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A Tale Of Two Calving Systems On The Canadian Prairies

Researchers at Agriculture and Agri-Food Canada’s research centres in Brandon, Swift Current and the Western Beef Development Centre in Lanigan, Sask. conducted a two-year study to evaluate the effects of early (March-April ) or late (May-June) calving under traditional and non-traditional conditions. In all, 120 cows at Brandon, 60 at Swift Current and 100 at Lanigan were allocated to early (EC) and late (LC) calving groups. All calves were weaned at approximately 205 days in early October (EC) and early January (LC). The goal was to evaluate the effect of early or late calving on cow and calf performance using different feeding systems and diets in these different environments, and the factors that influence the profitability of a calving system.

COW AND CALF PERFORMANCE

Four different feeding systems, pasture grazing, swath grazing, bale grazing and drylot were used to manage the cow herd throughout the year. At Swift Current, pastures were primarily native forages while Brandon and Lanigan pastures were mainly tame varieties, primarily crested wheat-grass and brome grasses in mixture with alfalfa. To hold down costs, all the cows were swath grazed and bale grazed as long as possible in the fall and winter months on swaths of Baler oats, Red proso millet and Ranger barley and grass-legume round bales. During extended periods of extreme cold they were brought into the drylot and supplemented with rolled barley. Late-calving cows had 45 per cent more days on grazing and 60 per cent fewer days in the drylot than earlycalving cows.

All diets on both the calving systems met the nutrient requirements of pregnant and lactating cows with the exception of late-calving cows in July, the second month after calving, when average protein levels dipped on the pastures. The early cows by comparison were in the drylot during the second month after calving receiving rolled barley to meet their energy and protein needs. In general all four feeding systems met the lactating beef cow’s energy and protein requirements at different times of the year.

Minimal differences were noted in the body condition score (BCS) of the cows on either calving system. BCS is an indicator of body fat reserves which play a large role in a cow’s reproductive performance. Cows will fluctuate throughout the year but the goal is to maintain energy reserves at an adequate level with a BCS between 2.5 and 3.0. Early-calving-system cows were generally able to maintain condition from pre-calving to breeding although the scores on early cows at Swift Current lost 1.3 on their average BCS at one point and Brandon late cows dropped by 0.6. However both groups never scored below the target minimum of 2.5 so their performance levels were unaffected.

Late-calving cows lost some condition from breeding to weaning during periods of cold and heavy snow but still able to maintain sufficient fat cover to maintain good reproductive performance.

No effect was observed on cow reproductive performance between the two calving systems. Average calving span, the time from first calf to the last calf, was shorter for late-calving cows than early ones (58 versus 55 days). That suggests a slight advantage in terms of a slightly shorter reproductive cycle, however these results weren’t uniform across all sites. Just the reverse occurred at Swift Current where the calving span of the late cows was three days longer than the early cows. Swift Current experiences warmer temperatures as early as mid-July and this may have affected cow and bull performance during the breeding season. On the other hand late-calving cows at Lanigan had a 10-day shorter calving span than the early cows at that location.

Late-born calves were heavier at birth and 60 days of age compared to the early-born calves. However, during the calving-to-weaning growth period, calves in the LC system had a lower average daily gain resulting in lighter weaning weights. In this study, calves in both calving systems were weaned at the same age, with LC calves being weaned in early January. Average outside temperature starts to decrease in October thereby increasing nutrient requirements of the growing calf which would put an increased demand on the cow. By managing the cows in different feeding systems, energy and protein requirements were met for the cow which would help to maintain good milk production. It would therefore be expected that calf growth would be sustained throughout the fall. However, with decreasing forage quality in the fall and the ability of the March-born calf to utilize pasture forage more efficiently at an older age are factors that can affect calf growth rate. Even though energy requirements were met for the LC cow during lactation, decreasing temperatures in the fall and winter impacted LC calf growth rate.

Calf health can also affect calf performance up to pre-weaning age. Average calf vaccination and treatment costs were higher for the early-born calves compared to the late-born ones. This same trend occurred at all three locations, where LC costs were lower than the EC costs by approximately 15.4 per cent.

Labour requirements for the earlycalving system are typically higher, and in this study they were 8.3 per cent more than for late-calving cows.

CONCLUSIONS

The effects of two calving systems at three western Canadian locations were evaluated in different environments and years. Cows calving in summer maintained body weight from breeding to weaning through extended grazing programs that reduced labour and total cost. Feed quality was adequate to meet cow requirements in both calving systems and resulted in no difference in cow reproductive performance. Finally, cows in the late-calving system were managed in extended grazing systems for a longer period than the early-calving cows without compromising reproductive and BCS levels. Treatment and labour costs were also lower for the calves in the late-calving system; therefore this would suggest additional savings for the late-calving cows.

LynneGirardinisaruminantnutritionist New-LifeFeeds,Saskatoon,Dr.BartLardner iswiththeWesternBeefDevelopmentCentre andDr.AlanIwaasa,AAFCSwiftCurrent, ShannonScott,AAFCBrandon.

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