Calf Birthweight Objectives - Mississippi State University
The objective for any producer should be to have as large a calf as possible born to the cow without complications. In most cases the larger the calf at birth, the faster his growth rate, the heavier the weaning weight, and the better the returns to the producer. Match the birthweight of the bull to the size and age of the cow that will have the calf. Low-birthweight bulls are an advantage for heifers, but not necessary or desirable for larger, mature cows.
Is having low-birthweight calves truly the objective a producer should have? Do not get caught up in single-trait selection, and then further into your breeding program wish you had made another choice. The objective should be to have the largest calf you can without problems.
The first thing to remember regarding birthweight is that you will not starve a small calf out of a little cow or heifer. The producers who stop feeding heifers in the last trimester of a pregnancy (to make the calf smaller) usually have a weak cow that will not breed back, will not milk, and will have a stunted calf at weaning. You can overfeed heifers, and sometimes cows, and cause problems, but you are not likely to cause a calf to be appreciably smaller, in utero, by withholding feed from its mother.
The most obvious answer to controlling birthweight is to select a bull that has the genetic potential to sire calves with small birthweights. At one time, producers would routinely select an Angus bull to breed to heifers. Angus had the reputation for producing low-birthweight calves. This is not absolutely true. Also, Brahman cattle were said to be born "like a piece of spaghetti -- long and loose." Some of the largest calves weighed, and unfortunately pulled, have been sired by Brahman and Angus bulls. With the push for larger cattle, birthweights were disregarded. There are more birthweights of 100 or more pounds found, independent of breed and including Angus and Brahman, than producers want to realize. You can no longer look at breed, but you must look at individuals within a breed, to determine low-birthweight bulls. Most breed associations provide EPD's (Expected Progeny Differences) for birthweight, weaning weight, maternal milk, and yearling weight for animals in that particular breed. These are estimates of an individual animal's performance within his or her breed -- it is Angus compared to Angus, Simmental to Simmental, etc., not between breeds. All of these numbers are generated from breed averages for a trait. Breed average is 0, or the benchmark from which all numbers are generated. It is important for producers to know, or have at least a general knowledge of, what the breed average is for each trait in which they are interested. A breed average of 0 for birthweight may be different for a Longhorn and a Chianina. As a guideline, the larger the mature weight of a breed or an individual within a breed, generally the larger the birthweight of that animal.
The objective of most breeding programs is to wean the largest calf possible from each cow. Birthweight and postpartum growth are usually closely related. Generally, calves with large weaning weights (600+ pounds) do not have low birthweights. There are a few bulls that combine small birthweights with large weaning and yearling weights, but they are rare. Most of the time, if calves are big at weaning, they were big at birth.
Low birthweights mean different things to different producers. A cow should have the largest calf she can without complications. Obviously this weight differs if a producer is dealing with a 1,200-pound mature cow, which has had several births, and a 900-pound, first-calve heifer. The 1,200-pound cow could easily have a calf weighing more than 90 pounds, but the 900-pound heifer would likely experience calving problems if calving to the same bull. Conversely, it would be an economic disadvantage to breed a calving-ease bull to the 1,200-pound cow. In most cases, the calf would be much smaller than necessary and would have a slower rate of growth. When you determine optimum birthweights, consider the size, age, and previous calvings when selecting a bull. You will almost never experience calving problems when the calf birthweight is not more than 8% of the cow's bodyweight (80-pound calf/1,000-pound cow).
Another way to determine calf-birthweight maximums, especially in heifers, is to measure the pelvic size of each heifer. This is done with a tool that determines the minimum height and width of the pelvis. This measurement gives the producer an estimate of the size of calf a heifer can birth without complications. A minimum measurement of the pelvis (width x height) is 160 cm-squared for 12- to 14-month-old heifers. These are not absolute numbers, but can give producers an idea how each heifer compares to her contemporaries and whether or not even a low-birthweight bull (70 to 75 pounds or below) would reduce potential calving problems. These measurements give the producer an idea of which heifers are not good risks to calve unassisted.
You should also remember that when crossbreeding, you get heterosis or hybrid vigor in utero as well as after the calf is born. Use moderation in selecting bulls for a crossbreeding program.
Some research has also indicated that Brahman purebred and Brahman-crossbred cows have the ability to control or reduce the birthweight of calves in utero. The opposite may be true when breeding Brahman bulls to English-type cows. Extremely large calves can be the results of these matings. Calf birthweight is the single factor most closely related to difficulty at birth.
