HerefordSire":muhlh5o5 said:
Brandonm22":muhlh5o5 said:
Are there differences in efficiency between cows even when they weigh the same? Yes and certainly it is quite possible too improve efficiency without decreasing frame size or body weight. THAT said, flesh is a living thing. Every pound of animal has to be fed every day. IF there is 400 pounds more animal there that 400 pounds has to be fed.
Metabolism
Zerbini et al. (1996a) found that in working cows, glucose is an important energy source for the muscles; it is also important during reproduction. Fatty acids were found to be important for the synthesis of milk fat as well as reproductive hormones. Non-esterified fatty acids (NEFAs) and ß-hydroxybutyrate were found to increase in working cows whereas glucose, magnesium and inorganic phosphorous decreased.
Zerbini et al. (1996a) found a greater loss in body weight in working non-supplemented cows than in working supplemented ones. Glucose was decreased in non-supplemented cows, which stimulated the release of NEFAs from adipose tissue (150% increase in the plasma). Fatty acids were mobilised from the fat depots even in well-fed animals. This suggests that NEFAs are the principal fuel for the muscle tissue of working dairy cows. Reduction in NEFAs in poorly fed working cows explains the low conception rate. Energy restriction affects reproductive performance at the hypothalamic or pituitary level. This could be due to inhibition of gonadotropin-releasing hormone (GnRH).
http://www.ilri.org/InfoServ/Webpub/Ful ... odule3.htm
"We predict the intake based on how big the animal is and how fast the animal grew," Carstens explains. "So an animal that eats less than predicted will have a negative (in this case that is good) net feed intake or improved net feed efficiency. An animal that eats more than predicted would have a positive net feed intake or poor net feed efficiency. Obviously the animals we are trying to identify and propagate through selection are those animals that eat less than predicted.
"The value in looking at net feed intake as an alternative measure of feed efficiency is that we can account for feed requirements for maintenance and growth with this trait," Carstens adds. "Australian research has shown that net feed intake is moderately heritable and is independent of the animal's growth rate."
Preliminary results to date
While most of the data for this project are still being analyzed, one thing is clear: These animals with so much in common definitely have differences in terms of net feed intake and efficiency.
Steers in the low NFI group (meaning more efficient), ate 17 percent less feed than the high NFI group, even though their growth was similar. In terms of profitability, that's a significant difference. Carstens explains, "If we use a ration cost of $120 a ton, and … if efficiency could be improved by 10 percent, through selection, we can save about $25 per animal in feed costs to put 600 pounds of gain on a feedlot steer."
Why are some animals able to maintain themselves with relatively less feed intake?
"Other research suggests the reason the low NFI cattle consume less feed, though they weigh the same and gain the same, is that the low NFI animals have lower maintenance energy requirements," Carstens explains. "One of the questions we're trying to ask, beyond the physiological indicators, is do these animals have lower maintenance energy requirements?
"Roughly, if we break it down and look at a cow herd from conception to weaning," he says, "looking at the total energy required on an annual basis, about 70 percent of the total feed energy that goes into that cow herd to produce weaned calves is going toward cow maintenance. It's big chunk.
"The key is can we do it without impairing the cow's productivity?" he asks. "This is why we need to conduct more research to make sure that two or three generations down the road we don't end up with cattle that reproduce less efficiently or produce tougher carcasses."
http://www.texascattleraisers.org/issue ... easure.asp
