2 Questions about Mature cow weight

[Aero]

in my eyes a 1200lb cow is more productive than a 1600lb cow.she does it on 30% less grass an feed.

it's actually 20% less. the cow would have to weigh 994 lb to consume 30% less than a 1600 lb cow.

metabolic weight correlates directly to nutritional requirements when looking at cow weight alone.

1600 lb cow metabolic wt = 253 lb
1200 lb cow metabolic wt = 203.9 lb (80.6% of 253)
994 lb cow metabolic wt = 177 lb (70% of 253)

[met wt = weight^.75]

 

[Aero]

"Animal Units" converted by using "Metabolic Weights":

http://www.ag.ndsu.nodak.edu/dickinso/r ... animal.htm

i had a mistake in my first post and deleted it. by the time i got the corrected post up, you had this one. did you read my first post then go find that one or is it some weird coincidence?

 

[DiamondSCattleCo]

http://www.ag.ndsu.nodak.edu/dickinso/research/1997/animal.htm

I've always questioned the accuracy of that study. In effect its saying, and someone correct me if I'm wrong, that large heavy cows require less feed (based on a %age of cow weight) than small cows. And that flies in the face of dozens of other studies on the subject, especially ones done up here that show as temperature drops, larger animals require more energy (based on a %age of cow weight) than do smaller cows.

Rod

 

[Aero]

as temperature drops, larger animals require more energy (based on a %age of cow weight) than do smaller cows.

i think i read somewhere that your assumption on this is incorrect also. if i remember correctly, larger cows had a lower (surface area)/lb ratio and would actually lose less energy.

if you look at a sphere [exagerated example (but relevant)] and its surface area you will see what they mean.

5' diameter sphere (small cow)
surface area = 314 ft^2
volume = 524 ft^3

6' diameter sphere (large cow)
surface area = 452 ft^2
volume = 905 ft^3

2 rules
heat disipation of almost any sort correwlates strongly to surface area.
1 lb of animal (when looking at the entire animal) has the same amount of energy no matter how big it is.

to look at % of energy lost in the same weather, it basically comes down to a (surface area)/volume coefficient for energy loss due to weather.

small cow rate of energy reserve loss = 314/524 = 0.599

big cow rate of energy reserve loss = 452/905 = 0.499

a pretty big difference. whether this is right, i dont know. I am just illustrating the stuff i read.

 

[bigbull338]

i really cant tell a differance in how much they eat.because they are all on pasture an hay.but heres what i figure.a 1200lb cow will consume 18 to 24lbs a day.a 1500lb will be at 24 to 30.an 1800 will be at 24 to 36.so on the highside an 1800lb cow will eat 50% more.all my beefmasters maintain their weight an raise a calf.

 

[MikeC]

http://www.ag.ndsu.nodak.edu/dickinso/research/1997/animal.htm

I've always questioned the accuracy of that study. In effect its saying, and someone correct me if I'm wrong, that large heavy cows require less feed (based on a %age of cow weight) than small cows. And that flies in the face of dozens of other studies on the subject, especially ones done up here that show as temperature drops, larger animals require more energy (based on a %age of cow weight) than do smaller cows.

Rod

By using the same assumptions........would a larger cow absorb more heat when in a high heat environment, thus raising the body temps to intolerable extremes. I think not.

Some studies attempt to propose energy requirements based on square footage of exposed area of a cow.

Would a longer, but one with the same hip height, be less efficient than one with shorter length?

If smaller cows are that much more efficient, why do we not all raise "Minis"?

 

[Aero]

By using the same assumptions........would a larger cow absorb more heat when in a high heat environment, thus raising the body temps to intolerable extremes. I think not.

I would say the theory explained in my previous post would favor the smaller cow in high temos and the larger cow in lower temps.

