Monday, September 3, 2007

Calf Birth Weight - Actual versus Tape Measure

A Truly 'laboring' Labor Day weekend!

My fall calving got started this past few days, and because one of the calves born was so very small I decided to try out a set of old bathroom scales that have a big platform and an elevated dial with big numbers for viewing weight results. This little heifer calf was a surprise finding on August 30th when the Animal Compassion Foundation was having another visit with my herd. Anne was thinking on her feet and volunteered her belt to use to measure the newborn and a pen to mark the spot. She was obviously a very little girl, and I ventured the guess that she couldn't weight more than 45 pounds.

We got back to the house and measured Anne's belt and found that she had measured 24 1/2 inches around, and it was a good snug belt measure around her heart girth, the little heifer was totally interested and cooperative. I figured the belt measure probably, because it was a thick leather belt, added some length to the measurement, and later on that evening I went out and measured her again with my tape, and I measured her at 24 inches. While 24 inches got her closer to the mark when you use the tape conversion chart in the Breeder's Guide, I still wasn't convinced that her actual weight was 51 pounds, which is what you get when you use the 4.5 pound increments to back into an off the chart 24 inch heart girth.

The following day I decided to try out my old scales on this little heifer. I found a light weight section of that stick on the floor tile type stuff in the barn, and decided that would work fine. It was nice and sturdy, yet was very manageable. I put the section of floor tile down on the ground, put the scales on my new weighing platform, and weighed her and myself twice for good measure. She was an exact 40 pound little heifer. The difference of 11 pounds is very significant, that is over a 25% error in birth weight estimation.

I decided to go through this same process with each of my newborns. Besides this little heifer, I had four other calves born August 30th through Sept. 2nd. Of those three of them were cooperative, the 27 1/2 inch bull calf born on August 30 to Hill's Dana already found it too much grand fun to scamper about for me pick him and get an actual weight.

August 31st a heifer calf was born to MsRae. She measured 26 inches, and per the tape conversion chart should have weighed 60 pounds, but in fact she weighed more! She had an actual weight of 65 pounds. I also had Mike confirm these same results himself, and it was an accurate weight of 65 pounds -- and she is pictured here.

September 1st a bull calf was born to Madonna (and I actually happened to be out at pasture hanging around in the Ranger and she calved about 40 feet away from me!). This bull calf measured 26 1/4 inches, and had an actual weight of 60 pounds. So in this instance the tape conversion to weight was quite acceptably accurate, and again I had Mike duplicate the weighing process for confirmation.

Then on the afternoon of September 2nd, Polly (pictured here to the right)decided it was time to calve. This calving went on for a bit too long for my comfort, I even called to try to reach a vet just in case I had a problem on my hands. But in between rushing to the house and calling the vet and leaving a message of impending problems, she had delivered a healthy bull calf. (So of course I rushed back to the house and left another message for the vet that all was well!) I tape measured this newborn at a whopping 27 1/2 inches, and had Mike confirm the tape measurement as well this time. We both weighed the little guy and he weighed all of 60 pounds. But, per the tape conversion he should have weighed about 67 pounds -- a greater than 10% error, which in this business is a highly material error.

So what does all this mean to the breeder who relies on tape measure conversion to estimate weight? It means you probably ought to be getting some actual weights as well until, or if, you feel comfortable visually estimating weight and understanding how the tape should perhaps be adjusted for what your eyes tell you.

As well, it could be that I don't handle the tape measure properly. With that in mind, if I haven't been pulling the tape snugly enough around the heart girth then I have a whole lot of historical birth weights that are over-estimated. However, the results from the little study shown here indicate the tape can create error both on the high and low side. I am going to continue to both use a tape measure for weight and get an actual weight with the remainder of my fall calves to get a sense of the average error rate as well as try to understand why.

Earlier I mentioned that Polly (who is also a first calf heifer) was having a more lengthy birth than I like to see. She actually was effectively yelling with her efforts, so I was even more alarmed. It's very unusual for any of my cattle to get vocal over calving. Polly's bull calf measured 27 1/2 inches, yet it only weighed 60 pounds. So, what was structurally different in Polly's bull versus Madonna's (also a first calf heifer) bull that would create an error using a tape measure? To my eye he has wider shoulders and is thicker through the heart girth, a deeper little guy -- yet at a glance looks about the same size/stature as Madonna's 26 1/4 inch bull. So obviously the confirmation of the newborn has a great impact on using a tape measure for an accurate birth weight.

MsRae's heifer is an example of the error to the light side using a tape measure. She weighed a full five pounds more than the tape measured estimate. Why? Perhaps because she has good balance all over, her dam certainly does. How does the tape measure consider a deep evenly made newborn that extends on through to the hind quarters? I don't think it can.

Regardless, I'll continue this small study of tape versus actual weight and see what the final results tell me about my own errors in tape measuring as well as errors due to the actual structure of the calf, and periodically update those results here on my blog.