Like most cattleman, I am always trying to find more information on breeding and genetics. Therefore, a recent learned paper put out by the University of Kentucky Department of Agriculture caught my eye. It had a promising headline---“Selection and Management Practices to Increase Consistency in Beef Cattle”----and was written by two gentlemen who specialize in “animal science”. That should have been my warning; right there! By the time I was through reading the article I was thoroughly confused. Every technique they had discussed to “increase consistency” had been dismissed.
But we will start at the beginning, as the animal scientists do:
“There are two types of variation that concern the beef industry: genetic and phenotypic. <em>Genetic variation</em> in a population (calf crop) is diversity of genotypes for a particular trait. In other words, if all calves have similar genotypes for birth weight, the calf crop would have very little genetic variation in birth weight. If calves in the crop have different genotypes for birth weight, there would be a great deal of genetic variation. <em>Phenotypic variation</em>, on the other hand, would be the actual (or total) variation expressed in the calves. Genetic variation is a part of phenotypic variation, but environmental variation (management) also makes an important contribution.”
Well we’re good so far. I agree that seed stock producers are responsible for diminishing or eliminating genetic variation. The more out-crossing there is in a purebred herd, the more variability there will be in the males and females coming from that herd.
"If a breeding program is to be successful at producing bulls with less genetic variation, practices should be used that will increase the percentage of homozygosity in those bulls."
The "gold standard" for homozygous gene pairs in a bull is line breeding. Look back to all of the great names in cattle breeding from history and you will find almost exclusively line breeders. The purebred and commercial cattlemen, who purchased from them, did so because they could readily see an improvement in uniformity of offspring and an improved phenotype not found in their herd prior to the use of the pre-potent bull.
At this point, the article proposes a number of different methods to reduce genetic variation by, as they say, stacking pedigrees. First on the list is to breed to animals with similar EPD's! (By the way, when I hit spell check on my computer, EPD was "questioned" more times than any other word. Does my computer know something the average American seed stock producer does not when it come to reducing genetic variability?) In my view, the largest problem with EPD's is its tendency to single-trait select.
And here the reader suddenly finds himself on a yo-yo. First the learned authors say, stacking EPD’s…
“…is the most effective way to make rapid change in the trait for which selection is being made!”
But wait! In practically the next sentence they say....
“…there is no evidence that fixation of any trait has occurred in cattle populations using maximum single trait selection. Due to genetic correlations, single-trait selection can have a detrimental effect on other important traits. For example, single-trait selection for maximum growth can result in increased birth weights and reduced milking ability in the cow herd.”
But when the scientists finally get around to breeding like-to-like, they again focus on EPD’s for their definition but jump from there to their conclusion
“Based on basic genetic principles and verified by beef cattle research, the method of breeding like to like does not significantly reduce trait variability.”
More than 100 years ago, Thomas Shaw didn’t have the “advantage” of EPD’s when he described like-to-like breeding:
"When the parents are much alike in breeding and in all essential characteristics, this law is sufficiently uniform in its action to justify the breeder in looking for progeny similarly endowed."
Of course, it must be admitted Shaw was not using “science”. He was considering parental lineage and by observation was selecting the animals to be mated based on their individual merits, not a computer spreadsheet. That’s why he wound up with the conclusion that breeding like-to-like results in “sufficiently uniform” progeny.
Our scientists however aren’t able to come up with success depending solely on EPD’s. They are forced to admit:
"If the cows in the herd are being mated to bulls with similar EPDs, their offspring on the average are expected to have the same EPD. Therefore, this herd is not making genetic progress, and the progeny produced will likely have no less variation than if corrective or progressive matings were used."
Our experts turn next to in-breeding and fortunately an expert from a much earlier generation---Robert Bakewell---is not around to consider their introductory statement:
“Theoretically, inbreeding should be an effective means of reducing genetic variability; however, research with beef cattle has shown that this reduction in variation is slight, even when inbreeding is practiced in combination with single-trait selection for growth over many generations."
If they had been using prepotent bulls at the outset, they would have seen a major reduction in variation. To start with a mongrel animal on both sides would take a lifetime or two to achieve the expected prepotency they are seeking. Thus, they wound up with “slight” results. And why bother with single trait select along the way? They had already told us at the outset of this article that single trait selection, using EPD's, didn’t work. Why spoil the in-breeding test by using them again? They certainly can’t jump to their conclusion that in-breeding adversely affects: “fertility, survivability, longevity and performance.”
As Gearld Fry would say: "We have been lied to!" The list of adversely-affected characteristics can be improved in an amazingly short period of time if line breeding and selection are practiced correctly. But our authors are quickly moving on to cross-breeding. One has to wonder how they can consider that in a paper whose goal is to reduce variability. Nevertheless here we go:
"Commercial producers….may be concerned that crossbreeding could increase variation. Although crossbreeding may increase genetic variation slightly, research indicates that phenotypic variation is not adversely affected. However, crossbreeding systems do have the potential to increase variation if they are not implemented correctly. Advantages of crossbreeding in a commercial operation >ar outweigh any potential increases in variation, however."
Here, apparently, they must be talking about pounds of weaning weight; certainly a list of the advantages of cross-breeding can’t include a reduction in variation. But the authors are ready to throw up their hands. Their review of the means of reducing genetic variation in calves makes it apparent that none are effective in reducing phenotypic variation. With that “fact” in hand, they conclude that management is the only way producers will get the uniformity they’re looking for.
“The most effective tool to reduce variation in calf weaning weight is to have a limited breeding season. Considering that if calves approaching weaning gained 2 lbs a day, it would take only a difference of 50 days in birth date to result in calves with a difference of 100 lbs in weaning weight.”
Finally then something that only a scientist in a university would think would work: a one day breeding season!
At least it would guarantee that all the calves weighed the same at weaning. Veterinarians and pharmaceutical salesmen will appreciate the increase in business spurred by the synchronization techniques suggested to shorten the calving season.
To me the article actually conclusively demonstrates only one thing: the authors indeed have degrees in animal science, not animal husbandry!