Some studies attempt to propose energy requirements based on square footage of exposed area of a cow.

we must have woken up on the same frequency today. :shock:

If smaller cows are that much more efficient, why do we not all raise "Minis"?

metabolic weight :tiphat:

 

[milkmaid]

Sounds right, Aero. We've been covering surface area, metabolic rate, energy use and loss, etc in class recently... I don't know the subject well enough (yet! lol) to chime in on this discussion, but your figures look and sound familiar. Think you're right on.

 

[Aero]

As long as they wean at least 50% of their body weight, I don't care how big they are.

to continue my metabolic weight sermon, my theory (which i think is the next logical step after % of dam weight) is to use a Metabolic Weight Ratio.

Metabolic Weight Ratio = calf weight / dam's metabolic weight

if you look at % weaned and expect 50+% from each cow, you are giving the big cows an unfair shake.

with this rule:
1000 lb cow must bring in a 500 lb calf.
1500 lb cow must bring in a 750 lb calf

the problem is that the big cow has to raise a calf that weighs 50% more and she didnt consume 50% more resources.

1000 lb met wt = 178 lb
1500 lb met wt = 241 lb

the big cow only consumed 35% more resources, but her calf has to weigh 50% more.

if you look at metabolic ratio as a measure of weaning merit, the 1500 lb cow's calf only has to weigh 675 lb to raise the same amount of calf/resources consumed. this would mean that their Met Wt Ratio is the same (2.8 lb of calf / lb of met wt).

say you decide that your cows should wean with a 2.8 MWR:

cow weight | Met Wt | calf weight
1000 | 178 | 498
1100 | 191 | 535
1200 | 204 | 571
1300 | 217 | 608
1400 | 229 | 641
1500 | 241 | 675
1600 | 253 | 708
1700 | 265 | 742
1800 | 276 | 773
the weights above show the same "efficiency" regardless of the cow weight.

notice that the 1000 lb cow raises 50% of her weight and the 1800 lb cow only has to raise 43% of her weight to be as efficient.

 

[Cowdirt]

As long as they wean at least 50% of their body weight, I don't care how big they are.

to continue my metabolic weight sermon, my theory (which i think is the next logical step after % of dam weight) is to use a Metabolic Weight Ratio.

Metabolic Weight Ratio = calf weight / dam's metabolic weight

if you look at % weaned and expect 50+% from each cow, you are giving the big cows an unfair shake.

with this rule:
1000 lb cow must bring in a 500 lb calf.
1500 lb cow must bring in a 750 lb calf

the problem is that the big cow has to raise a calf that weighs 50% more and she didnt consume 50% more resources.

1000 lb met wt = 178 lb
1500 lb met wt = 241 lb

the big cow only consumed 35% more resources, but her calf has to weigh 50% more.

if you look at metabolic ratio as a measure of weaning merit, the 1500 lb cow's calf only has to weigh 675 lb to raise the same amount of calf/resources consumed. this would mean that their Met Wt Ratio is the same (2.8 lb of calf / lb of met wt).

say you decide that your cows should wean with a 2.8 MWR:

cow weight | Met Wt | calf weight
1000 | 178 | 498
1100 | 191 | 535
1200 | 204 | 571
1300 | 217 | 608
1400 | 229 | 641
1500 | 241 | 675
1600 | 253 | 708
1700 | 265 | 742
1800 | 276 | 773
the weights above show the same "efficiency" regardless of the cow weight.

notice that the 1000 lb cow raises 50% of her weight and the 1800 lb cow only has to raise 43% of her weight to be as efficient.

Makes a lot of sense Aero. Would be a more reasonable expectation.

 

[DiamondSCattleCo]

Actually, these aren't guesses and assumptions, but rather studies done by the University of Saskatchewan (world class Ag department). A large cow is less efficient, and takes ever increasing amounts of energy in comparison to a small cow when the mercury drops. Its not just related to surface area, however I'll need to dig out the paper to remember what their actual hypothesis was.

