder conformation |
12 |
5 |
-7* |
|
Udder injury |
1 |
2 |
1 |
|
Legs and feet |
3 |
8 |
5*
|
|
Metabolism |
4 |
5 |
1 |
| Digestion |
6 |
4
|
-2 |
| Respiration |
0 |
0 |
0 |
| Miscellaneous |
3 |
9 |
6* |
*These differences are statistically significant.
Differences in reasons for disposal for udder conformation and legs and feet were easy to rationalize. Because cows in the small line had shorter legs, their udders were closer to the ground and more likely to have functional problems. Because the legs and feet of cow in the large line supported more body weight than those of cows in the small line, the legs and feet of cows in the large line were under more stress. The greater disposal of cows in the large line for
miscellaneous reasons is not as easily explained; however, cows in the large line seemed more predisposed to infections of various forms.
Response for Productive Life of Cows
Cows in the small size line had 88 days longer Productive Life than cows in the large size line. Small line cows (n = 157) averaged 658.3 days and large line cows (n = 119) averaged 570.6 days for Productive Life. Typically, advocates for type traits in selection programs argue that 9 type traits are important for longevity of cows; however, the results of this study suggest that genetic selection for increased Holstein body size results in decreased longevity.
A RETURN TO THE ORIGINAL PROTOTYPE
Figure 1 has the silhouettes of two cows from the front view. The cow on the left has been the ideal of the Holstein breed since 1977. The cow on the right has the silhouette that research suggests will have optimum performance in dairy herds in most environments around the world at this time. The cow on the right is not as tall, is not as wide in the chest floor (nor as wide in the rump), but she is wider through the shoulder region than the cow on the left. The cow on the right has flesh and muscle in the shoulder region from which to draw reserves to aid fertility and health; however, the cow on the left has little but bone in the shoulder region.
An argument provided by registered Holstein breeders is that cows need a wide chest floor to provide room for the heart and lungs. The heart and lungs of cows don’t hang down between their front legs!! Mother Nature made cattle to look more like the silhouette of the cow on the right (Figure 1). On the other hand, the silhouette of the cow on the left (Figure 1) is a tall frontended cow with “uphill run”, which creates a pinched body area where the neck connects to the 10 body. The silhouette of the cow on the left resulted from registered breeders selecting for cattle that they thought were pleasing to look at. However, a smarter approach would be to allow cows to tell dairy producers (by analysis of data on many cows in commercial environments) what cows need to look like to be functional.
Table 6 has the optimum type scores for survival of Holsteins on a scale of 1 to 9 for three countries. There are similarities between the countries for many of the traits, especially for udder traits. However, the optimum scores are sometimes very different for countries. In particular, for traits related to sharpness and body size, optimum scores are much more in agreement for Germany and the USA than they are between those two countries and Canada. Canada and the USA are geographic neighbors, but there are distinct differences between the dairy industries in the two countries. Canada has a milk quota system that fosters a high milk price for dairy producers; therefore, profit margins will sustain much greater investment in input costs for cow care than other places in the world. Also, Canada has a higher percentage of registered cows in its data collection systems than the USA and other most other countries, and registered breeders are more likely to keep cows in herds that are attractive to look at (i.e., big and sharp) than are commercial milk producers.
The take-home message from Table 6 is that not all countries, and not all dairy producers within countries, will share identical selection goals – nor will all traits be equivalent predictors of survival across environments. However, it is becoming reasonably clear which traits are best predictors of survival of cows in most places in the world.
Table 6. Optimum score for Holstein survival (on scale of 1 to 9).
| Trait |
USA 1 |
Germany 2 |
Canada 3 |
Dairy form
(sharpness) |
3(round) |
5 |
9
(very sharp) |
| Stature |
2 (low set) |
3 (low set) |
9 (very tall)
|
| Strength |
3 (narrow) |
1 (very narrow) |
9 (very wide) |
|
Body depth |
3 (shallow) |
2 (shallow) |
7 (deep) |
|
Rump angle |
5 |
7 (slope) |
5 |
| Rump width |
3 (narrow) |
3 (narrow) |
5 |
| Rear legs-side view |
5 |
3 (straight) |
5 |
| Foot angle |
7 (steep) |
9 (very steep) |
6
|
| Udder depth |
9 (very shallow) |
9 (very shallow) |
6 |
| Udder cleft |
7 (strong) |
9 (very strong) |
8 (strong) |
| Teat placement |
7 (close) |
9 (very close) |
6 |
| Fore udder |
8 (strong) |
9 (very strong) |
9 (very strong) |
| Rear udder height |
8 (high) |
8 (high) |
9 (very high) |
| Rear udder width |
7 (wide) |
- |
9 (very wide) |
| Teat length |
3 (short) |
5 |
4 |
1 Caraviello et al. 2004. J. Dairy Sci. 87:2677.
2 Buenger et al. 2001. J. Dairy Sci. 84:1531.
3 Sewalem et al. 2004 J. Dairy Sci. 87:3938.
CONCLUSIONS
Dairy producers should not attempt to overcome deficiencies in heifer growth by selecting sires for larger mature body size. If heifers lack adequate body size, factors other than genetics almost certainly are the causes. Cows that are bred to be larger continue to grow more after first calving than cows that are bred to be somewhat smaller. Once a cow reaches optimum size, continued growth beyond that size is not economically desirable and is detrimental to survival. Only traits that are documented to increase productivity and efficiency should be included in selection goals. Udder depth, foot angle, somatic cell count, cow fertility, calving ease, and survival are examples of traits known to impact profitability of milk production. Over the long term, selection for traits with documented positive impact on profitability should result in cows of optimum appearance. Recent estimates of genetic relationships of survival with type traits suggest that more moderately-sized cows with less sharpness (and udders held well above the ground) are the most likely to survive the longest in dairy herds in most places in the world. |