Welcome to the second of the series of articles regarding the production of meat for people to eat. At the conclusion of the first article I left you with a question of Jim Bradfords “Fertility is the Governer of Growth.” Prior to dissecting and analyzing this quote of Bradfords it’s important to gain a fundamental understanding of fertility.
Firstly, What is Fertility?
Quite simply it is the successful fusing of the node sperm cell with the female ovum. The resulting unit quickly becomes the embryo, which then grows and differentiates to become the foetus. At approximately day 283 past this successful fusing of those initial male and female units the calf is born.
How is Fertility Measured?
Pregnancy checking is the standard measure of fertility. Normally pregnancy checking occurs about forty to seventy days post joining. The fertility measure is then expressed as a percentage of those cows assessed/deemed to be positively in calf or pregnant, against the number of cows exposed, that is joined to the bull/s or artificially inseminated.
What Pregnancy Rates Should Be Able to be achieved?
This is a difficult question to answer because so many factors impact on the Fertility outcome. However, in a normal commercial beef enterprise targeting the production of beef for people to eat on the New England, the following targets should be attainable
- i) Maiden Heifers 85 – 90%
- ii) Two Year Olds 88 – 92%
- iii) Three Year Olds to Ten Year Olds 92 – 96%
Its now possible to attempt to interpret Bradfords quote.
How Does Fertility Govern Growth?
Quite simply, without the successful fusing of the male sperm cell with the female ovum there is no pregnancy. Without the pregnancy there is no foetus, there is therefore no calf to grow, that is, put on kilograms of beef per day, per unit of land.
How much potential growth can be lost by poorer fertility?
Consider the following example:
In a 340 self replacing, keeping 45 maidens and joining them at 14 months weighing 300kg.
|Maidens: 45 head Preg Rate 85%|
|Maidens: 45 head Preg Rate 80%|
|2yr Olds: 36 head Preg Rate 88%|
|2yr Olds: 34 head Preg Rate 84%|
|3yr-10yrs Old: 230 head Preg Rate 92%|
|3yr-10yrs Old: 210 head Preg Rate 88%|
|Grand Total = 280||Grand Total = 249|
There is a potential loss in this example of 31 calves which at weaning should weigh 250Kg, which is 7,750Kg @ $2.00/Kg = $15,500. By inference fertility not only governs growth it also controls profitability. Note there is a reduction of thirty-one calves. It is the total not the rate at which these calves grow that is being measured. The impact of growth rate will be discussed at a later date.
What factors impact fertility?
Like almost all traits there genetic an environmental component to fertility. The genetic contribution to fertility is low, the estimates range from 0-15%. That is only about 10% of the variation measured for the trait can be attributed to the genetic make-up of the cows and bull. The remaining 90% of that variation is due to the environment, that is the nutrition, the disease and the management for the trait.
Managing females to optimize fertility.
- i) Heifers. Should the decision be taken to join maidens at 14 months be sure they weigh 280Kg as a minimum and that they have had an even and adequate growth rate for their whole life. This will ensure they won’t be compensating at the time of joining. If they are making compensatory gain then they are more likely to lay down excessive fat, which will mean reduced fertility. Keep the heifers in 2+ body conditions so they can be put on a rising plan of nutrition just prior to joining and during the nominated joining period.
Depending on whether you are opting to maximize pressure on fertility the suggested time for joining heifers is two to three cycles, that is 6 to 9 weeks. Remember to add a few days because the bulls, particularly yearlings, will spend the first 2 to 4 days adjusting to the new paddock and the fact that he is with a group of females. When selecting bulls to place with heifers remember that they will only weigh 280-320Kg so try to use yearlings (500-550Kg) or lighter older bulls that have shown reasonable agility during mating. As well as ensuring heifers are on a rising plane of nutrition for three weeks prior to joining. Be sure the essential trace elements for optimal fertility aren’t lacking. Remember selenium can be a problem on the New England. Vitamin A.D.E injections may be worth considering but that are short term its best to be sure the pasture mix is adequate and able to provide that rising plane.
Its preferable to join heifers a month earlier than the main cow mob, this enables them more opportunity of building themselves up as two year olds once they have calved so that their conception rates will be optimized.
Reproductive diseases, such as heptosperosis, are today easily managed by using an effective 7:1 inoculation program.