I find all these theories over the years to be interesting. If you look at papers written in the 50s to the early 80s (or thereabouts), the overriding theme was "smaller is better", economic efficiency wise. When you start hitting the mid 80s and on into new millenium, they preach "bigger is better". The overriding theme here was that feed efficiency between big cows and small cows was identical, however the fixed cost of keeping each was the same, so why not have the bigger cow? Now we're starting to see a reversal on that theme.

My own experience over the years bears out from the 50s. I run small to moderate frame animals around here (12 - 1300lbs), whereas my neighbors run larger framed animals (15-1600 lbs). Their animals are approximately 30% heavier, however they feed 50% - 60% more feed throughout the winter. A good friend of mine has some _really_ inefficient Simm crosses (not picking on Simms here guys, just my buddies cows), and his feed costs throughout winter run closer to 80% higher. I fed his cows for him one winter and couldn't believe the difference.

Aero, a couple thoughts on your dissertation:

1) Large framed cows tend to have less backfat than small framed animals.
2) Pencil gutted cows may have less surface area, however they also have less backfat than deep ribbed cows.
3) Heat doesn't always travel UP in a cow, but rather transfers through the hide wherever organs contact. In other words cows can and do transfer a great deal of heat out their bellies. Hence the old saw: Keep a cows belly warm, and a horse's back warmer.

Mike, Aero - I can't comment on hotter climates at all since we only have a couple months of the year when it gets really hot. But I do know what works in the cold, and its definitely not large framed cattle. I believe what makes a good cow for the north is one with plenty of back and belly fat. A heavy brisketed cow will keep easier in the winter than a light brisketed cow, and small framed animals (IN GENERAL) tend to hold onto more fat reserves as a percentage of total body weight (if you can believe the stats coming back from the packers anyway).

Rod

 

[greenwillowhereford II]

The "optimum" 1200# cow weight is as much based on the finish weight of her offspring in the feedlot as anything else.

 

[ANAZAZI]

The fodder cosumed wilst bringing forth a 205 day calf is one thing, any cow big or small does some work this part of the year.
However; there is still half a year until she calves again. and in this half year big cows just cost extra money because they eat so much!

 

[Oldtimer]

There is my perfect cow...She isn't pretty- but she is 11 years old, under a 5 frame (the cow behind her is barely a 5 frame), weighs less than 1200 lbs- stays in good shape every year- deep so she can handle the cold weather- calves on the first cycle every year-has enough milk, but not so much her bag still isn't bad as an old gal- and brings in a March/April calf that weighs over 600 lbs in Oct when I wean....

The problem is- with all the "bigger, better, faster" bulls that are now being marketed- how do you keep that "perfect" cow....I know from personal screw up- I fell into the New Designs and all the other top bulls that were being promoted- and besides frame leaping (not creeping) up on heifers kept- I ended up with several more that were having bags go bad- 3-4 year olds coming in late or open- a bigger feed bill- and no real change in weight of calves- or price paid for calves ...

Thats my goal now- is to get back to this cow- the middle of the road cow....I know of at least a half dozen seedstock producers that never went with the bigger better faster trend and still have good "moderate" cattle....And several commercial producers that have or are trying to go back....
I think the reason their cattle is the "hot" market is because of the demand since so many now want to see more moderate cows again and are going that direction... Locally I know several large commercial operations now using their bulls, which should make more commercial heifers available...

 

[greenwillowhereford II]

Good post Old Timer.

Usually it is the registered stock producers that get accused of feeding too much, and raising cattle that can't work for the commercial producer. From the very beginning, I decided that to the best of my ability, I would raise purebred stock that could go to work for anybody and perform as well or better than what they had. Now, I have a friend with a sizable commercial herd, who came over to look at my cows who were on prairie hay and a 2-3# cubes per day. He was surprised at how well fleshed they were. His cattle are pampered compared to mine, with liquid feed among other amenities put out for them every day, and many more acres of better pasture per head.