The objective for any producer should be to have as large a calf as possible born to the cow without complications. In most cases the larger the calf at birth, the faster his growth rate, the heavier the weaning weight, and the better the returns to the producer. Match the birthweight of the bull to the size and age of the cow that will have the calf. Low-birthweight bulls are an advantage for heifers, but not necessary or desirable for larger, mature cows.
Is having low-birthweight calves truly the objective a producer should have? Do not get caught up in single-trait selection, and then further into your breeding program wish you had made another choice. The objective should be to have the largest calf you can without problems.
The first thing to remember regarding birthweight is that you will not starve a small calf out of a little cow or heifer. The producers who stop feeding heifers in the last trimester of a pregnancy (to make the calf smaller) usually have a weak cow that will not breed back, will not milk, and will have a stunted calf at weaning. You can overfeed heifers, and sometimes cows, and cause problems, but you are not likely to cause a calf to be appreciably smaller, in utero, by withholding feed from its mother.
The most obvious answer to controlling birthweight is to select a bull that has the genetic potential to sire calves with small birthweights. At one time, producers would routinely select an Angus bull to breed to heifers. Angus had the reputation for producing low-birthweight calves. This is not absolutely true. Also, Brahman cattle were said to be born "like a piece of spaghetti -- long and loose." Some of the largest calves weighed, and unfortunately pulled, have been sired by Brahman and Angus bulls. With the push for larger cattle, birthweights were disregarded. There are more birthweights of 100 or more pounds found, independent of breed and including Angus and Brahman, than producers want to realize. You can no longer look at breed, but you must look at individuals within a breed, to determine low-birthweight bulls. Most breed associations provide EPD's (Expected Progeny Differences) for birthweight, weaning weight, maternal milk, and yearling weight for animals in that particular breed. These are estimates of an individual animal's performance within his or her breed -- it is Angus compared to Angus, Simmental to Simmental, etc., not between breeds. All of these numbers are generated from breed averages for a trait. Breed average is 0, or the benchmark from which all numbers are generated. It is important for producers to know, or have at least a general knowledge of, what the breed average is for each trait in which they are interested. A breed average of 0 for birthweight may be different for a Longhorn and a Chianina. As a guideline, the larger the mature weight of a breed or an individual within a breed, generally the larger the birthweight of that animal.
The objective of most breeding programs is to wean the largest calf possible from each cow. Birthweight and postpartum growth are usually closely related. Generally, calves with large weaning weights (600+ pounds) do not have low birthweights. There are a few bulls that combine small birthweights with large weaning and yearling weights, but they are rare. Most of the time, if calves are big at weaning, they were big at birth.
Low birthweights mean different things to different producers. A cow should have the largest calf she can without complications. Obviously this weight differs if a producer is dealing with a 1,200-pound mature cow, which has had several births, and a 900-pound, first-calve heifer. The 1,200-pound cow could easily have a calf weighing more than 90 pounds, but the 900-pound heifer would likely experience calving problems if calving to the same bull. Conversely, it would be an economic disadvantage to breed a calving-ease bull to the 1,200-pound cow. In most cases, the calf would be much smaller than necessary and would have a slower rate of growth. When you determine optimum birthweights, consider the size, age, and previous calvings when selecting a bull. You will almost never experience calving problems when the calf birthweight is not more than 8% of the cow's bodyweight (80-pound calf/1,000-pound cow).
Another way to determine calf-birthweight maximums, especially in heifers, is to measure the pelvic size of each heifer. This is done with a tool that determines the minimum height and width of the pelvis. This measurement gives the producer an estimate of the size of calf a heifer can birth without complications. A minimum measurement of the pelvis (width x height) is 160 cm-squared for 12- to 14-month-old heifers. These are not absolute numbers, but can give producers an idea how each heifer compares to her contemporaries and whether or not even a low-birthweight bull (70 to 75 pounds or below) would reduce potential calving problems. These measurements give the producer an idea of which heifers are not good risks to calve unassisted.
You should also remember that when crossbreeding, you get heterosis or hybrid vigor in utero as well as after the calf is born. Use moderation in selecting bulls for a crossbreeding program.
Some research has also indicated that Brahman purebred and Brahman-crossbred cows have the ability to control or reduce the birthweight of calves in utero. The opposite may be true when breeding Brahman bulls to English-type cows. Extremely large calves can be the results of these matings. Calf birthweight is the single factor most closely related to difficulty at birth.
