TIME OF CALVING II — THE FINISHING TRIAL

A three-year study looking at changing the time of calving in beef cow herds in Western Canada from March/ April (early) to May/June (late) is showing that the move to later calving has potential to lower production costs by better matching feed requirements of the cow to forage availability, and reducing labour and animal health costs through to weaning.

Many producers who have switched to later calving are quick to point out the advantages of calving on grass. But, it has also meant making adjustments down the road when it comes to weaning and marketing, or backgrounding and finishing those later-born calves. Ultimately, the market price of the calves and the cost of purchasing additional feed supplies, if necessary, will affect overall profitability.

The time-of-calving study has branched out to evaluate the implications of changing the calving season on post-weaning management of feeder steers through to slaughter. Ultimately, researchers hope to be able to use the data from the time-of-calving-to-weaning study and the time-of-calving-post-weaning trials to analyse the economics of each production system from birth to slaughter.

The studies are being carried out by Agriculture and Agri-Food Canada at the Brandon Research Centre and Semi-Arid Prairie Agriculture Research Centre at Swift Current, Sask., and at the Western Beef Development Centre at Lanigan, Sask.

The calving-to-weaning segment will wrap up when the late-born 2009 calves are weaned in December. The final performance report and economic analysis is expected early in the new year.

The post-weaning trial began with the 2007 calf crop and is continuing with the 2008 steers, the last group of which will go into the final finishing stage this fall. All of the 2009-born steers will be weaned and placed into their backgrounding programs by the end of the year.

Each year, the steers from all three locations have been transported to the Brandon Research Centre, where they are separated into four groups: early calved (E) in a rapid-finishing (RF) program; early calved (E) in a slow-finishing (SF) program, late calved (L) in a rapid-finishing program (RF), and late calved (L) in a slow-finishing (SF) program.

The RF program is the conventional regime with an approximate 90-day backgrounding period, followed by finishing in a feedlot. The SF program involves a longer backgrounding period with a lower targeted rate of gain that makes greater use of forages by grassing the steers through the summer and swath grazing into the fall, finishing up with a short keep in the feedlot. This will examine the premise that maximizing forages in the backgrounding and finishing program is a less expensive way to finish calves. As well, longer backgrounding periods are commonly used to allow smaller-framed steers to achieve greater skeletal growth before fattening, thereby increasing the finished weight.

The steers are routinely weighed and ultrasound scanned for backfat throughout the post-weaning trial. They are shipped in groups of 10 to 20 when they reach the targeted average backfat of eight millimetres, which is expected to result in most of the cattle grading AA. The carcasses are graded, a compositional analysis is done on the beef, and

samples of the cooked product will be taste tested.

PERFORMANCE RESULTS FROM THE FIRST YEAR

Data are now available for the 2007-born calves finished out from the summer of 2008 through to the first quarter of 2009.

“Preliminary results show that the time of calving and finishing program interact to alter the age and weight at which the steers reached their designated slaughter endpoint,” says Dr. Hushton Block, research scientist at Brandon. “The most substantial effect noted was the interaction between the time of calving and the finishing program for the age of steers at slaughter.”

The reference group is the conventional scenario with the early-calved E steers in the rapid-feeding (RF) program. They took an average of 13.9 months to finish. The late L steers in the RF program took 2.5 months longer to finish, requiring 16.4 months on average to reach the targeted backfat thickness.

“A possible explanation for this observation is that the later-calved steers were in the feedlot throughout the summer and the warmer temperatures may have reduced intake and rate of gain, whereas the early-calved steers had already gone to slaughter before the heat of summer,” Block comments. The feed intake data have yet to be analysed.

Compared with the reference group, moving the E steers to the slow-feed (SF) program required an additional 8.3 months of feeding, or a total of 22.2 months on average to reach the targeted backfat thickness.

The surprise was the late steers in the SF program. They required an average of 20.3 months on feed, which was 1.9 months less than the 22.2 months for the early-calved calves in the SF program.

One would reasonably expect that if moving to later calving had the effect of increasing the age at slaughter by 2.5 months and slower finishing had the effect of increasing the age at slaughter by 8.3 months, the combination of later calving and slower finishing would increase the age at slaughter by the sum of the two independent effects, or 10.8 months, relative to the reference group, Block states.

Statistically, the L steers in the SF program should have taken 24.7 (13.9+10.8) months to finish.

“Surprisingly, combining later calving with a slower finishing program increased the total time on feed by only 6.4 months relative to the reference group (20.3 – 13.9). This indicates that the independent effects of late calving and slow finishing are not fully additive,” Block observes. He believes that this anomaly can be attributed to the warm summer weather having less of an impact on the smaller, L steers than on the larger, E steers.

What it all seems to be boiling down to is the weather effect on the calves at the various stages of development when they are weaned in different seasons and put into either a rapid-finishing program or a slow-finishing program.

“The important point coming to the forefront for producers is to choose cattle that finish the fastest in whatever feeding system they are using,” Block suggests.

CARCASS TRAITS

Final weight, hot carcass weight, and ribeye area are highly correlated with age at slaughter. There were no inconsistencies in this regard in the first year of the trial.

“Regardless of time of calving, the rapid-finished steers were younger at slaughter and had lower dressing per cent and lower average fat thickness than the slow-finished steers. The greater average fat thickness of the slow-finished steers may explain the greater dressing per cent,” Block says.

But, there is no apparent explanation for the greater average fat thickness given that ultrasound backfat and grade fat did not differ, he adds. The methodology and timing for measuring average fat thickness, backfat and grade fat are slightly different, but they are all measurements of the same characteristic.

In the first-year data, only the proportion of the steers that graded AA was significantly affected by the finishing program — slower finishing decreased the proportion of steers that graded AA. Most of the rest of the steers graded AAA.

Due to the small amounts of data analysed to date and the statistical method used to assess the marbling scores, the research team can’t yet conclusively state that the proportion grading AAA is significantly affected by the finishing program. Data from the whole trial should help to sort this out.

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