More on carcass weight feed conversion

This past week I’ve been working with research data looking at various combinations of wheat middlings (midds) and distillers dried grains with solubles (ddgs) in grow-finish diets. I’ve also been reviewing the recent literature on these diets. The result of this effort is to further support my blog of a few weeks ago that the US industry must start examining feed conversion on a carcass weight basis.

Let’s look at some of the published data so you can better understand what I’m talking about. In a Journal of Animal Science paper (JAS 90:2620-2630), KState researchers fed diets containing various combinations of ddgs and midds to grow-finish pigs with an average on-test weight of 102.5 lb. Pigs were fed to a constant sale date. The converted data table from the publication follows.

At first glance, the differences in feed conversion don’t look that great with increased ddgs and midds in the diet. However, the control pigs were 11.2 lb heavier at slaughter than the 30/20 diet pigs with a 14.3 lb heavier carcass.

If you convert the starting weight to a carcass weight (75% yield), you can do the math to determine the impact of the diets on efficiency of carcass weight gain. The conversion numbers become 4.15, 4.36, 4.32 and 4.41 for the 0/0, 30/0, 30/10 and 30/20 diet treatments. This is a much larger difference between treatments than using liveweight conversion estimates.

These numbers can also now be used to estimate more closely the economic impact of the various diets or what you must discount the higher fiber diets relative to corn soy-soy diets to have the same return over feed costs. For example, the 30/20 diet had a 6.3% worse carcass weight conversion. This suggests that for this diet to be economical it must cost somewhere in the range of 6.3% less than the 0/0 diet since both treatments have carcasses that were paid a similar price per pound. Note that I same somewhere near 6.3% as the impact of more days needs to also be computed into the costs and return equation.

Using liveweight feed conversion, the impact of the diets on the income side of the equation is missed since it doesn’t account for the differences in income associated with differences in yield and carcass weight.

DDGS, % 0 30 30 30
Midds, % 0 0 10 20
Final wt 296.8 294.4 288.2 285.6
Liveweight ADG 2.31 2.28 2.21 2.18
Liveweight F/G 3.06 3.00 3.09 3.11
Carcass Yield 74.2 73.4 72.7 72.1
Carcass wt 220.2 215.8 209.7 205.9

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