Wednesday, April 24, 2024

Laying down the fat

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We should not be single-trait selecting for feed efficiency in our national cow herd. This was the message from Professor Wayne Pitchford at a recent Beef + Lamb New Zealand genetics workshop in Feilding.
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Pitchford said that instead we should be selecting for females that are more productive and profitable as part of a balanced selection programme.

For the past eight years, Pitchford, an Associate Professor in Animal Breeding and Genetics at the University of Adelaide, has led the Beef CRC’s Maternal Productivity Programme. Two of the objectives of this programme were to: 

  • Look at reducing the maintenance cost of the cow herd by selecting for feed efficiency
  • Investigate what effects this might have on herd productivity and profitability. 

The measure of feed efficiency used is called Net Feed Intake (NFI), which measures the amount of feed an animal eats and is adjusted for growth. More feed-efficient animals eat less (low NFI) than expected based on their growth while less feed-efficient animals (high NFI) eat more. 

Feed efficiency and productivity in the cow herd: The trial used two groups of heifers that had been selected for three generations for low and high NFI. Each of these two groups was put on a low-feed and a high-feed ration.

On a low-feed ration both groups ate about the same amount, but on a high-feed ration the high NFI animals ate more than the low NFI animals with 50% of this difference in feed eaten going into fat.

“This is exactly what we don’t want more feed-efficient animals to do,” Pitchford said. “We want them to eat less all of the time, not just when feed is plentiful.

“It appears that in selecting for growth we have been selecting for increased appetite, not metabolic efficiency, which is not what we want.”

Wayne Pitchford: “It appears that in selecting for growth we have been selecting for increased appetite, not metabolic efficiency, which is not what we want.”

Other research done as part of the maternal productivity project showed that fatter cows are considerably more productive than leaner cows, particularly when feed is limited. When feed is abundant all the time, leaner cows can match the performance of fatter cows. Research has also shown that more feed efficient animals are leaner.

These two findings have major implications in areas subject to seasonal fluctuations in grass growth, which is the situation in New Zealand. Leaner, more feed-efficient cows would need to be supplemented for a significant period of the year to match the performance of the fatter, less feed efficient ones. The issue then becomes one of supplementary feed costs and profitability.

“You want females with the ability to lay down fat when feed is plentiful and cheap, and carry it on their backs to times of the year when feed is scarce and expensive,” Pitchford said. “If we place too much emphasis on feed efficiency in our cow herds we will get them too lean and reduce their productivity.” 

Feed efficiency in the feedlot: The research also included a feedlot trial using finishing steers. Three groups of steers were selected for high NFI, medium NFI and low NFI based on the EBVs of their parents and fed the same ration for a period.

The low NFI steers ate 6% less feed than the high NFI group, had a 4% better weight gain, and produced 24% less fat. This equates to a 9% difference in feed conversion efficiency.

“So finishing animals that are genetically more feed efficient not only eat less feed but also grow faster and are leaner.

“This is great news for feedlotters as it will reduce their feed costs and fat produced.”

Pitchford said only 50% of the difference in feed intake could be explained by differences in fatness; the other 50% could not be explained. The fat he was referring to was subcutaneous fat and in replying to a question from the floor he explained that there was no relationship between intramuscular fat (marbling) and NFI. This meant that a breeder could select for more feed-efficient animals and better marbling at the same time. 

Summary:

  • We can select for feed efficiency in cattle, but it is not easy
  • More feed-efficient animals are leaner, eat less and grow faster – a feedlotters dream
  • Single-trait selection for NFI in the cow herd run in a typical NZ hill-country environment will result in reduced productivity
  • Adopt a balanced selection policy based on profitability, using an appropriate index, when choosing herd sires
  • Up to 50% of the variation in NFI can be explained by fat depth (animals that eat more are fatter). The other 50% cannot be explained.

More: Country-Wide

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