sue said:
Let's not confuse calving ease with birth weight> I feel alot of Shorthorn breeders really dont understand the difference between the two:
Hillside Leader is siring calves that come unassisted then his CE will rise to a posititve number provided information is turned in to ASA. In other words selection for just a( -)BEPD does not always give a breeder enough information THAT'S WHY WE SHOULD PRINT CALVING EASE EPD'S IN SALE CATALOGS.
THE FOLKS IN THE NORTH should be happy to know that even if a sire is consistantly throwing 100-110 lb birth weight calves and they all come unassisted well then this bull would still have the more desirable CALVING EASE EPD (+). If you look at a bull like SASKVALLEY BONANZA OR MANY OF THE SASKVALLEY BULLS UP THERE. Thank you Saskvalley for printing CE in the catalog. Suppose I am a breeder in alabama and I am looking at a bull in Canada- epds help sort the differences.
Are you still confused Joe or Grant ?
Let me review again: If you have a +3.0 CE bull and a -11.0 CE bull the + is better then the - regardless of the weight of the calves - CE is a measure of calving unassisted. BEPD is a measure of calf weight at birth . It's a tool and since ASA added it alot refuse to print because they just dont get it? Be sure and record the ww weights of Hillside Leader and Yearling wts too alot of his calves are not recorded.
Sue,
I don’t think I’ve ever been confused on the difference between birth weight and calving ease – in fact I’ve read a fair amount of the research related to the subject – including US, Australian and European research. All of these conclude much of the same thing (and we all know this) –there is a high negative correlation between birth weight and calving ease, i.e. as birth weights increase, calving ease decreases.
As work at Iowa State noted however, the problem with the data set is that most of the early work (using the Angus Association’s records) is from information representing predominately first calf females and their calving ease. Because few people in that breed used anything but low birth weight bulls for heifers – the data has a built in bias toward these same bulls. Because of this there was very little reliable data on the “calving ease” impact of heavier birth weight bulls. Also there was very little data on birth weight and calving ease impacts on mature females, so many bulls that were never used on heifers have little to no actual data in their EPD's. As such the Iowa State research recommended using birth weight EPD’s as the most reliable indicator of calving ease for first calf females. I don’t know how the Shorthorn data set was developed, so I can’t comment on the exact effect on our breed, but I would assume the trends would be similar.
What has been noted in some more recent work is the cumulative effective of this selection pressure. We all know that birth weight is highly correlated with weaning and yearling weights, so as selection pressure is placed on lowering birth weight (or increased calving ease) we tend to see a decrease in the size of the next generation. As these animals enter production it requires an even greater emphasis on selecting for easier calving, since they are generally smaller than the preceding generation. If this continues the end result is either a significant loss of total performance in the gene pool or selection for phenotypic traits, like smaller bone, less muscle, etc. that could enhance the calving process.
The most obvious answer and the one that much of the research substantiates is that selection pressures should look for optimums among birth weight, growth, mature size, etc. so that succeeding generations of cattle will meet the total needs of the industry. From a purely economic perspective, this gets to the issue most commercial producers face – how do I optimize the total dollar returned per cow owned. Using this model, we have to balance the desire for 100% live calf crop with the need for maximum pounds at market/harvest. As some of our American breeds are finding out – producers are more than willing to risk losing a calf or two a year in order to increase weaning weight 50 pounds. Why – in a 50 cow herd with $1 per pound 500 lb. weaned calves, that equates to an increase in profit of $1400 (48 calves at an increase value of $50 per head minus the 2 lost @$500 each).
I fully agree with you that, in order to make progress, we need our breeders to submit data on all their calves – otherwise the relevance of our data base is minimized. One of our biggest problems is that, for many of our cattle, the numbers of observations are so low that it makes it difficult to get a level of accuracy that you can be comfortable with. And, as I think we found with the Canadian cattle (Grant or Bob correct me if I’m wrong), getting a baseline established for their EPD’s, when there was no previous data, was difficult and may explain the high degree of variability that is being found.
In addition, in looking at the work of Bonsma and others, the observations that Grant made about the role of skeletal design in the female, have great relevance. As we have redesigned the American bovine to meet the “eye appeal” test we have negatively impacted the natural birth path way. By elevating the hip bones we have increased the “push” required to get a calf down the birth canal. That’s why it seems a Bos Taurus bred female seems to be able to give birth to a baby elephant with no trouble – their pelvic and hip area is designed to accommodate the birth of the calf.