- ii) Cows. As mentioned above 2yr Olds should be given that extra month to build themselves up prior to joining. Managing the nutrition of cows that have calved is quite tricky, particularly during periods of extended dry spells. Best fertility rates are achieved when the cow is exhibiting a body condition of more than 3. If the cow is only in condition score 2 to 2- at the time of calving she will often slip in to Lactation Anoestrous. In other words she will be milking at the expense of using energy to ‘cycle’ and ovulate. As a result she may not cycle prior to the bulls being removed or she will cycle very late in the breeding season. Cows should be joined for a period of three cycles that is nine weeks and again it is worth allowing the bull 3-5 days to adjust to their new environment. The shorter the anticipated breeding season the higher the joining percentage should be. That is, if the breeding the season is to be restricted to 2 cycles then suggest 3% bulls, that is 3 bulls for every hundred cows. If the breeding season is to be three cycles and the country is accessible and the paddocks not to large then suggest the joining percentage should be 2%; 2 bulls to every hundred cows. Cows do need to be structurally sound to cope with the act of mating, particularly since there has been an emphasis on improving growth rates and producing feeder steers capable of achieving carcase weights up to 400Kg. Do not overlook the ‘structure’ of the cowherd. Watch for angulations in the hock and stifle. If these joints are to straight it is difficult for the joint to perform its function of absorbing the weight of bulls that can often weigh in excess of 1000Kg. Good contact points with the ground, that is feet are also important to ensure the act of mating is an success.
As with the heifers selenium, vitamins eg. A.D.E and disease control eg. Heptospirosis need considerations.
Remember conception cannot occur unless the cow ovulates. Feed, disease control and body condition at the time of joining are essential considerations.
At the time of pregnancy checking, be ruthless, an empty cow is a passenger. Fertility may not be all that highly heritable but infertility most defiantly is. Cows that calve every second year produce heifers that calve every second year. Therefore while the price for cow meat is upwards of $3.50/Kg H.S.C.W cash them in. The hamburger trade is doing the productivity of our cowherds a huge favor at the moment.
- iii) Bulls. We have talked about measures for fertility amongst the female population and about joining percentages. What fertility measure is there to help us with measuring the bull’s performance reproductively?
The most useful the scrotal circumference. Up to a point the more live sperm cells produced the more likely a bull is of ‘covering’ his fifty cows in a 65-66 day joining period. The larger the circumference, again up to a point, the more viable sperm cells a bull can produce. Scrotal tone, scrotal shape including the obvious presence of the epididymis also important considerations.
Thirty-six centimeters is the minimum recommended scrotal circumference for 2-year-old bulls if they are to achieve at the levels talked about previously. Be careful not to fall into the trap, if thirty-six is good and adequate then forty-five centimeters is best. Always consider the body weight, body condition, and age of the bull when considering tossing a bull out on scrotal measurement.
Significantly it has been shown that bulls with less than then thirty-six centimeter circumference can do more heifers that reach puberty that is exhibited there first effective cycle later in life.
The service capacity test has been shown to give trend line indications as to how many cows a bull may service in a normal nine-week joining period. However the repeatability of this test is sometimes hard to achieve. Service ability is certainly worthwhile. That is, are all the parts working, is the penis broken? Is the penis free from warts are the secondary sex glands free from infection. Seminal vesiculitis; an infection of the secondary sex glands will render bull temporarily sterile (up to six weeks). It can only be detected by rectal palpation.
The final component of the service ability test is to watch the bull mount and be confident that he is able to serve dismount and move onto the next. Once again structural soundness is so important to a bull “achieving his tally”. As with the cow watch for joint angle particularly the stifle and hock make sure the feet are sound and that the back pasterns in particular aren’t to straight. Bulls with the slightest signs of arthritis will not achieve very high tally’s that is pregnancy rate. Arthritis is a painful disease of the joints toe dragging is an indicator of this. If the bull experiences pain when mating then he normally won’t come back for more, thereby reducing pregnancy rates.
The issue of single sire mating is a difficult one. Remember if a bull is incapable of serving a cow or if his sperm count is not higher enough to achieve successful conceptions then the fertility rate will be low. Be sure to watch single sire mated cow groups for sire activity, is he actually serving? Are their cows returning? It is advisable to rotate sires if the single sire mating practice is to be adopted.
It s good practice not to mate yearling bulls with older 4-5-6 year old bulls. The older bulls will dominate the yearlings and may cause severe damage.
Vibriosis is a reproductive disease transmitted by bulls, to optimize fertility be sure bulls are vaccinated against vibriosis to eliminate lost due to the disease. Bulls should also be vaccinated with 7:1 to control heptospirosis.
Bull nutrition needs to be carefully managed, bulls need to be on a rising plane of nutrition just prior to and during the joining period. The bulls don’t need to be fat, suggest 2+ and 3- body condition score. Bull sperm production is impaired by fat around the scrotum so don’t let the bulls get to fat. Fat bulls are much less active and heavier and therefore likely to be less likely to successfully place the sperm cell in contact with the ovum.
Fertility is the base from which any successful beef operation should be launched. Remember fertility is not all that highly heritable in fact the order of 90% of the expression of fertility as measured by pregnancy rate is attributable to Nutrition, Disease control and Management.
In next issue we will discuss calving ease remember Dr Rex Butterfields quote
“Dead calves have distressingly poor growth rates”